Secondary and Tertiary Composite Particles

Abstract

The present invention relates to a method for making secondary composite particles, secondary composite particles, a method for making tertiary composite particles, tertiary composite particles, and a secondary electrochemical cell utilizing the secondary or tertiary composite particles as the active material of the negative electrode of a secondary electrochemical cell, each tertiary composite particle comprising a plurality of secondary composite particles embedded in a second matrix made primarily of carbon, each secondary composite particle comprising a plurality of primary particles embedded in a first matrix, the primary particles being composed primarily of silicon, and the first matrix comprising silicon and carbon.

Description

[Technical field]

[0001] The present invention relates to a method for producing secondary composite particles, secondary composite particles, a method for producing tertiary composite particles, tertiary composite particles, and secondary electrochemical cells utilizing the secondary or tertiary composite particles as the active material of the negative electrode of a secondary electrochemical cell. [Background technology]

[0002] To achieve the Paris Agreement targets under the UN climate treaty, a significant increase in the use of renewable energy and electricity will be required in many sectors of society currently running on fossil fuel energy. A key to achieving these targets is access to rechargeable batteries with good specific energy.

[0003] Lithium is 0.534 g / cm 3 It has a relatively very low density of 1.0 and the half-reaction Li + +e - →Li 0 Lithium has a high standard reduction potential of -3.045 V for 1000 sq. m. This makes it an attractive candidate for fabricating electrochemical cells with high specific energy. However, secondary (rechargeable) electrochemical cells with negative electrodes of metallic lithium have been shown to suffer from a persistent problem of dendrite formation on charging, which tends to short out the electrochemical cell after a few charge-discharge cycles.

[0004] The dendrite problem was solved by applying a negative electrode capable of releasably storing lithium atoms by intercalation. Such batteries are known as lithium-ion secondary batteries (LIBs). The electrochemical properties of LIBs are directly influenced by the physical and chemical properties of the active material of the negative electrode. The selection and tailoring of materials, as well as appropriate structural modification and design of the active materials, both affect the battery performance [Non-Patent Document 1]. The key issue in this regard is how to reliably and reversibly store lithium atoms at high volumetric density when the battery is charged, and then convert the lithium into ions (Li) when it is discharged over a large number of successive charge-discharge cycles. + The goal was, and still is, to find an active material that can release charge as a charge.

[0005] Currently, the majority of commercially available LIBs use graphite as the negative electrode active material. Graphite can accommodate / fill one lithium atom per six carbon atoms by intercalation with little shape deformation, and has a theoretical specific energy of 372 mAh / g. Commercial secondary LIBs with graphite anodes typically obtain a specific energy of 100-200 Wh / kg, making, for example, a medium-sized electric vehicle battery weighing several hundred kilograms. This level of specific energy is likely insufficient to realize the goals of the Paris Agreement.

[0006] One strategy to improve the specific energy of LIBs is to find materials with higher lithium ion storage capacity than graphite, which is used as the negative electrode active material. One interesting and much-studied candidate in this regard is silicon, due to its high ability to store lithium atoms by diffusion and alloying. At typical ambient temperatures, the most lithiated phase of silicon has a theoretical specific capacity of 3579 mAh / g Li 3.75 The negative electrode is Si [Non-Patent Document 1]. Silicon negative electrodes also have the advantage that they make it possible to provide attractive operating potentials that reduce safety concerns regarding lithium deposition upon cell overcharging [Non-Patent Document 2].

[0007] The lithiation and delithiation of silicon induces huge volume expansions and contractions, respectively, in the silicon material. The most lithiated state, Li 3.75 In Si, silicon material has a volume about 320% larger than that in the non-lithiated state. It has been reported that the relatively large volume change accompanying lithiation and delithiation cycles can cause cracking and / or dissipation of silicon electrodes and / or repeated formation of a solid electrolyte interface (SEI) layer, leading to various problems in the performance of LIBs, such as loss of electrical contact, loss of active material in the electrodes, and ineffective electron transfer [Non-Patent Documents 1, 2].

[0008] Nanostructuring of silicon materials has been investigated as a solution to overcome the volume expansion problem, since nanoscale Si particles can better accommodate volume fluctuations [Non-Patent Document 2]. It has been demonstrated that the use of nanoscale particles in electrodes can provide electrodes with outstanding properties due to their small particle size, which leads to effects such as improved electrical conductivity, improved mechanical and optical properties [Non-Patent Document 1]. Furthermore, since nano-sized particles have a very high surface area to volume ratio, negative electrodes with nano-sized active materials can provide excellent charge / discharge capacity due to the highly available surface for lithium ion adsorption / desorption [Non-Patent Document 1].

[0009] The interatomic distance between silicon atoms increases as they expand when accommodating lithium ions (lithiation). In crystalline silicon, the expansion creates large anisotropic stresses within the electrode material, leading to increased fracturing and disintegration of the silicon material. This anisotropic stress has been found to be reduced in many anode structures when the silicon material itself is amorphous [5].

[0010] In LIBs with liquid electrolytes, a solid electrolyte interface (SEI) often forms upon first lithiation. The formation of the SEI layer irreversibly consumes lithium and represents an irreversible capacity loss for the electrochemical cell [Non-Patent Document 1]. It is therefore advantageous to form a stable SEI layer to limit the SEI-induced loss of lithium upon the first lithiation / charging of the cell. A stable SEI layer can be obtained by coating the silicon surface with appropriate elements to avoid direct contact between the silicon and the electrolyte [Non-Patent Document 1], but it has been demonstrated that in the event of cracking, an unprotected surface appears.

[0011] Carbon has been studied and utilized in LIBs with nanostructured silicon as the active material in the anode, both as a coating material and / or as a composite with silicon. Many silicon-carbon structures have been reported in the literature, ranging from simple mixtures of silicon to complex forms of silicon and graphene or graphite. These complex structures exhibit excellent cyclability and capacity, but suffer from the need for a large number of charge-discharge cycles to reach high coulombic efficiency, and require complex multi-step synthesis processes to scale up to commercial production levels [Non-Patent Document 2].

[0012] From Sourice et al. (2016) [Non-Patent Document 2], a method is known for producing nanoscale amorphous silicon particles with a carbon shell / coating by a two-stage laser pyrolysis process, in which a gas stream of silane diluted in an inert gas enters a first reaction zone irradiated by a CO2 laser, which decomposes the silane gas into amorphous silicon core particles. Ethylene is then added to the gas with the formed silicon core particles, and the mixture is passed through a second reaction zone and irradiated by a CO2 laser, which decomposes the ethylene into a carbon shell deposited on the silicon core particles. The amorphous silicon particles with a carbon coating have been found to have excellent specific capacity and high charge / discharge cycle capabilities.

[0013] Patent document 1 discloses a compound of the formula SiC xdiscloses an active material for the negative electrode of a LIB, comprising a silicon-containing compound of the formula: x=0.05-1.5, and the carbon concentration in the material follows 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 the surface region of the active material. This document informs that the carbon may be covalently bonded to the silicon, and further that the silicon-containing compound may be in particulate form and have an amorphous molecular structure. Furthermore, paragraph

[0030] of Patent Document 1 discloses that if the carbon content in the active material is too low, i.e., if x is less than 0.05, the active material may be deteriorated due to cracks.

[0014] US Patent No. 5,999,333 discloses a reactor and method for producing crystalline or amorphous silicon particles by chemical vapor deposition of a silicon-containing precursor onto seed particles in a heated and rapidly rotating reactor space. The silicon-containing gas may be diluted in a carrier gas and may be one of SiH4, Si2H6, SiHCl3 or a mixture thereof. The carrier gas may be one of hydrogen, nitrogen, and argon. SiO x , SiC x , SiN x By introducing a second precursor gas, liquid, material, etc., such as C, O, or N in combination with silicon, amorphous carbon, graphite, low crystalline carbon, or short range ordered graphene structures, the formed silicon particles can be given an outer layer of the second material having a lower silicon content than the core material of the particle.

