Silicon composite manufacturing method

Abstract

The present invention relates to a method for producing a silicon composite by pyrolysis of at least one silicon precursor in the presence of porous particles, silicon being deposited in the pores and on the surface of said porous particles, said silicon composite having a target content of Si between 35% and 60% by weight, said method being carried out at an average temperature T between 300° C. and 500° C. and a concentration C of said silicon precursor between 30% and 100% by volume during normal operation. The method comprises at least one stage A during which a change Δ of at least one of the parameters T and C occurs relative to normal operation and optionally relative to a further stage A, ΔT=10℃~130℃, and ΔC=2%~70% by volume. This is provided that during stage A, 0.1% to 50% of said target content of silicon is deposited, or that during two or more stages A, in total, at most 50% of said target content of silicon is deposited.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon composite by thermal decomposition of at least one Si precursor in the presence of porous particles, wherein silicon is deposited within the pores and on the surface of the porous particles, and the silicon composite has a target silicon content of 35% to 60% by weight. [Background technology]

[0002] As a storage medium for electrical current, lithium-ion batteries (LIBs) are currently the most practical electrochemical energy storage means with the highest energy density. LIBs are particularly used in portable electronic devices, tools, and electric mobility applications such as bicycles, scooters, and automobiles. Graphite carbon is widely used as the anode active material. A drawback is the relatively low electrochemical capacity of such carbons, theoretically at most 372 mAh per gram of graphite, which corresponds to only about one-tenth of the theoretically achievable electrochemical capacity of lithium metal. Alternative anode active materials include the addition of silicon, as described, for example, in EP 1730800 B1 and EP 3335262 B1. Silicon forms an electrochemically active binary alloy with lithium, enabling a very high electrochemically achievable lithium content of up to 3579 mAh per gram of silicon.

[0003] The intercalation and deintercalation of Li-ions into silicon has the disadvantage of being accompanied by very large volume changes, which can reach 300% in the case of complete intercalation. Such volume changes impose severe mechanical stresses on the silicon-containing active material, which can result in its shattering. This process, also known as electrochemical comminution, results in the loss of electrical contact between the active material and the electrode structure, resulting in an irreversible loss of the electrode's capacity.

[0004] Furthermore, the surface of the Si-containing active material can react with components of the electrolyte to form a passivating protective layer (solid electrolyte interphase; SEI). The formed components are no longer electrochemically active. The lithium bound there is no longer available to the system, resulting in a significant decrease in the capacity of the LIB. Due to volume changes in silicon during the charge / discharge process of the LIB, the SEI periodically ruptures, exposing more of the free surface of the Si-containing active material and allowing further SEI formation. In LIBs, the amount of mobile lithium corresponding to the available capacity is limited by the positive electrode material, so the positive electrode material is gradually consumed, resulting in a decrease in capacity after just a few cycles.

[0005] Known anode active materials for LIBs include Si-C composite particles, in which silicon from a gas or liquid precursor is intercalated into porous carbon particles. The advantage of Si-C composites is that the silicon is finely distributed and embedded in a carbon framework that allows for volumetric changes of the silicon while maintaining electrical contact with the silicon. Such Si-C composites are fabricated, for example, by vapor deposition of one or more Si precursors into the pores of a porous carbon matrix. The introduction of silicon into the porous structure is also known as chemical vapor infiltration (CVI).

[0006] When Si composites are produced by CVI, Si precursors are typically used at low absolute and partial pressures, and therefore at low concentrations. Long reaction times are therefore required to achieve a high Si content in the silicon-containing material. Otherwise, thick Si layers, also known as rough silicon, form on the outside of the particles. These thick Si layers are detrimental in that, in contact with the electrolyte and during cycling, combined with constant modification of the SEI, they lead to heavy structuring of the particle surface. Furthermore, optimal adjustment of the process parameters requires accurate knowledge of all reaction parameters, which must usually be determined empirically. Furthermore, because the porous matrices used exhibit a certain degree of variability in terms of their pore size and particle size distribution, it is very difficult to avoid over-infiltration, which leads to thick Si layers. For productivity reasons, continuous infiltration at relatively high concentrations of the silicon precursor (Si precursor) and / or at relatively high temperatures can result in the formation of thick Si layers.

[0007] WO 2022 / 029422 A1 discloses Si-C composites containing 25-65% silicon by mass, produced by CVI. The composites consist of meso- and microporous C scaffolds containing numerous domains of nanoscale elemental silicon within the pores and on the surface. They can be produced from porous C particles and silane in a fluidized-bed reactor at a temperature of 450°C and reduced pressure. To prevent the formation of a thick Si layer (rough bulk silicon), a silane concentration of less than 20% by volume was used throughout. This high dilution ratio inevitably results in long reaction times and large consumption of inert gas, reducing the economic viability of the process. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] EP 1730800 B1 [Patent Document 2] EP 3335262 B1 [Patent Document 3] WO 2022 / 029422 A1 Summary of the Invention [Problem to be solved by the invention]

[0009] In this context, it is an object of the present invention to provide a method for producing silicon-containing materials that can be obtained more quickly and economically than known production methods while ensuring high cycle stability when used as a negative electrode active material in lithium-ion batteries, and therefore, the formation of a thick silicon layer should be avoided. [Means for solving the problem]

[0010] The present invention relates to a method for producing a silicon composite by thermal decomposition of at least one Si precursor in the presence of porous particles, wherein silicon is deposited within the pores and on the surface of said porous particles, said silicon composite having a target Si content of 35% to 60% by weight, wherein in normal operation the method is carried out under the following conditions: - Average temperature T of 300℃~500℃ and - a concentration C of said Si precursor in the feed gas stream between 30% and 100% by volume. The method comprises at least one stage A, in which a change Δ in at least one of the parameters T and C occurs relative to normal operation, and optionally a further change Δ relative to stage A, wherein ΔT = 10℃~130℃, and ΔC=2% to 70% by volume, However, during step A, 0.1% to 50% of the aforementioned target content of silicon is deposited, or during two or more steps A, a total of at most 50% of the aforementioned target content is deposited.

[0011] The present invention further provides a further method substantially corresponding to the method described above, which further method is carried out under the following conditions in normal operation: - Average temperature T of 300℃~500℃, a concentration C of the Si precursor between 30% and 100% by volume, and a volumetric flow rate VS of the Si precursor of 0.01 to 20 NL / h based on 1 g of the porous particles; This further method likewise comprises at least one step A, in which a change Δ of at least one of said parameters T, C and VS relative to normal operation and, optionally, a further change Δ relative to step A occurs, wherein ΔT=10℃~130℃, ΔC = 2% to 70% by volume and ΔVS=0.01 to 10NL / h, However, during step A, 0.1% to 50% of the aforementioned target content of silicon is deposited, or during two or more steps A, a total of at most 50% of the aforementioned target content is deposited. [Effects of the Invention]

[0012] One advantage of the method according to the present invention is that the conversion rate of the Si precursor during the entire process is greater than 30%, which is accompanied by particularly uniform deposition of silicon on, and especially within, the porous particles, resulting in a silicon composite that exhibits high stability for use as an anode active material for LIBs.

[0013] By dividing the infiltration reaction into stages with different process parameters, a reduction in the overall process time can be targeted, coupled with high productivity. Surprisingly, it was found that under static conditions, the conversion rate of the supplied Si precursor is not constant but rather varies over the reaction time, resulting in a non-optimal utilization of the Si precursor in a static process mode. This can be compensated for by a suitable deposition reaction process mode, resulting in an improved conversion rate.

[0014] Furthermore, the method according to the present invention surprisingly overcomes the disadvantage of forming a thick Si layer, so that the Si composite obtained by this method has high electrochemical performance.

[0015] In normal operation, the volumetric flow rate VS of the Si precursor fed to the reactor can be set to 0.01 to 10 NL / h, preferably 0.01 to 5 NL / h, per gram of porous particles used. The volumetric flow rate can be measured by a commonly used method, such as using a tachometer.

[0016] ΔVS can be set to 0.01 to 5 NL / h, preferably 0.01 to 2 NL / h per 1 g of the porous particles used.

