Method for preparing a silicon composite

Abstract

The invention relates to a process for producing a silicon composite, which is the thermal decomposition of at least one silicon precursor in the presence of porous particles, wherein silicon is deposited in 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, wherein in the regular operation the process is carried out at an average temperature T of 300 to 500°C and a concentration C of the silicon precursor of 30 to 100% by volume. The process comprises at least one phase A, in which a change Δ of at least one of the parameters T and C is effected relative to the regular operation and optionally relative to further phases A, wherein ΔT = 10 to 130°C and ΔC = 2 to 70% by volume. With the proviso that during a phase A 0.1 to 50% of the target silicon content is deposited, or over two or more phases A a total of at most 50% of the target silicon content is deposited.

Description

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

[0002] As storage medium for electric currents, lithium ion batteries (LIB) are the most practical and highest energy density electrochemical energy storage means currently available. LIBs are used, inter alia, in the field of portable electronic products, for tools and for electrically driven vehicles, such as bicycles, scooters or cars. Graphitic carbon is widely used as active material for the negative electrode (anode). The disadvantage is that the electrochemical capacity of such carbon is relatively low, with a theoretical electrochemical capacity of at most 372 mAh per gram of graphite, which corresponds to only about one tenth of the theoretically achievable electrochemical capacity of metallic lithium. Alternative active materials for the negative electrode use silicon adducts as described, for example, in EP 1730800 B1 or EP 3335262 B1. Silicon forms binary electrochemically active alloys with lithium, which allow a very high electrochemically achievable lithium content of up to 3579 mAh per gram of silicon.

[0003] The insertion and extraction of lithium ions in silicon is accompanied by very high volume changes, which can be up to 300% in the case of complete insertion. These volume changes subject the silicon-containing active material to severe mechanical stress, as a result of which the active material can crack. This process, also known as electrochemical wear, leads to a loss of electrical contact in the active material and in the electrode structure and thus to an irreversible loss of electrode capacity.

[0004] In addition, the surface of the silicon-containing active material can react with components of the electrolyte to form a passivating protective layer (Solid Electrolyte Interphase; SEI). The components formed are no longer electrochemically active. The lithium incorporated therein is no longer available to the system and thus leads to a significant capacity loss of the lithium ion battery. Due to the volume change of silicon during the charging / discharging process of the LIB, the SEI periodically cracks, thus exposing more free surface of the silicon-containing active material, which is then exposed to further SEI formation. Since the amount of mobile lithium corresponding to the available capacity in a lithium ion battery is limited by the positive electrode material, its consumption increases continuously and the capacity decreases after a few cycles.

[0005] Known active materials for LIB anodes include Si-C composite particles, in which silicon from a gaseous or liquid precursor is embedded in a porous carbon particle. The advantage of Si-C composites is that the silicon is finely distributed and embedded in the carbon skeleton, which can withstand the volume change of the silicon and at the same time maintain electrical contact to the silicon. Such Si-C composites are prepared, for example, by vapor deposition of one or more silicon precursors in the pores of a porous carbon matrix. The introduction of silicon into the porous structure is also referred to as chemical vapor infiltration (CVI).

[0006] If the silicon composite is prepared by CVI, the silicon precursor is usually used at low absolute pressure and partial pressure and thus at a lower silicon precursor concentration, so that long reaction times are required to achieve a high silicon proportion in the silicon-containing material, since otherwise a thick silicon layer (also referred to as coarse silicon layer) forms on the outside of the particles. These thick silicon layers are detrimental, as they come into contact with the electrolyte and, during cycling, they cause severe structuring of the particle surface and constant reformation of the SEI. Furthermore, the optimal adjustment of the process parameters requires precise knowledge of all the reaction parameters, which must usually be determined empirically. In addition, the porous matrix used exhibits a certain range of variation in its pore size and particle size distribution, so that avoiding excessive infiltration leading to a thick silicon layer is very challenging. If the infiltration is carried out continuously at a relatively high concentration of the silicon precursor (Si precursor) and / or at a relatively high temperature for reasons of productivity, a thick silicon layer also forms.