[0015] From US Pat. No. 5,399,433 it is known that a mixture of silane and a hydrocarbon selected from the group of ethene, ethane, propane and acetylene can be simultaneously fed into a plasma-enhanced chemical vapor deposition reactor to produce silicon-carbon composite powders, in which the C / Si weight ratio at the surface of each particle is at least three times the average C / Si weight ratio of all particles, and the particle itself has a diameter of less than 300 nm.

[0016] From Sung et al. (2021) [Non-Patent Document 6], a method for producing a carbon-based material for use in a negative electrode active material for a lithium secondary battery is known, comprising a carbon-based core material, a silicon coating layer disposed by CVD on the entire surface of the core material, and a carbon coating layer disposed on the silicon coating layer, wherein the silicon coating layer comprises silicon particles and a silicon-carbon-based amorphous matrix. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] US Patent Application Publication No. 2012 / 0107693 [Patent Document 2] International Publication No. 2018 / 052318 [Patent Document 3] European Patent Application Publication No. 3428999 [Non-patent literature]

[0018] [Non-Patent Document 1] Qi et al. (2017), "Nanostructured anode materials for lithium-ion batteries: principle, recent progress and future perspectives", J. Mater. Chem. A, vol. 5, pp. 19521-19540 [Non-Patent Document 2] Sourice et al. (2016), "Core-shell amorphous silicon-carbon nanoparticles for high performance anodes in lithium-ion batteries", Journal of Power Sources, vol. 328, pp. 527-535. [Non-Patent Document 3] Sourice et al. (2015), "One-Step Synthesis of Si@C Nanoparticles by Laser Pyrolysis: High Capacity Anode Material for Lithium-Ion Batteries", ACS Appl. Mater. Interfaces, vol. 7, pp. 6637-6644, DOI: 10.1021 / am5089742 [Non-Patent Document 4] https: / / en.wikipedia.org / wiki / Amorphous_solid [Non-Patent Document 5] Berla, Lucas A.; Lee, Seok Woo; Ryu, Ill; Cui, Yi; Nix, William D. (2014), "Robustness of amorphous silicon during the initial lithiation / delithiation cycle", Journal of Power Sources. 258: 253-259.Bibcode:2014JPS...258..253B. doi:10.1016 / j.jpowsour.2014.02.032. [Non-Patent Document 6] Sung, J., Kim, N., Ma, J. et al. (2021) Subnano-sized silicon anode via crystal growth prototype inhibition mechanism and its application in a battery pack. Nat Energy 6, 1164-1175. https: / / doi.org / 10.1038 / s41560-021-00945-z [Non-Patent Document 7] Morten Wetjen et al (2018) "Morphological Changes of Silicon Nanoparticles and the Influence of Cutoff Potentials in Silicon-Graphite Electrodes" Journal of The Electrochemical Society, 165 (7) A1503-A1514 [Non-Patent Document 8] Reciprocal Relations in Irreversible Processes. I.Lars Onsager Phys. Rev. 37, 405 (1931) [Non-Patent Document 9] Reciprocal Relations in Irreversible Processes. II.Lars Onsager Phys. Rev. 38, 2265 (1931) [Non-Patent Document 10] BH Toby, RB Von Dreele, GSAS-II: the genesis of a modern open-source all purpose crystallography software package, Journal of Applied Crystallography, 46 (2013) 544-549. [Non-Patent Document 11] AA Coelho, TOPAS and TOPAS-Academic: an optimization program integrating computer algebra and crystallographic objects written in C plus, Journal of Applied Crystallography, 51 (2018) 210-218. [Non-Patent Document 12] RW Cheary, AA Coelho, JP Cline, Fundamental parameters line profile fitting in laboratory diffractometers, Journal of Research of the National Institute of Standards and Technology, 109 (2004) 1-25. [Non-Patent Document 13] P. Thompson, ED Cox, JB Hastings, Rietveld Refinement of Debye-Scherrer Synchrotron X-ray Data from Al2O3, Journal of Applied Crystallography, 20 (1987) 79-83. Summary of the Invention [Problem to be solved by the invention]

[0019] A primary object of the present invention is to provide a method for producing secondary composite particles suitable for use as active material in negative electrodes in rechargeable lithium ion electrochemical cells.

[0020] It is a further object of the present invention to provide a method for making tertiary composite particles suitable for use as active material in negative electrodes in rechargeable lithium ion electrochemical cells.

[0021] It is a further object of the present invention to provide secondary composite particles suitable for use as an active material in a negative electrode in a rechargeable lithium ion electrochemical cell, and suitable for making tertiary composite particles suitable for use as an active material in a negative electrode in a rechargeable lithium ion electrochemical cell.

[0022] It is a further object of the present invention to provide tertiary composite particles suitable for use as the active material in the negative electrode of a rechargeable lithium ion electrochemical cell.

[0023] It is a further object of the present invention to provide a negative electrode for a lithium-ion secondary electrochemical cell comprising the secondary or tertiary composite particles. [Means for solving the problem]

[0024] The present invention is based on the discovery of secondary and tertiary composite particles that are particularly suitable for use as active materials in negative electrodes in rechargeable lithium ion electrochemical cells. The resulting electrochemical cells have improved capacity and cyclability.

[0025] In a first aspect, the present invention relates to a method for producing secondary composite particles, wherein said secondary particles comprise a plurality of primary particles embedded in a first matrix, said primary particles being composed primarily of silicon and said first matrix comprising silicon and carbon; The method comprises: forming a first gas mixture comprising a first precursor gas of a silicon-containing compound and a second precursor gas of a carbon-containing compound, such that an atomic ratio of silicon to carbon in the first gas mixture, Si:C, is in the range of [0.1, 10]; preheating the first gas mixture to a temperature of 300-500°C; introducing the preheated first gas mixture into a reactor space and forming a second gas mixture by mixing the first gas mixture with a reactor gas, the reactor gas being preheated to a temperature such that the temperature of the second gas mixture is between 500 and 1200°C; maintaining the second gas mixture in the reactor volume for a period of time to form exhaust gases and condensed particles; cooling and collecting the condensed particles; Includes.

[0026] As used herein, the term "consisting primarily of silicon" means that the phase and / or particle comprises at least 50% silicon by weight, i.e., 50-100% by weight Si. In one embodiment, the primary particles comprise at least 80%, preferably at least 90%, more preferably at least 95%, more preferably at least 96%, more preferably at least 97%, more preferably at least 98%, more preferably at least 99%, and most preferably at least 99.5% silicon by weight.

[0027] The interval notation used in this specification follows the international standard ISO 80000-2, where square brackets "[ " and " ]" denote the bounds of a closed interval, and parentheses "( " and " )" denote the bounds of an open interval. For example, [a, b] is the closed interval that includes all real numbers from a (inclusive) to b (inclusive):

number

number

[0028] In one embodiment of the invention, the atomic ratio of silicon to carbon in the first gas mixture may be [0.1, 8], preferably [0.2, 6], more preferably [0.3, 4], more preferably [0.5, 3], more preferably [0.8, 2], and most preferably [1, 1.5].

[0029] In one embodiment of the present invention, the condensed particles may be cooled to a temperature below 450°C, preferably below 400°C, more preferably below 350°C, and most preferably below 300°C.

[0030] In one embodiment of the invention, the first gas mixture may be preheated to a temperature of 350-475°C, preferably 375-450°C, and most preferably 400-425°C, prior to injecting the first gas mixture into the reactor space.