[0017] The silicon composite may have a target content of silicon (obtained by deposition from a Si precursor) of 40% to 55% by weight, preferably 42% to 50% by weight, based on the total weight of the silicon composite.

[0018] The target Si content can be determined empirically by repeated sampling during the process.

[0019] The target Si content is preferably measured during the process by analyzing the composition of the off-gas stream by at least one method selected from the group consisting of gas chromatography, mass spectrometry, infrared spectroscopy, and thermal conductivity measurement.

[0020] The target Si content is particularly preferably determined by continuous analysis of the off-gas composition by gas chromatography or thermal conductivity measurement. The off-gas stream can be withdrawn directly at the reactor outlet for gas composition analysis. The deposited silicon can also be measured indirectly by quantifying the hydrogen present in the off-gas if hydrogen is not used to dilute the silane.

[0021] The average temperature T can be set to 315°C to 475°C, preferably 330°C to 450°C in normal operation. Average temperature during normal operation T Ris defined as the average of all temperatures in normal operation. Temperature is understood to mean the in-process temperature in the means of controlling the process. If the temperature of stage A changes by ΔT without interrupting the supply of Si precursor, the heating or cooling stage is considered to be part of stage A. Then, the average temperature of stage A (T A ) is used.

[0022] ΔT is 20°C to 100°C, preferably 20°C to 50°C.

[0023] In normal operation, the concentration C is 30% to 100% by volume, preferably 50% to 100% by volume.

[0024] The value of C preferably relates to the concentration of the Si precursor in the reaction gas, i.e., generally, the concentration in the reaction gas supply line to the reactor. The reaction gas typically contains the Si precursor and / or an inert gas such as nitrogen. The concentration of the Si precursor in the supplied reaction gas can be adjusted by a suitable metering device such as a rotameter.

[0025] ΔC is 5 to 60% by volume, preferably 10 to 50% by volume.

[0026] It is preferred if the change Δ in at least one of the parameters C, T and VS is carried out continuously from the beginning to the end of stage A. In a specific embodiment, the change can also be carried out stepwise.

[0027] Depending on the measured target content of Si, the change Δ may be initiated or terminated, i.e., phase A may be initiated (deviation from normal operation) or terminated (return to normal operation) depending on the change Δ.

[0028] The method is preferably carried out at a pressure of less than 0.7 MPa. In particular, the pressure is substantially constant during the process, where substantially means that the pressure may have a fluctuation range of ±0.1 MPa.

[0029] The production of Si composite particles according to the present invention can be carried out in any reactor commonly used for Si infiltration. Reactors selected from fluidized bed reactors, retort ovens, tubular reactors, and rotary kilns are preferred. These reactors can be configured in any orientation, from horizontal to vertical. Fixed-bed reactors can be operated as open or closed systems, such as pressure reactors. Reactors capable of homogeneously mixing the porous particles with the silicon-containing raw material formed during the infiltration of the Si precursor (only the final product is referred to as the silicon composite) are particularly preferred. This is advantageous for the most homogeneous deposition of silicon within the pores and on the surface of the porous particles. The most preferred reactors are fluidized bed reactors, rotary kilns, pressure reactors, and bed reactors.

[0030] The process according to the invention is preferably carried out in a reactor equipped with a tight clearance agitator.

[0031] The process can also be carried out in a cascade reactor system containing two or more reactors.

[0032] Carrying out the process in a cascade reactor system has the advantage that the lengthy reactor cooling and heating stages are shortened compared to carrying out the process in only one reactor, which can result in economic advantages. Cascade reactor systems can also offer the advantage that individual reactors can be precisely configured for their purpose. Cascade reactor systems are generally more scalable because reactors of various quantities can be combined with each other to form individual stages. Adaptation of temperatures, volumetric flow rates, and concentrations can also be achieved by carrying out Stage A and normal operation in different reactors within the reactor cascade. DETAILED DESCRIPTION OF THE INVENTION

[0033] The method according to the invention comprises at least three steps: First stage: Reactor A is filled with porous particles, the particles are pretreated, and then the pretreated particles are transferred to reactor B or a reservoir vessel, or the raw material is left in reactor A. Second stage: Reactor B is passed through with a gas containing a Si precursor and typically an inert gas. Si-free precursors may also be present; the reactor is temperature-controlled to a temperature at which thermal decomposition of the Si precursor occurs on the surface and within the pores of the porous particles. In addition to normal operation, a process profile is established that includes at least one stage A in which at least one of the parameters T, C, and VS is varied. The reaction can be carried out under negative or positive pressure. After introducing silicon into the pores of the porous particles, the Si composite is transferred to Reactor C or to a reservoir vessel for intermediate storage, or the raw material remains in Reactor B. Third stage: Post-treatment of the Si composite for surface functionalization and / or coating of the silicon-containing particles. The particles are cooled to a predetermined temperature, and the Si composite is removed from reactor C and preferably transferred directly to a storage container or directly filled into a suitable container.

[0034] In a first step, the porous particles are loaded into a heatable and / or vacuum-resistant and / or pressure-resistant reactor A. This loading may be done manually or automatically.

[0035] The loading of the porous particles into reactor A can be carried out in an inert gas atmosphere or preferably in ambient air. Usable inert gases include hydrogen, helium, neon, argon, krypton, xenon, nitrogen, carbon dioxide, or mixtures thereof, such as forming gas. Argon or nitrogen is preferred.

[0036] Automatic filling can be achieved by metering screws, rotary star valves, vibrating conveyors, plate weighers, belt weighers, vacuum weighing systems, negative pressure weighing, or other weighing systems, for example, from silos or other container systems.

[0037] The purpose of particle pretreatment in the first stage reactor A is to remove air / oxygen, water or dispersants such as surfactants or alcohols, and impurities from the particles. This can be achieved by inerting with inert gas (see previous paragraph), increasing the temperature up to 1000 °C, reducing the pressure up to 1 Pa, or by a combination of the individual process steps.

[0038] An additional purpose of the first stage of pretreatment is to modify the chemical surface structure of the porous particles with additional substances. This can be done before or after drying, and a heating step can be performed before the raw material is transferred to reactor B. The substances can be added to the reactor in gas, solid, or liquid form, or in solution form. Mixtures, emulsions, suspensions, aerosols, or foams are also possible. Possible substances include carbon dioxide, water, sodium hydroxide solution, potassium hydroxide solution, hydrofluoric acid, phosphoric acid, nitric acid, hydrochloric acid, ammonia, ammonium hydrogen phosphate, lithium nitrate, sodium nitrate, potassium nitrate, lithium chloride, sodium chloride, potassium chloride, lithium bromide, sodium bromide, potassium bromide, and alkoxides.

[0039] The transfer of the porous particles to further reactors or vessels can be carried out via downpipes, continuous conveyors, flow conveyors / suction or pressure conveying devices (e.g., vacuum conveyors, conveying blowers); mechanical conveyors (e.g., powered roller conveyors, screw conveyors, hanging conveyors, over / under conveyors, bucket conveyors, rotary star valves, chain conveyors, scraper conveyors, conveyor belts, vibrating conveyors); gravity conveyors (e.g., chutes, roller tracks, ball tracks, rail tracks).

[0040] In the second stage, the pretreated raw material is heated in reactor B to an average temperature of 300°C to 500°C, particularly preferably 315°C to 475°C, and particularly preferably 330°C to 450°C.

[0041] During the temperature change, temperature arrival, or temperature profile execution, reactor B can be alternately or simultaneously passed through with gases consisting of at least one inert gas and / or at least one reactive component consisting of at least one Si precursor and / or at least one Si-free precursor. Different gas compositions can be sequentially used or can be varied within the specified composition parameters during the second stage.

[0042] Preferred Si-free precursors (precursors that do not contain Si precursors) are one or more hydrocarbons. Carbon is generally deposited within the pores and on the surfaces of the porous particles by pyrolysis of the hydrocarbons.

[0043] The Si-free precursor preferably contains no further components or one or more inert gases and / or one or more reactive components such as hydrogen, and / or one or more dopants. The dopants may include compounds containing boron, nitrogen, phosphorus, arsenic, germanium, iron, or nickel. The dopants are preferably selected from the group consisting of ammonia, diborane, phosphane, germane, arsane, and nickel tetracarbonyl.

