It mainly consists of amorphous silicon particles and their use as active anode materials in secondary lithium-ion batteries.

Abstract

This invention relates to a method for manufacturing predominantly amorphous silicon particles, the particles prepared therefrom, and a secondary electrochemical battery using these particles as the negative electrode active material of a secondary electrochemical battery, wherein the predominantly amorphous silicon particles comprise the formula: Si (1‑x) M x The compound wherein 0.005 ≤ x < 0.05 and M is at least one substituent element selected from C, N or mixtures thereof, and wherein the particle exhibits a peak at about 28° and a peak at about 52° when subjected to XRD analysis with non-monochromatic CuKα radiation, and wherein the two peaks have a full width at half maximum (FWHM) of at least 5° when fitted with Gaussian peaks.

Description

Technical Field

[0001] This invention relates to a method for producing silicon particles that are primarily amorphous, the particles prepared therefrom, and a secondary electrochemical battery using these particles as the negative electrode active material of a secondary electrochemical battery. Background Technology

[0002] A significant increase in the use of renewable energy and electrification will be necessary in many parts of our current fossil fuel-driven societies to meet the goals of the Paris Agreement under the UN Climate Change Convention. A key component in achieving these goals is the availability of rechargeable batteries with excellent specific energy.

[0003] For the half-reacting Li + +e - →Li 0 For example, lithium has a concentration of 0.534 g / cm³. 3 The extremely low density and high standard reduction potential of 3.045V make lithium an attractive candidate for fabricating electrochemical cells with high specific energy. However, secondary (rechargeable) electrochemical cells with metallic lithium anodes have been shown to be hampered by the persistent problem of dendrite formation during charging, which tends to short-circuit the electrochemical cell after a few charge-discharge cycles.

[0004] The dendrite problem can be solved by using a negative electrode that can releasably store lithium atoms by inserting them. These batteries are called secondary lithium-ion batteries (LIBs). The electrochemical properties of LIBs are directly affected by the physical and chemical properties of the negative electrode active material. Material selection and preparation, as well as appropriate structural modification and design of the active material, affect battery performance [1]. In this regard, the key issue has been and remains the same: to find a way to reliably and reversibly store lithium atoms at a high volume density during multiple consecutive charge-discharge cycles, and then release them as ions (Li ions) during discharge. + Active materials that release lithium.

[0005] Currently, most commercially available lithium-ion batteries (LIBs) use graphite as the negative electrode active material. Graphite can accommodate / package one lithium ion per six carbon atoms with minimal deformation through intercalation and has a theoretical specific energy of 372 mAh / g. Commercially available secondary LIBs with graphite negative electrodes typically achieve specific energies of 100-200 Wh / kg, for example, in the fabrication of medium-sized electric vehicle batteries weighing several hundred kilograms. This energy level may not be sufficient to achieve the goals of the Paris Agreement. Background Technology

[0007] One strategy to improve the specific energy of lithium-ion batteries (LIBs) lies in finding materials with higher lithium-ion storage capacity than graphite for use as active materials in anodes. In this regard, silicon is an interesting and well-studied candidate due to its large capacity for storing lithium atoms through diffusion and alloying. At typical ambient temperatures, the maximally lithiated phase of silicon is Li. 3.75 Si has a theoretical specific capacity of 3579 mAh / g [1]. Silicon anodes also have the benefit of providing an attractive operating potential and reducing safety issues associated with lithium deposition when the battery is overcharged [2].

[0008] Lithification and delithiation of silicon lead to significant volume expansion and contraction, respectively, in silicon materials. 3.75 In its maximum lithiation state, silicon materials have a volume that is about 320% larger than in the non-lithiation state. The relatively large volume changes associated with lithiation and delithiation cycles have been reported to cause cracking and / or dissipation and / or repeated formation of the solid electrolyte interphase (SEI) layer in silicon electrodes, which can lead to a range of problems with LIB performance, such as loss of electrical contact, loss of active material in the electrode, and ineffective electron transfer [1,2].

[0009] The nanostructure of silicon materials has been studied as a solution to overcome the problem of volume expansion because nanoscale Si particles can better accept volume changes [2]. It has been shown that the use of nanoscale particles in electrodes can provide electrodes with outstanding properties due to the effects such as improved conductivity, improved mechanical and optical properties caused by small particle size [1]. In addition, due to the extremely high surface area to volume ratio of nanoscale particles, anodes with nanoscale active materials can provide excellent charge / discharge capacity due to the highly available surface for lithium ion adsorption / desorption [1].

[0010] The interatomic spacing between silicon atoms increases as they accept lithium ions (lithiation), allowing the particles to expand to a volume up to 320% larger than their original volume. For crystalline silicon, this expansion results in large anisotropic stresses within the electrode material, leading to increased cracking and breakage of the silicon material. It has been found that this anisotropic stress is reduced in a variety of anode configurations if the silicon material itself is amorphous [5].

[0011] For LIBs with a liquid electrolyte, a solid electrolyte interface (SEI) is typically formed during the first lithiation. The formation of the SEI layer irreversibly consumes lithium and represents an irreversible capacity loss in the electrochemical cell [1]. Therefore, it would be advantageous to form a stable SEI layer to limit the lithium loss caused by the SEI during the first lithiation / charging of the cell. It has been shown that coating the silicon surface with suitable elements to avoid direct contact between silicon and the electrolyte can provide a stable SEI layer [1], but if cracking occurs, an unprotected surface will be exposed.

[0012] Carbon has been studied and used together with silicon as an active material in LIBs with nanostructured silicon as the anode, as a coating material and / or composite material. A variety of silicon-carbon structures have been reported in the literature, ranging from simple mixtures of silicon with graphene or graphite to complex geometries. These complex structures can exhibit excellent cyclability and capacity, but are hampered by the need for multiple charge-discharge cycles to achieve high coulombic efficiency, and they require multi-step synthesis processes, which is complicated for scale-up to commercial production levels [2].