[0031] The term "reactor gas" as used herein encompasses exhaust gases formed by previous secondary particle generation and / or any inert gas at the applied reaction temperature. Inert in this context means chemically inert to the condensed particles. Examples of suitable inert gases include hydrogen, nitrogen, noble gases such as helium, neon, argon, or any other gas that does not chemically react with the precursor gas at the reaction temperature.

[0032] In one embodiment of the present invention, the temperature of the second gas mixture is between 500 and 1200°C, preferably between 550 and 1000°C, more preferably between 600 and 880°C, and most preferably between 650 and 700°C.

[0033] The first gas mixture of precursor gases, in one exemplary embodiment, may further include one or more inert gases, i.e., gases that do not chemically react with the precursor gases at the reaction temperature, such as hydrogen, nitrogen, noble gases such as argon, neon, helium, and other gases that may be used to affect heating, cooling, particle formation rate, or mass transfer, but do not leave chemical impurities in the final particle product. Heating of the precursor gases in the reaction chamber may be achieved by convection, conduction, radiation, laser, mixing with a warm gas, or any other known method.

[0034] Without being bound by theory, it can be said that this process can be satisfactorily explained by the following: When a silicon-containing gas, e.g., silane, reaches its reaction temperature, the silane gas starts releasing hydrogen atoms and forming higher silanes, and as more and more hydrogen leaves the silane molecule, it eventually forms a phase composed mainly of silicon, hereafter referred to as the primary particles.

[0035] With further increase in temperature, the second precursor gas containing C atoms also starts to react with the silane and with the already formed primary particles to form a first matrix containing silicon and carbon. As the reaction proceeds, the ratio of the first precursor gas of the silicon-containing compound to the second precursor gas of the carbon-containing compound decreases until there is no more first precursor gas available.

[0036] Thus, the secondary particles will create an outer region with a high percentage of barrier atoms (i.e., carbon) and a core of multiple primary particles composed mainly of silicon. These initial primary particles may still have a high percentage of hydrogen in them and are therefore somewhat soft at the reaction temperature. Such small particles have very high diffusion rates (Brownian motion) and they constantly collide and agglomerate into larger particles. Further growth occurs from the gas phase to these particles and within a temperature-dependent time frame, the particles coalesce into more or less spherical, e.g., spheres, or ovoid, oblong particles.

[0037] At some point, the hydrogen content within the silicon primary particles decreases to a level where the viscosity increases enough that coalescence stops. There may still be some partial coalescence, but spheres can still be recognized. Within the secondary composite particles, silicon nano-domains still remain as a signature of the original process.

[0038] The aggregate size is determined primarily by the concentration and reaction time, and by maintaining the reaction at high temperatures, the reaction time can be made very short.

[0039] Finally, the process is terminated when the temperature is reduced to a level where no further reaction or coalescence can occur, i.e. below 500°C.

[0040] Optionally, termination may be facilitated by a centrifuge that separates large particles from smaller particles, thus selectively stopping the largest particles.

[0041] Note that plasma reactions or sputtering processes are probably not suitable for this step as they do not have the same reaction rate selectivity as thermally activated processes: they are more likely to give a uniform distribution of the elements which limits diffusion, resulting in less benefit from each impurity atom.

[0042] As described in the prior art, the same nano-domains can be observed growing, for example, as a layer on the surface of graphite. In the present invention, the particles are instead formed while freely suspended in the gas, allowing for much higher reaction rates and are not limited by the diffusion rate of the gas into the powder deposit or by the limitations of the available surface area. Thus, the present invention allows for much higher productivity and / or shorter reaction times. The present invention also provides a complete manufacturing process that avoids the use of graphite, which has a Li-ion storage capacity ten times lower than silicon.

[0043] The first matrix of secondary composite particles with embedded primary particles acts as a silicon diffusion barrier. These first matrices can be carbon-rich. In some embodiments, these first matrices can contain at least 50% carbon. In other embodiments, the first matrix can contain at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5% carbon, or can be composed of 100% carbon.

[0044] In an embodiment, the first matrix may comprise between 50% and 99.5%, between 50% and 99%, between 50% and 95%, or between 50% and 90% carbon.

[0045] When lithium enters and leaves the secondary composite particles during use in LIB batteries, some amount of silicon co-diffusion can be expected. This is not widely recognized, but it is difficult to explain many degradation phenomena without assuming some degree of silicon co-diffusion (see, for example, [Non-Patent Document 7], especially FIG. 4, [Non-Patent Document 8], [Non-Patent Document 9]). CC bonds are generally more than 50% stronger than Si-Si bonds. CC double bonds are 200% stronger. Thus, the carbon-rich first matrix acts as a strong silicon diffusion barrier. The silicon diffusion barrier has a lower cycle capacity than silicon, so its amount should be limited. It must form strong covalent bonds with silicon and be easy to introduce in gaseous form.

[0046] The diffusion barrier preferably does not irreversibly trap lithium, which means that carbon is favored over oxygen and nitrogen. Furthermore, the second precursor gas should be one that reacts at a slightly higher temperature than the first precursor gas. This again favors more hydrocarbons over nitrogen and oxygen containing gases.

[0047] The secondary composite particles may be individual spheres or may reach a more asymmetric shape by coalescence or partial coalescence. For any given reaction, a distribution of sizes is expected, i.e., can be described using D10, D50, and D90 estimated from DLS measurements. The size distribution of secondary composite particles may be quantified by their DLS equivalent mass, which is a measure of how much mass there is in the aggregate and the solvent it drags along during the DLS measurement. In one embodiment, the secondary composite particles may have a D50 measured by DLS, i.e., at least 2 times, at least 5 times, at least 10 times, or at least 20 times the size of the primary particles measured by TEM.

[0048] The key dimension of an individual secondary composite particle is its radius, which is an indication of the maximum distance lithium will diffuse in silicon. The radius of an individual particle may be measured directly from SEM or TEM images. If, for simplicity, it is assumed that all composite particles are spherical, there is also a one-to-one relationship between the surface area per gram measured in a BET measurement (Brunauer-Emmett-Teller measurement) and the average particle radius. The average radius measured in this way with BET has been shown to be in good agreement with visual estimates from microscopy. The BET surface area per gram also correlates directly with the maximum distance lithium will diffuse by itself. The maximum lithium diffusion distance again affects both the gradient that can be expected and the amount of lithium that will pass through any given part of the surface. These parameters again affect practical parameters such as the charging time of an electric vehicle and the rate of deterioration of the battery. It was found that secondary composite particles with diameters (measured by SEM) of 200 nm or less are less likely to form cracks during initial cycles.

[0049] The secondary composite particles may be used directly in the anode. In a preferred embodiment, the secondary composite particles may further include an outer coating for protection from oxidation in air or reaction with the electrolyte and may be used directly in the anode. However, they would still have some limitations. For particles smaller than 1 micron, there would be a limit to how thick the electrode can be before ion transport in the electrolyte becomes a bottleneck. Due to their high silicon content, the secondary composite particles also expand and contract with each cycle, which leads to the continuous new formation of the SEI. In one embodiment, the coating applied to the secondary particles is made by exposing the secondary particles to a carbon-containing gas and heating it to a coating temperature where the gas reacts with the secondary particles. In one embodiment, the coating temperature is 30°C to over 1000°C, preferably 300°C to 800°C, most preferably 600°C to 800°C.

[0050] Because the reaction rate in the gas reaction to form particles from precursor gases can vary significantly depending on which gases are used as the first and / or second precursor gases and the reaction rate at which the particles are formed, the atomic ratio C:Si in the precursor gases may deviate significantly from the average atomic ratio C:Si in the particles produced. Thus, as used herein, the phrase "the relative amounts of the first and second precursor gases are adapted so that the particles formed have an atomic ratio C:Si in the range of ..." means that the relative amounts of the mixed and homogenized first and second precursor gases are adjusted so that when the precursor gas mixture is heated to the intended reaction temperature and reacted to form the particles, the resulting particles have the intended atomic ratio.