[0007] WO 2022 / 029422 A1 discloses a Si-C composite prepared by CVI, which contains 25 to 65% by weight of silicon. The composite consists of a mesoporous and microporous carbon skeleton, which contains a plurality of nanoscale elemental silicon domains inside its pores and on its surface. It can be prepared from porous carbon particles and silane at a temperature of 450°C and under reduced pressure in a fluidized bed reactor. In order to prevent the formation of a thick silicon layer (coarse bulk silicon), a silane concentration of less than 20% by volume is always used. This high dilution necessarily leads to longer reaction times and higher inert gas consumption, thus reducing the economic efficiency of the method.

[0008] Against this background, it was an object of the present application to provide a process for preparing a silicon-containing material which, when used as an active material in LIB anodes, ensures high cycle stability, while being obtained more quickly and thus more economically than by known preparation methods. The formation of a thick silicon layer should therefore be avoided.

[0009] The invention relates to a method for producing a silicon composite, which is the thermal decomposition of at least one silicon precursor in the presence of porous particles, wherein silicon is deposited in the pores of the porous particles and on the surface of the porous particles and the target silicon content of the silicon composite is 35 to 60% by weight, wherein in the regular operation the method is carried out under the following conditions:

[0010] - an average temperature T of 300 to 500°C and

[0011] - a concentration C of the silicon precursor in the supplied gas stream of 30 to 100% by volume.

[0012] The method comprises at least one phase A, in which a change Δ of at least one of the parameters T and C is effected relative to the regular operation and optionally relative to further phases A, wherein

[0013] ΔT = 10 to 130°C and

[0014] ΔC = 2 to 70% by volume,

[0015] with the proviso that during a phase A 0.1 to 50% of the target silicon content is deposited, or during two or more phases A at most 50% of the target silicon content is deposited in total.

[0016] The invention also provides a further method which essentially corresponds to the above-mentioned method, wherein in the regular operation the further method is carried out under the following conditions:

[0017] - an average temperature T of 300 to 500°C,

[0018] - a concentration C of the silicon precursor of 30 to 100% by volume and

[0019] - a volume flow rate VS of the silicon precursor of 0.01 to 20 NL / h based on 1 g of porous particles.

[0020] The further method likewise comprises at least one phase A, in which a change Δ of at least one of the parameters T, C and VS is effected relative to the regular operation and optionally relative to further phases A, wherein

[0021] ΔT = 10 to 130°C,

[0022] ΔC = 2 to 70% by volume and

[0023] ΔVS = 0.01 to 10 NL / h,

[0024] with the proviso that during a phase A 0.1 to 50% of the target silicon content is deposited, or during two or more phases A at most 50% of the target silicon content is deposited in total.

[0025] One advantage of the process according to the present application is that the conversion of the silicon precursor is greater than 30% over the entire process duration. In addition, the silicon is then deposited particularly uniformly on and especially in the porous particles, resulting in the resulting silicon composite having high stability in the application as active material in a LIB negative electrode.

[0026] The division of the infiltration reaction into multiple stages with different process parameters allows targeted shortening of the overall process duration and at the same time an increase in product performance. Surprisingly, it was found that under static conditions the conversion of the silicon precursor provided does not remain constant but changes over the course of the reaction duration, with the result that the static process mode does not achieve optimal utilization of the silicon precursor. This is compensated for by adjusting the process mode of the deposition reaction, thereby increasing the conversion.

[0027] In addition, the process according to the present application surprisingly overcomes the disadvantageous formation of thick silicon layers, with the result that the silicon composite obtained by the process has high electrochemical performance.

[0028] In routine operation, the volume flow VS of the silicon precursor supplied to the reactor can be 0.01 to 10 NL / h, preferably 0.01 to 5 NL / h, per gram of the porous particles used. Determination of the volume flow can be achieved by customary methods, such as by means of a rotameter.

[0029] AS can be 0.01 to 5 NL / h, preferably 0.01 to 2 NL / h, per gram of the porous particles used.

[0030] The silicon composite can have a target silicon (obtained by deposition from the silicon precursor) content of 40 to 55% by weight, preferably 42 to 50% by weight, based on the total weight of the silicon composite.

[0031] The target silicon content can be determined empirically by repeated sampling during the process.

[0032] It is preferred that the target silicon content is determined during the process by analyzing the composition of the offgas stream with at least one method selected from the group consisting of gas chromatography, mass spectrometry, infrared spectroscopy and thermal conductivity measurement.