[0013] According to Sourice et al. (2016)[2], a method for producing nanoscale amorphous silicon particles with carbon shells / coatings via a two-stage laser pyrolysis is known, wherein a silane gas stream diluted in an inert gas is introduced into a first reaction zone irradiated by a CO2 laser to decompose the silane gas into amorphous silicon core particles. Then, ethylene is added to the gas containing the formed silicon core particles, and the mixture is conveyed to a second reaction zone and irradiated with a CO2 laser to decompose the ethylene into carbon shells deposited on the silicon core particles. Amorphous silicon particles with carbon coatings were found to have excellent specific capacity and high charge / discharge cycle capability.

[0014] US 2012 / 0107693 discloses active materials for LIB anodes, including those with the chemical formula: SiC x The silicon-containing compound shown can have a carbon content of 0.05 to 1.5, and the carbon concentration in the material conforms to the relationship A ≤ B, where A is the molar concentration ratio of carbon to silicon at the center of the active material, and B is the molar concentration ratio of carbon to silicon on / at a surface region of the active material. The document states that carbon can be covalently bonded to silicon and that the silicon-containing compound can be particulate and have an amorphous molecular structure. Paragraph

[0030] of US 2012 / 0107693 further discloses that if the carbon content in the active material becomes too low, i.e., if x becomes less than 0.05, the active material can deteriorate through cracking.

[0015] According to EP 2 405 509, the active materials for the negative electrode of a rechargeable LIB are known to include those with the chemical formula: SiA x H y The amorphous silicon-based compound shown is wherein A is carbon, nitrogen, or a combination thereof, and wherein x>0, y>0, and 0.1≤x+y≤1.5. The active material can be particulate and coated with a carbon layer. The active material can be prepared by sputtering with hydrogen and Si and C targets or by plasma method using hydrogen, silane gas, and nitrogen.

[0016] WO 2018 / 052318 discloses a reactor and method for producing crystalline or amorphous silicon particles by chemical vapor deposition of a silicon-containing precursor onto seed particles within a heated and rapidly rotating reactor space. The silicon-containing gas can be diluted in a carrier gas, which can be one or a mixture of SiH4, Si2H6, or SiHCl3. The carrier gas can be one of hydrogen, nitrogen, or argon. The process can be accomplished by introducing C, O, or N in combination with silicon, such as SiO2. x SiC x SiN x A second precursor gas, liquid, or material with an amorphous carbon, graphite, low-crystalline carbon, or low-range ordered graphene structure, providing a second material outer layer with a lower silicon content than the core material of the formed silicon particles.

[0017] Wang et al. (2013)[6] are one of several research groups that have published the formation of secondary particles from silicon nanoparticles and carbon precursors, such as pitch, and the use of these particles in Li-ion batteries. Secondary particles reduce the interfacial area between silicon and electrolyte, and thereby reduce the formation of the solid electrolyte interphase (SEI), which is known to consume both lithium and electrolyte, thereby gradually reducing the battery capacity. The formation of the SEI in the first stage is quantified by measuring the coulombic efficiency (CE) of the first lithiation cycle, and the thickness and quality of the SEI can be further estimated using XPS. Jeff Dahn (1995)[7] has demonstrated that the CE of carbon formed from pitch or sugar is improved if carbonization can occur at >500 °C, preferably >700 °C, more preferably >800 °C for at least two hours. Escamilla-Perez et al. (2019)[8] even pyrolyzed at 900 °C for 3 hours.

[0018] EP 3 025 702 A1 discloses extremely pure nanoparticle amorphous silicon powder, which can preferably be alloyed with electron donors and / or electron acceptors. Furthermore, it discloses a method for producing silicon powder and a reactor for using in the production of silicon powder. The silicon powder according to this invention can be preferably used for the production of semiconductor starting materials, semiconductors, and thermocouples recovered from waste heat energy, specifically thermocouples stable at high temperatures.

[0019] KR 2016 / 0009807 discloses silicon nanoparticles and methods for their preparation. Specifically, this document relates to silicon nanoparticles containing silicon as an active component and having an amorphous or amorphous phase by having an excess of atomic P or atomic B exceeding doping limits inside / outside the nanoparticles, and relates to methods for preparing the nanoparticles. The resulting silicon nanoparticles can improve the charge / discharge cycle (lifetime) of secondary batteries using silicon nanoparticles as a negative electrode material by having a secondary phase of an amorphous or amorphous phase that acts as a buffer against the volume expansion and contraction that occurs during the charging / discharging of silicon. Summary of the Invention

[0020] The main objective of this invention is to provide a method for producing silicon-containing particles that are primarily amorphous and suitable for use as an active material in the negative electrode of a rechargeable lithium-ion electrochemical battery.

[0021] Another objective of the present invention is to provide particles containing predominantly amorphous silicon prepared by this method.

[0022] Another objective of the present invention is to provide a negative electrode material comprising particles of predominantly amorphous silicon.

[0023] Another objective of the present invention is to provide a secondary electrochemical cell having a negative electrode comprising particles of predominantly amorphous silicon. Detailed Implementation

[0024] This invention is based on the discovery that applying a mixture of silicon precursor gas and a relatively small amount of substituted element precursor gas heated to a temperature in which the gas decomposes and reacts to form solid particles produces heat-resistant silicon particles with a predominantly amorphous structure—in the sense that similar particle samples without the guest element and heated for the same duration cannot withstand the temperature at which no measurable portion transforms into a crystalline phase. From an economic perspective, the ability of silicon particles to maintain an amorphous state at relatively high temperatures is beneficial by enabling higher yields and improving tolerance to heat treatment during subsequent production steps. When the particles are used as active materials in the anodes of secondary lithium-ion batteries, they are also beneficial from a battery performance perspective because nanoscale amorphous Si particles exhibit improved tolerance to volume changes associated with lithiation and delithiation and provide an anode with improved cycleability.

