Silicon-based micro-sized particles and their use in

Abstract

The present invention relates to silicon and carbon-based composite particles wherein each of the silicon-based composite particles consists of a bulk material having a plurality of nanoscale silicon domains embedded therein, and wherein 5, based on the total mass of the silicon-based composite particles, the bulk material comprises a total amount of carbon from 1 to 40 wt% wherein the bulk material comprises a plurality of nanoscale silicon domains embedded in a first matrix, the first matrix comprises nanoscale silicon carbide domains, and when subjected to XRD analysis with unmonochromatic CuK [alpha] radiation, the particles exhibit a peak having a full width at half maximum (FWHM) in the range of 0.5 DEG to 8 DEG at about 28 DEG, and a peak having a FWHM in the range of 1 DEG to 10 DEG at about 36 DEG.

Description

Technical Field

[0001] This invention relates to silicon-based particles suitable for use as active materials in the negative electrode of secondary lithium-ion batteries (LIBs) and methods for preparing the same. Background Technology

[0002] Carbonaceous fossil fuels currently account for approximately 80% of global energy demand. The majority of fossil fuels are burned to varying degrees of cleanliness, releasing exhaust / combustion gases into the atmosphere. These emissions contribute to major pollution problems, global warming, and ocean acidification. Consequently, there is a growing expectation and interest in developing and implementing climate-neutral and pollution-free alternatives.

[0003] Electricity is a versatile form of energy that produces virtually no pollution when used to provide heat, power electric motors, operate electronic devices, and more. Furthermore, several sectors of society require portable energy storage for electrification. Secondary lithium-ion batteries (LIBs) are currently the best commercially available battery type for applications requiring high volumetric and gravimetric energy storage density and efficient capacity transfer. However, batteries with even higher storage densities than currently available LIBs are needed to fully utilize this electrification option.

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

[0005] Existing technology

[0006] Silicon is known to have a relatively strong ability to absorb lithium and form silicon-lithium alloys. At typical ambient temperatures, the most lithiated phase of silicon is Li. 3.75 Si has a theoretical specific capacity of 3579 mAh / g, which differs from graphite's theoretical specific energy of 372 mAh / g. Therefore, the battery industry has been seeking solutions for over a decade to utilize silicon as an active material in the anode of secondary lithium-ion batteries (LIBs).

[0007] However, lithium absorption causes significant volume fluctuations in silicon materials. In Li 3.75In its most lithiated state, silicon has a volume approximately 320% larger than its unlithiated state. Furthermore, the electrolyte in contact with the active material surface typically reacts, forming a lithium-containing solid phase called the solid electrolyte interphase (SEI). This SEI layer represents the irreversible loss of lithium in the electrochemical battery, which correspondingly reduces its energy storage capacity. Because SEI formation primarily occurs during the first charge-discharge cycle, the magnitude of the irreversible lithium loss associated with SEI formation is typically represented by a first cycle efficiency (FCE) measurement.

[0008] Furthermore, volumetric changes in silicon materials during lithiation and delithiation (charge / discharge) cycling have shown to cause serious problems leading to structural degradation / decomposition (disintegration, breakage, fragmentation) of silicon materials and instability of the SEI layer, resulting in unacceptably low cycling performance and large capacity loss of the LIB. The integrity problem of silicon materials has been proposed to be addressed by applying silicon in the form of nanoscale particles (typically less than 200 nm), preferably with a surface coating.

[0009] Sourice et al. (2016) [Ref 1] disclosed the production of amorphous silicon core particles with a diameter of 30 nm by laser-driven chemical vapor phase pyrolysis (LCVP) of silane gas diluted in helium. These particles were then coated with a 1 nm thick carbon coating produced by a second LCVP stage using ethylene gas. It was reported that after 500 charge / discharge cycles, these particles retained 1250 mAh·g at a C / 5 rate. -1 The capacity remains at 800 mAh.g at 2C. -1 It has a capacity and an excellent coulomb efficiency of 99.95%.

[0010] It is also known that nanoscale silicon-based particles containing other elements can be prepared on an industrial scale by thermally inducing the decomposition of a precursor gas mixture. Such examples are known from WO 2021 / 160824, which discloses the preparation of silicon alloyed with 0.05 to 2 atomic% C and / or N with a diameter of 10 to 200 nm by simultaneously thermally inducing the decomposition of silicon- and carbon-containing gases. In one exemplary embodiment, Si is shown to be prepared by circulating a homogeneous gas mixture of silane and ethylene preheated to 400°C, and then allowing the mixture to flow into a reactor. 0.98 C 0.02 The particles, wherein the mixture is mixed with heated nitrogen to bring the resulting gas mixture to a temperature of 810°C. The relative amounts of the gases in the final gas mixture in the reactor are approximately 28 mol% silane, 1.5 mol% ethylene, and the remainder (approximately 70 mol%) nitrogen. The residence time is approximately 1 second. These particles are described as having a homogeneous structure.

[0011] Orthner et al. 2021 [Ref 2] reported a study on the formation of amorphous silicon-based particles by passing a mixture of silane and ethylene gases diluted in nitrogen at atmospheric pressure through tubular hot-wall reactors at 640, 690, and 1100°C. Residence times ranged from 1 to 5 seconds. The gas mixtures had concentrations of 10 to 30 vol% silane and 0 to 11.3 vol% ethylene. Particles prepared at 640°C and 690°C were found to be amorphous and homogeneous, with little or no partial crystallization observed in those prepared at 640°C and 690°C, respectively. Particle sizes ranged from 80 to 300 nm, with an average size of 200 nm. XRD analysis showed no SiC formation. XPS analysis indicated that the carbon content in the amorphous particles decreased almost linearly from the particle surface to the particle bulk. The initial capacity of these particles was found to be 3070 mAh / g, which decreased to 2200 mAh / g after the second cycle, but the coulombic efficiency remained above 99.5%. This high coulombic efficiency is attributed to the formation of a low SEI layer due to the relatively high carbon presence at the particle surface. However, the particles prepared 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 Si crystal size was found to be 70 nm. Orthner also noted that the formation of SiC was unfavorable, as the particles exhibited significantly lower initial cycle efficiency and specific capacity (917 mAh / g) compared to pure Si.

[0012] WO 2022 / 200606 discloses that heat treatment at relatively high temperatures and for long durations can transform amorphous structures into crystalline structures. This document discloses the formation of carbon alloy silicon particles by thermally inducing the decomposition of a precursor gas mixture as described in WO 2021 / 160824 above, followed by heat treatment at 800 to 900°C for 10 to 240 minutes. Particles with a diameter of 25 to 180 μm are disclosed. 2 / g of BET (approximately 15 to 110 nm in diameter), 0.05 to 20 atomic percent of total C and / or N content, and containing heat-treated particles of nanoscale microcrystals with a diameter of 1 to 15 nm embedded therein.

[0013] It is also known that calcining nanoscale silicon particles in a carbon matrix can provide stable particles and reduce the formation of the SEI layer. Wang et al. (2013) [Ref 3] disclosed the preparation of composite particles (Si / αC) by pyrolyzing a mixture of 50-100 nm nanoscale silicon particles in coal tar pitch, followed by pulverizing the pyrolyzed mixture to form a composite in which Si particles are embedded in an amorphous carbon matrix. The composite with 20 wt% Si was found to exhibit stable lithium storage capacity over extended cycling. This composite anode provided a capacity of 400.3 mAh / g and a high capacity retention of 71.3% after 1000 cycles. This can be explained by the fact that the silicon nanoparticles are encapsulated in the (Si / αC) composite by amorphous SiOx and amorphous carbon, which provides sufficient conductivity and strong elasticity to suppress the stress generated by the reaction of Si with Li during charging / discharging.

[0014] Zhu et al. (2018) [Ref 4] reported a study investigating the correlation between key physical parameters and electrochemical properties of silicon particles when used as an anode in a liquid incubator (LIB). This study included silicon particles denoted as S1, S2, and S3, with wavelengths of 41.4, 36.11, and 7.33 m, respectively. 2 Three samples of crystalline silicon particles with a BET specific surface area of ​​ / g were prepared. This corresponds to D50 particle sizes of approximately 50, 100, and 150 nm. Each of the three particle samples was mixed with conductive carbon and sodium alginate binder and then applied to a copper conductor to form three anode samples with S1, S2, and S3 particles, respectively. The amount of active material loaded in each anode sample was approximately 0.5 mg / cm³. 2Anode samples were assembled in CR2032 coin-type half-cells with identical electrolytes and cathodes to investigate the effect of silicon particle size at the anode on the electrochemical properties of the cells. The results showed that all three cells with S1, S2, and S3 exhibited reversible capacities of approximately 2500 mAh / g, while the initial cycle coulombic efficiencies (FCEs) obtained using S1, S2, and S3 were 78.51%, 83.12%, and 89.26%, respectively. The strong positive correlation between particle size and initial cycle efficiency is attributed to the difference in specific area. The increased specific area of ​​the smaller-sized Si anode inevitably promotes the SEI formation reaction at the electrode-electrolyte interface, leading to high irreversible capacity due to SEI formation. However, the rate capability of the Si anode was found to be enhanced due to the smaller particle size. This is attributed to the shorter Li diffusion distance of the smaller-sized Si anode. At a rate of 20C, the delivered capacities of S1, S2, and S3 were found to be 992.23 mAh / g, 323.17 mAh / g, and 233.43 mAh / g, respectively. Furthermore, the cycling performance of Si anodes with different particle sizes was found to exhibit excellent cycling stability with smaller particle sizes. After 300 cycles, the capacity retention rates of S1, S2, and S3 were 96.12%, 93.98%, and 76.73%, respectively. As reported in the literature, this result is attributed to the fact that larger Si particles are more prone to fragmentation and cracking during repeated charge-discharge cycles, especially when the particle size is greater than 150 nm.

[0015] Another factor supporting the use of small silicon particles, reported by Rhenlund et al. (2017) [Ref 5], is diffusion-controlled trapping of lithium in the electrode. Their research showed that during cycling, small amounts of elemental lithium are trapped within the active electrode material due to bidirectional diffusion, causing lithium to migrate into the bulk of the active material, which significantly increases the time required for lithium extraction. This Li trapping mechanism was demonstrated using silicon particles with a D50 of 50 nm.

[0016] Sung et al. (2021) [Ref. 6] reported a study on the nucleation and growth mechanisms of silicon-containing and carbon films on carbon substrates. This study included computer simulations based on density functional theory (DFT) and the synthesis of films by thermal decomposition of a mixture of silane and ethylene gases at 475°C with silane only up to a 10:7 ratio. 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. Films were grown to thicknesses of 20–25 nm or 60–70 nm, taking approximately 45 min and 78 min respectively. The specific size of the graphite particles used during film deposition is not explicitly stated in this literature, but based on Sung et al. (2021), ... Figure 3 As shown, the graphite particles used are essentially spherical with a diameter of approximately 10 µm. DFT calculations indicate that the carbon atoms released from the simultaneous decomposition of silane and ethylene act as inhibitors to silicon crystal growth, as demonstrated by Sung et al. (2021). Figure 1 The schematic diagram illustrates the formation of intercalated SiC and C layers between silicon microcrystals (reproduced herein). Figure 1 This was achieved through [the following method / method]. The calculations further showed that the lower the silane to ethylene ratio, the smaller the silicon crystallites in the membrane became. This result was confirmed by analysis of the synthesized membranes; in pure Si membranes, the silicon crystallites had sizes in the range of 40 nm, while in the membrane with the lowest carbon content, the silicon and carbon membranes had silicon crystallites of 3.8 nm, and in the membrane with the highest carbon content, the silicon crystallites were 0.85 nm. The membrane was found to exhibit the best cycling stability (comparable to graphite and therefore acceptable for commercial use), synthesized with a silane to ethylene ratio of 10:5 and composed of silicon with 36.8 at% C (corresponding to 20.1 wt% C), and exhibited a specific capacity of 2000 mAh / g. The silicon crystallites in this membrane had an average particle size of 0.97 nm. As expected, the document also reports that the specific capacity and FCE of the synthesized membrane decreased significantly with increasing carbon content in the membrane. However, it is expected that the capacity would not decrease with increasing membrane thickness. The results are described in Sung et al. as an indication that the amount of Si can be increased without any side effects of Si size growth, which is a serious limitation on high specific capacity via chemical vapor deposition processes.

[0017] Document CN 115 881 931 A1 discloses a composite material for secondary lithium batteries, its preparation method, and its applications. This new composite material comprises nano-silicon and carbon atoms, with the carbon atoms atomically uniformly distributed within the nano-silicon. The carbon and silicon atoms combine to form amorphous Si-C bonds, and no SiC crystallization peaks are observed in X-ray diffraction (XRD). Solid-state nuclear magnetic resonance (NMR) analysis of the 29Si NMR spectrum of this 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, with an area ratio of (0.1, 5.0) between the Si-C and silicon peaks. The average particle size D of this new composite material is also disclosed. 50 The size ranges from 1 nm to 50 μm, with carbon atoms accounting for 0.5-50% of the total mass of the composite material. Summary of the Invention

[0018] Purpose of the invention

[0019] The main objective of this invention is to provide silicon-based particles suitable for use as active materials in the negative electrode of secondary lithium-ion batteries.

[0020] Another object of the present invention is to provide a method suitable for large-scale industrial preparation of these silicon-based particles.

[0021] Invention Description

[0022] The present invention relates to silicon and carbon-based particles suitable for use as active materials in the negative electrode of a secondary lithium-ion battery, and can be considered as an improvement on the secondary particles described in European patent application number EP 22158616.7.

[0023] The particles described in EP 22158616.7 are prepared by injecting a homogeneous gas mixture containing a first silicon-containing precursor gas and a second carbon-containing precursor gas, with a Si:C atomic ratio ranging from near zero to 10, into a reactor space where the reaction temperature is maintained in the range of 500 to 1200°C, most preferably 700 to 900°C. The precursor gas mixture can be preheated to a temperature ranging from less than 300 to 500°C. XRD analysis of the resulting particles revealed that they are composites of amorphous silicon and a carbon matrix in which nanoscale domains of amorphous silicon are embedded. The particle size ranges from 10 nm to 1 µm, and these particles are described as having a Si:C ratio in the range of [0.2, 7], most preferably [1, 4]. This corresponds to a total carbon content in the particles ranging from 12.5 to 83.3 at% (5.8 to 68.1 wt%).

[0024] In an exemplary embodiment of EP 22158616.7, the precursor gas is a silane and ethylene with a Si:C molar ratio of 1:1, preheated to approximately 400°C. The gas mixture is injected into a reactor space containing nitrogen, which is heated to a temperature of 810°C for the gas mixture generated inside the reactor. The residence time is less than 0.5 seconds. The resulting particles are described as a composite of amorphous silicon and a carbon matrix, with a particle size ranging from 10 nm to 1 µm and containing multiple nanosized domains of amorphous silicon with an average crystallite size of 1.7 nm embedded therein. The total carbon content of the particles is 35 atoms.

[0025] Table 1 of EP 22158616.7 lists the initial cycle capacity and cycling ability measured for samples of particles with a total carbon content ranging from 14 to 35 atomic%. The table shows that particles with the highest carbon content (35 atomic%) have an optimal cycling ability of 621 cycles, down to a worst initial cycle capacity of 1000 mAh / g with a reduced capacity up to 20%, while particles with the lowest total carbon content of 14 atomic% have a worst cycling ability of only 36 cycles and an optimal initial cycle capacity of 2200 mAh / g.

[0026] Terminology Explanation

[0027] In EP 22158616.7, three adjectives, "primary," "secondary," and "tertiary," are used when referring to particles. These adjectives refer to the level of the particle assembly, not the number of any elements that make up the particle. A primary particle is a particle that can subsequently be embedded in a secondary particle but does not contain any particles other than itself. A secondary particle is a particle that contains multiple primary particles. A tertiary particle is a particle that contains multiple secondary particles.