[0044] The reaction gas can be added continuously or intermittently, and the rate of addition can be varied during the reaction time.

[0045] The temperature, pressure, pressure change or differential pressure measurement and gas flow rate measurement of reactor B can be performed using commonly used measuring instruments and methods. With typical calibration, the same measurement results can usually be obtained even with different measuring instruments.

[0046] During the entire pyrolysis period, reactor B can be passed an amount of Si precursor relative to the weighed amount of porous particles such that a sufficient amount of Si is deposited for the target volume of the Si composite to be produced.

[0047] Heating of reactor B in the second stage can be carried out at a constant heating rate or at several different heating rates, which can be adjusted depending on the process configuration, for example, the reactor size, the amount of porous particles in the reactor, the stirring technique, or the planned reaction time.

[0048] The reactor B in the second stage can be heated at a heating rate of 1° C. to 100° C. per minute, preferably 2° C. to 50° C. per minute.

[0049] The temperature at which the decomposition of the Si precursor begins may vary depending on the porous particles used, the Si precursor used, and other boundary conditions of the decomposition, such as the partial pressure of the Si precursor during decomposition and the presence of other reactive components, such as catalysts, that affect the decomposition reaction.

[0050] During the decomposition of the Si precursor in the second stage, the temperature can be kept constant or varied, with the goal of achieving nearly complete conversion of the Si precursor during the contact time between the gas and the stirred bed, producing a Si composite suitable for the application.

[0051] The target temperature for SiH4 is 300°C to 500°C, preferably 315°C to 475°C, and particularly preferably 330°C to 450°C. The target temperature for HSiCl3 is 380°C to 1000°C, and preferably 420°C to 600°C. The target temperature for H2SiCl2 is 350°C to 800°C, and preferably 380°C to 500°C.

[0052] In the second stage, in addition to the Si precursor, Si-free precursors such as C precursors can also be used, either sequentially or alternately in a mixture with the Si precursor, with the aim of targeted functionalization of the as-formed silicon surface.

[0053] The gas from the second stage may consist of an inert gas and / or at least one reactive component containing Si and / or at least one Si-free precursor in potentially varying compositions. The one or more Si precursors can generally be introduced into reactor B in a mixed form, or separately, or mixed with an inert gas component, or as a pure substance. In the second stage, the bed of porous particles is preferably continuously recycled. Recycling can be achieved via one or more stirring means or by the rotational movement of the reactor itself (e.g., an intensive mixer from Maschinenfabrik Gustav Eirich) or a combination thereof. The moving bed motion is characterized by a Froude number between 1 and 10. The Froude number is preferably between 1 and 6, particularly preferably between 1 and 4.

[0054] The thermal decomposition of the Si precursor in the presence of the porous particles is preferably carried out at a pressure of 0.05 MPa to 5 MPa, particularly preferably 0.08 MPa to 0.7 MPa.

[0055] The progress of the reaction in the second stage is preferably monitored analytically to detect the end of the reaction and thus keep the reactor occupation time as short as possible. Methods for monitoring the progress of the reaction include, for example, temperature measurement to determine whether the reaction is exothermic or endothermic, measuring the progress of the reaction by changing the ratio of solid to gaseous reactor contents, and also methods that can monitor the composition of the gas space, which changes during the reaction. In a preferred variation of this method, the composition of the gas phase is measured by a gas chromatograph and / or a thermal conductivity detector and / or an infrared spectrometer and / or a Raman spectrometer and / or a mass spectrometer. In a preferred embodiment, the water content is measured using a thermal conductivity detector, and / or optionally, the presence of any chlorosilanes is measured using a gas chromatograph or a gas infrared spectrometer.

[0056] In a further preferred variant of the method, reactor B / gas outlet position is equipped with a technical solution for removing the condensable or resublimable by-products that occur. In a particularly preferred variant, silicon tetrachloride is condensed and removed separately from the Si complex.

[0057] In the third stage of the method, the Si-containing particles in reactor C are post-treated and / or passivated and / or coated. For this purpose, reactor C is preferably purged with oxygen, particularly a mixture of an inert gas and oxygen. This allows the surface of the Si composite to be modified and / or functionalized and / or passivated. For example, it is possible to cause the reaction of any reactive groups present on the surface of the Si composite. For this purpose, it is preferable to use a mixture of nitrogen, oxygen, and optionally alcohol and / or water, preferably containing at most 20% by volume, particularly preferably at most 10% by volume, and particularly preferably at most 5% by volume of oxygen and preferably at most 100% by volume, particularly preferably at most 10% by volume, and particularly preferably at most 1% by volume of water. This step is preferably carried out at a temperature of at most 250°C, particularly preferably at most 100°C, and particularly preferably at most 50°C. Passivation of the particle surface may also be carried out with a gas mixture containing an inert gas and an alcohol. Here, nitrogen and isopropanol are preferably used. However, it is also possible to use methanol, ethanol, butanol, pentanol, or long-chain and branched alcohols and diols.

[0058] Particle passivation can also be achieved by dispersion in a liquid solvent or solvent mixture, which can include isopropanol or aqueous solutions. In a third step, particle passivation can also be achieved by coating with C-, Al-, and B-containing precursors at temperatures between 200 and 800 °C, optionally followed by treatment in an oxygen-containing atmosphere.

[0059] Acceptable aluminum-containing precursors include trimethylaluminum ((CH3)3Al), aluminum 2,2,6,6-tetramethyl-3,5-heptanedionate (Al(OCC(CH3)3CHCOC(CH3)3)3), tris(dimethylamido)aluminum (Al(N(CH3)2)3), and aluminum triisopropanolate (C9H 21 AlO3).

[0060] Boron-containing precursors that can be used include borane (BH3), triisopropyl borate ([(CH3)2CHO]3B), triphenylborane ((C6H5)3B), and tris(pentafluorophenyl)borane (C6F5)3B.

[0061] In a third step, an after-coating of the particles with a solid electrolyte can also be introduced, for example by pyrolysis of tert-butyllithium and trimethyl phosphate.

[0062] In a third step, the Si-complex can in principle be removed from the reactor C, optionally preserving the inert gas atmosphere present in the reactor C. This can be done by the following discharge methods: pneumatically (through super- or sub-atmospheric pressure); mechanically (rotary star valve, plate-type discharger, discharge screw / stirring means in the reactor, belt-type discharger); gravimetrically (double flap valve / ball valve, optionally vibration-assisted).

[0063] If a hydrocarbon is used in the third stage, and / or if a hydrocarbon is used as a Si-free precursor in addition to the Si infiltration during the second stage, the target temperature employed is the temperature at which decomposition of the hydrocarbon begins and carbon deposits in the pores and on the surface of the porous particles. The target temperature selected in this embodiment is preferably in the range of 250°C to 1000°C, particularly preferably 350°C to 850°C, and most preferably 400°C to 650°C.

[0064] Technical requirements of the reactor and any specifics regarding specific variants of the invention: Reactor A: The reactor is at least temperature controllable. The reactor may be vacuum-resistant. - A system for preheating, drying and inactivating porous particles. - A target / metered addition system for porous particles may be connected. - Removal of impurities from the dry / porous particles may be achieved by connecting a system that allows removal of condensable or re-sublimable substances. - It is possible to connect a system for transferring the porous particles to reactor B. Reactor B: The reactor is at least temperature controllable. - comprising stirring means according to the invention. - System for metering reaction gases. - Reactive gas exhaust system. To simplify the method, a hydrogen separator may be connected. - To remove condensable or resublimable by-products that occur in the gaseous reaction products, it is possible to connect a container that allows the removal of by-products by condensation or resublimation. - It is also possible to connect a system to transfer raw materials to reactor C or a reservoir vessel. Reactor C: The reactor is at least temperature controllable. - A system for removing condensable or resublimable by-products. - It is possible to connect a container that allows the removal of by-products by condensation or resublimation. - System for the metered addition of reactive gases for functionalization. - Reactive gas exhaust system. - It is possible to connect a system for transferring raw materials to the reservoir container.

[0065] The reactor may be temperature-controllable, pressure-resistant, and vacuum-resistant at the same time, and all combinations are possible, but each reactor may also have only one of the above characteristics.