[0051] The C:Si ratio throughout the particle (or powder) can be measured using a "total carbon" measurement, for example by burning a sample of the particle and measuring the amount of carbon dioxide formed. Local variations can be estimated using TEM / EELS (electron energy loss spectroscopy) or XRD (x-ray diffraction) on crystallized samples.

[0052] It is within the ordinary skill of a person skilled in the art to tailor the relative amounts of the first and second precursor gases to form the intended particles. For example, tailoring the relative amounts of the precursor gases for a given first and second precursor gas and intended reaction temperature can be obtained prior to the manufacturing stage by simply conducting trial and error tests to determine the relative amounts to be applied at this gas mixture and reaction temperature.

[0053] X-ray diffraction (XRD) (which may also be referred to in the literature as powder X-ray diffraction (PXD) when XRD is applied to particulate materials) gives different diffraction patterns for crystalline and amorphous materials, respectively. Crystalline materials tend to give sharp peaks, Bragg peaks, in XRD measurements due to the high order and symmetry in their atomic structure. For crystalline silicon materials, XRD analysis typically gives sharp peaks at 28.4°, 47.4°, and 56.1° in the measured diffraction pattern. In comparison, amorphous materials, which lack the long-range order characteristic of crystalline molecular structures, typically result in broader peaks being significantly "smeared" in the measured diffraction pattern. Amorphous silicon typically gives rounded peaks at 28° and 52°. These rounded peaks can be fitted using Gaussian fitting to reduce noise and to obtain well-defined values ​​for the peak maxima and widths. Such fitting can be performed by any skilled XRD operator.

[0054] Also, the sharpness of the peaks may be applied to distinguish between crystalline and amorphous materials. The full width at half maximum (FWHM) of the XRD peak of crystalline silicon is less than 2°, while the FHWM of amorphous silicon is typically greater than 4° when measured with a diffractometer applying non-monochromated CuKα radiation and using Gaussian fitting to reduce measurement noise. The full width at half maximum (FWHM) is the width of the peak curve measured between points on the y-axis that are half the maximum amplitude of the peak curve (after subtraction of background signals and / or signals from the sample holder). A sample containing both amorphous and crystalline silicon will obtain a diffraction pattern in the 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 may be applied to estimate the crystalline fraction of the sample from the ratio of the area under the Bragg peak above the broad peak of the amorphous to the combined area of ​​the broad peak and the Bragg peak. The linear background should be subtracted from the results prior to calculation.

[0055] The angles and angle tolerances in XRD analysis applied herein refer to the use of a diffractometer applying non-monochromated CuKα radiation. Because this radiation has high intensity and a wavelength of 1.5406 Å, which corresponds well with the interatomic distances in crystalline solids, making the analysis sensitive to the presence of crystalline phases in silicon particles. XRD analysis applying a diffractometer using CuKα radiation is a natural choice 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 other wavelengths may give different angles and angle tolerances. However, those skilled in the art know how to convert these values ​​from one radiation source to another.

[0056] Amorphous materials (see, for example, ref. [Non-Patent Document 4]) have some internal structure that provides short-range order on atomic length scales due to the nature of chemical bonds. This internal structure may be considered to consist of interconnected building blocks. These blocks may or may not be similar to the basic structural units found in the corresponding crystalline phase, i.e., they may or may not provide the material with very small crystal-like domains. Furthermore, for very small crystals, relaxation of surface and interface effects distorts the atomic positions and reduces 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 on such length scales.

[0057] Therefore, since it is difficult to determine by structural characterization techniques whether the silicon material of the particles produced in the first step of the manufacturing method is completely amorphous or contains small crystalline domains on the atomic length scale, the term "mainly amorphous" used herein encompasses silicon materials with 100% amorphous molecular structure to silicon materials containing very small crystalline domains on the atomic length scale (practically undetectable by XRD analysis).In addition, even if the material contains very small crystallites, typically less than 1 nm, it is reasonable to believe that the advantages of amorphous materials in the anode (i.e., less directional stress and faster charging) are maintained, and atoms with nearest neighbor distances distorted by grain boundaries constitute the same mass fraction as atoms with all nearest neighbors in crystalline order.

[0058] The average diameter of the primary particles may be assessed by Rietveld refinement of X-ray powder diffusion (XPD) data after exposing the secondary particles to a heat treatment that crystallizes the primary particles therein, for example at 900°C for 30 minutes. The width of the Bragg peak can then be used to determine the crystallite size using Rietveld refinement of the XPD data. When the crystallites are smaller than a few hundred nanometers, there is a predictable broadening of the peak. A skilled operator can use this to estimate the typical crystallite size, assuming a unimodal or multimodal distribution.

[0059] An example of the determination of the average diameter of the primary particles, after a heat treatment that crystallizes them, may include, for example, fitting XPD data calculated from a model of crystalline Si to experimental data obtained by XPD measurement of a sample of secondary particles using the least squares method, the so-called Rietveld refinement. The Rietveld refinement can be performed using freely available software such as GSAS-II [Non-Patent Document 10] or commercial software such as Topas [Non-Patent Document 11]. The instrumental contribution to the width of the Bragg peak should be described by the Thomson-Cox-Hastings pseudo-Voight function [Non-Patent Document 13], calculated from the instrumental geometry ("fundamental parameters approach" [Non-Patent Document 12]) or experimentally determined from a highly crystalline standard material such as NIST SRM 640f silicon. The instrumental contribution to the Bragg peak remains fixed during the Rietveld refinement. Any additional broadening of the observed Bragg peaks is due to small crystallite size and is assumed to have a Lorentzian shape. This crystallite size broadening is modeled by refining an additional contribution β to the calculated Bragg peak width that varies with scattering angle as follows:

number

[0060] The term "first precursor gas of silicon-containing compound" used herein refers to any silicon-containing compound that is in gaseous state and reacts to form Si particles at intended reaction temperature.Suitable examples of first precursor gas include, but are not limited to, silane (SiH4), disilane (Si2H6), and trichlorosilane (HCl3Si), or their mixtures.

[0061] Similarly, the term "carbon-containing compound second precursor gas" as used herein refers to any carbon-containing compound that, when heated to the intended reaction temperature, causes C atoms to be incorporated into the matrix surrounding the formed Si particles. Examples of suitable carbon-containing compound second precursor gases include, but are not limited to, alkanes, alkenes, alkynes, aromatic compounds, and mixtures thereof. In an exemplary embodiment, the carbon-containing compound second precursor gas may be at least an organosilane or a hydrocarbon, and may preferably be methane (CH4), ethane (C2H6), propane (C3H8), ethene (C2H4), ethyne (C2H2), cyclohexane, cyclohexene, toluene, benzene, or mixtures thereof.

[0062] A particularly preferred exemplary embodiment of the precursor gas, i.e. a homogeneous gas mixture of gaseous silicon-hydrogen compounds and gaseous substitutional element C-hydrogen compounds, is either silane (SiH4) or disilane (Si2H6) mixed with a hydrocarbon gas selected from one of methane (CH4), ethane (C2H6), propane (C3H8), ethene (C2H4), ethyne (C2H2), cyclohexane, cyclohexene, toluene, benzene and mixtures thereof. The partial use of larger and more stable cyclic structures is likely to be preferred, because this is likely to increase the ratio of C-C and Si-C bonds in the first matrix.