[0028] Since this application focuses only on the "secondary" level of the assembly, for clear reasons, the term "nanoscaled domain" is preferred here over "primary particle," and "silicon-based composite particle" is preferred over "secondary particle." Therefore, the term "nanoscaled domain" in this invention corresponds to "primary particle" in EP 22158616.7, and the term "silicon-based composite particle" in this invention corresponds to "secondary particle" in EP 22158616.7.

[0029] However, this does not mean that the nanoscale domains of the present invention are necessarily the same as the previous primary particles, and similarly, it does not mean that the silicon-based composite particles of the present invention are necessarily the same as the previous secondary particles. In some embodiments of the present invention, these particles may differ in chemical composition and / or structure from the primary and secondary particles of EP 22158616.7.

[0030] First aspect of the invention - Silicon-based composite particles of the invention

[0031] The essential difference between the silicon-based particles of this invention and those of EP 22158616.7 is that the latter particles should have an amorphous structure, as this is considered to improve the cycling performance of these particles when used as active electrode materials in secondary lithium-ion batteries (LIBs). However, the particles of this invention undergo post-production annealing, resulting in at least partial crystallization of both the nanoscale silicon domains of the particles and the first matrix containing silicon and carbon, as this treatment has been shown to increase the electrochemical properties of the particles.

[0032] As a prior secondary particle of EP 22158616.7, the silicon-based composite particles of the present invention are considered composite particles, wherein each particle has a “raisin in a bun dough”-like structure having multiple tiny nanoscale silicon domains (“raisins”) embedded in a bulk material (“bread dough”) of silicon and carbon. Therefore, as used herein, the term “composite particle” refers to multiple nanoscale silicon domains, each constituting a first chemical phase, distributed within a silicon and carbon-containing bulk material constituting at least one second chemical phase of the particle. Although local variations in silicon and carbon in the matrix may vary with production history and subsequent annealing, the nanoscale silicon domains are expected to be major contributors to lithium storage capacity.

[0033] Experimental experience and testing on particle formation demonstrate that reaction temperature can alter reaction kinetics and mechanisms during the growth of silicon-based composite particles. This is supported by, for example, the temperature dependence of silanes and hydrocarbons, and more precisely by the fact that the Si-H bond vibrations of silanes are more reactive than the CH bonds of hydrocarbons at lower temperatures.

[0034] Unbound by theory, it is believed that the early stages of homogeneous nucleation (in which nanoscale domains of silicon form) produce slightly fluid, liquid or semi-solid droplets at the reaction temperature. When the carbon-containing precursor gas becomes readily available for the reaction, it is thought that amorphous SiC and / or C layers form around and as part of these droplets, thus preventing the silicon nanoscale domains from coalescing and / or growing into larger silicon domains. As shown in Sung et al. (2021) [Ref 6], the carbon layers force the silicon domains to remain at a small nanoscale size.

[0035] These liquid or semi-liquid silicon droplets with carbon layers then undergo two competing processes—droplet aggregation (driven by Brownian motion) and solidification (gradual removal of hydrogen from Si or C precursor molecules). Droplets that meet before solidification (at least one droplet) aggregate into near-spherical silicon-based composite particles. The aggregation process depends only slightly on temperature, but droplet formation, gas consumption, and the solidification process (hydrogen removal) are all exponential functions of temperature.

[0036] Therefore, at relatively high reaction temperatures above 700-750°C, the initially formed droplets are believed to solidify into nanoscale silicon domains and release hydrogen very rapidly, giving them only a limited aggregation time before the aggregates become less fluid and particle growth is restricted. Moreover, the high temperature can induce a large number of particle formations, thus leaving very little gas around the particles to allow for continued particle growth after the initial droplet formation. CVD growth of carbon and silicon on the formed droplets also occurs more rapidly at higher temperatures. This is believed to be the reason why particles prepared at high temperatures (at least 700-750°C) and under other identical conditions tend to produce small particles with diameters down to a few tenths of a nm and have a higher carbon content compared to particles formed at decomposition temperatures below 700°C with the same gas mixture. In this case (using high temperatures), the "dough" comprises a silicon and carbon alloy.

[0037] However, the particles of the present invention are synthesized at a relatively low decomposition temperature of 450 to 700°C. At these temperatures, it is believed that the solidification of the droplets is delayed, allowing for a significantly greater time to aggregate nanoscale silicon domains into relatively large and nearly spherical micron-sized aggregates. Simultaneously, the gas consumption rate is also reduced, thus requiring a longer residence time to achieve commercially relevant precursor conversions. If both the reaction temperature and time can be controlled, relatively large particles can be grown and particle size controlled. It is thought that in this case, the silicon-based composite particles mainly consist of "raisins" of densely packed nanoscale silicon domains with amorphous SiC and / or C layers along the boundaries between the "raisins." In this case, the "dough" (bulk material) comprises amorphous SiC located at the boundaries between the silicon domains of the densely packed aggregates of nanoscale silicon domains. x And / or a few atomically thin amorphous C layers. This provides a relatively high volumetric silicon density in the form of relatively large multiple nanoscale silicon domains within the particle agglomerates. This structure is considered to have some similarity to the structure of a silicon and carbon-containing film disclosed in Sung et al. (2021) [Ref 6], in which the film is disposed on micron-sized carbon particles. However, there is a fundamental difference: the particles of the present invention have this composition throughout the entire particle, from its core to its outer surface.

[0038] Therefore, without being bound by theory, it is considered that the bulk material containing silicon and carbon (before annealing) is an amorphous SiC surrounding nanoscale silicon domains. x The matrix / network of amorphous SiC. x The matrix / network may contain Si atoms covalently bonded to both C and Si atoms, and C atoms bonded to both C and Si atoms. It is anticipated that a majority of the carbon atoms in the bulk material are bonded to at least one silicon atom. This is clearly distinguished from products obtained from prior art powders produced by depositing silicon particles into a porous carbon matrix. After annealing, the amorphous SiC... x It can partially crystallize into nanoscale SiC domains (in addition to nanoscale silicon domains). It is also anticipated that the annealing according to the invention will induce some solid-state diffusion effects in the matrix / network of the bulk material, which can form C, Si, and SiC in the matrix / network. x Phase / domain. Therefore, the term "first matrix comprising nanoscale silicon carbide domains" as used herein encompasses C, Si, and SiC in the matrix / network. x Phase / Domain.

[0039] Particles that meet after solidification remain individual particles. Particles that meet in the intermediate stage between the "fluid" and solid states can aggregate to form large clusters of small particles, where laser diffraction or DLS can give larger values, while BET indicates much smaller particle sizes.

[0040] A characteristic property of the particles of this invention is that they have a substantially uniform carbon concentration from the particle center outwards to the outer surface of the particle; that is, the carbon concentration toward the particle surface does not, or at least does not increase significantly. See, for example, [link to relevant documentation]. Figures 5 to 8 And its content will be discussed below.

[0041] Without being bound by theory, it can be inferred that gas preheating plays a crucial role. By reducing the need for heating the gas in the reaction chamber, the reactions of all gas fractions become more similar, and the gas is consumed under more constant conditions. Preheating ensures rapid heating even of the coldest gas fractions, resulting in a more consistent gas ratio throughout the reaction.

[0042] The advantage of applying a mixture of silicon-containing and carbon-containing precursor gases in a protected atmosphere through condensation and chemical vapor deposition is that this method provides excellent control, meaning that if an element is introduced into the reactor, then that element will therefore be present in the resulting particles. For example, if the silicon-containing precursor gas is silane and the carbon-containing precursor gas is hydrocarbon, then the reactor will primarily contain elements hydrogen, carbon, silicon, and typical inert gas elements (nitrogen, argon, etc.), with only very small amounts of oxygen (the remainder being air).

[0043] Furthermore, in one embodiment, when the particles according to the invention are made by condensation and chemical vapor deposition of a hydrogen-containing precursor gas, the resulting particles can contain a significant amount of hydrogen in the bulk material, primarily bonded to C atoms.

[0044] In theory, when the hydrogen content is reduced to < 1 atom per silicon or carbon atom, the particles can be expected to become solid. Hydrogen bonded to silicon at lower temperatures can leave more easily than hydrogen bonded to carbon, so a hydrogen content of < 1 atom per carbon should be readily achievable. In one embodiment, these particles may contain up to 30 atomic% hydrogen or less prior to post-production annealing. However, post-production annealing will remove some or most of the hydrogen content, such that the term "unintentional impurity," as used herein, may in one embodiment cover less than 20 atomic% H, more preferably less than 15 atomic%, more preferably less than 10 atomic%, more preferably less than 5 atomic%, and most preferably less than 1 atom.

[0045] Ideally, oxygen should be absent from the particles, as its presence leads to lithium atom loss (irreversible bonding) and reduces the initial cycle efficiency of the LIB when used as an active material in the anode. However, in practice, it may be difficult to protect the particles from any contact with ambient oxygen; therefore, the term "unintentional impurity," as used herein, may contain up to 4 atomic% oxygen in one embodiment, but preferably less than 0.5 atomic%. Thus, in one embodiment, the total oxygen content of the particles according to the invention is less than 4 atomic%, preferably less than 3 atomic%, more preferably less than 2 atomic%, more preferably less than 1 atomic%, and most preferably less than 0.5 atomic%.

[0046] Therefore, in one embodiment, the resulting particles will primarily contain silicon and carbon, and may contain less than 1 atomic% to 20 atomic% hydrogen, less than 0.5 atomic% to 4 atomic% oxygen, and ultimately trace amounts of unavoidable impurities.

[0047] However, when measuring actual products, oxygen levels of 0.3–4 wt% are frequently detected, but this is usually due to air exposure that occurs after production is complete, such as during the preparation of characterization samples.

[0048] Nanoscale domain

[0049] The nanoscale silicon domains of the particles of this invention are considered to be substantially pure silicon phase. However, due to the presence of carbon in the precursor gas mixture, some carbon can enter these nanoscale silicon domains, albeit in small amounts. The lattice constant determined by XRD analysis (after rapid crystallization at, for example, 900°C for 30 minutes) matches the lattice constant of pure silicon. Furthermore, based on experience with carbon gettering from, for example, solar silicon, the inventors have not found reports of high carbon mobility at these temperatures. This is an indication of very low carbon content (if present in the nanoscale domains). The XRD analysis of the particles prior to crystallization matches quite well with the XRD analysis of amorphous silicon, while electron energy loss spectroscopy (EELS) (averaged over a slightly larger region containing both the nanoscale domains and the binding matrix) records the presence of carbon. This indicates the presence of some carbon in the nanoscale domains. In addition, since the precursor gas also contains hydrogen, the particles may contain some hydrogen due to incomplete dissociation of the precursor gas.

[0050] Therefore, as used herein, the term "nanoscale silicon domain" refers to nanoscale silicon particles that may contain small amounts of carbon and / or hydrogen. Based on the quality of the nanoscale silicon domain, the silicon content is considered to be at least 90 atomic percent and can be as high as 98 to 100 atomic percent.

[0051] The advantage of nanoscale silicon domains is that they increase lithiation capacity without compromising cycle performance when used as active materials in secondary lithium-ion batteries. Lithiation capacity is increased by providing silicon domains with a high capacity storage volume for lithium atoms, and cycle capability is increased because nanoscale silicon is more robust and better withstands volume fluctuations associated with lithiation / delithiation cycling than larger silicon domains. Furthermore, since lithiation of silicon domains implies significant opening / breaking of Si-Si bonds, it is highly attractive that Si-C and CC bonds remain intact in the lithiation state, thereby preserving the particle structure in situ.

[0052] X-ray diffraction (XRD) (also referred to in the literature as powder X-ray diffraction (PXD) or X-ray powder diffraction (XPD) when applied to particulate materials) yields different diffraction patterns for crystalline and amorphous materials, respectively. As used herein, the abbreviations XRD and XPD are used interchangeably because X-ray diffraction analysis is applied to particles according to the invention. Crystalline bulk materials, due to their high degree of order and symmetry in their atomic structure, tend to produce sharp, Bragg peaks in XRD measurements. For crystalline silicon, XRD analysis typically produces sharp peaks at 28.4°, 47.4°, and 56.1° in the diffraction pattern measured with CuKα radiation. Silicon carbide (SiC) typically produces sharp Bragg peaks at 35.6°, 60.0°, and 71.7°. In contrast, amorphous materials, lacking the long-range order characteristic of crystalline atomic structure, typically give broader peaks that are significantly more “fuzzy” in the measured diffraction patterns. Amorphous silicon typically produces circular peaks at 28° and 52°. These circular peaks can be fitted with Gaussian curves to obtain well-defined values ​​for peak maximum and width. This fitting can be performed using any skilled XRD operator. For such circular peaks, the higher angular equivalents can be blurred, and therefore this application focuses on the characteristics of the lowest angular / highest amplitude peaks for each material.

[0053] Similarly, peak "sharpness" can be used to distinguish between crystalline and amorphous materials. The typical full width at half maximum (FWHM) of XRD peaks in crystalline silicon is usually less than 2°–4°, while the FWHM of amorphous silicon is typically greater than 4° when measured with a diffractometer applying unmonochromatic CuKα radiation and using Gaussian fitting. The FWHM is the width of the peak curve measured between points on the y-axis that represent half the maximum amplitude of the peak curve (after subtracting background signals and / or signals from the sample holder). Samples containing both amorphous and crystalline silicon will yield a diffraction pattern in XRD analysis that shows both the sharp Bragg peaks typical of the crystalline phase and the broader, more Gaussian peaks typical of the amorphous phase. The diffraction pattern can be used to estimate the crystallinity of the sample based on the ratio of the area above the amorphous broad peak below the Bragg peak to the total area of ​​the broad peak and the Bragg peak. Linear background should be subtracted from the calculations before calculation.

[0054] In the XRD analysis used herein, the angles and angular tolerances refer to the use of a diffractometer employing unmonochromatic CuKα radiation. This radiation has a high intensity and a wavelength of 1.5406 Å, which corresponds well to the interatomic distances in crystalline solids, making the analysis sensitive to the presence of crystalline phases within silicon particles. XRD analysis using a diffractometer with CuKα radiation is a natural selection for the same reason and is therefore the most widely used method in XRD analysis, well-known and mastered by those skilled in the art. Other diffractometers applying radiation with different wavelengths can give different angles and angular tolerances. However, those skilled in the art will know how to convert these values ​​from one radiation source to another.

[0055] Furthermore, the crystalline nanodomains of silicon (less than several hundred nanometers) exhibit characteristic peak broadening of the Bragg peak obtained by X-ray powder diffraction (XPD). This peak broadening can be used to determine the average diameter of the nanoscale domains (embedded in the silicon-based composite particles) through Rietveld refinement of XPD data, for example, from XPD analysis of silicon-based composite particles in single-mode or multi-mode distributions. Since the particles of the present invention undergo post-production annealing (which at least partially crystallizes the nanoscale silicon domains), Rietveld refinement of the XPD data should preferably be performed after annealing.

[0056] Rietveld analysis of XPD data to determine the average particle size is well known and practiced by those skilled in the art. An example of such analysis might involve fitting calculated XPD data from a crystalline Si model to experimental data obtained from XPD measurements of a sample of silicon-based composite particles using a least-squares method (so-called Rietveld refinement). Rietveld refinement can be performed using freely available software (e.g., GSAS-II [Ref 7]) or commercial software (e.g., Topas [Ref 8]). The instrument's contribution to the Bragg peak width should be calculated using the instrument's geometry ("fundamental parameters approach" [Ref 9]) or described by the Thomson-Cox-Hastings pseudo-Voigt function [Ref 10], which is experimentally determined from highly crystalline standard materials such as NIST SRM 640f silicon. During Rietveld refinement, the instrument's contribution to the Bragg peak remains constant. All additional broadening of the observed Bragg peak is assumed to be due to small crystallite size and the presence of a Lorentz shape. This crystallite size broadening is modeled by refining the additional contribution β to the calculated Bragg peak width, which varies with the scattering angle as follows:

[0057] Where λ is the X-ray wavelength used in the XPD measurement. β is the additional full width at half maximum (FWHM) of the Bragg peak at a scattering angle of 2θ, i.e., the width in degrees between the top and bottom of the peak. The value of τ (average crystallite diameter / size) is allowed to vary freely during the Rietveld refinement and converges to a value that gives the best agreement between experimental and calculated XPD data.