[0066] A temperature-controllable reactor is generally a reactor that can be operated so that the internal temperature can be adjusted in the range of -40° C. to 1000° C. Smaller temperature ranges are also possible.

[0067] It is preferred that reactors A, B and C are the same vessel, in other words the process can also be carried out in only one reactor. In principle it is not excluded that reactors A, B and C are the same vessel.

[0068] It may be provided that the normal operation process and at least one of Stage A are carried out in one reactor. In a specific embodiment, normal operation and Stage A can be carried out in separate reactors.

[0069] During the process, the porous particles and resulting Si composites can generally be in the form of a fixed bed or a moving bed with mixing. Mixing to obtain a moving bed of porous particles / resulting Si composites is preferred in reactors A, B, and C. However, during pyrolysis of the Si precursor in the second stage, the particles generally must be mixed. This ensures uniform contact of all porous particles with the reaction gas and uniform temperature distribution in the bed. Particle recirculation can be achieved by internal stirring within the reactor or by moving the entire reactor around an agitator.

[0070] Further preferred configurations of reactors A, B, and C are stationary reactors equipped with moving agitation means for recirculation. The purpose of the recirculation is to ensure as uniform contact of the porous solid with the reaction gas as possible. Preferred geometries are cylindrical reactors, conical reactors, spherical or polyhedral rotationally symmetric reactors, or combinations thereof. The movement of the agitation means is preferably rotational. For reactors A, B, and C operated vertically, a configuration in which one or more agitation means mix the bed material by rotational movement, for example, via a main stirrer shaft, is preferred. A further configuration of vertically operated reactors A, B, or C is characterized by the use of a conveying screw. For reactors A, B, or C operated horizontally, a configuration in which one or more agitation means mix the bed material by rotational movement, for example, via a main stirrer shaft, is preferred. For reactors A, B, or C operated vertically, stirring means are preferred, selected from the group including helical stirrers, spiral stirrers, anchor stirrers, or stirring means that generally convey the bed material axially or radially, or both axially and radially. Wall clearance can be reduced by additional scrapers on the stirring means. In addition to moving stirring means, reactors A, B, or C can also have rigid internal members such as baffles.

[0071] Suitable materials for the construction of reactors A, B or C include, in principle, all materials that exhibit the required mechanical strength and resistance under the respective process conditions. In terms of chemical resistance, reactors A, B or C can be constructed both from suitable solid materials and from chemically non-resistant (pressure-resistant) materials with special coatings or plating on the media-contacting parts.

[0072] A cascade reactor system is a system in which at least two reactors are connected. There is no upper limit to the number of reactors. The number of reactors A, B, and C, which are opposed to each other, as well as their size, shape, material, and configuration, may be different. The reactors may be directly connected to each other or may be spatially separated from each other so that they are fed via a movable reservoir vessel. It is also conceivable to connect two or more reactors B to each other and carry out each reaction step in a separate reactor B.

[0073] The Si precursor and the Si-free precursor are preferably gaseous, liquid, solid (e.g., sublimable), or any composition of matter consisting of substances in different states of matter. In one variation of the method, the Si precursor is fed directly to the bulk of the porous particles in the reactor, for example, from below, or from the side, or via a special agitator.

[0074] Si precursors include monosilane (SiH4), disilane (Si2H6) and its higher linear, branched or cyclic homologs, neopentasilane (Si5H 12 ), cyclohexasilane (Si6H 12 ), chlorine-containing silanes such as trichlorosilane (HSiCl3), dichlorosilane (HSiCl2), chlorosilane (HSiCl), tetrachlorosilane (SiCl4), hexachlorodisilane (Si2Cl6) and further linear, branched or cyclic homologues, e.g. 1,1,2,2-tetrachlorodisilane (Cl2HSi-SiHCl2), chlorinated and partially chlorinated oligo- and polysilanes, methylchlorosilanes, e.g. trichloromethylsilane Preferably, the silicon compound is selected from the group consisting of silane (MeSiCl), dichlorodimethylsilane (MeSiCl), chlorotrimethylsilane (MeSiCl), tetramethylsilane (MeSi), dichloromethylsilane (MeHSiCl), chloromethylsilane (MeHSiCl), methylsilane (MeHSi), chlorodimethylsilane (MeHSiCl), dimethylsilane (MeHSi), trimethylsilane (MeSiH) and mixtures of the silicon compounds mentioned.

[0075] In particular, the Si precursor is selected from the group consisting of monosilane, disilane, trichlorosilane, dichlorosilane, methylsilane and mixtures thereof.

[0076] Further reactive components which may be present in the reaction gas are hydrogen or hydrocarbons selected from the group consisting of aliphatic hydrocarbons having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms, such as methane, ethane, propane, butane, pentane, isobutane, hexane, cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane; unsaturated hydrocarbons having 1 to 10 carbon atoms, such as ethene, acetylene, propene, methylacetylene, butylene, butyne (1-butyne, 2-butyne), isoprene, butadiene, divinylbenzene, vinylacetylene, cyclohexadiene, cyclooctadiene, and the like; cyclic unsaturated hydrocarbons, such as cyclopropene, cyclobutene, Aromatic hydrocarbons such as cyclopentene, cyclohexene, cyclohexadiene, cyclopentadiene, dicyclopentadiene, and norbornadiene, for example, benzene, toluene, p-, m-, and o-xylene, styrene (vinylbenzene), ethylbenzene, diphenylmethane, and naphthalene, and other aromatic hydrocarbons such as phenol, o-, m-, and p-cresol, cymene, nitrobenzene, chlorobenzene, pyridine, anthracene, phenanthrene, myrcene, geraniol, thioterpineol, norbornane, borneol, isoborneol, bornane, camphor, limonene, terpinene, pinene, pinane, carene, phenol, aniline, anisole, furan, and furfural. Furfuryl alcohol, hydroxymethylfurfural, bishydroxymethylfuran, and a plurality of compounds, such as natural gas condensates, petroleum distillates, coke oven condensates, mixed distillates comprising product streams of fluid catalytic crackers (FCC), steam crackers, Fischer-Tropsch synthesis plants, or more generally, mixed distillates comprising hydrocarbon-containing material streams from wood, natural gas, petroleum, and coal processing.

[0077] The porous particles for the method according to the invention are preferably selected from the group consisting of hard carbon, soft carbon, mesocarbon, amorphous carbon in the form of microbeads, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes and graphene, oxides such as silicon dioxide, aluminum oxide and silicon-aluminum mixed oxides, magnesium oxide, lead oxide and zirconium oxide, carbides such as silicon carbide, boron carbide, nitrides such as silicon nitride, boron nitride, and other ceramic materials of the formula: Al a B b C c Mg d N e O f Si g (where 0≦a, b, c, d, e, f, g≦1, but at least two coefficients a to g are greater than 0, and a×3+b×3+c×4+d×2+g×4≧e×3+f×2.)

[0078] The ceramic material may be, for example, a binary, ternary, quaternary, pentanary, hexanary or heptaneary compound, preferably a ceramic material having the following formula: Non-stoichiometric boron nitride BN z (In the formula, z=0.2~1), Non-stoichiometric carbon nitride CN z (In the formula, z=0.1~4 / 3), Boron carbonitride B x CN z (In the formula, x=0.1~20, z=0.1~20, x×3+4≧z×3), Boron nitride oxide BN z O r (In the formula, z=0.1~1, r=0.1~1, 3≧r×2+z×3), Boron Carbonitride Oxide B x CN z O r (In the formula, x=0.1~2, z=0.1~1, r=0.1~1, x×3+4≧r×2+z×3), Silicon Carbon Oxide Si x CO z(In the formula, x=0.1~2, z=0.1~2, x×4+4≧z×2), Silicon carbonitride Si x CN z (In the formula, x=0.1~3, z=0.1~4, x×4+4≧z×3), Silicon boron carbonitride Si w B x CN z (In the formula, w=0.1~3, x=0.1~2, z=0.1~4, w×4+x×3+4≧z×3), Silicon boron carbon oxide Si w B x CO z (In the formula, w=0.10~3, x=0.1~2, z=0.1~4, w×4+x×3+4≧z×2), Silicon carbonitride boron oxide Si v B w CN x O z (wherein v = 0.1 to 3, w = 0.1 to 2, x = 0.1 to 4, z = 0.1 to 3, v × 4 + w × 3 + 4 ≥ x × 3 + z × 2), and Aluminum boron silicon carbonitride oxide Al u B v Si x CN w O z (In the formula, u=0.1~2, v=0.1~2, w=0.1~4, x=0.1~2, z=0.1~3, u×3+v×3+x×4+4≧w×3+z×2)

[0079] The porous particles are preferably amorphous carbon selected from the group consisting of hard carbon, soft carbon, mesocarbon, microbeads, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes, graphene and mixtures thereof.