[0025] Therefore, in a first aspect, the present invention relates to a method for producing a composite: Si (1-x) M xA method for determining a compound containing predominantly amorphous silicon particles, wherein 0.005 ≤ x < 0.05 and M is at least one substituent element selected from C, N, or combinations thereof, and wherein, when subjected to XRD analysis with non-monochromatic CuKα radiation, the particles exhibit a peak at approximately 28° and a peak at approximately 52°, and wherein, when fitted with Gaussian peaks, the two peaks have a full width at half maximum (FWHM) of at least 5°.

[0026] The methods include:

[0027] - A homogeneous gas mixture that forms a first precursor gas of a silicon-containing compound and at least one second precursor gas of a compound containing a substituent element M.

[0028] - A homogeneous gas mixture of first and second precursor gases is injected into the reactor space, wherein the precursor gases are heated to a temperature in the range of 700 to 900°C, thereby causing the precursor gases to react and form particles, and

[0029] - Collect the particles and cool them to a temperature ranging from ambient temperature to approximately 350°C.

[0030] And among them

[0031] - Adjust the relative amounts of the first and second precursor gases so that the formed particles have an M:Si atomic ratio in the range of [0.005, 0.05).

[0032] In exemplary embodiments, the homogeneous gas mixture may further comprise other inert gases, such as hydrogen, nitrogen, argon, neon, helium, and other gases that can be applied to influence heating, cooling, particle formation kinetics, or mass transfer without leaving chemical impurities in the final particulate product. Heating of the precursor gas in the reaction chamber can be achieved by convection, conduction, radiation, laser, mixing with a hotter gas, or any other known method.

[0033] The particles prepared by the first aspect of the present invention are particles containing mainly amorphous silicon, wherein:

[0034] Particle inclusion formula: Si (1-x) M x The compound shown,

[0035] Where 0.005 ≤ x < 0.05 and M is at least one substitution element selected from: C, N, or combinations thereof, and

[0036] When subjected to XRD analysis with non-monochromatic CuKα radiation, the particles show a peak at approximately 28° and a peak at approximately 52°, with both peaks having a full width at half maximum (FWHM) of at least 5° when fitted with Gaussian peaks.

[0037] In a second aspect, the present invention relates to the negative electrode of a secondary lithium-ion electrochemical battery, comprising:

[0038] -At least one particulate active material,

[0039] - Adhesive materials, and

[0040] -Current collector substrate,

[0041] In this process, at least one particulate active material is embedded in a binder material to form a negative electrode material, which is then deposited as a negative electrode material layer on a current collector substrate.

[0042] Its features are,

[0043] - At least one particulate active material or one of them is a particulate material containing mainly amorphous silicon prepared by the method according to the first aspect of the invention.

[0044] The chemical formula Si used herein will be interpreted and understood in accordance with IUPAC Recommendations 2005, IR-11.3.2, "Phases with variable composition". (1-x) M x Where 0.005 ≤ x < 0.05. That is, a chemical formula defines a single (phase) compound having a composition that can be altered only or partially by replacing Si atoms with M atoms in an amount specified by the variable “x”. Therefore, the term “silicon-containing particles” used herein refers to particles made of a silicon-dominant phase containing alloying elements distributed in the molecular structure of the silicon phase. Although the terms “phase” or “molecular structure” can be vague in the context of amorphous materials, the important characteristic is that M atoms are chemically bonded and dispersed in the alloy such that the nearest and second-nearest atoms of several typical M atoms are Si atoms.

[0045] Depending on which gases are used as the first and / or second precursor gases and the reaction temperature at which particles are formed, the reaction kinetics in the gaseous reaction from precursor gases to particles can vary significantly, such that the atomic ratio of M:Si in the precursor gases can deviate significantly from the atomic ratio of M:Si in the resulting particles. Therefore, the term “adjusting the relative amounts of the first and second precursor gases so that the formed particles obtain an atomic ratio of M:Si within the range of…” as used herein refers to adjusting the relative amounts of the first and second precursor gases to be mixed and homogenized so that when the precursor gas mixture is heated to the desired reaction temperature, the resulting particles obtain the desired atomic ratio and react to form particles.

[0046] The adjustment of the relative amounts of the first and second precursor gases to form the desired particles is within the scope of ordinary skill of those skilled in the art. For example, the relative amounts and reaction temperatures to be applied when using the gas mixture can be determined by simply performing trial-and-error tests, prior to the production stage, to obtain changes in the relative amounts of the precursor gases for a given first and second precursor gases, as well as the desired reaction temperature.

[0047] Alternatively, the atomic ratio of M:Si in the formed particles can be monitored / determined by analyzing the tail gas leaving the reactor in a mass spectrometer to determine how much of the first and second precursor gases were reacted / consumed inside the reactor and subsequently, indirectly, by determining the relative amounts of M and Si in the formed particles. For example, by adjusting the flow rates of the first and second precursor gases injected into the reactor and applying a mass spectrometer to measure the composition of the tail gas leaving the reactor to determine the fraction of the injected first and second precursor gases converted into particles, this information can be used to extrapolate the atomic ratio of M:Si in the formed particles and adjust the feed rates of the first and second precursor gases to obtain the desired atomic ratio of M:Si in the formed particles. (Chemical formula Si) (1-x) M x Where 0.005 ≤ x < 0.05, corresponding to an M:Si atomic ratio in the range of [0.005025, 0.0526), ​​such that in one example embodiment, the M:Si atomic ratio in the formed particles can be in the range of [0.005, 0.05], preferably in the range of [0.01, 0.04], more preferably in the range of [0.01, 0.03], and most preferably in the range of [0.01, 0.02]. These atomic ratios approximately correspond to the chemical formula: Si (1-x) M x The material shown is primarily amorphous silicon, wherein 0.005 ≤ x < 0.05, preferably 0.01 ≤ x ≤ 0.04, more preferably 0.01 ≤ x ≤ 0.03, and most preferably 0.01 ≤ x ≤ 0.02. M is a substitution element selected from C or N.