[0033] The determination of the target silicon content is particularly preferably carried out by continuous analysis of the offgas composition by gas chromatography or thermal conductivity measurement. The offgas stream can be taken directly at the reactor outlet for gas composition analysis. The determination of the deposited silicon can also be achieved indirectly by quantitative determination of the hydrogen present in the offgas, provided that the hydrogen is not used for silane dilution.

[0034] The average temperature T in routine operation can be 315 to 475°C, preferably 330 to 450°C.

[0035] The average temperature T in routine operationR defined as the average of all temperatures in the regular operation. Temperature is to be understood as the temperature in the process, by which the process is controlled. If the temperature in phase A is changed by AT without interrupting the feed of the silicon precursor, a heating phase or a cooling phase is considered to be part of phase A. Then the average temperature (T A ) of phase A is used.

[0036] AT can be from 20°C to 100°C, preferably from 20°C to 50°C.

[0037] In the regular operation, the concentration C can be from 30 vol.% to 100 vol.%, preferably from 50 vol.% to 100 vol.%.

[0038] The value of C is preferably related to the concentration of the silicon precursor in the reaction gas, i.e. typically to its concentration in the feed duct of the reactor into which the reaction gas is fed. The reaction gas typically comprises the silicon precursor and / or an inert gas such as nitrogen. The concentration of the silicon precursor in the supplied reaction gas can be adjusted by a suitable metering device such as a rotary flow meter.

[0039] AC can be from 5 vol.% to 60 vol.%, preferably from 10 vol.% to 50 vol.%.

[0040] It is preferred that the change A of at least one of the parameters C, T and VS is performed continuously from the beginning to the end of phase A. In specific embodiments, the change can also be performed stepwise.

[0041] The change A can be started or terminated depending on the determined target silicon content. In other words, phase A can be started (deviation from the regular operation) or terminated (return to the regular operation) according to the change A.

[0042] It is preferred that the method is performed at a pressure of less than 0.7 MPa. In particular, the pressure is kept essentially constant during the method. By essentially here it is meant that the pressure can have a variation of ± 0.1 MPa.

[0043] The preparation of the silicon composite particles according to the present application can be performed in any reactor typically used for Si infiltration. Preferred are reactors selected from the group consisting of fluidized bed reactors, which can be oriented from horizontal to vertical, retorts, tube reactors, rotary kilns, and fixed bed reactors, which can be operated as open or closed systems, e.g. pressurized reactors. It is particularly preferred that the reactor allows for a homogeneous mixing of the porous particles and the silicon precursor with the silicon containing material formed during the infiltration (only the final end product is described as silicon composite material). This is advantageous for a as homogeneous as possible deposition of silicon in the pores and on the surface of the porous particles. Most preferred reactors are fluidized bed reactors, rotary kilns, pressurized reactors, bed reactors.

[0044] It is preferred that the process according to the present application is carried out in a reactor equipped with a close-clearance stirrer.

[0045] The process can also be carried out in a cascade reactor system comprising two or more reactors.

[0046] Carrying out the process in a cascade reactor system has the advantage over carrying out the process in only one reactor that the long cooling and heating phases of the reactor are reduced. This can result in economic advantages. A cascade reactor system additionally offers the advantage that the individual reactors can be precisely configured for their purpose. Cascade reactor systems are generally more scalable, since different numbers of reactors can be combined with one another to form the respective stages. Adjustments to the temperature, volumetric flow and concentration can also be made by carrying out stages A and the regular operation in different reactors in the reactor cascade.

[0047] The process according to the present application can comprise at least three stages:

[0048] Stage 1 : Filling of the reactor A with porous particles and pre-treatment of the particles, followed by transfer of the pre-treated particles to reactor B or to a storage container, or the material remains in reactor A.

[0049] Stage 2: Passing of a gas comprising a silicon precursor and usually an inert gas through reactor B. It is also possible for there to be no silicon precursor; the reactor temperature is controlled to a temperature at which the silicon precursor undergoes thermal decomposition on the surface and in the pores of the porous particles. A process profile is established which comprises, in addition to the regular operation, at least one stage A in which at least one of the parameters T, C and VS is changed. The reaction can be carried out under negative and positive pressure. After the introduction of silicon into the pores and onto the porous particles, the silicon composite is transferred to reactor C, or is stored to a storage container in between, or the material remains in reactor B.

[0050] Stage 3: Post-treatment of the silicon composite to functionalize the silicon- containing particle surface and / or to coat the silicon-containing particle surface. The particles are cooled to a specified temperature and the silicon composite is removed from reactor C and preferably transferred directly to a storage container or directly filled into a suitable container.