[0063] 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 to the reactor, and has been shown to depend 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. In general, the higher the reaction temperature, the higher the degree of dissociation of the precursor gas and thus the higher the production yield. Thus, since it has been observed that the predominantly amorphous silicon-containing primary particles maintain their predominantly amorphous structure at fairly high reaction temperatures, generally around 50° C. higher than the temperature at which the amorphous (pure) silicon particles are observed to transform into crystalline silicon, the method according to the first aspect of the invention has the advantage that the production yield is significantly improved compared to the production of amorphous (pure) silicon particles without compromising the preferred amorphous structure. Increasing the reaction temperature of the homogeneous mixture of the first and second precursor gases from 750° C. to 800° C. may result in an increase in the production yield of up to 20 percentage points. Because silicon hydride gases such as silane, disilane, etc. are relatively expensive, this feature provides a significant economic advantage to the method according to the present invention.

[0064] Thus, in an exemplary embodiment of the process according to the first aspect of the present invention, after injecting the homogeneous gas mixture into the reactor space, the temperature of the homogeneous gas mixture may be increased to a reaction temperature of 600-1100°C, preferably 700-900°C.

[0065] A further advantage of the relatively high reaction temperature is that it better drives the reaction of the precursor gases towards complete reaction and also more effectively expels hydrogen from the newly formed nuclei and nanoparticle phases, which is advantageous since hydrogen in the active material of the anode can cause irreversible loss of capacity of the electrochemical cell due to irreversible formation of lithium hydride.

[0066] The size of the particles produced by nucleation and growth in gas phase depends on the precursor gas concentration in condensation zone.Generally, the higher the precursor gas concentration, the larger the particles formed.To make smaller particles, the precursor gas can be diluted in an inert gas, such as hydrogen, preferably argon or nitrogen gas.Any inert gas, i.e., gas that does not chemically react with precursor gas or silicon particles, can be used for dilution purposes.

[0067] In an exemplary embodiment of the present invention, the secondary composite particles have a diameter of 10 to 250 μm. 2 / g, 15-170m 2 / g, 25-130m 2 / g, 35-130m 2 / g, or 10-50m 2 / g. Assuming for simplicity that these particles all have the same size (here diameter), are spherical or quasi-spherical and non-porous, these BET surface areas correspond to average particle sizes in the ranges of 10 nm to 200 nm, 15 nm to 150 nm, 20 nm to 100 nm, or 20 nm to 70 nm (approximate estimates). BET determination of particle surface area 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 is ISO 9277:2010.

[0068] In one embodiment, the secondary composite particles may have an average particle size in the range of 20 nm to 5 μm, preferably 100 nm to 4 μm, more preferably 250 nm to 3 μm, more preferably 500 nm to 2 μm, and most preferably 1 to 1.5 μm. In a second aspect, the present invention relates to the formation of tertiary particles.

[0069] In one embodiment of the invention, the primary particles may have an average diameter of less than 10 nm, less than 7 nm, less than 5 nm, less than 3 nm, or less than 2 nm. In another embodiment, the primary particles may have an average diameter between 0.5-10 nm, preferably 1-8 nm, more preferably 2-7 nm, more preferably 3-6 nm, and most preferably 4-5 nm.

[0070] A plurality of secondary composite particles according to the first aspect of the present invention may be aggregated into tertiary composite particles, wherein the plurality of secondary composite particles are covalently bonded into a network, which ensures mechanical cohesion, electronic transport, and ionic transport.

[0071] Here, the adjectives "primary", "secondary" and "tertiary" when referring to particles refer to the level in the particle's collection, not the number of elements that make up the particle. A primary particle is a particle that may later be embedded in a secondary particle and does not contain any particles other than itself. A secondary particle is a particle that contains at least a primary particle. A tertiary particle is a particle that contains at least a secondary particle.

[0072] The outer surface is then also partially and / or completely covered by a second matrix (or outer layer, or connective network layer), thus reducing the external surface area available to the electrolyte. This second matrix is ​​an electrically conductive, adhesive, lithium conducting matrix.

[0073] During cell operation, a solid electrolyte interface (SEI) layer will form on all anode material surfaces available to the liquid electrolyte. This layer is known to contain lithium, and if the surface area is large, this SEI formation will consume a lot of lithium from the cathode. There are many sources of Li loss in the anode, but the lithium lost in the SEI layer will be minimally proportional to the total surface area.

[0074] The second matrix of the tertiary composite particles may be obtained by many different methods such as spray drying, calcination followed by grinding, emulsion or microfluidics.

[0075] A carbonized polymer is one option for this second matrix, which can be formed in a number of ways. Multi-component second matrices are also possible.

[0076] In one embodiment, the production of tertiary composite particles is achieved by spray drying a solution of the secondary particles, a suitable spray solvent, and a carbon precursor. After spray drying, the tertiary particles can be crosslinked, pyrolyzed, or carbonized.

[0077] Possible combinations that have been successfully tried are shown in the table below.

[0078] TIFF2025507646000005.tif78153

[0079] Another method is to pyrolyze a slurry of similar composition into a porous slab, for example by heating the slurry to 600-1100 °C under inert conditions and then grinding to a suitable particle size, large enough that the final BET area is acceptable, small enough to be easy to handle when casting the electrode, and have sufficient internal Li conductivity to allow the desired charging rate. An example of a suitable average diameter of the tertiary composite particles may be 1-10 μm. Pitch-based slurries may need to be heated to obtain the appropriate viscosity to provide sufficient mixing and wetting.

[0080] Spray drying is beneficial in terms of more uniform size distribution, higher silicon material yield and sphericity, which is less likely to result in clogging of electrode casting equipment, whereas the milling route may have a cost advantage, which may disappear if the smaller sized particles usually need to be separated, which results in a lower silicon material yield.

[0081] Finally, it is also possible to form spheres by creating emulsions of different solvents or by microfluidic methods, which methods are known to those skilled in the art.

[0082] In one embodiment, the tertiary composite particles are Producing secondary composite particles using the method according to the first aspect of the present invention, It is produced by embedding the secondary composite particles in a second matrix made mainly of carbon and then crushing the second matrix into particles.

[0083] In one embodiment, the tertiary composite particles are Producing secondary composite particles using the method according to the first aspect of the present invention, Dispersing the secondary composite particles in a slurry containing a component mainly made of carbon; coating graphite particles with the slurry containing the secondary composite particles; The coated graphite particles are then heat-treated at a temperature of 700 to 1000°C to produce the composite.

[0084] The resulting tertiary composite particles may preferably be porous. The porosity of the particles may be assessed by FIB-SEM (Focused Ion Beam-Scanning Electron Microscopy), for example, by plotting a series of diameters (e.g., three) on an image of the particle and determining the solid to open area ratio along these segments.

[0085] In one embodiment, the tertiary composite particles may have a porosity of from 15% to 60%, preferably from 25% to 50%.

[0086] The resulting tertiary composite particles have an increased size compared to the secondary composite particles, which makes them easier to handle in electrode processing (smaller particles spread more easily, increasing the risk of loss during processing and health risks to workers).

[0087] This method may include an optional additional step of depositing a layer of conductive surface coating on the surface of the tertiary composite particles, which may be referred to as a film coating step. The film coating limits the access of the electrolyte to the inner pores and surface of the particles, and preferably the film coating does not fundamentally change the particle size. As a result, this film coating further reduces the total surface area (as can be measured by BET), thereby also reducing the interface between the liquid electrolyte and the anode surface, thereby also reducing the amount of SEI formation during the start-up of the battery cell, thereby again reducing the loss of expensive lithium in the first cycle. This film coating step also further reduces the direct contact of the liquid electrolyte with the silicon itself, thereby reducing the amount of SEI formation during the start-up of the battery cell ... x The probability of formation is also reduced. The coating may preferably be less than 10% of the total particle weight.