[0048] X-ray diffraction (XRD) (in the literature, when XRD is applied to particulate materials, it can also be referred to as powder X-ray diffraction (PXD)) provides different diffraction patterns for crystalline and amorphous materials. Due to their high degree of order and symmetry in their atomic structure, crystalline materials tend to provide sharp, Bragg peaks in XRD measurements. For crystalline silicon, XRD analysis typically provides sharp peaks at 28.4°, 47.4°, and 56.1° in the measured diffraction pattern. In contrast, amorphous materials, lacking the long-range order characteristic of crystalline molecular structures, typically provide noticeably more "fuzzy" broad peaks in the measured diffraction pattern. Amorphous silicon typically provides dome-shaped peaks at 28° and 52°. These dome-shaped peaks can be fitted using Gaussian fitting to reduce noise and obtain definitive values ​​for the maximum peak height and width. This fitting can be performed by any skilled XRD operator.

[0049] Additionally, peak "sharpness" can be used to distinguish between crystalline and amorphous materials. When measured using a diffractometer with non-monochromatic CuKα radiation and Gaussian fitting to reduce measurement noise, the typical full width at half maximum (FWHM) of XRD peaks for crystalline silicon is less than 2°, while that for amorphous silicon is typically greater than 5°. The FWHM is the width of the peak curve measured between points on the y-axis, and it is 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 diffraction patterns in XRD analysis that show both the sharp Bragg peaks typical of the crystalline phase and the broader, Gaussian peaks typical of the amorphous phase. The crystal fraction of the sample can be estimated using the diffraction patterns based on the ratio of the area under the Bragg peak above the broad peak in amorphous silicon to the total area of ​​the broad and Bragg peaks. Figure 6 As shown, the background line should be subtracted from the calculation before the calculation is performed.

[0050] As used in this paper, the angles and angular tolerances in the XRD analysis represent the use of a diffractometer employing non-monochromatic CuKα radiation, because the radiation has high intensity and corresponds well to the interatomic spacing in crystalline solids. The wavelength of the CuKα radiation makes the analysis sensitive to the presence of crystalline phases in silicon particles. For the same reason, XRD analysis using a diffractometer with CuKα radiation is the natural choice and is therefore the most widely used method in XRD analysis and is well-known and mastered by those skilled in the art. Other diffractometers using radiation with other wavelengths can provide different angles and angular tolerances. However, those skilled in the art will know how to convert these values ​​from one radiation source to values ​​from another. X-ray diffraction (XRD) analysis shows particles prepared by the method according to the first aspect of the invention, which have a predominantly amorphous molecular structure, such as... Figure 2As shown. This figure provides diffraction patterns representing measurements of three particulate samples prepared by the method according to the first aspect of the invention. The diffraction patterns measured for all three samples show a peak at approximately 28° and a peak at approximately 52°, and when estimated using Gaussian peak fitting, both peaks (for all samples) have an FHWM of approximately or greater than 5°. XRD analysis shows that the Si of the present invention... (1-x) M x (Where 0.005≤x<0.05) The particles mainly have an amorphous molecular structure. Unbound by theory, it is believed that in the molecular structure of the silicon host material, the substitution of Si atoms with elements M, such as carbon atoms, leads to a “disruption” in the silicon molecule, thereby preventing the formation of any long-range ordered silicon phase with the molecular structural characteristics of crystalline silicon during gaseous reaction processes and / or any reconstruction processes that may also occur at the same temperature.

[0051] Amorphous materials (see, for example, reference [4]) possess some internal structure that provides short-range order at the atomic length scale due to chemical bonding properties. This internal structure can be considered to consist of interconnected structural blocks. These blocks may or may not resemble the basic structural units present in the corresponding crystalline phase, i.e., they may or may not provide materials with extremely small crystalline-resembling domains. Furthermore, for extremely small crystals, surface relaxation and interface effects alter atomic positions, reducing structural order. Even state-of-the-art structural characterization techniques, such as X-ray diffraction and transmission electron microscopy, have difficulty distinguishing between amorphous and crystalline structures at these length scales.

[0052] Therefore, since it is difficult to provide structural characterization techniques to determine whether the silicon material of the particles prepared by the first aspect of the present invention is completely amorphous or contains small crystalline domains at the atomic length scale, the term "primarily amorphous" as used herein covers silicon materials with a 100% amorphous molecular structure to silicon materials containing extremely small crystalline domains at the atomic length scale (which are practically undetectable by XRD analysis). It is also reasonable to believe that even when the material contains extremely small crystals, typically less than 1 nm, such that the atoms with nearest-neighbor distances altered by grain boundaries constitute a similar mass fraction as atoms in which all nearest-neighbor atoms are in a crystalline order, the benefits of amorphous materials in the anode (i.e., lower directional stress and faster charging) are maintained. According to the first aspect, the particles containing primarily amorphous silicon prepared by the present invention encompass the formula: Si (1-x) M xAny particle of the compound shown, wherein 0.005 ≤ x < 0.05 and M is a substituent element selected from C or N, and wherein, when subjected to XRD analysis with non-monochromatic CuKα radiation, the particle shows a peak at about 28° and a peak at about 52°, and wherein, when fitted with Gaussian peaks, the two peaks have a full width at half maximum (FWHM) of at least 5°.

[0053] At least for some substituent elements, it was observed that particles according to the first aspect of the invention exhibited more heat-resistant, counterintuitive properties, i.e., the crystallization temperature increased with a smaller amount of substituent element M. Experiments conducted by the inventors showed that amorphous Si prepared from silane and ethylene, when exposed to a longer heat treatment (in this case, 2 hours), showed improved crystallization temperature. 0.96 C 0.04 The particles will remain amorphous up to 800°C, but will begin to crystallize at some temperature between 800 and 820°C. However, Si prepared using the exact same method... 0.92 C 0.08 This transformation was observed in the particles at temperatures between 780 and 800 °C. Figure 3 and 4 The X-ray characterization of the two materials after different thermal exposures is shown. For comparison, as... Figure 5 As shown, pure amorphous silicon particles of the same size were completely crystallized at temperatures far below 780°C. Unbound by theory, it can be inferred that crystallization is controlled by carbon or carbon vacancy migration, which explains the counterintuitive results. The XRD peaks first appear around 35°, which is typically associated with the SiC crystalline phase; therefore, increasing the amount of C can significantly increase the probability of SiC crystal formation.