[0051] In stage 1, the porous particles are filled into a reactor A which can be heated and / or vacuum- and / or pressure-resistant. The filling can be carried out manually or automatically.

[0052] Filling of reactor A with porous particles can be carried out in an inert gas atmosphere or preferably in ambient air. Useful inert gases include hydrogen, helium, neon, argon, krypton, xenon, nitrogen, carbon dioxide or mixtures thereof, such as synthetic gases. Argon or nitrogen is preferred.

[0053] The automatic filling can be done by a metering screw, a rotary star valve, a vibrating conveyor, a plate metering device, a belt metering device, a vacuum metering system, a negative weighing or any other metering system, e.g. from a silo or any other container system.

[0054] The purpose of the pre-treatment of the particles in reactor A in phase 1 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 an inert gas (see previous phase), increasing the temperature up to 1000 °C, reducing the pressure up to 1 Pa or combining the individual process steps.

[0055] The purpose of the pre-treatment in phase 1 can also be to change the chemical surface constitution of the porous particles with additional substances. This addition can be done before or after drying and can be followed by a further heating step before the material is transferred to reactor B. The substances can be added to the reactor in gaseous, solid or liquid form or in solution. 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, alkoxides.

[0056] The transfer of the porous particles into the further reactor or container can be done by a fall pipe, a continuous conveyor, a flow conveyor / suction or a pressurized conveying device, e.g. a vacuum conveyor, a conveying blower; a mechanical conveyor, e.g. a powered roller conveyor, a screw conveyor, a suspended conveyor, an up / down conveyor, a bucket conveyor, a rotary star valve, a chain conveyor, a flighted conveyor, a conveyor belt, a vibrating conveyor; a gravity conveyor, e.g. a chute, a roller track, a ball track, a railway track.

[0057] In phase 2, the pre-treated material is heated in reactor B to an average temperature of 300 °C to 500 °C, particularly preferably 315 °C to 475 °C and especially preferably 330 °C to 450 °C.

[0058] During the temperature change or upon reaching this temperature or during the temperature profile run, reactor B can alternately or simultaneously be passed through by a gas consisting of at least one inert gas and / or at least one reactive component, which consists of at least one silicon precursor and / or at least one silicon-free precursor. During phase 2, the different compositions of the gas can be continuous or can be changed within the parameters of the specified composition.

[0059] A preferred silicon-free precursor (precursor without silicon) is one or more hydrocarbons. Carbon can generally be deposited in the pores and on the surface of the porous particles by thermal decomposition of the hydrocarbons.

[0060] The silicon-free precursor is preferably free of additional components or one or more inert gases and / or one or more reactive components such as hydrogen and / or one or more dopants. Dopants can include compounds containing boron, nitrogen, phosphorous, arsenic, germanium, iron or nickel. Dopants are preferably selected from ammonia, diborane, phosphine, germane, arsine and tetracarbonylnickel.

[0061] The dosing of the reaction gas can be continuous or intermittent. The dosing rate can be varied during the duration of the reaction.

[0062] The temperature, pressure, pressure change or differential pressure measurement and gas flow measurement in reactor B can be determined with common measuring instruments and measuring methods. After a typical calibration, different measuring instruments will usually give the same measurement results.

[0063] During the entire duration of the thermal decomposition, an amount of silicon precursor can be passed through reactor B such that the amount of silicon deposited is sufficient to produce the target capacity of the silicon composite in terms of the amount of porous particles charged.

[0064] The heating of reactor B in phase 2 can be carried out at a constant heating rate or at a plurality of different heating rates. The heating rate can be adjusted depending on the configuration of the method, for example depending on the size of the reactor, the amount of porous particles in the reactor, the stirring technique or the planned reaction time.

[0065] The heating of reactor B in phase 2 can be carried out at a heating rate of 1 °C to 100 °C per minute, preferably 2 °C to 50 °C per minute.

[0066] The temperature at which the decomposition of the silicon precursor begins can depend on the porous particles used, the silicon precursor used and other boundary conditions of the decomposition, such as the partial pressure of the silicon precursor at the critical moment of the decomposition and the presence of other reactive components such as catalysts which influence the decomposition reaction.