[0058] Unrestricted by theory, it is assumed that the nanoscale SiC crystallites formed by post-production annealing of the particles according to the present invention are formed through solid-state diffusion. This solid-state diffusion rearranges the Si and C atoms in the molecular structure of the first matrix located between the nanoscale silicon domains, and forms SiC domains that are initially amorphous and gradually crystallize at least partially during post-production annealing. Due to the relatively high temperature and duration of annealing, it is expected that most of the final hydrogen content remaining from the particle synthesis is expelled and degassed, making the chemical composition of the SiC crystallites most likely close to 100% pure SiC. The size of the nanoscale SiC domains is found to be on the same order of magnitude as the nanoscale silicon domains.

[0059] annealing

[0060] Therefore, as mentioned above, the structure of the composite particles of the present invention—that is, multiple nanoscale silicon domains aggregated together and separated from each other by silicon- and carbon-containing layers several atoms thick—is considered to have some similarity to the structure described in the silicon- and carbon-containing film disclosed in Sung et al. (2021) [Ref 6], which is located on micron-sized carbon particles. However, the essential difference is that the particles of the present invention have this composition throughout the entire particle from the core to the outer surface, while the particles of Sung et al. are mainly composed of micron-sized graphite particles (which have a 50-70 nm thick film of this composite structure).

[0061] However, further structural differences can exist between the materials of the membranes of Sung et al. and the materials of the particles of the present invention. This is believed to be due to slightly different preparation processes. The particles of the present invention are prepared by free-space condensation and chemical vapor deposition (CVD) of silicon and carbon-containing precursor gases at 450 to 700°C, while the particles of Sung et al. (2021) are prepared by chemical vapor deposition of silane and ethylene gases on an amorphous substrate / amorphous carbon particles at 450°C.

[0062] The composite membranes described by Sung et al. are aggregates of nanoscale silicon domains with carbon and silicon carbide layers at the boundaries between nanoscale silicon domains. See, for example, Sung et al. Figure 1 The copied image is reproduced in this article as Figure 1 Sung et al. Figure 4 The XRD curves given in a) demonstrate that both the silicon and silicon carbide phases of this material contain microcrystals. The XRD curves include a rather “sharp” peak at about 28°, which indicates that the silicon domain is at least partially crystalline, and a peak at about 36°, which indicates the microcrystals of SiC.

[0063] In contrast, the particles of the present invention are substantially amorphous as they leave the decomposition chamber before undergoing the post-production annealing that characterizes the particles, as shown in photographs of the particle samples. Figure 2 As demonstrated by the XRD pattern (denoted as S1-1 herein), and described in detail in the following "Verification of the Invention" section. Figure 2 The XRD curve shows a broader peak at approximately 30°, indicating amorphous silicon. The curve shows no indication of a peak at approximately 36°, thus indicating the absence of a measurable amount of crystalline SiC. There is no indication of Si or SiC crystallites in the curve, as expected from the contents of the inventors' earlier work, such as disclosed in EP22158616.7.

[0064] An important aspect of the particles according to the invention is that they undergo post-production annealing, which causes structural changes in the "pristine" particles. This can be seen from... Figure 3 From this, we can see that Figure 3 XRD patterns of seven samples from exemplary embodiments labeled S1-1 to S1-7 are shown. These samples underwent post-production annealing at a heating rate of 1 or 4°C / min from ambient room temperature to an annealing temperature in the range of 850 to 1000°C. Annealing was terminated when the annealing temperature was reached. Table 1 summarizes the annealing conditions and the initial cycle efficiency and initial cycle capacity of the obtained samples. The XRD patterns marked "A" and "B" in the figure are from samples of the same embodiment S1 heat-treated at 1000°C and 1100°C, respectively. The electrochemical properties of these two samples were not investigated because the results of milder annealing indicated that these temperatures were too harsh.

[0065] Table 1. Comparison of electrochemical properties of samples exposed to different annealing processes. The reference is S1-1 particles without post-production annealing. Table 2 shows the XRD analysis results of the samples in Table 1. The reference is S1-1 particles that have not undergone post-production annealing. Therefore, it does not yet have two clearly defined peaks, but rather a very rounded peak around 30°.

[0066] Figure 3 The XRD patterns show a broad peak at approximately 30°, indicating that annealing at 850°C or higher causes a gradual structural change in the particles, resulting in a narrower peak shifting to approximately 28°. This suggests that the silicon domains within the particles gradually transform from amorphous to crystallites. Further XRD patterns indicate the gradual formation of a peak at approximately 36°, signifying the formation of SiC crystallites.

[0067] The initial cycle efficiency (FCE) and initial cycle capacity given in Table 1 indicate the existence of an optimal parameter window for post-production annealing. The S1 embodiment of the particles yields the optimal FCE and initial cycle capacity when heat-treated to 900°C at a heating rate of 1°C / min. Furthermore, if annealing continues to very high temperatures, it is expected that the nanocrystals will gradually form increasingly larger domains, losing the stabilizing effect of the Si-C bonds near the Si nanocrystals. Without theoretical constraints, it can be assumed that only the external C atoms in the SiC crystal actually possess stabilizing properties; therefore, maintaining many small SiC crystallites is better than having the same amount of SiC in larger crystallites.

[0068] Table 2 shows the crystallite sizes of Si and SiC crystallites in samples S1-1 to S1-6, as determined by Rietveld analysis, and the full width at half maximum (FWHM) of the Si peak at approximately 28° and the SiC peak at approximately 36°. The crystallite size of the particles of this invention is in the range of 1.2–2.9 nm. This also indicates that the structure of the particles of this invention differs from the structure of the film material reported by Sung et al., who reported sub-nanometer crystallites of SiC.

[0069] Furthermore, the above results indicate that annealing can be advantageously terminated before the particles become fully crystalline, but it results in a mixture of nanoscale amorphous and crystalline Si and SiC domains. Without being theoretically limited, this is thought to be due to hydrogen evacuation / degassing during particle growth via CVD, which can leave dangling bonds within the material, leading to poor conductivity (resulting in low capacity measurements) and low FCE (since dangling bonds are potential traps for lithium atoms). Post-production annealing is also thought to induce solid-state diffusion in the material, allowing Si atoms in the amorphous silicon domains to displace and eliminate dangling bonds during crystallization, and similarly, both Si and C can move and eliminate dangling bonds in the boundary regions between aggregated silicon domains. The latter will form SiC. Further annealing after optimization can lead to excessive crystal growth and SiC formation. Both are known to be detrimental to battery applications.

[0070] A further mechanism could be that the initially formed thin SiC layer creates barrier "fences" within the material. Annealing can cause these dense fences to recombine into pillar or mesh structures, opening pathways for lithium between SiC nanodomains. Finally, the crystal structure can provide a lower activation energy for Li diffusion, as the initial and final states involved in the transition are more likely to have the same energy. These last two phenomena can be correlated with a significant improvement in lithium transport kinetics.

[0071] Regardless of the structure of the heat-treated particles or the reason for their reaction, post-production annealing at heating rates of 1 to 5°C / min to temperatures in the range of 800 to 1100°C significantly increased the electrochemical properties of the particles. XRD analysis showed that the resulting particles became partially crystalline and exhibited a full width at half maximum (FWHM) of the Si peak at approximately 28°C in the range of 0.5°–8°C and a full width at half maximum (FWHM) of the SiC peak at approximately 36°C in the range of 1°–10°C.

[0072] The particles exiting the decomposition chamber of the particle forming reactor should be advantageously stabilized and prevent further post-processing particle growth due to, for example, the condensation of precursor gas residues leaving with the particles. This is achieved by characteristically cooling the particles between particle forming and annealing.

[0073] In this regard, the first consideration known to those skilled in the art is to achieve this by cooling the particles to a temperature equal to or below the preheating temperature of the precursor gas, since at those temperatures no gas condensation reaction occurs or only a negligible gas condensation reaction occurs, which generally means that the particles should be cooled to a temperature of less than 500°C.

[0074] Another consideration known to those skilled in the art is that the reaction between oxygen and silicon that occurs on the surface of ultrafine silicon particles when exposed to ambient air is highly exothermic and can lead to uncontrolled thermal escape oxidation of particle clumps. This implies cooling the particles to ambient air temperature to make them more robust to such thermal escape oxidation.

[0075] A third consideration known to those skilled in the art is that when the purpose of post-particle production of the present invention is to produce amorphous nanoscale silicon and / or amorphous nanoscale SiC domains of partially crystalline silicon-based composite particles, this purpose requires an annealing temperature of at least 700°C.

[0076] Therefore, those skilled in the art who apply these three known considerations will understand and appreciate the term "cooling the particles to room temperature" as used herein, which refers to cooling the particles to any temperature, ranging from approximately 25°C to 500°C, depending on whether the formed particles will be exposed to ambient oxygen after formation. Thus, in one embodiment of the invention, the particles extracted from the decomposition chamber are cooled to a temperature in the range of 25 to 500°C, preferably 100 to 450°C, more preferably 250 to 400°C, and most preferably 300 to 350°C.

[0077] Furthermore, in some embodiments, the ideal annealing temperature can depend on the carbon content of the silicon-based composite particles, and also on the particle size. In particles with higher carbon content, higher temperatures or longer annealing times may be required to achieve the optimal crystallite size, but the carbon content still ensures small nanodomains. In particles with lower carbon content, there is a greater risk of forming excessively large silicon domains, and the maximum temperature can advantageously be relatively lower compared to the former case with high carbon content. Adjusting the post-production annealing temperature is within the scope of ordinary skill of those skilled in the art.

[0078] In a first aspect, the invention relates to silicon-based composite particles, wherein the silicon-based particles have a total chemical composition comprising the following: - Total carbon content (C) based on the total mass of silicon-based composite particles 总 5 to 50 atomic percent, and - The balance consists of silicon and unintentional impurities. Its features are, - The silicon-based particles are made of bulk material. - The bulk material comprises multiple nanoscale silicon domains embedded in a first matrix, the first matrix comprising nanoscale silicon carbide domains, and - When subjected to XRD analysis with unmonochromatic CuKα radiation, the particles exhibit a peak at approximately 28° with a full width at half maximum (FWHM) in the range of 0.5° to 8°, and a peak at approximately 36° with an FWHM in the range of 1° to 10°.

[0079] As used herein, the terms "total chemical composition containing an element" and / or "total amount of an element" encompass the full content of that element in all components and portions of the silicon-based composite particles of the present invention, from their core center to their surface. The final content of the element in the surface coating located on the particles is excluded from the total content of the particles. Therefore, as used herein, the term "total content of an element" does not include the final "presence of the element in the surface coating deposited on the particles," but is limited to the amount of the element present in the bulk material of the silicon-based composite particles.

[0080] The total content of elements (e.g., silicon, carbon, hydrogen, and / or oxygen) in the particles can be determined by, for example, atomic absorption (AA), inductively coupled plasma mass spectrometry (ICP-MS), ICP-OES, or X-ray fluorescence analysis (XRF). These are well-known techniques to those skilled in the art. The total carbon content of the particles can also be determined by burning the particle sample and measuring / determining the amount of carbon dioxide formed. The total carbon content of secondary particles can also be determined by burning the particle sample and measuring / determining the amount of carbon dioxide formed. For coated particles, the elemental composition of the particles within the coating can be determined by cross-sectional analysis using focused ion beam scanning electron microscopy or tunneling electron microscopy (FIB-SEM or FIB / TEM) combined with electron dispersive spectroscopy (EDS) and / or electron energy loss spectroscopy (EELS). These are also well-known techniques to those skilled in the art. The hydrogen content can be estimated by pyrolyzing the sample in an inert atmosphere and measuring the emitted hydrogen gas using a mass spectrometer. These are well-known techniques to those skilled in the art.

[0081] As used herein, the term "void" is applied to mean "the majority of matter." That is, the "void material" of the particles for which protection is sought is the main component of the particle agglomerates.

[0082] As used herein, the term "nanoscale silicon domain" refers to multiple relatively large and nearly spherical silicon domains aggregated into an aggregate, wherein these silicon domains are at least partially embedded in an intervening layer containing a second material phase of silicon and carbon, and possibly SiC. Nanoscale silicon domains can be amorphous, partially crystalline (a mixture of amorphous and crystalline Si), and / or fully crystalline.

[0083] In one embodiment, the average diameter of these nanoscale silicon domains can advantageously be 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, more preferably 4 to 5 nm, more preferably 0.75 to 7.5 nm, more preferably 1 to 5 nm, more preferably 1.25 to 4 nm, more preferably 1.5 to 3 nm, more preferably 1.75 to 2.75 nm, and most preferably 2 to 2.5 nm, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, if necessary, after annealing that exposes the silicon-based composite particles to annealing to crystallize the nanoscale silicon domains therein.

[0084] As used in this paper, the term "first matrix" refers to an intervening layer containing a second material phase of silicon and carbon, and possibly SiC.

[0085] As used herein, the term “nanoscale silicon carbide domain” refers to multiple SiC domains formed in a first matrix during post-production annealing and may also be formed during particle synthesis.

[0086] In one embodiment, the average diameter of the nano-silicon carbide regions can advantageously be 0.5 to 10 nm, preferably 1 to 8 nm, more preferably 2 to 7 nm, even more preferably 3 to 6 nm, and most preferably 4 to 5 nm, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, if necessary, after annealing that exposes the silicon-based composite particles to crystallize the nano-silicon carbide regions therein.

[0087] In one embodiment, the total chemical composition of the silicon-based composite particles may advantageously include: - Total carbon content (C) based on the total mass of silicon-based composite particles 总 The atom percentage is 7 to 45 atomic%, preferably 10 to 40 atomic%, more preferably 15 to 35 atomic%, even more preferably 20 to 30 atomic%, and most preferably 23 to 27 atomic%. - Balance is silicon and unintentional impurities.

[0088] For some user applications, higher carbon content is advantageous because it provides greater stability, while for other user applications, lower carbon content is preferred because it provides greater capacity.

[0089] In one embodiment, when subjected to XRD analysis using unmonochromatic CuKα radiation, the particles of the present invention exhibit the following characteristics: - A peak at approximately 28°, having a full width at half maximum (FWHM) in the range of 0.8° to 7.5°, preferably 1.2° to 7.0°, more preferably 1.4° to 6.5°, more preferably 1.7° to 6.0°, more preferably 2.0° to 5.5°, more preferably 2.3° to 5.0°, more preferably 2.6° to 4.5°, and most preferably 2.9° to 4.0°. - A peak at approximately 36°, having a full width at half maximum (FWHM) in the range of 1.25° to 9.0°, preferably 1.5° to 8.0°, more preferably 1.75° to 7.0°, more preferably 2.0° to 6.0°, more preferably 2.5° to 5.0°, and most preferably 3.0° to 4.0°.

[0090] Narrow particle size distribution

[0091] In one embodiment, the particles according to the invention can advantageously have a median volume-weighted diameter D in the range of 1 to 9 µm. 50 and the volume-weighted diameter ratio D in the range of 1 to 9 90 / D10 And D 10 D 50 and D 90 The volume-weighted particle size was determined by laser diffraction analysis according to standard ISO 13320:2020.

[0092] In one embodiment, the silicon-based composite particles of the present invention can advantageously have a median volume-weighted diameter D of 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. 50 As determined by laser diffraction analysis according to standard ISO 13320:2020.

[0093] Laser diffraction analysis can also be used to provide the volume-weighted particle size distribution (D) of silicon-based composite particles. 10 and D 90 And used to determine D 90 / D 10 ratio.