[0054] Another advantageous property of the particles according to the first and second aspects of the invention is that the lower content of the substituent element M (when M is carbon) provides an increase in lithium mobility and a decrease in resistivity. Therefore, the particles according to the invention have the advantage of achieving relatively high temperature tolerance / crystallization temperature at a low substation level with minimal / negligible adverse effects on the capacity and transport properties of the active material / particles.

[0055] Another advantageous property of the particles according to the first and second aspects of the invention is that a low content of the substituent element M generally indicates a higher charge capacity of the material, since it is known that none of the substituent elements M can accommodate as much lithium as silicon.

[0056] 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 to form Si particles at the desired reaction temperature. Examples of suitable first precursor gases include (but are not limited to) silanes (SiH4), disilanes (Si2H6), and trichlorosilanes (HCl3Si), or mixtures thereof. Similarly, as used herein, the term "second precursor gas of a compound containing a substituent element M" refers to any compound that contains a substituent element M, is in the gaseous state, participates in a gaseous reaction, and, when heated to the desired reaction temperature, results in the introduction of M atoms into the molecular structure of the formed Si particles. Examples of suitable second precursor gases include (but are not limited to) alkanes, alkenes, alkynes, aromatic compounds, or hydrides of N, hydrogen cyanide, and mixtures thereof.

[0057] A particularly preferred example embodiment of the precursor gas, namely a homogeneous gas mixture of gaseous silicon and hydrogen compounds and gaseous substitution element M and hydrogen, is a silane (SiH4) or silane (Si2H6) mixed with a hydrocarbon gas selected from methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), acetylene (C2H2), and mixtures thereof.

[0058] The interval notation used in this article conforms to the international standard ISO 80000-2, where square brackets “[” and “]” represent closed interval boundaries, while parentheses “(” and “)” represent open interval boundaries. For example, [a, b] is a closed interval containing every real number from a (inclusive) to b (inclusive): And (a, b) is the left half of the open interval from a (excluding) to b (including):

[0059] The yield in a gas-phase reaction process, defined as the ratio of the mass of the precursor gas fed into the reactor to the mass of the generated particles, has been shown to depend on process parameters such as the concentration of the precursor gas in the condensation zone, the reaction temperature in the condensation zone, and / or the residence time of the condensed gas in the condensation zone. Generally, the higher the reaction temperature, the higher the degree of dissociation of the precursor gas, and therefore the higher the yield. Therefore, since the particles of the present invention containing predominantly amorphous silicon are observed to maintain their predominantly amorphous structure at temperatures significantly higher than the temperatures at which amorphous (pure) silicon particles are observed to transform into crystalline silicon (approximately 50°C higher), the method according to the first aspect of the invention has a significantly improved yield advantage compared to the production of (pure) silicon particles without compromising on the favorable amorphous structure. Increasing the decomposition temperature of the homogeneous mixture of the first and second precursor gases from 750°C to 800°C can provide a yield increase of up to 20%. This characteristic provides a significant economic benefit to the method according to the invention, as silane gases, such as silane, disilane, etc., are expensive.

[0060] Therefore, in an exemplary embodiment of the invention according to a first aspect of the invention, a homogeneous gas mixture can preferably be injected and heated to a temperature in the range of 740 to 850°C, preferably in the range of 780 to 830°C, and most preferably in the range of 790 to 820°C, but the maximum permissible temperature here depends on the residence time before the particles cool to a temperature at which crystallization cannot occur. Precise temperature limits for specific reactor geometries and residence times can be established through trial-and-error experiments.

[0061] Another advantage of the relatively high reaction temperature is that the dissociation reaction of the precursor gas becomes more driven towards complete dissociation, and thus more effectively expelling hydrogen from the condensed phase. This is advantageous because hydrogen in the negative electrode active material can potentially cause irreversible loss of electrochemical battery capacity through the irreversible formation of lithium hydride.

[0062] The particle size of particles prepared by nucleation and growth in the gas phase depends on the concentration of the precursor gas in the condensation zone. Generally, the higher the precursor gas concentration, the larger the particles formed. To enable the preparation of smaller particles, the precursor gas can be diluted in an inert gas, such as hydrogen (e.g.). Choosing hydrogen to dilute the precursor gas has the advantage of avoiding the feeding of any "external" elements into the formation process and thus producing ultra-high purity particles. Alternatively, an inert gas, such as a rare gas, can be used to dilute the precursor gas. Any inert gas, i.e., a gas or silicon particle that does not chemically react with the precursor gas, can be used for dilution purposes.

[0063] In exemplary embodiments of the invention according to the first and second aspects of the invention, the particles containing predominantly amorphous silicon can have a size of 10 to 250 μm. 2 / g, preferably 15 to 170m 2 Within the range of / g, more preferably, 25 to 130m 2 Within the range of / g, and most preferably 35 to 130m 2 The BET surface area is within the range of / g. For simplicity, if we assume that these particles are spherical or quasi-spherical and non-porous, then these BET surface areas correspond to an average particle size in the range of (roughly estimated) 10 to 200 nm, preferably 15 to 150 nm, preferably 20 to 100 nm, and most preferably 20 to 70 nm. The determination of particle surface area using BET is well known to those skilled in the art. An example of a standard that can be applied to determine the BET surface area of ​​particles containing predominantly amorphous silicon according to the first and second aspects of the invention is ISO 9277:2010.