[0067] During the decomposition of the silicon precursor in phase 2, the temperature can remain constant or change. The aim is to convert the silicon precursor substantially completely to produce a silicon composite suitable for the application during the contact time of the gas with the stirred bed.

[0068] The target temperature for SiH4may be 300 °C to 500 °C, preferably 315 °C to 475 °C, particularly preferably 330 °C to 450 °C. The target temperature for HSiCl3may be 380 °C to 1000 °C, preferably 420 °C to 600 °C. The target temperature for H2SiCl2may be 350 °C to 800 °C, preferably 380 °C to 500 °C.

[0069] In addition to the silicon precursor, a silicon-free precursor such as a carbon precursor can also be used in stage 2. This can be done continuously or alternately as a mixture with the silicon precursor. The aim is to carry out a targeted functionalization of the newly formed silicon surface.

[0070] The gas phase from stage 2 can consist of an inert gas which can change in composition and / or at least one silicon-containing reactive component and / or at least one silicon-free precursor. The one or more silicon precursors can generally be introduced into reactor B in mixed form or individually or in a mixture with the inert gas component or as a pure substance.

[0071] In stage 2, the bed consisting of porous particles is preferably recirculated continuously. Recirculation can be achieved by one or more stirring devices or by a rotational movement of the reactor itself, for example a power mixer from Maschinenfabrik Gustav Eirich, or a combination thereof. The state of motion of the moving bed 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.

[0072] The thermal decomposition of the silicon precursor is preferably carried out in the presence of the porous particles at 0.05 MPa to 5 MPa, particularly preferably at 0.08 to 0.7 MPa.

[0073] The progress of the reaction in stage 2 is preferably monitored in an analytical manner in order to detect the end of the reaction and thus to keep the reactor occupancy time as short as possible. Methods for observing the progress of the reaction include, for example, temperature measurements for determining the exothermicity or endothermicity, determining the progress of the reaction by changing the ratio of solid to gaseous reactor contents, and further methods which allow the changing composition of the gas space during the reaction to be monitored. In a preferred variant of the method, the composition of the gas phase is determined by means of 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 determined using a thermal conductivity detector and / or any chlorosilane optionally present is determined using a gas chromatograph or a gas infrared spectrometer.

[0074] In a further preferred variant of the method, reactor B / gas outlet position is equipped with a technical solution for removing any condensable or resublimable by-products which occur. In a particularly preferred variant, silicon tetrachloride is condensed and removed separately from the silicon composite material.

[0075] In stage 3 of the process, the silicon-containing particles in reactor C are post-treated and / or passivated and / or coated. To this end, reactor C is preferably purged with oxygen, in particular with a mixture of an inert gas and oxygen. This allows the silicon composite material surface to be modified and / or functionalized and / or deactivated. For example, reactions of any reactive groups present on the silicon composite material surface can be effected. To this end, a mixture of nitrogen, oxygen and, optionally, an alcohol and / or water is preferably used, which preferably contains up to 20 vol.%, particularly preferably up to 10 vol.% and especially preferably up to 5 vol.% of oxygen and preferably up to 100 vol.%, particularly preferably up to 10 vol.% and especially preferably up to 1 vol.% of water. This step is preferably carried out at a temperature of up to 250°C, particularly preferably up to 100°C and especially preferably up to 50°C. Deactivation of the particle surface can also be achieved by means of a gas mixture containing an inert gas and an alcohol. Here, nitrogen and isopropanol are preferably used. However, methanol, ethanol, butanol, pentanol or longer-chain and branched alcohols and diols can also be used.

[0076] Deactivation of the particles can also be achieved by dispersion in a liquid solvent or solvent mixture. This can contain isopropanol or an aqueous solution. Deactivation of the particles in stage 3 can also be carried out by coating using C-, Al- and B-containing precursors at temperatures of 200-800°C and, optionally, subsequent treatment with an oxygen-containing atmosphere.

[0077] Useful aluminium-containing precursors include trimethylaluminium ((CH3)3Al), aluminium 2,2,6,6-tetramethyl-3,5-heptanedionate (Al(OCC(CH3)3CHCOC(CH3)3)3), tris(dimethylamino)aluminium (Al(N(CH3)2)3) and triisopropylaluminium (C9H 21 AlO3).

[0078] Useful boron-containing precursors include borane (BH3), triisopropylborate ((CH3)2CHO]3B), triphenylborane ((C6H5)3B) and tris(pentafluorophenyl)borane (C6F5)3B.