[0094] In one embodiment, the silicon-based composite particles of the present invention may advantageously have a Di in the range of 1.5 to 8, preferably 2 to 7, more preferably 2 to 6, and most preferably 3 to 5, as determined by standard ISO 13320:2020. 90 / D 10 ratio.

[0095] The present invention has a median volume-weighted diameter D in the range of 1 to 9 µm. 50 The implementation of relatively large-diameter particles has the advantage of achieving relatively high initial cycle efficiency. After the fabrication and assembly of a secondary lithium-ion battery, it needs to undergo its first charge / discharge cycle (usually referred to as formation). During formation, lithium ions are released from the active material of the positive electrode during the charging phase, migrate through the electrolyte, and are absorbed by the active material of the negative electrode. Then, during the discharge phase, the opposite occurs. However, it is known that fewer lithium ions return to the positive electrode during the discharge phase than leave the positive electrode during the charging phase. It is known that the loss of (available) lithium in the battery during the first cycle increases linearly with the increase of the total surface area of ​​the active material, and depending on the type of electrode used, this loss typically leads to a decrease in the battery's energy storage capacity of 2% to 20%.

[0096] Furthermore, it has a volume-weighted diameter ratio D in the range of 1 to 9. 90 / D 10 The relatively narrow particle size distribution of the particles according to the present invention has the following advantages, especially when D 50 When the diameter is relatively high: there will be relatively fewer "oversized" particles, i.e., the particle size D... 99The fraction cannot become so large as to significantly reduce the material's capacity and cycling ability. As particles become larger, the diffusion distance for lithium atoms migrating into and out of the particles becomes longer, while the surface current density increases, thus increasing charge transfer resistance. Both mechanisms increase the risk of lithium being diffusely trapped inside the particles. Excessively large particles are therefore partially inactive as active materials. The largest particles also carry the risk of excessive absolute expansion, which could lead to cell delamination or other damage. Furthermore, a narrow size distribution also means the presence of very few very small particles, i.e., particles with a much higher surface area per unit weight, thereby contributing to lithium loss during cycling.

[0097] Therefore, the silicon-based particles of this exemplary embodiment of the present invention have a relatively low D 90 / D 10 Ratio and relative large D 50 The combination of particle sizes provides the following combined effect: providing active material with a relatively small minimum size fraction (which leads to a relatively high FCE loss) and a relatively small maximum size fraction (partially "dead" or "inactive"), thus enabling the use of particles with a relatively large average diameter, exhibiting favorable first-cycle efficiency without compromising charge / discharge rate or stability.

[0098] Internal "shell-like region"

[0099] In one embodiment, the particles according to the invention may further comprise: - These particles contain one or more internal shell-like spatial regions within the bulk material, these regions having an increased carbon content, wherein the peak carbon content of elemental carbon is C 峰 Comparative average carbon content C 平均 Higher by 1 to 15 atomic percentage points, and among them - The peak carbon content (C) of each of one or more internal shell-like spatial regions within the bulk material. 峰 and average carbon content C 平均 It was determined by electronic energy loss spectral elemental analysis along a straight line from at least the particle core to but not including the particle surface, wherein variations at length scales less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm were smoothed.

[0100] As used herein, the term "internal shell-like spatial region within the bulk material" refers to a localized increase in carbon content within a pellet aggregate, which is shaped into an inner layer including a pellet core. If two or more of these internal shell-like spatial regions / layers exist, they should preferably be spaced apart from each other. They are generally substantially concentric and achieve similar results. Figure 4The TEM image shows a Russian nesting doll-like structure, with several shell-like layers marked with reference numeral 2 in the figure. These one or more relatively carbon-rich layers have a three-dimensional shape similar to a shell / coating deposited on the outer surface of a particle, except that the layer is located within the particle agglomerate rather than on its outer surface.

[0101] A mapping of elemental balances by electron energy loss spectroscopy (EELS) using straight lines traversing and passing through the particle nuclei of particles with these internal shell-like layers will typically show, as... Figure 5 The figure shown is illustrated in this exemplary embodiment. The particle diameter is approximately 800 nm, and it comprises four of the shell layers labeled with reference numeral 2 in the figure. As can be seen, the total Si and C content within the particles is substantially uniform. The curves for Si and C content are horizontal. Therefore, the (average) elemental ratio Si:C at the particle core is substantially equal to the (average) elemental ratio Si:C at the outer region of the particle near its surface. Figure 5 The EELS plot shows a sharp increase at the surface. This is because the particulate sample was coated with a surface layer of amorphous carbon.

[0102] Each internal shell layer is shown in the EELS plot by the decreasing peak of Si content and the corresponding increasing peak of carbon content. The plot also presents a cross-section of the TEM image, showing the same cross-section applied in the EELS analysis, to show that the oppositely oriented peaks in Si and C content on the curves along this line are due to the internal shell layers. Figure 5 The overlapping pin-like vertical lines in the image show each of the corresponding peaks for increasing carbon content and decreasing silicon content at these locations, starting from the particle center, consistent with the ring-like peaks shown on the TEM image. These corresponding peak pairs for increasing C and decreasing Si are shown on the graphs for C and Si content, respectively. Therefore, C... 峰 Compared to C 平均 A difference of at least one atomic percentage point is an indication of the presence of a relatively carbon-rich embedded shell-like layer according to the present invention.

[0103] In one implementation, C 峰 The determination of the content can advantageously include eliminating variations in small length scales, such as < 2 nm and most preferably < 1 nm, by digital filtering of the signal noise.

[0104] Digital filtering of signal noise during measurements is a standard procedure in most experimental processes and is therefore well known to those skilled in the art. One way to do this is to recalculate each data point as the average of several neighboring data points from the original dataset. In a Gaussian filter, the contribution of neighboring data points is weighted based on their distance from the data point to be calculated according to the Gaussian distribution function. Therefore, in one implementation, these measurements can be smoothed by using a Gaussian digital filter or by averaging measurements taken over multiple adjacent spatial measurement regions. The width of the digital filter should be < 5 nm, preferably < 2 nm, and most preferably < 1 nm to avoid removing information relevant to actual concentration changes.

[0105] In one embodiment, the C content of at least one relatively carbon-rich shell layer is determined by electron energy loss spectroscopic elemental analysis. 峰 And determine C 平均 It was obtained through the following methods: - Prepare cross-sectional slices less than 70 nm thick, including the center of the particle, using focused ion beam (FIB). - Perform EELS elemental analysis along a straight line extending from the center of the slice to the outer surface of the cross-section, then - Optionally, the measurements are smoothed by using a Gaussian digital filter or by averaging measurements taken from multiple adjacent spatial measurement regions, and - Apply a local maximum value to the carbon content of the first peak of carbon content at a certain distance from the particle center along the line to limit the C content of the first peak. peak And, if present, perform C on the corresponding pairs of peaks with increased carbon content and decreased silicon content present on the line. 峰 Similar determinations, and - The C content is determined by averaging the C content at all measurement points outside the surface area along this line. 平均 .

[0106] As used herein, the term "core" refers to the volumetric center region of a particle, while the term "outer surface region" refers to the particulate matter immediately adjacent to its outer surface (i.e., from the particle surface to 1 to 10 nm below the particle surface). However, this term excludes any surface coating (if present) and strictly refers to the bulk particulate matter at the surface region.

[0107] The effect of one or more shell-like layers observed in exemplary embodiments of the particles according to the invention indicates that there may be an upper limit to the carbon concentration. Without being bound by theory, it is believed that this is because the increased carbon concentration at the shell-like layers contributes to stabilization and reduces lithium mobility. At relatively low increases in carbon concentration, stabilization is observed to be dominant, while at higher carbon contents, the effect of reduced lithium mobility becomes more significant than the increase in stability. Empirical observations by the inventors suggest that the local increase in carbon at one or more shell-like layers can advantageously be less than 15 atomic percentage points. That is, if the average carbon content of the particle is 20 atomic%, then the (local) carbon content at the peak of the one or more shell-like layers should preferably not exceed 35 atomic percentage points.

[0108] In one embodiment, the C of the at least one relatively carbon-rich shell-like layer 峰 It is advantageous to have a higher carbon content (C) than the average carbon content (C). 平均 The range is 1 to 12 atomic percentage points higher, preferably 1 to 10 atomic percentage points higher, more preferably 2 to 8 atomic percentage points higher, more preferably 3 to 6 atomic percentage points higher, and most preferably 4 to 5 atomic percentage points higher.

[0109] When used as the active material for the negative electrode of a secondary LIB, relatively high cycling stability was observed in exemplary embodiments of particles according to the invention having one or more internal shell-like layers.

[0110] Unbound by theory, it is believed that the increased cycling performance observed in such multilayered particles could be due to the electron flow in the anode passing only through the solid phase. Lithium ions absorb electrons and begin to diffuse into the silicon-based particle primarily at a few locations on the particle surface (at the contact point) and exit at the same location. When this occurs, the lithium-ion flow moves in the same direction and can pull silicon atoms out of the silicon-based particle, causing silicon to leak into the electrolyte. However, high-carbon regions within the bulk mass of the silicon-based particle are believed to act as partial barriers to this flow and thus disperse lithium diffusion over a larger area within the silicon-based particle. It is also thought that the carbon-rich phase / regions in the silicon-based particle are more likely to prevent silicon from passing through, thus making the silicon-based particle more stable for charge / discharge cycling. This one or more relatively carbon-rich embedded shell-like layers can be considered as “armoring” the silicon-based material. On the other hand, if these carbon-rich rings are too carbon-rich, the lithium diffusion barrier can become too high, resulting in a lower measured practically usable charge capacity for a given charge / discharge rate.

[0111] In one embodiment, when measured at a pressure of 4 tons in cylindrical spheres with a diameter of 1 cm, the particles according to the invention can advantageously have (with or without a surface coating) a value higher than 1.10. -6S / cm, preferably > 1.10 -5 S / cm, more preferably > 1.10 -4 S / cm, more preferably > 1.10 -3 S / cm, more preferably > 1.10 -2 S / cm and optimal value > 1.10 -1 Conductivity in S / cm.

[0112] In one embodiment, the silicon-based composite particles according to a first aspect of the invention are characterized in that the particles have a total chemical composition comprising: - Total carbon content (C) based on the total mass of silicon-based composite particles 总 5 to 50 atomic percent, and - The balance is silicon and unintentional impurities, wherein the unintentional impurities include less than 20 atomic% H and / or less than 4 atomic% O, and wherein: - The silicon-based particles are made of bulk material. - The bulk material includes multiple nanoscale silicon domains embedded in a first matrix, the first matrix comprising nanoscale silicon carbide domains, and - When subjected to XRD analysis with unmonochromatic CuKα radiation, the particles exhibit a peak at approximately 28° with a full width at half maximum (FWHM) in the range of 0.5° to 8°, and a peak at approximately 36° with an FWHM in the range of 1° to 10°.

[0113] In a particularly preferred embodiment, the elemental composition of the particles of the present invention may advantageously be: - Total carbon content C: 5 to 30 atomic%, preferably 6 to 25 atomic%, preferably 7 to 20 atomic%, more preferably 8 to 15 atomic%, more preferably 9 to 14 atomic%, or most preferably 10 to 12 atomic%. 总 , - The total amount of oxygen in the particles is 0.1 to 4 atomic% O, preferably 0.2 to 3 atomic% O, more preferably 0.3 to 2 atomic% O, even more preferably 0.4 to 1 atomic% O, or most preferably 0.5 to 1 atomic% O. - The total amount of hydrogen in the particles is less than 5 atomic%, preferably less than 1 atomic%, and - The balance is Si and unintentional impurities.

[0114] Surface coating

[0115] In one embodiment, the silicon-based composite particles may further comprise an outer coating. This outer coating may be designed, for example, to enhance antioxidant stability, improve electronic conductivity, provide strong chemical bonding between the matrix and the particles, or improve dispersion characteristics. The outer coating may be further optimized to promote electron transport, lithium transport, and / or charge transfer reactions. The outer coating may be further optimized to obtain a thin and stable SEI layer. The outer coating material may include carbon, metal-organic frameworks, organic molecules, oxides such as Li. x Si y O, Ti x O, Al x O or any combination thereof. The coating may have 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. The coating may be applied using wet chemical methods, CVD, ALD, or other techniques.

[0116] In a preferred embodiment, the particles according to the invention further comprise 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.

[0117] In particular, the carbon coating in the 1–10 nm range can be characterized with considerable precision using Auger spectroscopy. Furthermore, FIB-TEM cross-sectional images will clearly show the separation of the carbon coating from the particles, with a distinct contrast between the heavy silicon atoms and the lighter carbon atoms. This characterization can be performed by those skilled in the art. Similarly, any oxide coating can be clearly separated from the silicon substrate using the same method.

[0118] In one embodiment, the coating applied to the silicon-based composite particles is made by exposing the silicon-based composite particles to a carbon-containing gas and heating them to a coating temperature at which the gas reacts with the silicon-based composite particles. In one embodiment, the coating temperature is from 30°C to 1200°C, preferably from 300°C to 1000°C, and most preferably from 600°C to 900°C.

[0119] Annealing of particles with and without coatings revealed that annealing has separate beneficial effects on both the coating and the particles. Without being bound by theory, it can be speculated that the carbon coating applied to the particles from hydrocarbons or other organic precursors will also contain a significant amount of hydrogen. During moderate annealing, the carbon can disperse some hydrogen and undergo cross-linking, including the formation of several aromatic rings. This can increase the electronic conductivity of the powder. Simultaneously, densification of the carbon coating in this phase can block lithium transport.

[0120] Further annealing can then reform the carbon again into a structure in which a larger proportion of the carbon undergoes ring formation, providing a further increase in electronic conductivity, while simultaneously increasing the lithium conductivity of the sample. It appears that the optimal temperature window for promoting transport through the coating is similar to the optimal temperature for forming nanocrystals. At very high temperatures, it is known that unfavorable SiC can form at the boundary between the coating and silicon—this is not the case in the samples of this invention, due to limited carbon migration at the relevant temperatures.

[0121] As illustrated in one example below, powders can exhibit good surface kinetics (electronic and lithium conductivity) without annealing that causes structural changes (as described above, which produces a mixture of amorphous and crystalline Si and SiC domains). In such cases, it is generally observed that the crystal structure gradually increases when these particles are studied as active materials in the anode of a LIB, as loosely bonded Si or C atoms move around due to Li until they encounter a stronger anchor in the nanocrystals. This phenomenon has also been documented as cycling of amorphous silicon nitride and can be referred to as “electrochemical annealing.” This gradual improvement in kinetics is not beneficial in commercial batteries, where it is more desirable for the battery to initially possess its full capacity. Therefore, thermal annealing is preferred over electrochemical annealing. The combined effect of the gradual improvement in bulk conductivity with the non-single behavior of annealing and coating conductivity can produce unexpectedly poor results in the intermediate temperature range of 700–800°C, where the coating can be in its densest state. The lithium conductivity of the coating is difficult to measure as a free parameter, while electronic conductivity can be measured by simply compressing the powder into spheres and measuring the electronic DC resistance between the two surfaces of the compressed spheres. Our conductivity measurement was performed by applying a force of 4 metric tons to cylindrical powder spheres with a diameter of 1 cm and a thickness of approximately 1 mm. Given the resistance and sphere size, the resistance can be calculated by those skilled in the art.

[0122] The raw, untreated powder from this invention can have a content of < 1.10. -6 The initial conductivity is measured in S / cm. Uncoated annealing can increase the conductivity by orders of magnitude. After annealing, a carbon coating of 2 nm or larger can increase the conductivity to >1.10. -1 S / cm.

[0123] Grinding

[0124] Almost all of the aforementioned silicon-based composite particles are formed into spherical or near-spherical shapes after formation. However, spherical or near-spherical particles can aggregate into unidirectional or multidirectional chains. These chains of aggregated particles are broken into individual particles and / or small particle clusters through a relatively mild grinding process, namely a grinding process with forces (feed and grinding pressure) sufficient to break the aggregated particle chains, resulting in a more uniform particle size distribution, but not so large that most particles have had their surface geometry altered by the grinding process.