[0064] The particles containing predominantly amorphous silicon according to the first and second aspects of the present invention may also be coated with a surface coating, preferably a carbon coating with a thickness of 0.05-3 nm, more preferably 0.2 to 1 nm, to improve surface properties, reduce the risk of fire, and promote the formation of a stable solid electrolyte interface (SEI). The present invention does not depend on any specific coating material or particle coating method, but any coatings and coating methods known to those skilled in the art for coating silicon particles can be applied.

[0065] The advantage of the relatively high heat resistance of the predominantly amorphous silicon particles of the present invention lies in the fact that the particles will better withstand the temperatures associated with the formation of carbon coatings—and / or the formation of composite particles containing silicon nanoparticles—through pyrolysis without exhibiting any obvious transformation to a crystalline state. The predominantly amorphous silicon particles of the present invention, containing carbon coating or carbon plating, can maintain their predominantly amorphous structure even through the pyrolysis process. The quality of pyrolysis will generally depend on the temperature, and it can preferably reach 600°C, 700°C, or preferably 800°C or even 900°C to obtain high-quality carbon material coatings or carbon coatings.

[0066] The predominantly amorphous structure of the silicon-containing particles of this invention makes them well-suited for use as active materials in the negative electrode of secondary lithium-ion electrochemical batteries (cells). The amorphous structure is known to allow for initial charging with lower overvoltages, they are more resistant to stress, and the particles are more resilient to volume changes associated with lithiation / delithiation cycles, both during charging and discharging.

[0067] In a third aspect, the present invention relates to particles containing predominantly amorphous silicon, wherein:

[0068] Particle inclusion formula: Si (1-x) M x The compound shown,

[0069] Where 0.005 ≤ x < 0.02 and M is at least one substitution element selected from: C, N, or combinations thereof, and

[0070] When subjected to XRD analysis with non-monochromatic CuKα radiation, the particles exhibit a peak at approximately 28° and a peak at approximately 52°, and when fitted with Gaussian peaks, both peaks have a full width at half maximum (FWHM) of at least 5°.

[0071] As used herein, the term "active material" generally refers to a compound / material of an electrode (negative and positive electrode) that acquires and donates lithium ions and electrons to generate or store energy, i.e., the material undergoes lithiation and delithiation during the charge / discharge cycle of an electrochemical battery. More specifically, the active material of the negative electrode according to the third aspect of the invention refers to particles containing predominantly amorphous silicon according to the first or second aspect of the invention.

[0072] In secondary electrochemical cells, the chemical half-cell reactions at the electrodes transition from oxidation to reduction reactions during the charge and discharge states of a charge / discharge cycle. As used herein, the term "negative electrode" refers to the electrode on the oxidizing side of the electrochemical cell where the chemical reaction occurs during discharge; that is, the negative electrode is the electron-generating electrode when electrical energy is extracted from the electrochemical cell. In the literature, the negative electrode may also be referred to as the anode. In this document, the terms anode and negative electrode may be used interchangeably.

[0073] The negative electrode according to the third aspect of the invention can be applied to any conductive substrate known or conceivable by a person skilled in the art for use as a current collector in a secondary lithium-ion electrochemical battery. Examples of suitable conductive substrates include (but are not limited to) foils / sheets of graphite, aluminum, or copper.

[0074] The negative electrode according to the third aspect of the invention can be made of any binder material known or conceivable to a person skilled in the art as a binder suitable for use as a negative electrode in a secondary lithium-ion electrochemical battery. Examples of suitable binders include (but are not limited to) styrene-butadiene copolymer (SBR), carboxymethyl cellulose (CMC), ethylene-propylene-diene methylene (EPDM), and polyacrylic acid (PAA).

[0075] In exemplary embodiments, the negative electrode material may further comprise a particulate conductive filler material mixed with the particulate active material and embedded together in a binder material. The negative electrode according to the third aspect of the invention can utilize any conductive filler material known or conceivable to those skilled in the art for use as a negative electrode in a secondary lithium-ion electrochemical battery. Examples of suitable particulate conductive fillers include (but are not limited to): carbon allotropes, such as graphene, reduced graphene oxide, elastic polymers, predominantly carbon-containing materials prepared by pyrolysis of carbon-rich materials, carbon black, carbon nanotubes, or mixtures thereof.

[0076] In a fourth aspect of the invention, particles containing predominantly amorphous silicon according to the first or second aspect of the invention can be used to form composite particles via a post-production step comprising the pyrolysis of a carbon-containing material containing a plurality of predominantly amorphous silicon particles of the invention. The composite particles can then be reused as battery electrodes, and each composite particle can contain, for example, 10 to possibly one million predominantly amorphous silicon particles of the invention and a certain amount of carbon formed by heat treatment of a precursor material containing carbon atoms. Such precursor material can be, for example, large carbon-dense molecules, such as petroleum or bitumen. Alternatively, the precursor material can be a highly cross-linked material, such as resorcinol-formaldehyde or melamine-formaldehyde, wherein pyrolysis can be used to form nanoporous materials or aerogels. The pyrolysis process can be carried out at >600°C, preferably >700°C, or more preferably >800°C. Example composite particles can have a size similar to graphite particles currently used in batteries, i.e., an average cross-sectional distance of, for example, 2 to 5 micrometers.

[0077] In a fifth aspect of the invention, the predominantly amorphous silicon particles according to the first and second aspects of the invention can be formed using graphene or graphene oxide as a conductive additive and a protective barrier for the electrolyte to form composite particles. The composite particles can then be reused as battery electrodes and can contain, for example, 10 to possibly one million predominantly amorphous silicon particles of the invention and a certain amount of graphene or reduced graphene oxide formed by heat treatment of a precursor material containing graphene oxide or graphene oxide. The reduction process can be carried out at >600°C, preferably >700°C, or more preferably >800°C. Example composite particles can have a size similar to the graphite particles currently used in batteries, i.e., for example, an average cross-sectional distance of 2 to 5 micrometers. The composite particles may also include binders or other components to ensure the geometric stability of the composite particles in subsequent production steps.