[0080] The porous particles preferably have a density measured by helium pycnometry of 0.1 to 7 g / cm 3 , and particularly preferably 0.3 to 3 g / cm 3 This is the volumetric capacity (mAh / cm) of a lithium-ion battery. 3 ) is advantageous for increasing

[0081] The porous particles preferably have a diameter percentile d of ≧0.5 μm, particularly preferably ≧1.5 μm, most preferably ≧2 μm. 50 The particle size distribution has a volume weighted diameter percentile d 50 is preferably ≦20 μm, more preferably ≦12 μm, and most preferably ≦8 μm.

[0082] The volume-weighted particle size distribution of the porous particles is preferably determined by the diameter percentile d 10 ≥ 0.2 μm and d 90 ≦20.0 μm, particularly preferably d 10 ≥ 0.4 μm and d 90 ≦15.0 μm, most preferably d 10 ≥ 0.6 μm and d 90 ≦12.0 μm.

[0083] The porous particles preferably have a diameter percentile d of ≦10 μm, particularly preferably ≦5 μm, particularly preferably ≦3 μm, most preferably ≦2 μm. 10 The particle size distribution has a volume weighted diameter percentile d 10 is preferably ≧0.2 μm, particularly preferably ≧0.5 μm, most preferably ≧1 μm.

[0084] The porous particles preferably have a diameter percentile d of ≧4 μm, particularly preferably ≧8 μm. 90 The particle size distribution has a volume weighted diameter percentile d 90 is preferably ≦18 μm, more preferably ≦15 μm, and most preferably ≦13 μm.

[0085] The volume-weighted particle size distribution of the porous particles preferably has a width d of ≦15.0 μm, more preferably ≦12.0 μm, particularly preferably ≦10.0 μm, particularly preferably ≦8.0 μm, and most preferably ≦4.0 μm. 90 -d 10 It has.

[0086] The volume-weighted particle size distribution of the Si composites producible by the method according to the invention preferably has a width d of ≥ 0.6 μm, particularly preferably ≥ 0.8 μm, most preferably ≥ 1.0 μm. 90 -d 10 It has.

[0087] The volume weighted particle size distribution of the porous particles can be measured by static laser scattering using the Mie model according to ISO 13320 using a Horiba LA 950 measuring device with ethanol as the dispersion medium for the porous particles.

[0088] The porous particles are preferably in the form of individual particles. The particles may be, for example, isolated or agglomerated. The porous particles are preferably non-agglomerated, preferably non-agglomerated. Agglomerated generally means that during the production process of the porous particles, primary particles are first formed and grow together and / or the primary particles are linked to each other, for example, via covalent bonds, thus forming agglomerates. Primary particles are generally isolated particles. Agglomerates or isolated particles may form agglomerates. Agglomerates are loose collections of agglomerates or primary particles bound to each other, for example, via van der Waals interactions or hydrogen bonds. Agglomerates that have agglomerated can be easily broken down into agglomerates again by common kneading or dispersion processes. Agglomerates can only partially break down into primary particles by such processes. The presence of porous particles in the form of agglomerates, agglomerates, or isolated particles can be visualized, for example, using a conventional scanning electron microscope (SEM). In contrast, static light scattering methods for measuring matrix particle size distribution or particle size cannot distinguish between agglomerates and agglomerates.

[0089] The porous particles may have any morphology, for example, segmented, flaky, spherical, or needle-like, with segmented or spherical particles being preferred. Morphology can be characterized, for example, by the sphericity ψ or sphericity S. According to Wadell's definition, sphericity ψ is the ratio of the surface area of a sphere of equal volume to the actual surface area of the object. For a sphere, ψ is 1. According to this definition, the porous particles for the method according to the present invention preferably have a sphericity ψ of 0.3 to 1.0, particularly preferably 0.5 to 1.0, and most preferably 0.65 to 1.0.

[0090] TIFF0007723763000001.tif44170

[0091] The porous particles are preferably ≥ 0.2 cm 3 / g, particularly preferably ≥ 0.6 cm 3 / g, most preferably ≥ 1.0 cm 3 / g, which is advantageous for obtaining high-capacity LIBs. The gas permeable pore volume was determined by nitrogen gas adsorption measurements in accordance with DIN 66134.

[0092] The porous particles are preferably open-pored. Open porosity generally means that the pores are in communication with the particle surface, for example via channels, and preferably allow exchange of substances with the environment, in particular exchange of gaseous compounds. This can be demonstrated by gas adsorption measurements (analysis according to Brunauer, Emmett and Teller, "BET"), i.e., specific surface area. The porous particles preferably have a specific surface area of ≥ 50 m 2 / g, particularly preferably ≥ 500m 2 / g, most preferably ≥ 1000m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (with nitrogen).

[0093] The pores of the porous particles may have any diameter, i.e., generally in the range of macropores (>50 nm), mesopores (2-50 nm), and micropores (<2 nm). Porous particles can be used with any mixture of different pore types. Preference is given to using porous particles with less than 30% macropores, particularly preferred are porous particles with no macropores, and very particularly preferred are porous particles with at least 50% pores with an average pore diameter of less than 5 nm, based on the total pore volume. It is very particularly preferred if the porous particles have only pores with a pore diameter of less than 2 nm (measurement methods: in the mesopore range, pore size distribution according to BJH (gas adsorption) according to DIN 66134, in the micropore range, pore size distribution according to Horvath-Kawazoe (gas adsorption) according to DIN 66135; pore size distribution in the macropore range is evaluated by mercury porosimetry according to DIN ISO 15901-1).

[0094] 0.3cm 3 / g, particularly preferably less than 0.15 cm 3 Porous particles with a gas-impermeable pore volume of less than 1 / g are preferred. These can also be used to increase the capacity of LIBs. The gas-impermeable pore volume can be calculated using the following formula: Gas-impermeable pore volume = 1 / pure material density - 1 / skeletal density

[0095] Pure material density is the theoretical density of a porous particle based on the phase composition or density of the pure material (assuming no closed pores). Pure material density data is available to those skilled in the art, for example, from the Ceramic Data Portal of the National Institute of Standards (NIST, https: / / srdata.nist.gov / CeramicDataPortal / scd). For example, the pure material density of silicon oxide is 2.203 g / cm. 3 The density of pure boron nitride is 2.25 g / cm 3 The density of pure silicon nitride is 3.44 g / cm 3 The density of pure silicon carbide is 3.21 g / cm3 Skeletal density is the actual density (gas permeability) of the porous particles measured by helium pycnometry.

[0096] The porous particles generally serve as the starting material for producing silicon composites. The pores and surfaces of the porous particles are preferably free of silicon, particularly silicon obtained by deposition of a Si precursor.

[0097] The silicon composites obtained by the method according to the invention, which are formed by depositing silicon in the pores and on the surface of porous particles, have a diameter percentile d in the range of 0.5 to 20 μm. 50 The particle size distribution may have a volume weighted particle size distribution having a value of d 50 The value is preferably at least 1.5 μm, particularly preferably at least 2 μm. Diameter percentile d 50 is preferably at most 13 μm, particularly preferably at most 8 μm.

[0098] The volume weighted particle size distribution of the silicon composite is preferably determined by the diameter percentile d 10 ≧0.2μm~d 90 ≦20.0 μm, particularly preferably d 10 ≧0.4μm~d 90 ≦15.0 μm, especially d 10 ≧0.6μm~d 90 ≦12.0 μm.