[0125] Therefore, in one embodiment, the silicon-based composite particles according to the first aspect of the invention further comprise mildly abrasive particles having a generally spherical shape as determined by the following criteria: - 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% of all sub-segments of the circumference of the particles shown in the SEM image of the material are arcs. - Each arc in the SEM image has an arc length s determined by the formula s = r·π / 180·θ, where r is the radius of a circle whose circumference has the same curvature as 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) between the arc and the center of the circle. - The angle θ is in the range of 10 to 360°.

[0126] In one embodiment, the silicon-based composite particles according to the first aspect of the invention have a particle size of 0.2 to 10 μm, as determined by standard ISO 9277:2010. 2 / g, preferably 0.3 to 8 m 2 / g, more preferably 0.4 to 6 m 2 / g and the optimal value is 0.5 to 4m 2 / g of BET surface area.

[0127] Characteristics of the particles used

[0128] The above description of these silicon-based composite particles is largely directed at “raw” particles, as they are produced with or without annealing.

[0129] However, when silicon-based composite particles according to the first aspect of the invention are incorporated into the negative electrode of a battery, the Bragg peak can be difficult to discern using normal XPD measurements. The beam size is typically very broad and passes through a significant amount of electrode material, making it possible to probe not only the particles but also the surrounding carbon sources, such as graphite or conductive carbon additives. In this case, the silicon peak may be nearly invisible on the shoulder of the graphite peak, and the 111 peak (at 28°, with CuKα radiation) can be difficult to quantify, such as... Figure 14 As shown in 14a) and 14b), XPD diagrams of commercially relevant mixtures of particles and graphite mixed in a weight ratio of 15:85 according to the first aspect of the invention are presented.

[0130] like Figure 14 As shown in a), with the main graphite peaks displayed at their full height, the crystalline graphite signal completely masks the weak XPD pattern from nanocrystalline silicon. Figure 14 In b), it is in Figure 14 An extreme close-up of the XPD plot shown in a) shows that the SiC peak is almost indistinguishable near the graphite peak, while the Si peak is largely obscured by the graphite peak.

[0131] This problem can be addressed by using transmission electron microscopy (TEM) in diffraction mode. The narrow beam of electron diffraction measurements allows for high selectivity and can display the same information as XPD measurements. Using focused ion beam (FIB) in scanning electron microscopy (SEM), thin TEM layers can be prepared such that these layers include cross-sections of individual particles. 2D diffraction patterns can then be collected.

[0132] Figure 15 a) shows the diffraction pattern of the original particle. Figure 15 b) shows similar particles after repeated lithiation and delithiation in a battery. The radius of the diffraction rings shown in the image is uniquely correlated with the 2θ of the peak in the XPD plot and is a function of the relationship between the electron beam wavelength and the XPD beam wavelength. This relationship is well known to those skilled in the art. In these images, the TEM used an accelerating voltage of 200 kV, resulting in an electron wavelength of 0.025 Å, much smaller than the 1.5418 Å measured by XPD. Nevertheless, using Bragg's law, the interatomic spacing (d) can be calculated from both sources in the same manner. Moreover, in Figure 15 In a), the rings corresponding to Si and SiC can be clearly identified. Figure 15 In the cyclic particles in b), the Si phase appears more amorphous with shallower rings, but the SiC rings are distinct. This is consistent with literature findings that crystalline silicon is amorphous during lithiation cycling. These diffraction patterns are integrated over 360 degrees in the tangential direction (i.e., perpendicular to 2θ) to have a 1D pattern. Figure 16 These 1D patterns are shown in the figure.

[0133] Can come from Figure 15 The information from the 2D images in a) and 15b) can be converted into 1D images, and the 2θ angle can be converted into a Cu radiation equivalent value for comparison with XPD results, such as... Figure 16As shown. The intensity is shown as a function of distance from the center of the ring, integrated over the entire circle in the tangential direction to remove noise and convert the 2D image into a 1D representation. The x-axis in this image is the number of pixels from the image center, which is related to d and 2θ, while the y-axis is the integrated beam intensity. Many TEM instruments will produce dots instead of circles due to details of the sensor setup, which those skilled in the art will be able to correct for before integrating around the circle. Figure 16 As shown, the Si and SiC peaks clearly appear in the expected positions. Therefore, there is complete equivalence between the XPD peaks identified in the claims and the diffraction peaks derived from TEM diffraction.

[0134] When lithiation and subsequent delithiation occur, the crystalline silicon phase transforms into an amorphous form. A comparison of similar particles (made using the same methods / process parameters), one being pristine and the other having undergone several lithiation / delithiation cycles, was made by… Figure 15 The images in 15a) and 15b) are shown. As described above, the two images are processed to give... Figure 16 The two superimposed curves / graphs shown are illustrated. The thick solid line / curve corresponds to the original particles, while the thin dotted line / curve corresponds to the lithiation / delithiation cycle particles. (As shown in...) Figure 16 The SiC peak at 35.8° seen above is actually the same in both graphs. However, the peak at 28.5° is significantly broadened in the graph from the cycloidized particles. The fact that the silicon phase in the particles has become amorphous through lithiation does not change the fact that Si crystallites were present when the particles were initially introduced into the electrode before the first lithiation. Using... Figure 3 The TEM technique shown to produce similar XRD curves can demonstrate that the Si and SiC phases do not change in size or position in many cases during lithiation, so although the Si peak broadens, the materials can be considered to originate from the same source.

[0135] Second aspect of the invention - method for preparing particles

[0136] The silicon and carbon-based composite particles according to the invention are preferably produced by condensation and chemical vapor deposition (CVD) of a mixture of silicon-containing precursor gas and carbon-containing precursor gas in a protected atmosphere (i.e., containing little or no oxygen).

[0137] Therefore, in a second aspect, the present invention relates to a method for producing silicon-based particles, wherein the method comprises: - A reactor with a decomposition chamber is used, the decomposition chamber containing 5.10 3 up to 6.10 5 The first reactor gas, with an initial pressure in the range of Pa and a first reactor temperature in the range of 450°C to 650°C, - A precursor gas mixture is formed, the precursor gas mixture comprising a first precursor gas containing a silicon compound and a second precursor gas containing a carbon 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. - Injecting the precursor gas mixture into the decomposition chamber, and mixing the precursor gas mixture with the first reactor gas to form a second reactor gas mixture, characterized in that the method further comprises: - The second reactor gas mixture is held in the decomposition chamber for a residence time of 10 to 300 seconds, while 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 temperature of the first reactor. - The gas mixture in the second reactor is maintained in the decomposition chamber for a residence time of 10 to 300 seconds, and during this residence time, the injected precursor gas mixture is subjected to at least one temperature change from the first reaction temperature to the second reaction temperature and then back to the first reaction temperature, wherein... - The absolute temperature difference between the first and second reaction temperatures is in the range of 1 to 100°C, preferably 3 to 75°C, more preferably 5 to 50°C, even more preferably 10 to 35°C, and most preferably 20 to 25°C. - These particles were extracted from the decomposition chamber. - Cool the particles to room temperature, and - Heat the particles at a heating rate in the range of 1 to 5°C / min until an annealing temperature in the range of 800 to 1000°C, and then cool the particles.

[0138] As used in this article, the term "absolute temperature change of X°C" means that the temperature difference between the first and second reaction temperatures can make the second reaction temperature X°C lower or X°C higher than the first reaction temperature.

[0139] In an embodiment of the second aspect of the invention, the absolute temperature difference between the first and second reaction temperatures is in the range of 5 to 100°C, more preferably 10 to 75°C, more preferably 15 to 50°C, more preferably 20 to 40°C, and most preferably 25 to 35°C.

[0140] In an embodiment of the second aspect of the invention, the temperature of the first reactor is 475 to 630°C, preferably 500 to 620°C, more preferably 525 to 600°C, and most preferably 550 to 580°C.

[0141] In an embodiment of the second aspect of the invention, the dwell time can advantageously be 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, more preferably 30 to 50 seconds, more preferably 0.2 to 280 seconds, preferably 0.5 to 250 seconds, more preferably 1 to 230 seconds, more preferably 1.5 to 200 seconds, more preferably 5 to 180 seconds, more preferably 10 to 150 seconds, more preferably 15 to 100 seconds, more preferably 25 to 75 seconds, and most preferably 2 to 50 seconds.

[0142] In an embodiment of the second aspect of the invention, the atomic ratio Si:C in the precursor gas mixture can be in the range of 0.3 to 40, preferably 0.4 to 30, more preferably 0.5 to 25, more preferably 0.6 to 20, more preferably 0.8 to 15, more preferably 1.0 to 10, more preferably 1.2 to 4, more preferably 1.5 to 2.0, more preferably 0.3 to 40, preferably 0.4 to 35, more preferably 0.5 to 30, more preferably 0.6 to 25, more preferably 0.8 to 20, more preferably 1.0 to 15, more preferably 1.5 to 12, more preferably 2 to 10, and most preferably 2.5 to 7.5.

[0143] With D from 1 to 9 µm 50 and D in the range of 1 to 9 90 / D 10 The implementation of particles with a relatively narrow particle size distribution ratio can be prepared by maintaining the second reactor gas mixture in the decomposition chamber for a residence time ranging from 10 to 300 seconds, while 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.

[0144] This can be achieved by controlling the flow conditions so that the majority, preferably all, particles in the gas phase within the reactor are exposed to the same average temperature conditions and duration (residence time) as closely as possible before extraction and cooling. In conventional continuous flow reactors, thermal convection typically becomes dominant when the reaction time exceeds a few seconds, making laminar flow difficult to achieve. The residence time of any single atom or particle in the reactor can vary greatly depending on the path taken. This means that more precursor gas leaves the reactor unconsumed, or many particles leave the reactor still very small. Simultaneously, there is no clear upper limit to particle size, as some particles can circulate within the reactor for a considerable period.

[0145] In one embodiment, the method according to the invention may further include the application of a tubular hot-wall reactor, wherein a constant flow of a preheated mixture of precursor gases and a preheated first gas are simultaneously injected at one end, and wherein the flow conditions through the reactor are laminar, thereby ensuring a predictable travel time before the particles are extracted at the opposite end.

[0146] Another way to ensure nearly identical processing conditions is to inject a mixture of preheated precursor gases into a closed hot-wall reactor and extract the entire batch when the desired residence time is achieved by flushing or vacuum suction, or to allow the particles to grow to a certain weight so that they settle out of the gas phase and are then collected and extracted. Specifically, rapid acceleration at the edges can result in heavier particles settling out, as in cyclone particle separators.

[0147] The latter solution, which allows particles to grow until they fall from the gas phase, can have a significant sorting effect on the resulting particles. This sorting effect can be strong enough to achieve the desired Dg when including particles with a smaller size fraction. 90 / D 10 The narrow particle size distribution of the ratio means that these particles remain entrained in the gas phase and leave the reactor along with the gas in which they are entrained when the particles are collected.

[0148] In one embodiment, the method according to the second aspect of the invention can advantageously achieve the following: maintaining the temperature of the second reactor gas mixture inside the decomposition chamber: - A reactor with a tubular hot-walled decomposition chamber, the tubular hot-walled decomposition chamber having a first end and a second end, and - A preheated precursor gas mixture at a constant volume flow rate and a preheated first reactor gas at a constant volume flow rate are injected into the first end, thereby forming a second reactor gas mixture at a constant volume flow rate inside the tubular hot-wall decomposition chamber. - Under laminar flow conditions with a Reynolds number less than 2000, the gas mixture in the second reactor is allowed to pass from the first end through the tubular hot-wall decomposition chamber to its second end, and - At the second end, a second reactor gas mixture, including the formed particles, is extracted. or - A reactor having a closed hot-walled decomposition chamber containing the gas from the first reactor, and - The preheated precursor gas mixture is injected into the hot-wall decomposition chamber at the first moment to form the second reactor gas mixture, and - When the residence time is calculated from the first moment, both the gas mixture and the formed particles from the second reactor are extracted from the hot-wall decomposition chamber by vacuum suction or flushing. or - The application is a reactor having a closed hot-walled decomposition chamber containing the first reactor gas and a cooling collection chamber at the bottom of the decomposition chamber. - The preheated precursor gas mixture is injected into the hot-wall decomposition chamber to form the second reactor gas mixture, and - The second reactor gas mixture is held in the hot-wall decomposition chamber until the formed particles grow to the size at which they settle out of the second reactor gas mixture and fall into the collection chamber by gravity.

[0149] An exemplary embodiment of the present invention, comprising one or more internal shell-like layers, can be prepared by allowing thermal convection to transport gas between different regions of the decomposition chamber, which are respectively heated to a first reaction temperature and a second reaction temperature. The particles carried by the gas flow can exchange energy through convection and / or radiation with the chamber walls, meaning that the temperature controlling particle growth varies with their position within the decomposition chamber.

[0150] As used herein, the term "initial pressure" takes into account that the pressure in the free space chamber of the reactor can vary during the injection of the precursor gas mixture, such that the initial pressure refers to the pressure of the reactor gas in the free space chamber at the moment the injection of the precursor gas begins.

[0151] As used herein, the term "residence time" refers to the time range from the moment the injected precursor gas begins to decompose and form seed crystals to the moment when these seed crystals grow and transform into the desired product particles extracted from the free space chamber of the reactor. In the case of continuous production using a single-pass reactor such as a hot-walled tubular reactor, where the precursor gas is continuously injected at one end and the resulting particles are extracted at the opposite end, residence time refers to the time range from the injection of a certain volume of precursor gas until the particles produced therefrom leave the opposite end of the tubular reactor.

[0152] In an alternative embodiment, the preparation method can be a batch method using a reactor with a closed free space chamber. In this embodiment, the injection of precursor gas will increase the pressure within the free space chamber, and the residence time refers to the time range from the moment the precursor gas is first injected until the gas and particulate contents of the free space chamber are extracted and collected by flushing or vacuum suction.

[0153] In one embodiment, at least one temperature change from the first reaction temperature to the second reaction temperature is obtained by: - A reactor with a hot-wall decomposition chamber, the hot-wall decomposition chamber comprising at least one first zone and at least one second zone, wherein the at least one first zone has a wall temperature equal to the first reaction temperature, and the at least one second zone has a wall temperature equal to the second reaction temperature, and - The precursor gas mixture is transported during the hot-wall decomposition via thermal convection between the at least one first zone and the at least one second zone. or - A reactor with a hot-walled decomposition chamber, the hot-walled decomposition chamber comprising an injection zone and a first decomposition zone, the first decomposition zone having a wall with a wall temperature equal to the first reaction temperature, and - Turbulence is formed in the injected precursor gas mixture within the decomposition chamber, which transports the second reactor gas mixture between the injection zone and the first decomposition zone of the hot-wall decomposition chamber. or - A reactor with a tubular hot-wall decomposition chamber, the tubular hot-wall decomposition chamber comprising a plurality of alternating first and second zones, wherein the first zones have a wall temperature equal to the first reaction temperature, and the second zones have a wall temperature equal to the second reaction temperature, and - The precursor gas mixture (optionally mixed with the first reactor gas to form the second reactor gas) is injected into the first end of the tubular hot-wall decomposition chamber, and the precursor gas mixture (optionally the second reactor gas mixture) is passed through the tubular hot-wall decomposition chamber under laminar flow conditions at a Reynolds number of less than 2000.

[0154] Particle size also depends on temperature. High temperatures and low residence times will produce small particles. Low temperatures and long residence times will produce larger particles. Further, even smaller particles can be obtained by diluting the silane or silane / hydrocarbon mixture with, for example, H2, argon, or N2. This method can also be carried out at low pressures (<100 mbar), atmospheric pressure, or higher. Alternatively, the pressure can be varied during particle growth. In one embodiment, after a selected residence time for particle growth, the particles can be extracted by rinsing or vacuum.