[0078] In a sixth aspect of the invention, particles containing predominantly amorphous silicon according to the first and second aspects of the invention can be used as a barrier to the electrolyte to form composite particles. The composite particles may also contain conductive additives. The composite particles can then be used again as battery electrodes and may contain, for example, 10 to possibly one million predominantly amorphous silicon particles of the invention. The elastic binder can be any elastic polymer or plastic, including known elastomers such as imines, amides, silicones, styrene-butadiene rubber, and nitrile rubber. Example composite particles may have a size similar to that of graphite particles currently used in batteries, i.e., an average cross-sectional distance of, for example, 2 to 5 micrometers. Attached Figure Description

[0079] Figure 1 This is a graph showing the XRD analysis of silicon particles prepared at three different temperatures.

[0080] Figure 2 It is displayed in relation to Figure 1 In almost the same method, Si prepared at temperatures above 800°C remains completely amorphous. 0.99 C 0,01 and Si 0.98 C 0,02 Figures showing XRD analysis of various samples (samples R11_FA, R11_FB, and R11_FC).

[0081] Figure 3 The display shows that after heat treatment for 2 hours at 700℃ (R18-F1 700) and 800℃ (R18-F1 800) respectively, Si 0.96 C 0,04 The graph shows the XRD analysis results of the sample. The curves show that even after 2 hours at 800°C, Si... 0.96 C 0,04 Maintain amorphous state.

[0082] Figure 4 The display shows that after heat treatment for 2 hours at 700℃ (R18-F2 700) and 800℃ (R18-F2 800) respectively, Si 0.92 C 0,08 The graph shows the XRD analysis of Si. The curves show that after 2 hours at 700°C, Si... 0.92 C 0,08 It remains amorphous, but crystallization begins if exposed to 800°C for 2 hours.

[0083] Figure 5 This is a graph showing the XRD analysis of Si, which shows that the material completely crystallizes if exposed at 780°C for 2 hours.

[0084] Figure 6 The XRD patterns are of samples containing both crystalline and amorphous silicon, with the area below the Bragg peak marked in dark gray, and the area under the broad peak after subtracting the area against the straight background shown in light gray.

[0085] Verification of the invention

[0086] The invention will be described in further detail through exemplary embodiments.

[0087] Comparative Examples

[0088] Three (pure) silicon particle samples were prepared by preheating a homogeneous gas mixture of 33% silane diluted in hydrogen to approximately 400°C and introducing the gas into a decomposition reactor. The silane gas was then mixed with preheated hydrogen at temperatures of 710°C, 745°C, and 770°C, respectively. The residence time in the reactor was estimated to be 1.5 seconds. The resulting silicon particles were rapidly cooled to below 300°C and collected by filtration.

[0089] Then, the sample particles were analyzed by XRD to study their atomic structure. Particles prepared at 710 °C (in...) Figure 1 The particles (labeled RTF1) exhibit typical amorphous silicon XRD patterns, and the particles prepared at 745 °C (in...) Figure 1 The superscript labeled RTF2) has an XRD curve representing the formation of certain crystalline silicon, while the particles prepared at 770°C (in) Figure 1 The superscript labeled RTF3) has a typical XRD curve for crystalline silicon.

[0090] Example 1

[0091] An example embodiment of the present invention, in which silicon particles are primarily amorphous, can be prepared as follows:

[0092] A homogeneous mixture of silane gas and ethylene is preheated to approximately 400°C and introduced into the reactor chamber. The homogeneous mixture of silane gas and ethylene is further mixed with an inert gas (nitrogen), which is preheated to a temperature providing the resulting gas mixture temperature of 810°C. The final mixture contains approximately 28 mol% silane, 1.5 mol% ethylene, and the remainder (70 mol%) nitrogen, providing a C:Si atomic ratio of 0.05 in the gas mixture. However, the resulting particles have a C:Si atomic ratio of 0.02, meaning the particles are primarily composed of amorphous Si. 0.98 C 0.02 composition.

[0093] The residence time in the reactor is approximately 1.0 second. Afterward, the exhaust gas and particles exiting the reactor space are rapidly cooled and collected in a filter. The particles are analyzed by XRD to study their atomic structure. Figure 2 The results are shown as curves labeled R11_FA. XRD curves are typical for silicon, which has an amorphous molecular structure.

[0094] Example 2

[0095] Two other examples of particle preparation were carried out in a manner similar to that in Example 1, the difference being that for material R11_FB, the gas mixture was heated to 800°C in a reactor, and in sample R11_FC, the ethylene concentration was reduced by 50% to prepare Si. 0.99 C 0.01 These particle samples were analyzed by XRD, and... Figure 2 The results are displayed as curves labeled R11_FB and R11_FC, respectively. These two curves are typical for amorphous silicon.

[0096] Example 3

[0097] Three additional particle formulations were prepared in a manner similar to that in Example 1, except that the gas mixture contained silane, ethylene, ammonia, and nitrogen. These samples were characterized using differential scanning calorimetry (DSC) to determine the crystallization temperature based on the energy released during crystallization. For these low-content particles, nitrogen content was not as readily measurable as carbon content; however, based on linear extrapolation from the high-nitrogen-content sample and analysis of gas consumption during the reaction, the particle Si content was estimated to be as follows. x C y N z Composition: Si0 0.984 C 0.016 N0, Si 0.992 C 008 N0 and Si 0.976 C 0.012 N 0.012 .

[0098] All these samples show an increased crystallization temperature compared to the pure silicon comparison particles described above, where Si 0.976 C 0.012 N 0.012 The sample with the estimated composition had a maximum crystallization temperature of 794 °C. The other two samples showed crystallization temperatures at least 10 °C lower, i.e., slightly below 784 °C.