[0099] The silicon composite preferably has a diameter percentile d of ≦10 μm, particularly preferably ≦5 μm, particularly preferably ≦3 μm, most preferably ≦1 μm. 10 The particle size distribution has a volume weighted diameter percentile d 10 is preferably ≧0.2 μm, particularly preferably ≧0.4 μm, in particular ≧0.6 μm.

[0100] The silicon composite preferably has a diameter percentile d of ≧5 μm, particularly preferably ≧10 μm. 90 The particle size distribution has a volume weighted diameter percentile d90 is preferably ≦20 μm, particularly preferably ≦15 μm, in particular ≦12 μm.

[0101] The volume-weighted particle size distribution of the silicon composite has a width d of ≦15.0 μm, preferably ≦12.0 μm, particularly preferably ≦10.0 μm, in particular ≦8.0 μm, of which particularly preferably ≦4.0 μm. 90 -d 10 The volume-weighted particle size distribution of the silicon preferably has a width d of ≧0.6 μm, particularly preferably ≧0.8 μm, in particular ≧1.0 μm. 90 -d 10 It has.

[0102] The particles of the silicon composite are preferably particulate. The particles may be isolated or agglomerated. The silicon composite is preferably non-agglomerated, preferably non-agglomerated. The terms isolated, agglomerated and non-agglomerated have already been defined above with respect to the porous particles. The presence of the silicon composite in the form of agglomerates or agglomerates can be visualized, for example, using a conventional scanning electron microscope (SEM).

[0103] The Si composites may have any morphology, for example, segmented, flake-like, spherical, or needle-like, with segmented or spherical particles being preferred.

[0104] According to Wadell's definition, the sphericity ψ is the ratio of the surface area of a sphere of equal volume to the actual surface area. For a sphere, ψ is 1. According to this definition, the Si composite obtained by the method according to the present invention preferably has a sphericity ψ of 0.3 to 1.0, particularly preferably 0.5 to 1.0, and most preferably 0.65 to 1.0.

[0105] TIFF0007723763000002.tif49170

[0106] The cycling stability of LIBs can be further improved by the morphology and material composition, especially the specific surface area and internal porosity of silicon composites.

[0107] When the porous particles are comprised of a Si compound, e.g., silicon dioxide, the above wt. % data can be measured for silicon obtained via deposition from a Si precursor by subtracting the Si mass of the porous particles, as determined by elemental analysis, from the Si mass of the silicon composite, as determined by elemental analysis, and dividing the result by the mass of the silicon composite.

[0108] The volume of silicon deposited on the porous particles was calculated by dividing the mass of silicon obtained by deposition from the Si precursor in the total mass of the silicon composite by the density of silicon (2.336 g / cm 3 ) can be calculated as a fraction divided by

[0109] The pore volume P of a silicon composite can be determined from the sum of the gas-permeable pore volume and the gas-impermeable pore volume. The Gurvich gas-permeable pore volume of a silicon composite can be measured by nitrogen gas adsorption measurement according to DIN 66134.

[0110] The gas impermeable pore volume of a silicon composite can be determined according to the following formula, as described above: Gas-impermeable pore volume = 1 / skeletal density - 1 / pure material density

[0111] The pore volume P of the Si composite is preferably in the range of 0 vol % to 400 vol %, particularly preferably in the range of 100 vol % to 350 vol %, and particularly preferably in the range of 200 vol % to 350 vol %, based on the volume of silicon present in the Si composite and obtained from the deposition of the Si precursor.

[0112] The porosity of a silicon composite may be either gas permeable or gas impermeable. The volume ratio of gas permeable porosity to gas impermeable porosity of a silicon composite generally ranges from 0 (no gas permeable porosity) to 1 (all gas permeable). The volume ratio of gas permeable porosity to gas impermeable porosity of a silicon composite is preferably in the range of 0 to 0.8, particularly preferably 0 to 0.3, and particularly preferably 0 to 0.1.

[0113] The pores of the silicon composite can have any diameter, for example, in the range of macropores (>50 nm), mesopores (2-50 nm), and micropores (<2 nm). The Si composite can also consist of a mixture of different pore types. Preferably, it contains up to 30% macropores based on the total pore volume. Particularly preferred are Si composites that do not have macropores, and very particularly preferred are Si composites that have at least 50% pores based on the total pore volume and an average pore diameter of less than 5 nm. Particularly preferred are Si composites that consist only of pores with a diameter of at most 2 nm.

[0114] The Si composite consists of silicon structures having a structure size in at least one dimension of preferably at most 1000 nm, particularly preferably less than 100 nm, in particular less than 5 nm (measurement method: SEM and / or high-resolution transmission electron microscope (HR-TEM)).

[0115] The Si composite preferably comprises a Si layer having a layer thickness of less than 1000 nm, particularly preferably less than 100 nm, in particular less than 5 nm (measurement method: SEM and / or HR-TEM). The Si composite may also comprise silicon in the form of particles. The Si particles preferably have a diameter of at most 1000 nm, particularly preferably less than 100 nm, in particular less than 5 nm (measurement method: SEM and / or HR-TEM). The numerical value of the Si particles preferably relates to the diameter of the circumference of the particle in the micrograph.

[0116] The amount of crude silicon in the deposited silicon is preferably less than 3 mass %, more preferably less than 1 mass %, and most preferably less than 0.1 mass %.

[0117] The Si complex is preferably at most 100 m 2 / g, particularly preferably 30m 2 / g, and particularly preferably less than 10m 2 / g. The BET specific surface area is measured in accordance with DIN 66131 (using nitrogen). This reduces the formation of SEI and improves the initial coulombic efficiency when the Si composite is used as an anode active material for LIBs.

[0118] Furthermore, the silicon deposited from the Si precursor in the Si composite may contain a dopant selected from the group consisting of, for example, Li, Fe, Al, Cu, Ca, K, Na, S, Cl, Zr, Ti, Pt, Ni, Cr, Sn, Mg, Ag, Co, Zn, B, P, Sb, Pb, Ge, Bi, rare earths, and combinations thereof. Li and / or Sn are preferred. The content of the dopant in the Si composite is preferably at most 1% by weight, particularly preferably at most 100 ppm, based on the total weight of the Si composite as measurable by ICP-OES.

[0119] The Si composite has surprisingly high stability under compressive load and / or shear stress, as evidenced, for example, by the fact that the porous structure of the Si composite changes only slightly under compressive load (e.g., during electrode compression) and shear stress (e.g., during electrode fabrication) in SEM.

[0120] The Si composite may optionally contain additional elements such as carbon. The carbon is preferably present in the form of a thin layer having a thickness of at most 1 μm, preferably less than 100 nm, particularly preferably less than 5 nm, and particularly preferably less than 1 nm (measured by SEM and HR-TEM). The C layer can be present both in the pores and on the surface of the Si composite. The order of different layers in the Si composite can also be freely selected by appropriately repeating and the number of alternating metered additions of different precursors. Thus, a layer of a different material from the porous particles, such as carbon, can be first provided on the porous particles, followed by a layer of Si or Si particles. Furthermore, a layer of a different material from or identical to the material of the porous particles can also be provided on the Si layer or layer of Si particles, regardless of whether or not there is a layer of a different material between the porous particles and the Si layer or layer of Si particles.

[0121] The Si composite may contain ≦50% by weight, preferably ≦40% by weight, particularly preferably ≦20% by weight of additional elements. The Si composite may particularly preferably contain ≧1% by weight, particularly preferably ≧2% by weight of additional elements. The mass % values are based on the total mass of the Si composite. It is also possible for the Si composite to contain no additional elements.

[0122] The Si composite obtained by the method according to the present invention is suitable as an active material for the anode of a LIB, and the use of such an anode is suitable for the manufacture of a LIB. All the materials required for the manufacture are generally known. The manufacture of the components of such a battery and their assembly are carried out by methods well known in the field of battery manufacturing.

[0123] The Si composites obtained by the method of the present invention are characterized by significantly improved electrochemical behavior, resulting in LIBs with high volumetric capacity and excellent performance characteristics. The Si composites are permeable to Li ions and electrons, enabling charge transport. The resulting Si composites significantly reduce the SEI in LIBs. In addition, the design of the Si composite ensures that, even if the SEI peels off from the active material surface, it is at least very small in extent. These factors contribute to the high cycling stability of LIBs with anodes containing the Si composites obtained by the method of the present invention. [Example]

[0124] The following examples serve to further elucidate the invention described herein.