[0155] To achieve an average particle size > 500 nm, the reaction temperature typically needs to be relatively low (< 600°C) and the residence time long (> 10 s). In many reactor types (fluidized bed or flow-through reactors), controlling the reaction time is very difficult because some gases will flow through the short path of the decomposition chamber, while others will flow through the long path. This wide distribution will result in the production of small particles and low utilization of reactant materials for the gases using the short path, or excessive particle growth and aggregation in the gases using the long path. Therefore, in one embodiment, controlling the residence time to achieve size control and good utilization of the reactant gases can be advantageous. Long residence times mean that laminar flow or near-piston flow reactors will be more difficult to achieve due to the change in gas density as the precursor gas decomposes and produces light hydrogen.

[0156] One way to achieve a fairly uniform residence time is by increasing the pressure by filling the closed decomposition chamber. When the pressure increases to a point where the reaction rate becomes significant, the reaction will accelerate simultaneously in all parts of the chamber, resulting in fairly uniform growth conditions. The uniformity of growth conditions can also be enhanced by the medium filling ratio. If the chamber further has walls with temperature variations, this allows for thermal convection mixing of the gas and provides the desired temperature fluctuations to produce ring structures. The reaction can be stopped by evacuating or flushing the gas from the decomposition chamber and moving the particles and gas to a cold zone where the reaction has ceased.

[0157] Because silanes are consumed faster than most hydrocarbon precursors, this results in a gradient of increasing carbon content up to the particle surface. This can cause the particle core to expand more than the periphery, leading to particle breakage during cycling. By continuously feeding more gas into the chamber even after the reaction has begun, similar conditions can be maintained in the early and late stages of particle production, making the carbon content primarily controlled by temperature rather than primarily by the gas mixture. Furthermore, allowing a small amount of carbon precursor gas to be present at the start of silane filling can contribute to a smaller difference between the particle core and the circumference.

[0158] Continuous filling of a fixed volume can also facilitate turbulent mixing of gases, resulting in a more uniform gas concentration, and allow for the temperature variations required to form one or more shell-like layers within the bulk material of the particle.

[0159] As used herein, the term "first precursor gas of a silicon-containing compound" refers to any silicon-containing compound that is in the gaseous state and reacts at the intended reaction temperature to form Si particles. Examples of suitable first precursor gases include, but are not limited to, silanes (SiH4), dichlorosilanes (Si2H6), and trichlorosilanes (HCl3Si), or mixtures thereof.

[0160] Similarly, as used herein, the term "second precursor gas of a carbon-containing compound" refers to any carbon-containing compound that causes C atoms to bind to the matrix surrounding the Si particles formed when heated to the intended reaction temperature. Examples of suitable second precursor gases of carbon-containing compounds include, but are not limited to, alkanes, alkenes, alkynes, aromatic compounds, and mixtures thereof. In exemplary embodiments, the second precursor gas of a carbon-containing compound may be at least one organosilane or hydrocarbon, preferably methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), acetylene (C2H2), cyclohexane, cyclohexene, toluene, benzene, propylene, butene, pentene, or mixtures thereof. The gas phase may also contain less or more hydrogen.

[0161] A particularly preferred exemplary embodiment of the precursor gas (i.e., a homogeneous gas mixture of gaseous silicon and hydrogen compounds, and gaseous substitution element C and hydrogen compounds) is a mixture of silane (SiH4) or silane (Si2H6) with a hydrocarbon gas selected from: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H4). 10 ), ethylene (C2H4), acetylene (C2H2), propylene (C3H6), butene (C4H8), pentene (C5H4) 10 ), cyclohexane, cyclohexene, toluene, benzene, and mixtures thereof. The use of larger and more stable ring structures is preferred, as this will enhance the C / C bond ratio to Si-C bond in the first matrix.

[0162] The production yield in a gas-phase reaction process is defined as the ratio of the mass of the produced particles to the mass of the precursor gas fed into the reactor. This yield depends on process parameters such as the concentration of the precursor gas in the reaction zone, the reaction temperature, and / or the residence time of the precursor gas in the reaction zone. Generally, higher reaction temperatures result in higher dissociation of the precursor gas, and thus higher yields. Furthermore, residence time also significantly impacts the yield. Typically, longer residence times allow more injected gas to react and form particles. Therefore, from a yield perspective, using relatively long residence times to obtain larger particles is advantageous. This method thus offers the advantage of achieving high yields, which provides a significant economic advantage, as hydride gases such as silanes and silanes are relatively expensive.

[0163] In one embodiment, the method according to the second aspect of the invention can advantageously maintain the temperature of the second reactor gas mixture inside the decomposition chamber by: - A reactor with a tubular hot-walled decomposition chamber, the tubular hot-walled decomposition chamber having a first end and a second end, and - A preheated precursor gas mixture and a preheated first reactor gas mixture with a constant volume flow rate are injected at the first end, forming a second reactor gas mixture with a constant volume flow rate in the tubular hot-wall decomposition chamber. - The gas mixture in the second reactor is brought from the first end through the tubular hot-wall decomposition chamber to the second end under laminar flow conditions at a Reynolds number less than 2000, and - Extract the second reactor gas mixture containing the formed particles at the second end. or - A reactor having a closed hot-walled decomposition chamber containing the gas from the first reactor, and - The preheated precursor gas mixture is injected into the hot-wall decomposition chamber at the first moment to form the second reactor gas mixture, and - When the residence time is calculated from the first moment, the gas mixture and formed particles from the second reactor are extracted from the hot-wall decomposition chamber by vacuum suction or flushing. or - The application is a reactor having a closed hot-walled decomposition chamber containing the first reactor gas and a cooling collection chamber at the bottom of the decomposition chamber. - The preheated precursor gas mixture is injected into the hot-wall decomposition chamber to form the second reactor gas mixture, and - The gas mixture in the second reactor is held in the hot-wall decomposition chamber until the particles formed grow to a certain size, at which point they settle out of the gas mixture in the second reactor and fall into the collection chamber by gravity.

[0164] The term "substantially at a certain temperature" as used herein takes into account the difficulty in practice of maintaining and controlling the temperature of the gas mixture / precursor gas flowing inside a free-space chamber precisely at the desired temperature. In practice, there may be unintentional / unavoidable deviations in the temperature of the reactant gas mixture from the desired temperature of the reactant gas mixture by less than ±25°C, preferably less than ±10°C, and most preferably less than ±5°C.

[0165] In one embodiment, the method according to the second aspect of the invention may further include forming a carbon surface coating on the particles by vapor deposition at a temperature lower than the first coating temperature prior to the step of annealing the particles at an annealing temperature, wherein the annealing temperature is at least 50°C higher than the first coating temperature.

[0166] In one embodiment, the method according to the second aspect of the invention may further include applying a carbon precursor onto these particles by a wet chemical process to form a carbon surface coating prior to annealing. In one embodiment, the carbon precursor may advantageously be one or more of bitumen, pitch, polyacrylonitrile, polystyrene, sugar, or phenolic resin.

[0167] Third aspect of the invention

[0168] In a third aspect, the present invention relates to particles produced by a method according to a second aspect of the invention.

[0169] Fourth aspect of the invention - negative electrode for secondary lithium-ion electrochemical batteries

[0170] In a fourth aspect, the present invention relates to a negative electrode for a secondary lithium-ion electrochemical battery, the negative electrode comprising: - Active materials, - Adhesive materials, and - current collector substrate, The active material is characterized in that it is a silicon-based particle according to the first or second aspect of the present invention.

[0171] Fifth aspect of the invention - Use of particles in LIB

[0172] In a fifth aspect, the present invention relates to the use of particles according to the first or second aspect of the present invention in secondary lithium-ion electrochemical batteries. Attached Figure Description

[0173] Figure 1 It is from Sung et al. (2021) [ref 6] Figure 1 A copy of the image.

[0174] Figure 2 This is an XRD pattern of an exemplary embodiment of S1 prior to post-production annealing according to the present invention.

[0175] Figure 3 These are a series of XRD curves of S1 exemplary embodiments of the present invention, which have undergone different post-production annealing processes.

[0176] Figure 4 This is a TEM image of an exemplary embodiment of particles having multiple internal shell-like layers according to the present invention, S3.

[0177] Figure 5 yes Figure 4 The EELS plot of the S3 particles shown in the TEM image.

[0178] Figure 6 TEM images and EELS diagrams of an exemplary embodiment of particles according to S8 are shown.

[0179] Figure 7 TEM images and EELS plots of particles according to an exemplary embodiment of particles S8 of the present invention are shown.

[0180] Figure 8 The S8 exemplary embodiment of the particles according to the present invention is shown. Figure 7 TEM image and EELS plot of another particle besides the one shown.

[0181] Figure 9 and 10 The Fourier transform is shown, where the bandpass masks are centered at 0.314 and 0.252 nm, respectively, to highlight... Figure 7 Crystalline silicon and silicon carbide of an exemplary embodiment are shown in the TEM photograph of a).

[0182] Figure 11The cyclic data of particles according to the exemplary embodiment of S11 of the particles according to the present invention are shown in three forms: S11-1: No annealing S11-2: Anneal at 820°C for 2 hours S11-3: Coat with sugar, then anneal at 820°C for 2 hours. In all cases, the powder is mixed with graphite in a 50 / 50 ratio. Conversion-ratio test (3 cycles for each of C / 10, C / 5, C / 3, C / 2, C, 2C) Further testing of S11-2: 20x(C / 20+10xC / 3), after approximately 250 cycles: new multiplier test, then back to 25x(C / 10+10x1C / 3). For S11-3, after approximately 250 cycles (C / 10 + 20xC / 2), the result is 20x(C / 20 + 10xC / 2). The highest point of the slow cycle is used as the "maximum capacity" of S11-3.

[0183] Figure 12 Cycling data for S9 powder produced by the method described in this document are shown, followed by annealing at 650°C, PAN coating, and polymer crosslinking at 500°C. A pure graphite electrode is used as a reference, while the upper line shows a cell with 10 wt% silicon in 90 wt% graphite. The cycling program was 4xC / 20–3xC / 10–3xC / 5–3xC / 3–3xC / 2–3x1C–3x2C–1xC / 20, followed by a repeating set of 2xC / 10+20xC / 2. Capacity and FCE were measured in individual cells without graphite to reduce uncertainty, while graphite helps avoid electrode delamination, thus allowing for proper measurement of silicon degradation. The gradual increase in capacity during the first 50-ish cycle can be attributed to electrochemical annealing.

[0184] Figure 13 Cyclic data for S10 powder produced by the method described in this document are shown, with subsequent pitch coating and annealing at 900°C. The reference is a pure graphite electrode, while the upper line shows a cell with 15 wt% silicon in 85 wt% graphite. The cycling program was 4xC / 20–3xC / 10–3xC / 5–3xC / 3–3xC / 2–3x1C–3x2C–1xC / 20, followed by a repeating set of 2xC / 10+20xC / 2. Again, FCE and capacity were measured in separate cells without graphite. No gradual increase was observed when the powder was fully nanocrystalline—the powder started with maximum capacity.

[0185] Figure 14a) shows the XRD pattern of a commercially relevant mixture of particles according to the invention mixed with graphite at a weight ratio of 15:85, while Figure 14 b) shows a close-up of the same image, indicating the presence of the SiC peak, while the Si peak is still not properly identifiable on the shoulder of the graphite peak.

[0186] Figure 15 a) and 15b) show the TEM diffraction patterns of individual particles in the battery electrode. Figure 15 In image a), the beam of light is focused on unrecycled particles annealed at 890°C with approximately 16 wt% carbon. Figure 15 In image b), the beam has been focused onto recycled particles annealed at 925°C with approximately 12 wt% carbon. The arrow labeled 2θ indicates how the 2D diffraction of the image correlates with the 1D plot from XPD measurements.

[0187] Figure 16 It shows Figure 15 The results of the angular integrals of the images in a) and 15b) for CuKa PXD measurements, with the peak positions identified and recalculated as the corresponding 2θ values, demonstrate the equivalence of the measurement methods. The figure clearly shows the broadening of the Si peak in cycled silicon due to amorphization during lithiation and delithiation.

[0188] Figure 17 a) and 17b) are bar graphs showing the Rietveld refined estimate of Si crystallite size by X-ray powder diffraction (XPD) for particulate samples having carbon contents of 8, 11, 13, 15, 17 and 19 wt% respectively according to the invention, wherein the samples having the said carbon contents were annealed at temperatures of 600, 700, 800, 900, 1000 and 1100°C respectively. Figure 17 a) is a bar graph showing the estimated Si crystallite size grouped as a function of carbon content for samples annealed at different temperatures, while Figure 17 b) is a bar chart, representing the relationship between... Figure 17 The estimated Si crystallite size of the same samples in a) is now grouped as a function of annealing temperature. Samples are identified as amorphous with small bars marked with a crystallite size of 0.2, while negative bars indicate no measurement.

[0189] Figure 18 a) and 18b) are respectively similar to Figure 17 a) and 17b), but now for the estimated SiC crystallite size determined by Rietveld refinement such as X-ray powder diffraction (XPD) data.

[0190] Figure 19 a) and 19b) are examples of applications. Figure 17Bar graphs of the first-cycle lithiation capacity measured from the same particulate samples according to the invention in a), 17b), 18a), and 18b). Figure 19 a) shows the measured first-cycle lithiation capacity of the samples as a function of carbon content, while Figure 19 b) shows that the measured FCE grouping of the sample is a function of the annealing temperature.

[0191] Figure 20 a) and 20b) are shown in Figure 17 A bar graph of the first cyclic coulombic capacity (FCC) of the same sample of particles according to the invention used in a) to 19b). Figure 20 a) shows the measured first-cycle lithiation capacity of the samples as a function of carbon content, while Figure 20 b) shows that the measured FCE grouping of the sample is a function of the annealing temperature.

[0192] Figure 21 This is a graph showing the initial lithiation capacity measured when the particle sample according to the invention is mixed with different amounts of graphite and applied as the active material of the negative electrode in a secondary LIB. The x-axis represents the mass fraction of the particles according to the invention in the active material of the negative electrode, with the remainder being graphite.

[0193] Figure 22 This is a bar chart showing the FWHM of the Si peak at approximately 28°C for samples with different carbon contents and annealing temperatures (grouped by temperature). For amorphous samples, where the peak is not explicitly defined, the value has been fixed at 8 as a visual aid. Negative values ​​indicate missing data points.

[0194] Figure 23 This is a bar chart showing the FWHM of the SiC peak at approximately 36°C for samples with different carbon contents and annealing temperatures (grouped by temperature). For amorphous samples, where the peak is not explicitly defined, the value has been fixed at 10 as a visual aid. Negative values ​​indicate missing data points.

[0195] Figure 24 a) and 24b) show the particulate material according to the invention before a gentle grinding process ( Figure 24 a) and afterwards ( Figure 24 b) SEM image. In non-abrasive materials, the circumference of all particles can be regarded as an aggregate of basically circular circumferences, while in mildly abrasive materials, the circumference of some particles is non-circular, as shown by the white arrow.

[0196] Figure 25 It shows Figure 24 The subsection of the SEM image in b) shows an example where the circumference is an arc. Circumferential portions that are not part of an arc / circle and are the result of breakage caused by the grinding process are marked with dashed lines. Detailed Implementation

[0197] Verification of the present invention

[0198] The present invention will be described in more detail by way of exemplary embodiments.