[0099] References

[0100] 1Qi et al. (2017), "Nanostructured anode materials for lithium-ionbatteries: principle, recent progress and future perspectives", J.Mater.Chem.A, vol.5, pp.19521-19540

[0101] 2Sourice 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.

[0102] 3 Sourice et al.(2015),“One-Step Synthesis of Si@C Nanoparticles byLaser Pyrolysis:High Capacity Anode Material for Lithium-Ion Batteries”,ACSAppl.Mater.Interfaces,vol.7,pp.6637-6644,DOI:10.1021 / am5089742

[0103] 4 https: / / en.wikipedia.org / wiki / Amorphous_solid

[0104] 5 Berla,Lucas A.;Lee,Seok Woo;Ryu,Ill;Cui,Yi;Nix,William D.(2014),"Robustness of amorphous silicon during the initial lithiation / delithiationcycle",Journal of Power Sources.258:253–259.Bibcode:2014JPS...258..253B.doi:10.1016 / j.jpowsour.2014.02.032.

[0105] 6 Wang Y.K.,Chou S.L.,Kim J.H.,Liu H.K.and Dou S.X.,“Nano-compositesof silicon and carbon derived from coal tar pitch:Cheap anode materials forlithium-ion batteries with long cycle life and enhanced capacity“Electrochim.Acta,2013,93,213—221.

[0106] 7 Dahn,J.R.,Zheng,T.,Liu,Y.,Xue,J.S.,(1995),“Mechanisms for LithiumInsertion in Carbonaceous materials”Science,Vol.270,Issue 5236,pp.590-593.

[0107] 8 Escamilla-Perez, AM, Roland, A., Giraud, S., Guiraud, C., Virieux, H., Demoulin, K., Oudart, Y., Louvainac, N., and Monconduit, L., (2019), “Pitch-based carbon / nano-silicon composite, an efficient anode for Li-ion batteries”, RCSAdvances, Vol. 9, pp. 10546-10553.

Claims

1. A method for manufacturing inclusive: Si (1-x) C x A method for determining compounds containing predominantly amorphous silicon particles, wherein 0.005 ≤ x < 0.05, and wherein, when subjected to XRD analysis with non-monochromatic CuKα radiation, the particles exhibit a peak at 28° and a peak at 52°, and wherein, when fitted with Gaussian peaks, the two peaks have a full width at half maximum (FWHM) of at least 5°. The method includes: - A homogeneous gas mixture that forms a first precursor gas of a silicon-containing compound and at least one second precursor gas of a compound containing a substituted element C. - The homogeneous gas mixture of the first precursor gas and the second precursor gas is injected into the reactor space, wherein the precursor gas is heated to a temperature in the range of 700 to 900°C, causing the precursor gas to react and form particles, and - Collect the particles and cool them to a temperature ranging from ambient temperature to 350°C. And among them - Adjust the relative amounts of the first precursor gas and the second precursor gas so that the formed particles have a C:Si atomic ratio in the range of [0.005, 0.05).

2. The method according to claim 1, wherein, The first precursor gas is: silane (SiH4), silane (Si2H6), and trichlorosilane (HCl3Si) or a mixture thereof.

3. The method according to claim 1 or 2, wherein, The second precursor gas is selected from alkanes, alkenes, alkynes, or mixtures thereof.

4. The method according to claim 1 or 2, wherein, The relative amounts of the first precursor gas and the second precursor gas are adjusted so that the formed particles have a C:Si atomic ratio in the range of [0.01, 0.04].

5. The method according to claim 1 or 2, wherein, Before being inserted into the reactor space, the homogeneous gas mixture of the first precursor gas and the second precursor gas is preheated in the region to a temperature of 400 to 500°C, and then further heated to a temperature in the range of 740 to 850°C after being injected into the reactor space.

6. The method according to claim 1 or 2, wherein, The gas mixture also includes hydrogen, nitrogen, rare gases, or any other gas that will not chemically react with the precursor gas at a specified temperature.

7. The method according to claim 1 or 2, wherein, The relative amounts of the first precursor gas and the second precursor gas are adjusted by: adjusting the flow rates of the first precursor gas and the second precursor gas injected into the reactor and using a mass spectrometer to measure the composition of the tail gas leaving the reactor to determine the fraction of the injected first precursor gas and the second precursor gas converted into particles; using the fraction to estimate the C:Si atomic ratio in the formed particles; and adjusting the feed rates of the first precursor gas and the second precursor gas to obtain the desired C:Si atomic ratio in the generated particles.

8. The method according to claim 1 or 2, wherein, The method also includes the step of depositing a 0.05+3 nm thick carbon layer onto the surface of the aggregated particles.

9. The method according to claim 4, wherein, The relative amounts of the first precursor gas and the second precursor gas are adjusted so that the formed particles have a C:Si atomic ratio in the range of [0.01, 0.03].

10. The method according to claim 4, wherein, The relative amounts of the first precursor gas and the second precursor gas are adjusted so that the formed particles have a C:Si atomic ratio in the range of [0.01, 0.02].

11. The method according to claim 1 or 2, wherein, Before being inserted into the reactor space, the homogeneous gas mixture of the first precursor gas and the second precursor gas is preheated in the region to a temperature of 400 to 500°C, and then further heated to a temperature in the range of 780 to 830°C after being injected into the reactor space.

12. The method according to claim 1 or 2, wherein, Before being inserted into the reactor space, the homogeneous gas mixture of the first precursor gas and the second precursor gas is preheated in the region to a temperature of 400 to 500°C, and then further heated to a temperature in the range of 790 to 820°C after being injected into the reactor space.

13. The method according to claim 6, wherein, The rare gases are helium, neon, and argon.

14. The method according to claim 8, wherein, The method also includes the step of depositing a carbon layer of 0.2 to 1 nm thickness onto the surface of the aggregated particles.

15. The method according to claim 1 or 2, wherein, The second precursor gas is selected from methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), acetylene (C2H2), or mixtures thereof.

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