[0125] The following analytical methods and instruments were used for characterization:

[0126] <Inorganic analysis / elemental analysis> The carbon content reported in the examples was measured using a Leco CS 230 analyzer. O and, optionally, N or H content were measured using a Leco TCH-600 analyzer. Qualitative and quantitative analysis of other specific elements was performed by inductively coupled plasma (ICP) optical emission spectroscopy (Optima 7300 DV, Perkin Elmer). For this purpose, samples were subjected to acid digestion (HF / HNO3) in a microwave (Microwave 3000, Anton Paar). Quantitative analysis by ICP-OES is based on ISO 11885 "Water quality - Determination of selected elements by inductively coupled plasma optical emission spectroscopy (ICP-OES) (ISO 11885:2007); German translation of EN ISO 11885:2009" and is used for the analysis of acidic aqueous solutions (e.g., acidified drinking water, wastewater, other water samples, and aqua regia extracts of soils and sediments). The Si quantification method used typically has an accuracy of ±1% by mass.

[0127] <Particle size measurement> The particle size distribution was measured by the static laser scattering method using Horiba LA 950 in accordance with ISO 13320. In the preparation of the sample, special attention should be paid to the dispersion of the particles in the measurement solution to ensure that the size measured is the size of individual particles rather than the size of aggregates. The particles were dispersed in ethanol for measurement. Prior to measurement, the dispersion was sonicated at 250 W for 4 minutes using a Hielscher UIS250v laboratory ultrasonic device equipped with an LS24d5 sonotrode as needed.

[0128] <BET Specific Surface Area Measurement><0000​​​​​​​​​​​​​​​​​​​​​​​​​​​

number

[0133] <Throughput> The throughput indicates the mass % of Si measured per hour, calculated from the Si content (target Si content) (mass %) of the extracted product relative to the deposition time (h) of all stages.

number

[0134] [Example] In the examples, an attempt was made to produce a Si composite having a silicon ratio of 47 mass % to 49 mass %. The SiH4 used, quality 4.0, was obtained from Linde GmbH. In all examples, amorphous carbon was employed as the porous starting material: - Specific surface area=1636m 2 / g - Pore volume = 0.76 cm 2 / g - Average volume-weighted particle size D50 = 6.4 μm

[0135] Percentage of deposited silicon based on target content: Between 0.1% and 50% of said target content is deposited in stage A, or a total of at most 50% of said target content is deposited in two or more stages A.

[0136] The percentage of Si deposited in one stage A or during normal operation based on the target content indicates the relative percentage of Si deposited in the corresponding stage. For example, a target Si content of 48% by mass in a composite corresponds to a relative percentage of deposited Si of 100%. Also, 50% of Si deposited in stage A corresponds to a target Si content of 24% by mass in the composite.

[0137] Quantification of fine-grained and coarse-grained silicon in a sample can be performed using TGA analysis, which involves the reaction of silicon with oxygen to form SiO2. Different silicon species can be distinguished because thin silicon layers are more reactive to oxygen than thicker layers or Si particles. As a result, thin silicon layers react (gain mass) even at low temperatures (400–655°C), while thicker / coarser silicon structures only react at temperatures above 700°C. Ideally, silicon-containing composites used as anode active materials show no mass gain in TGA analysis in an oxygen-containing atmosphere above 800°C. This method also allows for the determination of elemental silicon content. Silicon that has previously been oxidized and passivated by contact with air is no longer involved in the reaction and is therefore not considered in TGA analysis.

[0138] To calculate the coarse silicon present, we need the residual mass (mred) from the TGA method and the mass difference (mdiff) resulting from the oxidation of the coarse silicon. Using the molar mass of O2 (32 g / mol) and the molar mass of SiO2 (60.08 g / mol), we can calculate the percentage of coarse silicon in the deposited silicon using the following formula:

number

[0139] [Comparative Example 1: Production in a reactor suitable for producing Si composites] In a tubular reactor, porous carbon particles (specific surface area = 1636 m) in a quartz glass boat were added. 2 / g, Grbic pore volume = 0.76 cm 3 / g, mean volume-weighted particle size D 50 2.2 g of SiH4 (=6.40 μm) was charged. After inerting with nitrogen, the reactor was heated to 410 °C. Once this temperature was reached, Si precursor (50% SiH4 in N2, 10 NL / h) was passed through the reactor. The decomposition reaction of SiH4 to Si was monitored and quantified by a thermal conductivity detector in the off-gas stream. After 2.1 g of Si was deposited, the SiH4 gas flow was switched to a pure nitrogen flow and heating was stopped. The reactor was cooled to room temperature while purging with N2, and the product was removed.

[0140] [Comparative Example 2: Production in a reactor suitable for producing Si composites] In a tubular reactor, porous carbon particles (specific surface area = 1636 m) in a quartz glass boat were added. 2 / g, Grbic pore volume = 0.76 cm 3 / g, mean volume-weighted particle size D 50 2.2 g of SiH4 (=6.40 μm) was charged. After inerting with nitrogen, the reactor was heated to 380 °C. Once this temperature was reached, Si precursor (50% SiH4 in N2, 10 NL / h) was passed through the reactor. The decomposition reaction of SiH4 to Si was monitored and quantified by a thermal conductivity detector in the off-gas stream. After 2.1 g of Si was deposited, the SiH4 gas flow was switched to a pure nitrogen flow and heating was stopped. The reactor was cooled to room temperature while purging with N2, and the product was removed.

[0141] [Example 1-2: Production of Si composite by the method according to the present invention with step A (subscript A indicates the parameters of step A)] In a tubular reactor, porous carbon particles (specific surface area = 1636 m) in a quartz glass boat were added. 2 / g, Grbic pore volume = 0.76 cm 3 / g, mean volume-weighted particle size D 50 After inerting with nitrogen, the reactor was A Once the target temperature was reached, monosilane was passed through the reactor as a mixture with nitrogen (concentration C A , volumetric flow rate of Si precursor VS A The decomposition reaction of SiH4 to Si was monitored and quantified by a thermal conductivity detector in the off-gas stream. A Once [g] of Si had been deposited, the experimental setup was switched to normal operation (subscript R): temperature T R , monosilane concentration C R , volumetric flow rate of Si precursor VS R Further, the amount of Si M R was deposited under normal operation. After that, the reactor was cooled to room temperature while purging with N2, and the silicon composite was removed. [Table 1]

[0142] [Examples 3-4: Production of Si composites by the method according to the present invention having two or more steps A] In a tubular reactor, porous carbon particles (specific surface area = 1636 m) in a quartz glass boat were added. 2 / g, Grbic pore volume = 0.76 cm 3 / g, mean volume-weighted particle size D 50 After inerting with nitrogen, the reactor was A1 Once the target temperature was reached, monosilane was passed through the reactor as a mixture with nitrogen (concentration C A1 , volumetric flow rate of Si precursor VS A1 The decomposition reaction of SiH4 to Si was monitored and quantified by a thermal conductivity detector in the off-gas stream. A1 Once [g] of Si had been deposited (stage (subscript) A1), the experimental setup was switched to normal operation: temperature T R , monosilane concentration C R , volumetric flow rate of Si precursor VS R and the Si content M R [g] deposited during normal operation. M R When [g] of silicon is deposited in normal operation (the target Si content M A1 +M R ), the experimental setup was switched again and a new change Δ was implemented (step (subscript) A2): temperature T A2 , monosilane concentration C A2 , volumetric flow rate of Si precursor VS A2 Further, the amount of Si M A2 [g] was deposited. After that, the reactor was cooled to room temperature while purging with N2, and the product was removed. [Table 2]

[0143] The reaction conditions for fabricating the Si composite and the material properties are summarized in Table 3 below. [Table 3] Selected parameter M R , M A , T R , T A , C R , C A , VS A , and V.S. R According to the results, the overall conversion rate of the Si precursor and the throughput of the experimental equipment can be significantly improved while maximizing the material performance.