[0199] Example - Granule Production

[0200] A series of samples of particles according to the invention (labeled herein as S1 to S6) were prepared by using a tubular steel chamber of approximately 30 liters, closed at both ends as a decomposition chamber. This chamber was connected to a feed nozzle and a valve that directed a filter to a vacuum pump at the first end. Half of the (longitudinal) sidewall of the tubular steel chamber, adjacent to the second end opposite the first end, was heated to a first reaction temperature, while the other half of the sidewall was heated to a second reaction temperature. The chamber was filled with a first reactor gas of nitrogen, hydrogen, and / or gaseous residues from a previous production, optionally including portions of ethylene and C2H4, in an amount sufficient to generate an initial gas pressure inside the steel chamber when the first reactor gas reached thermal equilibrium with the hot walls of the chamber. Each sample of particles is generated through the following process: a stream of silane (SiH4) is injected through a feed nozzle at a first volumetric flow rate and a preheated temperature of approximately 350°C, while simultaneously a stream of ethylene (C2H4) is injected at a second volumetric flow rate and a preheated temperature of 350°C, until the pressure within the steel chamber increases to a second gas pressure, which takes approximately 60 seconds. The injected precursor gas mixture is then held in the heated steel chamber for approximately 45 seconds. The total residence time is approximately 105 seconds. After the residence time is reached, the gas mixture within the steel chamber is then extracted via a filter by suction generated by a vacuum pump. Particles are collected from the reactor wall and the filter.

[0201] The applied temperature, pressure, and feed rate, as well as the total carbon content of the resulting particles, are summarized in Table 3.

[0202] D of samples S5 and S6 10 D 50 and D 90 Particle sizes were measured by laser diffraction analysis according to standard ISO 13320:2020 and were found to be 3.23, 8.25, and 18.7 µm for S5 and 3.56, 9.02, and 19.2 µm for S6. Other samples are expected to fall within the same region. This gives Di values ​​of 5.8 and 5.4 for S5 and S6, respectively. 90 / D 10 .

[0203] Table 3. Carbon content obtained from some process conditions applied to particle formation.

[0204] Verification of particle structure

[0205] The particles in exemplary embodiments S1 to S6 are produced due to temperature fluctuations during the CVD growth stage caused by the use of two temperature zones in the decomposition reactor. The heating zone has the temperature indicated above, while the cooler zone, including the silane nozzle and valve, is at a lower temperature, which can be as low as at least 350°C. The gas circulates between the hot and cold zones until most of the silane is consumed. This is intended to form embodiments with particles having an internal shell-like layer.

[0206] Figure 7 a) and 8a) are TEM images of two particles according to an exemplary embodiment of the particles of S8 according to the present invention, having particle sizes of approximately 3 µm and approximately 0.8 µm, respectively. The images show that the particles are very dense, with no identifiable pores, and are very homogeneous, with no identifiable phases or irregularities. (The images are obtained by tracing along the lines of...) Figure 7 The portions marked by the two white lines in a) and 8a) were analyzed on the particles. Elemental composition analysis based on electron energy loss spectroscopy (EELS) confirmed the homogeneity. As can be seen from the EELS plot, silicon content is the upper line and carbon content is the lower line, with both types of particles having a substantially uniform elemental ratio and an average carbon content of 14 atomic % (corresponding to 6.5 wt%).

[0207] The expected nanoscale crystalline domains of Si and SiC, anticipated to be found in the heat-treated particles, are identifiable in TEM images; however, some assistance is needed to distinguish the phases because the human eye cannot separate their individual lattice constants. The crystalline phases can be made visible via Fourier transform, where a bandpass mask centered at 0.314 nm and 0.252 nm corresponds to the highest distances between the lattice planes of crystalline silicon and silicon carbide, respectively.

[0208] Figure 9 It shows the use of Figure 7 The TEM image in a) shows the result of the sample's center being converted using a 0.314 nm bandpass mask. The conversion occurred at a portion of the particle, which included a graphite substrate, to which the particle sample was immobilized during analysis. Graphite is almost invisible, appearing in a slightly darker area at the bottom of the image, covering approximately 10% of the area. Above this relatively dark area are numerous bright spots indicating the presence of crystalline silicon. A relatively uniform and even distribution is noted. This indicates that the nanoscale domains of silicon are uniformly distributed throughout the particle. If in Figure 10 The same imprint was found, which showed the result of the transformation at the same part of the particle, where the bandpass mask was concentrated at 0.258 nm, thus marking the presence of nanoscale domains of crystalline silicon carbide.

[0209] The photographs were overlaid, with the crystalline phase labeled in one color and the crystalline silicon carbide phase labeled in a contrasting color. This result is not included in the application because these phases cannot be distinguished from each other in black-and-white reproduction. However, the overlaid photographs show that the silicon and silicon carbide crystals are spatially separated and entangled, as expected of a composite structure consisting of densely packed aggregates of silicon domains with layers of amorphous carbon and / or amorphous silicon carbide at the grain boundaries between them, and that the composite structure is crystallized and collected in the crystalline silicon carbide regions between the crystalline silicon domains by annealing.

[0210] Therefore, these results confirm that the particles of this embodiment, prepared at a relatively low temperature of 560°C and below one atmosphere, have a composite structure similar to the film described by Sung et al. (2021), but the composition is uniformly distributed throughout the particle from the core to the outer surface. This uniformity, relatively large particle size, and relatively low particle size distribution make the particles particularly suitable as active materials in the anode of secondary LIBs, as their size provides high initial cycle efficiency, they have a uniform distribution of a carbon-containing phase that provides excellent stability and a silicon phase that provides excellent lithium diffusivity (conductivity), and simultaneously have a relatively high silicon loading that provides high volumetric lithium storage capacity through numerous tiny nanoscale domains with excellent cycling performance (due to the stabilizing SiC domains).

[0211] Verification of annealing effect

[0212] The powders produced above are post-processed in a variety of different ways.

[0213] More carbon can be applied as a coating to increase conductivity. Care must be taken to minimize oxygen exposure of the powder prior to coating. In this embodiment, coating is achieved through gas coating and wet chemical coating with carbon precursors. The carbon precursors tested include polyacrylonitrile (PAN), polystyrene, bitumen (BIT), sugars, phenolic resins, and fumed hydrocarbon coatings. Thicker, yet still uniform, fumed coatings can be achieved by raising the temperature to a level where some hydrogen leaves the carbon. If the coating is applied at a temperature that does not remove all hydrogen, recombination during subsequent pyrolysis above 50°C appears to favor lithium transport through the layer. All of the above options present challenges for lithiation during deposition but can be activated by heat treatment.

[0214] Wet chemical coating can be performed by those skilled in the art of chemistry and involves a solution of a carbon precursor, a solvent capable of dissolving the precursor, and the powder to be coated. Mixing and homogenization are typically required, for example, using ultrasonic treatment. Finally, the solvent is removed, for example, in a spray dryer, a rotary evaporator, or simply by heating the solution to the point where the solvent evaporates. For the precursors mentioned herein, toluene can dissolve asphalt, dimethylformamide can dissolve polyacrylonitrile, tetrahydrofuran can dissolve polystyrene, and water or alcohol can dissolve sugars and phenolic resins. The total carbon applied after pyrolysis is a function of the initial carbon-precursor to particle ratio and can be adjusted by trial and error to suit any particular coating density. Typically, some carbon is removed during pyrolysis—how much is removed depends on the furnace, heating profile, precursor mass, powder amount, etc. In the experiments described herein, combinations were chosen to give approximately 1-2 wt% carbon after pyrolysis—sufficient to provide conductivity without significantly reducing the mass fraction of the powder and therefore its capacity. Further optimization can be made by those skilled in the art, provided that the heat treatment must be sufficient to optimize not only electron transport but also lithium transport.

[0215] Vapor phase coating can be carried out in the same type of reactor described for particle production, by heating the powder to a desired temperature and then exposing it to a desired coating gas. This process can be repeated / continued until the desired thickness is achieved, and this thickness can be measured using the methods described above. Again, the method must be adjusted to match the characteristics (quantity, BET++) of the powder, but this optimization can be performed by those skilled in the art. An important achievement is the need for high-temperature post-treatment to form the correct quality of carbon in the coating; therefore, optimization must be based on the results after heat treatment, rather than directly after coating.

[0216] In all cases, the heat treatment proceeds with a slow, gradual temperature rise to a plateau (where hydrogen is released from silicon atoms), continuing to the stage of carbon precursor crosslinking, then to the temperature at which hydrogen is expelled from the carbon, and finally to carbon recombination. Several of these processes are exothermic, thus requiring strict control to avoid excessively high temperatures.

[0217] Finally, the powder was used to form an electrochemical coin cell. We used a standard CMC binder with a pH-controlled aqueous buffer and a standard carbonate electrolyte with 2% fluoroethylene carbonate as the sole additive. Coin cells tend to underestimate FCE due to numerous other surface-generating losses. Therefore, the good FCE results shown in this document are expected to improve further in optimized commercial cells. Cells containing only silicon powder exhibited rapid delamination due to silicon expansion; therefore, these cells were only used for quantitative capacity and FCE.

[0218] For samples with good initial properties, we further prepared coin-shaped batteries using a mixture of the desired powder and flake graphite to ensure that degradation was primarily due to silicon degradation rather than delamination. Two examples are shown in Table 4, demonstrating the effect of electrochemical annealing (PAN) and excellent results for optimally treated particles (BIT).

[0219] To demonstrate that post-processing can also be applied to particles from other reactors with similar results, SiC powder produced via a 3:1 silane:ethylene flow was passed through a flow reactor. The powder was then heat-treated again and carbon-coated, this time with a sugar precursor. Three different stages of the powder were used to prepare batteries with 50 / 50 wt graphite and silicon particles. The results are shown in... Figure 11 In the middle. Heat-treated particles showed a significant improvement over untreated particles, with new improvements for coated particles, but since the treatment only went up to 820°C, electrochemical annealing could be seen again in the initial capacity increase.

[0220] Table 4. Overview of the particles used in verifying the annealing effect.

[0221] Further verification of the present invention

[0222] To further illustrate the invention, a series of particles were produced using the same method as the particles labeled S1 above, but with variations in the SiH4:C2H4 ratio resulting in variations in carbon content. As described above, the carbon content was evaluated by combustion measurements, and the carbon content was measured at [8, 11, 13, 15, 17, 19] wt%. These samples were given a thin gas-based carbon coating by CVD with ethylene gas at approximately 600°C, and subsequently annealed at temperatures of [700, 800, 900, 1000, and 1100]°C, respectively. The heating rate near the peak temperature was in the range of 0.4–1°C / s.

[0223] As described above, all powders were characterized using XPD, and estimates of the crystallite size of Si and SiC were calculated using Rietveld refinement of X-ray powder diffraction (XPD) of the particles.

[0224] The powder was then electrochemically characterized in the battery, where the active anode material consisted of 85 wt% of the relevant powder and 15 wt% of graphite. Additionally, conductive carbon and a binder were present in the same ratio as the aforementioned active materials. These batteries were used to obtain data on lithiation capacity and first-cycle coulombic efficiency (FCE) during the first cycle.

[0225] The series of particle samples prepared as shown in the above embodiments, having a total carbon content of 8 wt% (approximately 16.9 atomic%), the second series of similar particles having a total carbon content of 11 wt% (approximately 22.4 atomic%), the third series of similar particles having a total carbon content of 13 wt% (approximately 25.9 atomic%), the fourth series of similar particles having a total carbon content of 15 wt% (approximately 29.2 atomic%), the fifth series having a total carbon content of 17 wt% (approximately 32.4 atomic%), and the sixth series of similar particles having a total carbon content of 19 wt% (approximately 35.4 atomic%), were annealed at temperatures of 600, 700, 800, 900, 1000, and 1100°C, respectively.

[0226] Figure 17 , 18 Figures 19 and 20 show the measured Si and SiC crystallite sizes, initial battery lithiation capacity (mAh / g), and FCE for the combined samples. If no value was measured, a placeholder value is given in the figure for increased readability. For amorphous samples, a crystallite size of 0.2 was arbitrarily chosen to indicate that the measured sample was amorphous.

[0227] These figures clearly show that, for a given carbon content, Si and SiC crystallization occurs at some temperatures between 800 and 900°C, and the crystallite size increases with the peak temperature. A similar trend should be considered for increasing annealing time and slower heating rates.

[0228] For the lowest carbon content (8 wt%), the capacity was significant before annealing, indicating that the carbon-rich phase did not significantly impede lithium diffusion. For higher carbon contents, annealing was required to obtain significant capacity, and the transition appeared to be related to phase separation of the nanocrystals as required by this invention; however, there was no significant further increase in capacity as the crystallite size increased. Therefore, based on the capacity data, it can be assumed that annealing should only proceed to the temperature that yields the first crystallization, but based on the aforementioned literature, the crystallites should be kept as small as possible.

[0229] Similar conclusions can be drawn from the FCE data. The FCE in these batteries is not a direct measurement of the material's FCE, but rather is influenced by the same factors that affect battery life. FCE decreases due to surface area, surface degradation, particle breakage, loss from contact with individual particles, and electrode delamination. All of these factors also affect the battery's cycle life. Because the surface areas of these particle samples are very similar, FCE is primarily an expression of strains that can lead to reduced battery life. The very low FCE of C particles is largely attributed to large expansion and a lack of structural stability. For particles with the highest C content, FCE is negatively affected by capacity deficiency, meaning a similar initial cycle loss divided by a lower initial cycle capacity. It appears that FCE has an optimal value for intermediate heat treatment, thus providing the best stability at maximum capacity.

[0230] To obtain a proper evaluation of the actual FCE of the powder, a series of batteries were prepared in which the ratio of silicon composite powder to graphite according to the invention was varied. For this experiment, a powder with 15 wt% carbon was used, and this powder was composed of [15, 25, 35, 50] wt% active negative electrode material. The FCE of many of these batteries was measured and plotted on... Figure 21 The diagram clearly shows that the FCE increases with the fraction of the powder in this invention, and therefore must have a higher FCE than the graphite it replaces. By extrapolating to 100%, the FCE of the powder used in these batteries can be evaluated as high as 95%-96%, even though batteries with 85% silicon powder only show 85%-86% due to problems such as electrical contact loss in the electrodes.

[0231] Verification of grinding effect

[0232] The material, prepared by injecting a homogeneous first mixture of silane and ethylene gases at a molar ratio of 3.1:1, is heated to a preheated temperature of 300°C and then introduced into a reaction chamber where a homogeneous precursor gas mixture is fed into a closed chamber containing some preheated gas (residue from previous production batches) to form a second gas mixture at a temperature of 560°C. This relatively low reaction temperature ensures that dilution / heating variations become less critical for particle production. The second gas mixture is held for a long residence time of 45 seconds, during which time the chemicals are allowed to consume the reactants and increase particle size. Finally, the gas is pumped out of the chamber, stopping the reaction. This ensures a very similar history for all particles, as well as a very uniform size distribution, while maintaining good yields of silane and carbon precursors. The particles are then exposed to relatively gentle jet milling using a Spiral JetMill SSM100 from Schedio.

[0233] exist Figure 24Examples of the resulting particles can be seen in a) and 24b). Most of the surface is completely non-contacting, but the longest chains of the particles break into more uniformly sized sub-segments. Using a feed rate of 1.9 kg / h, a milling pressure of 3.5 bar, and a feed pressure of 6 bar resulted in a D90 / D10 ratio decreasing from 4.5 to 2.6, while the BET surface area remained only 2 m². 2 / g.

[0234] This improvement can be valuable because, when mixed with graphite, it allows for a more uniform distribution of the silicon composite material within the anode (without a maximum control). The material is also easily identifiable as it consists primarily of spherical particles, although some of these surfaces are the result of broken chains or spheres.

[0235] from Figure 24 b) shows a magnified SEM image of several particles. Figure 25 It shows what the arc of most of the circumference of the particle is like. Figure 25 These circumferential portions are marked with dashed lines. These circumferential portions are the result of cracking during the grinding process and do not form part of an arc / circle.

[0236] References

[0237] 1 Sourice et al. (2016), “Core-shell amorphous silicon-carbonnanoparticles for high performance anodes in lithium-ion batteries”, Journal of Power Sources , vol. 328, pp. 527-535.