[0088] An exterior surface coating on the tertiary composite may be achieved by a second spray drying where additional polymer from the slurry is left on the outside of the particles to dry. An exterior surface coating may also be grown using a thin slurry containing formaldehyde resin and crosslinking while the particles are suspended in the slurry. Other coating methods are described in the literature.

[0089] The carbon may be heat treated before and / or after surface coating to obtain good transport and adhesion properties. The following may be selected: -Only crosslinking / cyclization, most of the hydrogen remains in the carbon, low cost process, more elastic carbon phase (~300°C), -Carbonization at low temperatures (leaving amorphous silicon, making first cycle charging faster) (600-800°C), - Carbonization at medium temperatures (better carbon conductivity, better CE, but crystallizes Si) (800-1000°C), or -Carbonization at high temperatures (high carbon diffusion, risk of forming excess SiC at the Si-C interface, but potentially better carbon quality) (>1000°C)

[0090] In one embodiment, the surface coating may be made primarily of carbon.

[0091] In one embodiment, the surface coating of the tertiary particles may have a thickness of 1-500 nm, 5-250 nm, 7-100 nm, or preferably 10-50 nm to improve surface properties, reduce ignition risk, and promote the formation of a stable solid electrolyte interface (SEI). The present invention is not limited to a specific coating material or method for coating the particles, and any coating and coating method known to those skilled in the art for coating silicon particles may be applied.

[0092] The relatively high heat resistance of the predominantly amorphous silicon-containing particles of the present invention is advantageous in that the particles are able to withstand the temperatures associated with the formation of a carbon coating (and / or the formation of composite particles of silicon nanoparticles) by pyrolysis without significant conversion to a crystalline state. The carbon-surrounded or carbon-coated predominantly amorphous silicon-containing particles of the present invention may maintain their predominantly amorphous structure even through the pyrolysis process. The quality of pyrolysis is often temperature dependent, and it is preferred to use 600°C, 700°C, or preferably 800°C or 900°C to obtain a high quality carbon material coating, i.e., carbon encapsulation.

[0093] [particle] A third aspect of the invention relates to secondary composite particles, each secondary composite particle comprising a plurality of primary particles embedded within a first matrix, the primary particles being composed primarily of silicon, and wherein the first matrix comprises silicon and carbon.

[0094] These secondary composite particles may be used as the active material in the negative electrode in a lithium ion secondary electrochemical cell.

[0095] In one embodiment, the first matrix of the secondary composite particles is non-porous.

[0096] In one embodiment, the secondary composite particles may further comprise an outer coating. The outer coating is intended, for example, to improve the stability against oxidation, to provide a good and strong chemical bond between the matrix and the particle, or to improve the dispersion properties. The outer coating material may be carbon, organic molecules, Li x S y O, Ti x O, A1 x O, or any combination thereof. The coating may be applied using wet chemical methods, CVD, ALD, or other techniques.

[0097] A fourth aspect of the invention relates to tertiary composite particles, each of which comprises a plurality of secondary composite particles (as described in the third aspect of the invention) embedded in a second matrix, the second matrix being made predominantly of carbon, and each secondary composite particle comprising a plurality of primary particles embedded in a first matrix, the primary particles being composed predominantly of silicon, and the first matrix comprising silicon and carbon.

[0098] In one embodiment, the tertiary composite particles comprise graphite particles coated with a second matrix made primarily of carbon and having embedded therein a plurality of secondary composite particles according to the third aspect of the invention, the second matrix being graphitized by heating to a temperature of 700-1000° C. That is, this exemplary embodiment of the tertiary composite particles comprises graphite particles coated with a graphitized carbonaceous second matrix containing a plurality of secondary composite particles according to the third aspect of the invention.

[0099] In one embodiment, the tertiary composite particles according to the fourth aspect of the present invention may further comprise a second outer coating disposed on the outer surface of the second matrix. Examples of preferred outer coating materials are carbon, organic molecules, Li x S y O, Ti x O, A1 x O, or any combination thereof.

[0100] As used herein, the term "mainly composed of silicon" includes a phase containing at least 50% by weight of silicon. In other embodiments, the primary particles may contain at least 80%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5% silicon, or may be composed of 100% silicon.

[0101] In one embodiment, the total atomic ratio of silicon to carbon in the secondary composite particles may be in the range of [0.2, 7], [0.5, 5] or [1, 4].

[0102] In one embodiment, the primary particles may be predominantly amorphous.

[0103] In one embodiment, the primary particles may be predominantly crystalline.

[0104] In one embodiment, the primary particles may be a mixture of amorphous and crystalline.

[0105] In one embodiment, the tertiary composite particles may have an average diameter (weight average measured on a SEM image) of 1-40 μm, 2-20 μm, or 2-10 μm.

[0106] The composite structure of the secondary and tertiary composite particles of the present invention makes them well suited for use as the active material in the negative electrodes of lithium ion secondary electrochemical cells (batteries).

[0107] According to a fifth aspect, the present invention relates to a negative electrode for a lithium-ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a binder material; a current collecting substrate; Including, the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; one of said at least one particulate active material is a secondary composite particle according to the third aspect of the invention;

[0108] According to a sixth aspect, the present invention relates to a negative electrode for a lithium-ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a binder material; a current collecting substrate; Including, the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; one of said at least one particulate active material is a tertiary composite particle according to the fourth aspect of the invention;

[0109] According to a seventh aspect, the present invention relates to a negative electrode for a lithium-ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a binder material; a current collecting substrate; Including, the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; one of said at least one particulate active material is a tertiary composite particle; said tertiary composite particles comprising a graphite core particle surrounded by a coating of a plurality of secondary composite particles embedded in a second matrix, said second matrix being made primarily of carbon; each secondary composite particle comprises a plurality of primary particles embedded in a first matrix; said primary particles are composed mainly of silicon, said first matrix comprises silicon and carbon.

[0110] In one embodiment, the fifth to seventh aspects of the invention may further include a particulate conductive filler material.

[0111] A beneficial property of the particles according to the third and fourth aspects of the invention is that none of the substitutional elements C is known to accommodate as much lithium as silicon, so a lower content of substitutional element C typically means that the charge capacity of the material is higher.

[0112] A further beneficial property is that the co-diffusion of silicon during lithiation and delithiation is reduced, giving a more stable grain shape. A further beneficial property of the substitution element C is that the reduced expansion reduces inter-grain cracking, thereby preventing contact loss.

[0113] A further advantage is that the porous structure of the tertiary particles allows expansion of the individual primary and intermediate particles to occur without resulting in significant expansion of the electrode.

[0114] The term "active material" as used herein generally refers to the compounds / materials of the electrodes (anode and cathode) that take up and donate lithium ions and electrons to generate and store energy, i.e., the materials that undergo lithiation and delithiation during the charge-discharge cycle of an electrochemical cell.

[0115] In secondary electrochemical cells, the chemical half-cell reactions at the electrodes switch from oxidation to reduction reactions with the charge and discharge states of the charge and discharge cycle, respectively. As used herein, the term "negative electrode" is used to refer to the electrode of the electrochemical cell where the oxidation side of the chemical reaction occurs during discharge, i.e., the negative electrode is the electron generating electrode when drawing power from the electrochemical cell. The negative electrode is also sometimes referred to as the anode in the literature. The terms anode and negative electrode may be used interchangeably herein.

[0116] The negative electrode according to the fifth aspect of the present invention may employ any conductive substrate known or conceivable to those skilled in the art suitable for use as a current collector in a negative electrode of a lithium-ion secondary electrochemical cell. Examples of suitable conductive substrates include, but are not limited to, graphite, aluminum, or copper foils / sheets.

[0117] The negative electrode according to the third aspect of the present invention may employ any binder material known or conceivable to those skilled in the art suitable for use as a binder in a negative electrode of a lithium-ion secondary electrochemical cell. 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).