[0144] <Evaluation of Si composite particles in electrochemical cells> Example 5: The Si composite particles of Examples 1 to 4 of the present invention and the comparative example were tested as components of the negative electrode of a LIB. 29.71 g of polyacrylic acid (dried to constant weight at 85 °C; Sigma-Aldrich, M wPolyacrylic acid (~450,000 g / mol) and 756.60 g of deionized water were stirred on a shaker (290 1 / min) for 2.5 hours until dissolution of the polyacrylic acid was complete. Lithium hydroxide monohydrate (Sigma-Aldrich) was added in small portions to the solution until the pH reached 7.0 (measured using a WTW pH 340i pH meter and a SenTix RJD probe). The solution was then stirred on a shaker for another 4 hours. 3.87 g of the neutralized polyacrylic acid solution and 0.96 g of graphite (Imerys, KS6L C) were first placed in a 50 ml container and mixed at 2000 rpm with a planetary mixer (SpeedMixer, DAC 150 SP). Then, in each case, 3.35 g of the silicon composites from Examples 1-5 and Comparative Examples 1 and 2 were stirred at 2000 rpm for 1 minute. Next, 1.21 g of the 8% conductive carbon black dispersion and 0.8 g of deionized water were added and mixed in a planetary mixer at 2000 rpm. The mixture was then dispersed in a dissolver at 3000 rpm for 30 minutes at a constant temperature of 20°C. The ink was degassed again in a planetary mixer at 2500 rpm under vacuum for 5 minutes. The completed dispersion was applied to 0.03 mm thick copper foil (Schlenk Metallfolien, SE-Cu58) using a film stretching frame (Erichsen, Model 360) with a 0.06 mm gap. The resulting anode coating was dried at 50°C and 1 bar air pressure for 60 minutes. The average basis weight of the dried anode coating was 2.7 mg / cm. 2 , the film density is 0.8g / cm 3 It was.

[0145] Electrochemical tests were performed using a two-electrode button cell battery (CR2032 type, Hohsen Corp.). The electrode film was used as the counter electrode or negative electrode (Dm = 15 mm). It was based on lithium-nickel-manganese-cobalt oxide 6:2:2, with a content of 94.0% and an average basis weight of 15.9 mg / cm. 2A film (obtained from SEI) was used as the working electrode / positive electrode (Dm = 15 mm). A glass fiber filter paper (Whatman, GD Type D) saturated with 60 μl of electrolyte was used as the separator (Dm = 16 mm). The electrolyte used consisted of a 1.0 molar solution of lithium hexafluorophosphate in a 1:4 (v / v) mixture of fluoroethylene carbonate and diethyl carbonate. The cell was assembled in a glove box (<1 ppm H2O, O2), and the moisture content of all components used was less than 20 ppm in dry matter.

[0146] Electrochemical testing was performed at 20°C. The cells were charged using the constant current / constant voltage (cc / cv) method, with a constant current of 5 mA / g (equivalent to C / 25) in the first cycle and 60 mA / g (equivalent to C / 2) in subsequent cycles. Once the voltage limit of 4.2 V was reached, the cells were charged at a constant voltage until the current dropped below 1.2 mA / g (equivalent to C / 100) or 15 mA / g (equivalent to C / 8). The cells were discharged using the constant current (cc) method, with a constant current of 5 mA / g (equivalent to C / 25) in the first cycle and 60 mA / g (equivalent to C / 2) in subsequent cycles, until the voltage limit of 2.5 V was reached. The selected specific current was based on the coating weight of the positive electrode. The electrodes were selected to achieve a positive:negative capacity ratio of 1:1.2.

[0147] Table 4 shows the results of electrochemical tests on the full cells of the LIBs containing the Si composite materials of Examples 1 to 4 and Comparative Examples 1 and 2. [Table 4]

[0148] Comparative Example 1 exhibited high throughput coupled with good conversion of the Si precursor, but the coarse Si content was 0.6% (Table 3), and therefore only low cycle stability was achieved. Comparative Example 2 exhibited good electrochemical performance, but this was only achievable at low conversion and throughput (Table 4).

[0149] Inventive Examples 1-3 exhibit higher throughput and higher conversion relative to Comparative Example 2 while maintaining very good electrochemical performance. In contrast to Comparative Example 1, Examples 1-3 do not produce coarse Si and are therefore considered advantageous. By adjusting the temperature and silane concentration, Example 4 achieves better electrochemical performance than Comparative Example 1 while simultaneously exhibiting a high conversion.

Claims

1. 1. A method for producing silicon composites by chemical vapor infiltration by pyrolysis of at least one Si precursor in the presence of porous particles, wherein silicon is deposited within the pores and on the surfaces of the porous particles, the porous particles being amorphous carbon selected from the group consisting of hard carbon, soft carbon, mesocarbon, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes, graphene and mixtures thereof, the silicon composite having a target Si content of 35% to 60% by weight, and wherein in normal operation the method is carried out under the following conditions: - Average temperature T of 300°C to 500°C - a concentration C of said Si precursor between 30% and 100% by volume The method is carried out as follows: the method comprises at least one step A, in which a change Δ occurs in at least one of the parameters T and C relative to normal operation, and optionally, a change Δ occurs relative to step A; - ΔT=10℃~130℃, ΔC=2% to 70% by volume, with the proviso that during step A, 0.1% to 50% of said target content is deposited, or during two or more steps A, a total of at most 50% of said target content is deposited.

2. 1. A method for producing silicon composites by chemical vapor infiltration by pyrolysis of at least one silicon precursor in the presence of porous particles, wherein silicon is deposited within the pores and on the surfaces of the porous particles, the porous particles being amorphous carbon selected from the group consisting of hard carbon, soft carbon, mesocarbon, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes, graphene and mixtures thereof, the silicon composite having a target Si content of 35% to 60% by weight, and wherein in normal operation the method is carried out under the following conditions: - an average temperature T between 300 ° C and 500 ° C; a concentration C of said silicon precursor between 30% and 100% by volume; a volumetric flow rate VS of the silicon precursor of 0.01 to 20 NL / h based on 1 g of the porous particles; The method is carried out as follows: the method comprises at least one step A, in which a change Δ occurs in at least one of the parameters T, C and VS relative to normal operation, and optionally, a change Δ occurs further relative to step A, wherein: - ΔT=10℃~130℃, ΔC=2% to 70% by volume, - ΔVS=0.01~10NL / h, with the proviso that during step A, 0.1% to 50% of said target content is deposited, or during two or more steps A, a total of at most 50% of said target content is deposited.

3. The method according to claim 2, wherein VS during normal operation is 0.01 to 10 NL / h, particularly preferably 0.01 to 5 NL / h, based on 1 g of the porous particles.

4. The method according to claim 2 or 3, wherein ΔVS is 0.01 to 5 NL / h, preferably 0.01 to 2 NL / h, based on 1 g of the porous particles.

5. 3. The method of claim 1 or 2, wherein the silicon composite has a target Si content of 40% to 55% by weight, preferably 42% to 50% by weight.

6. 3. The method of claim 1 or 2, wherein the target content of Si is measured during the method by analysis of the composition of the off-gas stream by at least one method selected from the group consisting of gas chromatography, mass spectrometry, infrared spectroscopy, and thermal conductivity measurement.

7. 3. The method of claim 1 or 2, wherein the T during normal operation is between 315°C and 475°C.

8. 3. The method according to claim 1, wherein the C during normal operation is 40% by volume to 100% by volume, preferably 50% by volume to 100% by volume.

9. 3. The method according to claim 1 or 2, wherein ΔT is between 20°C and 100°C, preferably between 20°C and 50°C.

10. 3. The method according to claim 1 or 2, wherein ΔC is between 5% and 60% by volume, preferably between 10% and 50% by volume.

11. 3. The method according to claim 1, wherein the change Δ is carried out continuously from the start to the end of stage A.

12. 3. The method according to claim 1 or 2, wherein the method is carried out at a pressure of less than 0.7 MPa.

13. 3. The process according to claim 1 or 2, carried out in a reactor equipped with a tight clearance agitator.

14. 3. The process of claim 1 or 2, carried out in a cascade reactor system comprising two or more reactors.

15. 3. The method of claim 1 or 2, wherein the silicon precursor is selected from the group consisting of monosilane, disilane, trichlorosilane, dichlorosilane, methylsilane, and mixtures thereof.

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