[0238] 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 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 anodematerials for lithium-ion batteries with long cycle life and enhancedcapacity“ Electrochim. Acta, 2013, 93 , 213 —221. 4 Zhu et al. (2018), “Correlation between the physical parameters andthe 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 5 Rhenlund et al. (2017), “Lithium trapping in alloy formingelectrodes and current collectors for lithium based batteries”, Energy Environ. Sci ., 10, pp. 1350 – 1357, DOI: 10.1039 / c7ee00244k 6 Sung et al. (2021), “Subnano-sized silicon anode via crystal growthinhibition 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 7 B.H. Toby, R.B. Von Dreele, GSAS-II: the genesis of a modern open- source all purpose crystallography software package , Journal of AppliedCrystallography, 46 (2013) 544-549. 8 A.A. Coelho, TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C plus ,Journal of Applied Crystallography, 51 (2018) 210-218. 9 R.W. Cheary, A.A. Coelho, J.P. Cline, Fundamental parameters line profile fitting in laboratory diffractometers , Journal of Research of theNational Institute of Standards and Technology, 109 (2004) 1-25. 10 P. Thompson, E.D. Cox, J.B. Hastings, Rietveld Refinement of Debye-Scherrer Synchrotron X-ray Data from Al 2 O 3 , Journal of AppliedCrystallography, 20 (1987) 79-83。

Claims

1. A silicon-based composite particle, wherein the silicon-based particle has a total chemical composition comprising the following: - Based on the total mass of the silicon-based composite particles, the total carbon content C 总 5 to 50 atomic percent, and - The balance consists of silicon and unintentional impurities. Its features are, - The silicon-based particles are made of bulk material. - The bulk material comprises a plurality of nanoscale silicon domains embedded in a first matrix containing nanoscale silicon carbide domains, and - When subjected to XRD analysis with unmonochromatic CuKα radiation, the particles exhibit a peak at approximately 28° with a full width at half maximum (FWHM) in the range of 0.5° to 8°, and a peak at approximately 36° with an FWHM in the range of 1° to 10°.

2. The particles of claim 1, wherein when subjected to XRD analysis with unmonochromatic CuKα radiation, the particles exhibit: - A peak at approximately 28°, having a full width at half maximum (FWHM) in the range of 0.8° to 7.5°, preferably 1.2° to 7.0°, more preferably 1.4° to 6.5°, more preferably 1.7° to 6.0°, more preferably 2.0° to 5.5°, more preferably 2.3° to 5.0°, more preferably 2.6° to 4.5°, and most preferably 2.9° to 4.0°. - A peak at approximately 36°, having a full width at half maximum (FWHM) in the range of 1.25° to 9.0°, preferably 1.5° to 8.0°, more preferably 1.75° to 7.0°, more preferably 2.0° to 6.0°, more preferably 2.5° to 5.0°, and most preferably 3.0° to 4.0°.

3. The particles according to claim 1 or 2, wherein the chemical composition comprises: - Based on the total mass of the silicon-based composite particles, the total carbon content C 总 The atom percentage is 7 to 45 atomic%, preferably 10 to 40 atomic%, more preferably 15 to 35 atomic%, even more preferably 20 to 30 atomic%, and most preferably 23 to 27 atomic%. - Balance is silicon and unintentional impurities.

4. The particles according to any one of the preceding claims, wherein - If necessary, after exposing the silicon-based composite particles to annealing that crystallizes the nanoscale silicon carbide domains therein, the average diameter of the nanoscale silicon carbide domains, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, is in the range of 0.5 to 10 nm, preferably 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, and more preferably 4 to 5 nm. - If necessary, after exposing the silicon-based composite particles to annealing that crystallizes the nanoscale silicon domains therein, the average diameter of the nanoscale silicon domains, as determined by Rietveld refinement of X-ray powder diffraction (XPD) data, is in the range of 0.5 to 10 nm, preferably 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, more preferably 4 to 5 nm, more preferably 0.75 to 7.5 nm, more preferably 1 to 5 nm, more preferably 1.25 to 4 nm, more preferably 1.5 to 3 nm, more preferably 1.75 to 2.75 nm, and most preferably 2 to 2.5 nm.

5. The particles according to any one of the preceding claims, wherein the particles: - With a median volume-weighted diameter D in the range of 1 to 9 µm 50 ,as well as - Volume-weighted diameter ratio D in the range of 1 to 9 90 / D 10 And among them - D 10 D 50 and D 90 The volume-weighted particle size was determined by laser diffraction analysis according to standard ISO 13320:2020.

6. The particles according to any one of the preceding claims, wherein the particles: - Having a median volume-weighted diameter D of 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, as determined by laser diffraction analysis according to standard ISO 13320:2020. 50 ,and - Having a D value in the range of 1.5 to 8, preferably 2 to 7, more preferably 2 to 6, and most preferably 3 to 5 as determined by standard ISO 13320:2020. 90 / D 10 ratio.

7. The particles according to any one of the preceding claims, wherein the particles further comprise: - The particle has one or more internal shell-like spatial regions within its bulk material with increased carbon content, having a carbon content C higher than the average. 平均 Peak C of elements with carbon content 1 to 15 atomic percentage points higher 峰 And among them - The peak carbon content (C) of the element in each of the one or more internal shell-like spatial regions within the bulk material. 峰 and the average carbon content C 平均 It is determined by electronic energy loss spectral elemental analysis along a straight line extending from at least the particle core to, but not including, the particle surface, and wherein variations at length scales less than 5 nm, preferably less than 2 nm, and most preferably less than 1 nm are smoothed.

8. The particles according to any one of the preceding claims, wherein C 峰 In terms of average carbon content C 平均 The range is 1 to 12 atomic percentage points higher, preferably 1 to 10 atomic percentage points higher, more preferably 2 to 8 atomic percentage points higher, more preferably 3 to 6 atomic percentage points higher, and most preferably 4 to 5 atomic percentage points higher.

9. The particles according to any one of the preceding claims, wherein at least one relatively carbon-rich shell layer is determined by electron energy loss spectroscopy elemental analysis. 峰 It was obtained through the following: - Prepare cross-sectional slices less than 70 nm thick, including the particle center, using focused ion beam (FIB). - Perform EELS elemental analysis along a straight line extending from the center of the slice to the outer surface of the cross-section, then - Optionally, measurements can be smoothed by using a Gaussian digital filter or by averaging measurements taken from multiple adjacent spatial measurement areas, and - Along the line at a certain distance from the center of the particle, apply a local maximum value to the carbon content of the first peak of carbon content to limit the C content of the first peak. 峰 And, if present, perform C on the corresponding peaks of increased carbon content and decreased silicon content on the lines. 峰 Similar determinations, and - The C content is determined by averaging the C content at all measurement points outside the surface area along the line. 平均 .

10. The particles according to any one of the preceding claims, wherein the smoothing of variations in electron energy loss spectral elemental analysis is achieved by: - Use a Gaussian digital filter with a digital filter width of < 5 nm, preferably < 2 nm, and most preferably < 1 nm. or The average value is taken from measurements taken from multiple adjacent spatial measurement areas.

11. The particles according to any one of the preceding claims, wherein the particles further comprise an outer coating on their outer surface, wherein the coating is: - One or more of the following: amorphous or crystalline carbon allotropes selected from Li x Si y O, Ti x O or Al x O oxides of O, or metal-organic frameworks, 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 - An amorphous or crystalline carbon layer having a thickness of 0.5 to 20 nm, preferably 1 to 10 nm, and most preferably 2 to 7 nm, as determined by Auger spectroscopy.

12. The particles according to any one of the preceding claims, wherein the electrical conductivity of the particles is greater than 1.10 when measured in cylindrical spherical particles having a diameter of 1 cm under a pressure of 4 tons. -6 S / cm, preferably > 1.10 -5 S / cm, more preferably >1.10 -4 S / cm, more preferably > 1.10 -3 S / cm, more preferably > 1.10 -2 S / cm, and the optimal value is > 1.10 -1 S / cm.

13. The particles according to any one of the preceding claims, wherein the particles further comprise mild abrasive particles having a substantially spherical shape determined by the following criteria: - 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% of all sub-segments of the circumference of the particles shown in the SEM image of the material are arcs. - Each arc in the SEM image has an arc length s determined by the formula s = r·π / 180·θ, where r is the radius of a circle whose circumference has the same curvature as the arc, π is a mathematical constant equal to the ratio of the circle's circumference to its diameter, and θ is the angle in degrees between the arc and the center of the circle. - The angle θ is in the range of 10 to 360°.

14. Particles according to any one of the preceding claims, wherein the particles have a particle size of 0.2 to 10 μm as determined by standard ISO 9277:2010. 2 / g, preferably 0.3 to 8 m 2 / g, more preferably 0.4 to 6 m 2 / g and the optimal value is 0.5 to 4 m 2 / g of BET surface area.

15. A method for producing silicon-based particles, wherein the method comprises: - The application uses a reactor having a decomposition chamber containing a first reactor gas with a concentration of 5.

10. 3 up to 6.10 5 Initial pressure within the Pa range and first reactor temperature within the range of 450 to 650°C - A precursor gas mixture comprising a first precursor gas containing a silicon compound and a second precursor gas containing a carbon compound is formed, wherein the atomic ratio of silicon to carbon (Si:C) in the precursor gas mixture is in the range of 0.2 to 50. - Injecting the precursor gas mixture into the decomposition chamber, and mixing the precursor gas mixture with the first reactor gas to form a second reactor gas mixture, characterized in that the method further comprises: - The second reactor gas mixture is maintained in the decomposition chamber for a residence time ranging from 10 to 300 seconds, while 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 of the temperature of the first reactor. or - The second reactor gas mixture is maintained in the decomposition chamber for a residence time ranging from 10 to 300 seconds, and during said residence time, the injected precursor gas mixture is subjected to at least one temperature change from a first reaction temperature to a second reaction temperature and then back to the first reaction temperature, wherein... - The absolute temperature difference between the first reaction temperature and the second reaction temperature is in the range of 1 to 100°C, preferably 3 to 75°C, more preferably 5 to 50°C, more preferably 10 to 35°C, and most preferably 20 to 25°C. Then - Extract the particles from the decomposition chamber. - Cool the particles to room temperature, and - The particles are annealed by heating at a rate of 1 to 5°C / min to an annealing temperature in the range of 800 to 1000°C, and then the particles are cooled.

16. The method of claim 15, wherein the dwell 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, more preferably 30 to 50 seconds, more preferably 0.2 to 280 seconds, preferably 0.5 to 250 seconds, more preferably 1 to 230 seconds, more preferably 1.5 to 200 seconds, more preferably 5 to 180 seconds, more preferably 10 to 150 seconds, more preferably 15 to 100 seconds, more preferably 25 to 75 seconds, and most preferably 2 to 50 seconds.

17. The method according to claim 15 or 16, wherein the temperature of the first reactor 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 15 to 17, 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, or most preferably 350 to 370°C before injecting the homogeneous gas mixture into the reactor space.

19. The method according to any one of claims 15 to 18, wherein - The first precursor gas is one of the following: silane (SiH4), silane (Si2H6), trichlorosilane (HCl3Si), organosilane, or a mixture thereof, and - The second precursor gas is one of organosilanes or hydrocarbons. Preferred methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H4) are preferred. 10 ), ethylene (C2H4), acetylene (C2H2), propylene (C3H6), butene (C4H8), pentene (C5H4) 10 ( ), cyclohexane, cyclohexene, toluene, benzene, or a mixture thereof.

20. The method according to any one of claims 15 to 19, wherein the atomic ratio between silicon and carbon in the precursor gas mixture is in the range of 0.3 to 40, preferably 0.4 to 30, more preferably 0.5 to 25, more preferably 0.6 to 20, more preferably 0.8 to 15, more preferably 1.0 to 10, more preferably 1.2 to 4, more preferably 1.5 to 2.0, more preferably 0.4 to 35, more preferably 0.5 to 30, more preferably 0.6 to 25, more preferably 0.8 to 20, more preferably 1.0 to 15, more preferably 1.5 to 12, more preferably 2 to 10, and most preferably 2.5 to 7.

5.

21. The method according to any one of claims 15 to 20, wherein the first reactor gas is one or more of argon, nitrogen, or waste gas from previous particulate production.

22. The method according to any one of claims 15 to 21, wherein the method comprises changing the temperature from the first reaction temperature to the second reaction temperature by: - An application is made of a reactor having a hot-wall decomposition chamber comprising at least one first zone and at least one second zone, wherein the at least one first zone has a wall temperature equal to the first reaction temperature, and the at least one second zone has a wall temperature equal to the second reaction temperature, and - The precursor gas mixture is transported during hot wall decomposition via thermal convection between the at least one first zone and the at least one second zone; or - An application of a reactor having a hot-walled decomposition chamber comprising an injection zone and a first decomposition zone, wherein the first decomposition zone has a wall with a wall temperature equal to the first reaction temperature, and - Turbulence is formed in the injected precursor gas mixture within the decomposition chamber, which is used to transport the second reactor gas mixture between the injection zone and the first decomposition zone of the hot-wall decomposition chamber; or - An application is made of a reactor having tubular hot-walled decomposition chambers comprising multiple alternating first and second zones, wherein the first zone has a wall temperature equal to the first reaction temperature, and the second zone has a wall temperature equal to the second reaction temperature, and - The precursor gas mixture is injected into the first end of the tubular hot-wall decomposition chamber, optionally mixed with the first reactor gas to form the second reactor gas, and the precursor gas mixture and optionally the second reactor gas mixture are passed through the tubular hot-wall decomposition chamber under laminar flow conditions at a Reynolds number of less than 2000.

23. The method according to any one of claims 15 to 22, wherein the method comprises maintaining the temperature of the second reactor gas mixture in the decomposition chamber by: - A reactor with a tubular hot-walled decomposition chamber, the tubular hot-walled decomposition chamber having a first end and a second end, and - A preheated precursor gas mixture at a constant volume flow rate and a preheated first reactor gas at a constant volume flow rate are injected into the first end to form a second reactor gas mixture at a constant volume flow rate within the tubular hot-wall decomposition chamber. - Under laminar flow conditions with a Reynolds number less than 2000, the gas mixture in the second reactor is passed from its first end to its second end through the tubular hot-wall decomposition chamber, and - Extract the second reactor gas mixture containing the formed particles at the second end; or - A reactor having a closed hot-walled decomposition chamber containing the gas from the first reactor, and - At the first moment, the preheated precursor gas mixture is injected into the hot-wall decomposition chamber to form the second reactor gas mixture, and - When the residence time is calculated from the first moment, both the second reactor gas mixture and the formed particles are extracted from the hot-wall decomposition chamber by vacuum suction or flushing; or - The application uses a reactor having a closed hot-walled decomposition chamber containing the first reactor gas and a cooling collection chamber at the bottom of the decomposition chamber. - The preheated precursor gas mixture is injected into the hot-wall decomposition chamber to form the second reactor gas mixture, and - The second reactor gas mixture is held in the hot-wall decomposition chamber until the particles formed grow to the size at which they settle out of the second reactor gas mixture and fall into the collection chamber by gravity.

24. The method according to any one of claims 15 to 23, wherein the method further comprises, prior to the step of annealing the particles at the annealing temperature, forming a carbon surface coating on the particles by vapor deposition at a temperature lower than the first coating temperature, and wherein the annealing temperature is at least 50°C higher than the first coating temperature.

25. The method according to any one of claims 15 to 23, wherein the method further comprises applying a carbon precursor by a wet chemical method to form a carbon surface coating on the particles prior to the annealing.

26. The method of claim 25, wherein the carbon precursor is one or more of pitch, resin, polyacrylonitrile, polystyrene, sugar, or phenolic resin.

27. A silicon-based particle, characterized in that, Prepared by the method according to any one of claims 15 to 26.

28. A negative electrode for a secondary lithium-ion electrochemical battery, comprising: - Active materials, - Adhesive materials, and - current collector substrate, The active material is characterized in that it is a silicon-based particle according to any one of claims 1 to 14 or claim 27.

29. Use of the particles according to any one of claims 1 to 14 or claim 27 in a secondary lithium-ion electrochemical battery.

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