[0118] In an exemplary embodiment, the anode mass may further include a particulate conductive filler material mixed and embedded together with the particulate active material in the binder material. Anodes including the tertiary composite particles of the present invention may use any conductive filler material known or conceivable to those skilled in the art suitable for use as a conductive filler in the anode mass for the negative electrode of a lithium-ion secondary electrochemical cell. Examples of suitable particulate conductive filler materials include, but are not limited to, carbon allotropes such as graphene, reduced graphene oxide, elastomeric polymers, primarily carbon-containing materials produced by pyrolysis of carbon-rich materials, carbon black, carbon nanotubes, or mixtures thereof.

[0119] In one embodiment of the negative electrode according to the fifth or sixth aspect of the present invention, the conductive substrate may be a foil or sheet of either graphite, Cu or Al.

[0120] In one embodiment of the negative electrode according to the fifth or sixth aspect of the present invention, the binder may be any of styrene butadiene copolymer, carboxymethyl cellulose, ethylene-propylene-diene methylene (EPDM), polyacrylic acid (PAA).

[0121] In one embodiment of the negative electrode according to the fifth or sixth aspects of the invention, the anode mass may further comprise a particulate conductive additive material mixed with the particulate active material and embedded together within a binder material.

[0122] In one embodiment of the negative electrode according to the fifth or sixth aspect of the invention, the particulate conductive filler material may be carbon black, carbon nanotubes, graphene, or a mixture thereof. [Brief description of the drawings]

[0123] [Figure 1] Figure 1 shows the XRD analysis of 1.7 nm silicon nanoparticles (samples 10-A or 11-2) embedded in a carbon-rich matrix after heat treatment at 900° C. for 30 minutes. The average atomic content of the composite is 35% C and 65% silicon. [Diagram 2] XRD analysis of 3.4 nm silicon nanoparticles (sample R10B) embedded in a carbon-rich matrix after heat treatment for 30 min at 900° C. with a unimodal distribution of crystallite sizes. The average atomic content of the composite is 16% C and 84% silicon. [Diagram 3] TEM image showing crystalline silicon nanodomains in a secondary composite particle (sample R10A) after heat treatment at 900° C. for 30 minutes. [Figure 4] 1 is a series of TEM images showing secondary composite particles. [Diagram 5] FIG. 5 is a TEM image showing pure silicon nanoparticles of similar external dimensions to FIG. 4 that were not subjected to heat treatment. [Figure 6] 1 is an SEM image showing tertiary composite particles. [Figure 7] 1 is an SEM image showing a tertiary composite particle having a conductive coating. [Figure 8] 1 is a SEM image showing a cross section of a tertiary composite particle. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0124] The present invention will now be explained in further detail by means of exemplary embodiments.

[0125] [Comparative Example] Samples of (pure) silicon particles were produced by preheating a homogeneous gas mixture of 33% silane diluted in hydrogen gas to about 400° C., introducing this gas into a decomposition reactor, and mixing the silane gas with preheated hydrogen gas having a temperature of 710° C. The residence time in the reactor was less than 0.5 seconds. The resulting silicon particles were rapidly cooled to less than 300° C. and collected by filtration.

[0126] The sample particles were then analyzed by TEM, the image of which is shown in Figure 5. The analysis shows 40 nm pure silicon nanoparticles, with no visible subdomains inside.

[0127] [Example 1: Secondary Composite Particles: Samples 10-A and 11-2] Secondary composite particles according to an exemplary embodiment of the present invention may be made as follows.

[0128] A homogeneous mixture of silane gas and ethene in a molar ratio of 1:1 was preheated to about 400 °C and then introduced into the reactor chamber. Here, the homogeneous mixture of silane gas and ethene was further mixed with about 10 times more inert gas (nitrogen) preheated to a temperature such as to bring the temperature in the resulting gas mixture to 810 °C. MS was used to calculate the consumption of the different gases and to estimate the composition. EDS was used to qualitatively confirm the composition, but the accuracy of this measurement was not sufficient. The available quantities were not suitable for a "total carbon" measurement. However, the obtained secondary composite particles had an approximate atomic ratio of C:Si=0.35:0.65, i.e. The secondary composite particles consisted of mainly amorphous Si nanoparticles in an amorphous matrix of carbon and silicon, hereafter referred to as Sample 10-A.

[0129] The same process was repeated to obtain secondary composite particles consisting mainly of amorphous Si nanoparticles in an amorphous matrix of carbon and silicon, hereinafter referred to as Sample 11-2.

[0130] The residence time in the reactor was less than 0.5 seconds. The exhaust gas and particles leaving the reactor space were then rapidly cooled and collected in a filter. The particles were heat treated at 900°C for 30 minutes and then analyzed by XRD to investigate their atomic structure. The results are shown in Figure 1.

[0131] The XRD signal from the secondary particles is very narrow, but has a relatively clear and broad Bragg peak. In a Rietveld refinement, a crystallite size (diameter) of 1.7 nm is found for the inner nanoparticles. There is no indication of other crystalline phases.

[0132] [Example 2: Secondary composite particles: Sample R10B] Another embodiment of the particles was made in a similar manner to Example 1, except that the gas mixture had 50% more silane than ethene and was heated to 800°C in the reactor to make the material R10B, making a composite containing approximately 84 atomic % silicon and 16 atomic % carbon. Here, the majority of the silicon is located in silicon-dominant nanoparticles, which are again embedded in an amorphous matrix of carbon and silicon. The particles were heat treated at 900°C for 30 minutes and then analyzed by XRD, the results of which are shown in Figure 2. In Figure 2, the XRD signal from the secondary particles (R10B) with an estimated total of 16 atomic % C gives a better signal (both from a slightly larger sample and larger crystallites), with clear Si crystal reflections and no reflections from other phases. When fitting with a single Si phase, a crystallite size of 3.45 nm is obtained, which is a reasonably good fit. When fitting a bimodal distribution of crystallite sizes, an even better fit is obtained, especially of the first reflection (111). This corresponds to about 3 wt. % of Si nanodomains with a larger size of 14 nm and 97 wt. % of Si domains of about 3.4 nm.

[0133] [Example 3 - Tertiary particles] The tertiary particles shown in FIG. 6 were obtained by forming a slurry of secondary particles, phenolic resin and methanol solvent in the ratio 2:1:60 and spray drying it in a Buchi B-290 spray dryer at 170° C. with pump speed 40, aspirator 100 and nozzle gas flow 55.

[0134] Figure 6 is an SEM image of a tertiary composite particle of approximately 3 μm. Although there is clearly a carbon coating completely covering the secondary particle, the secondary composite particle is still visible.

[0135] The film-coated tertiary composite particles shown in Figure 7 were prepared by taking the tertiary particles shown in Figure 6, heat-treating them under vacuum at 200°C for 1 hour to crosslink them, and then forming a slurry of these heat-treated tertiary particles, phenolic resin, and methanol solvent in a ratio of 4:1:60, and spray-drying it in a Buchi B-290 spray dryer at 170°C with pump speed 40, aspirator 100, and nozzle gas flow 55. This formed an additional coating (film coating) that further protected the tertiary composite particles.

[0136] The tertiary particles shown in FIG. 8 were obtained by forming a mixture of secondary particles, polyacrylonitrile polymer, and dimethylformamide solvent in the ratio 2:1:40 and spray drying it in a Buchi B-290 spray dryer at 220° C. with pump speed 15, aspirator 100, and nozzle gas flow 55.

[0137] Figure 8 is a cross-sectional view of a tertiary composite particle. The secondary composite particles are again visible both on the surface and in the interior of the tertiary particle. Porosity is also visible, with a distinct outer "skin" protecting the inner voids.

[0138] [Sample Comparison] Various secondary composite particles were made with different atomic contents of silicon and carbon. These secondary composite particles were then used as part of the negative electrode for a lithium-ion secondary electrochemical cell along with a particulate conductive filler material, a binder material, and a current collecting substrate. The negative electrode was assembled into a lithium-ion electrochemical cell. The capacity and number of cycles to 20% capacity loss were measured. The results are shown in Table 1.

[0139] [Table 1]

[0140] Various tertiary composite particles were made based on the secondary composite particles listed in Table 1. These tertiary composite particles were then used as part of the negative electrode for a lithium-ion secondary electrochemical cell along with a particulate conductive filler material, a binder material, and a current collecting substrate. The negative electrode was assembled into a lithium-ion electrochemical cell. The capacity and number of cycles to 20% capacity loss were measured. The results are shown in Table 2.

[0141] [Table 2]

[0142] Now, one of ordinary skill in the art will understand that 1C means the charge / discharge rate is set to fully charge in 1 hour. 2C means twice as fast, fully charge / discharge in 30 minutes. It is advantageous to maintain a high capacity percentage at 2C.

[0143] As can be seen, the number of cycles before 20% capacity is lost increases from the typical value of 30 for regular pure silicon to about 300 for the material with 1500 mAh / g, and to 691 for the material with 800 mAh / g. These are 10-20 fold improvements, immediately bringing the materials into the suitable range for commercial use, even without an external coating to further extend cycle life.

[0144] The tertiary particles in Table 2 have the added advantage of easier transport of electrolyte between particles due to their larger size (compared to secondary particles), and therefore they can be used in thicker electrodes with more commercially suitable thicknesses / loadings than those used for the secondary particles in Table 1.

Claims

1. A method for producing secondary composite particles, the secondary composite particles comprising a plurality of primary particles embedded in a first matrix, the primary particles containing 90 to 100 wt % silicon based on the weight of the primary particles and having an average diameter of 0.5 to 10 nm, and the first matrix containing silicon and carbon; The method comprises: forming a first gas mixture comprising a first precursor gas of a silicon-containing compound and a second precursor gas of a carbon-containing compound, such that an atomic ratio between silicon and carbon in the first gas mixture is in the range of [0.1, 10]; preheating the first gas mixture to a temperature of 300-500°C; introducing the preheated first gas mixture into a reactor space and mixing the first gas mixture with a reactor gas to form a second gas mixture, the reactor gas being preheated to a temperature such that the temperature of the second gas mixture is between 500 and 880°C; maintaining the second gas mixture in the reactor volume for a period of time to form waste gases and condensed particles; and a step of cooling and recovering the condensed particles.

2. 2. The method of claim 1, wherein the first gas mixture is preheated to a temperature of 350 to 475°C, more preferably 375 to 450°C, and most preferably 400 to 425°C.

3. The first precursor gas is silane (SiH ４ ), disilane (Si ２ H ６ ), trichlorosilane (HCl ３ Si), organosilanes, or mixtures thereof; The second precursor gas is one of an organosilane or a hydrocarbon, preferably methane (CH ４ ), ethane (C ２ H ６ ), propane (C ３ H ８ ), ethene (C ２ H ４ ), ethyne (C ２ H ２ 3. The method for producing secondary composite particles according to claim 1, wherein the solvent is one of cyclohexane, cyclohexene, toluene, benzene, or a mixture thereof.

4. The method for producing secondary composite particles according to any one of claims 1 to 3, wherein the temperature of the second gas mixture is between 600 and 800°C, preferably between 650 and 700°C.

5. The first gas mixture further comprises one or more of hydrogen, nitrogen, or a noble gas such as helium, neon, argon, or any other gas that does not chemically react with the precursor gases at reaction temperatures. The method for producing secondary composite particles according to any one of claims 1 to 4.

6. 6. The method for producing secondary composite particles according to any one of claims 1 to 5, wherein the secondary composite particles are coated with carbon by exposing the secondary composite particles to a carbon-containing gas and heating the secondary composite particles to a coating temperature at which the gas reacts with the secondary composite particles, the coating temperature being from 30°C to over 1000°C, preferably from 300°C to 800°C, and most preferably from 600°C to 800°C.

7. Secondary composite particles, the secondary composite particles consist solely of a plurality of primary particles embedded in a first matrix; the primary particles contain 95 to 100 wt. % silicon, based on the weight of the primary particles, and have an average diameter of 0.5 to 10 nm; the first matrix consists solely of silicon and carbon; Secondary composite particles, wherein the total atomic ratio of silicon to carbon in said secondary composite particles is in the range [0.2, 7], preferably [0.5, 5], most preferably [1, 4].

8. The secondary composite particle of claim 7 further comprising an outer coating.

9. 9. Secondary composite particles according to claim 7 or 8, wherein the secondary composite particles have an average diameter of 20 nm to 5 μm, preferably 100 nm to 4 μm, more preferably 250 nm to 3 μm, more preferably 500 nm to 2 μm, most preferably 1 to 1.5 μm.

10. 10. Secondary composite particles according to any one of claims 7 to 9, wherein the primary particles have an average diameter of 1 to 8 nm, more preferably 2 to 7 nm, more preferably 3 to 6 nm, and most preferably 4 to 5 nm, and wherein the primary particles comprise at least 95%, more preferably at least 96%, more preferably at least 97%, more preferably at least 98%, more preferably at least 99%, and most preferably 99.5% silicon, based on the weight of the primary particles.

11. the primary particles are amorphous, or the primary particles are crystalline, or The secondary composite particles according to any one of claims 7 to 10, which are a mixture of these.

12. A tertiary composite particle comprising a particulate second matrix made primarily of carbon and further comprising a plurality of secondary composite particles according to any one of claims 7 to 11 embedded therein.

13. Tertiary composite particles comprising carbonized particles coated with a carbonized second matrix made primarily of carbon and having embedded therein a plurality of secondary composite particles according to any one of claims 7 to 11.

14. 14. The tertiary composite particle of claim 12 or 13, wherein the tertiary composite particle further comprises an outer conductive coating disposed on an outer surface of the second matrix, the outer conductive coating being made primarily of carbon.

15. Tertiary composite particles according to any one of claims 12 to 14, wherein the tertiary composite particles have an average diameter of 1 to 40 μm.

16. Tertiary composite particles according to any one of claims 12 to 14, wherein the second matrix of the tertiary composite particles has a porosity of between 15% and 60%, preferably between 25% and 50%.

17. 1. A negative electrode for a lithium ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a particulate conductive filler material; a binder material; a current collecting substrate; the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; A negative electrode, wherein one of the at least one particulate active material is the secondary composite particle according to any one of claims 7 to 11.

18. 1. A negative electrode for a lithium ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a particulate conductive filler material; a binder material; a current collecting substrate; the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; A negative electrode, wherein one of the at least one particulate active material is the tertiary composite particle according to any one of claims 12 to 16.

19. 1. A negative electrode for a lithium ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a binder material; a current collecting substrate; the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; A negative electrode, wherein one of the at least one particulate active material is the secondary composite particle according to any one of claims 7 to 11.

20. 20. The negative electrode of claim 19, further comprising a particulate conductive filler material.

21. 1. A negative electrode for a lithium ion secondary electrochemical cell, said negative electrode comprising: at least one particulate active material; a binder material; a current collecting substrate; the at least one particulate active material is embedded in the binder material to form an anode mass, the anode mass being deposited on the current collecting substrate as an anode mass layer; A negative electrode, wherein one of the at least one particulate active material is the tertiary composite particle according to any one of claims 12 to 16.

22. 22. The negative electrode of claim 21, further comprising a particulate conductive filler material.

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