[0079] In stage 3, a post-coating of the particles with a solid-state electrolyte can also be introduced by, for example, thermal decomposition of tert-butyllithium and trimethylphosphate.

[0080] In stage 3, the silicon composite material can in principle be removed from reactor C, optionally while maintaining the inert gas atmosphere present in reactor C. This can be accomplished by the following discharge methods: pneumatic (by means of a pressure above or below atmospheric pressure); mechanical (rotary star valve, plate-type discharge device, discharge screw / stirring device in the reactor, belt-type discharge device), gravimetric (double-flap valve / spherical valve, optionally assisted by vibration).

[0081] When a hydrocarbon is used in stage 3 and / or in addition to the silicon infiltration during stage 2, the target temperature used is the temperature at which the hydrocarbon starts to decompose and carbon is deposited in the pores of the porous particles and on the surface. Preferably, the target temperature chosen in this embodiment is between 250°C and 1000°C, particularly preferably between 350°C and 850°C and most preferably between 400°C and 650°C.

[0082] The technical requirements of the reactor and optional details of the specific variants of the application are as follows:

[0083] Reactor A:

[0084] - the reactor is at least temperature-controllable,

[0085] - the reactor can be vacuum-tight,

[0086] - a system for preheating, drying and inerting the porous particles,

[0087] - a system can be connected for targeted addition / dosing of the porous particles,

[0088] - drying / removal of impurities from the porous particles can be achieved by connecting a system capable of removing condensable or resublimable substances,

[0089] - a system can be connected through which the porous particles can be transferred into reactor B.

[0090] Reactor B:

[0091] - the reactor is at least temperature-controllable,

[0092] - comprises a stirrer device according to the application,

[0093] - a system for dosing the reaction gas,

[0094] - a system for discharging the reaction gas,

[0095] - in order to simplify the process, a hydrogen separator can be connected,

[0096] - in order to remove condensable or resublimable by-products that occur in the gaseous reaction products, a container can be connected that allows the removal of the by-products by condensation or resublimation,

[0097] - a system can be connected through which the material can be transferred into reactor C or a storage container.

[0098] Reactor C:

[0099] - the reactor is at least temperature-controllable,

[0100] - a system for removing condensable or resublimable by-products,

[0101] - a container can be connected which allows removal of the by-products by condensation or resublimation,

[0102] - a system for dosing the reaction gas for functionalization,

[0103] - a system for discharging the reaction gas,

[0104] - a system can be connected which enables transfer of the material into a storage container.

[0105] The reactors can be temperature-controllable, pressure-resistant and vacuum-resistant at the same time; all combinations are possible. However, individual reactors can also only realize one of the above-mentioned features.

[0106] Temperature-controllable reactors are generally reactors which are operable such that the internal temperature can be adjusted in a range between -40°C and 1000°C. Smaller temperature ranges are possible.

[0107] It is preferred that the reactors A, B and C are the same vessel, in other words, the method can also be carried out in only one reactor. It is in principle not excluded that the reactors A, B and C are the same vessel.

[0108] It can be provided that the method of the customary operation and the at least one phase A are carried out in one reactor. In one specific embodiment, the customary operation and phase A can be carried out in separate reactors.

[0109] The porous particles and the resulting silicon composite material can generally be in the form of a fixed bed or in the form of a thoroughly mixed moving bed during the method. It is preferred that the mixing in the reactors A, B and C is carried out to provide a moving bed of the porous particles / resulting silicon composite material. However, during the thermal decomposition of the silicon precursor in phase 2, the particles generally have to be mixed. This makes it possible to ensure uniform contact of all porous particles with the reaction gas or uniform temperature distribution of the bed. Recirculation of the particles can be achieved by stirring internal members in the reactor or movement of the entire reactor around a stirrer.

[0110] A further preferred configuration of reactors A, B and C is a fixed reactor with a mobile stirring device for recirculation. The purpose of the recirculation is to contact the porous solid with the reaction gas as uniformly as possible. The preferred geometry for this is a cylindrical reactor, a conical reactor, a spherically or polyhedrally rotationally symmetrical reactor or a combination thereof. The movement of the stirring device is preferably a rotational movement. For reactors A, B and C operated vertically, the preferred configuration is one stirring device or two or more stirring devices that mix the bed material by a rotational movement, for example by a main stirrer shaft. Another configuration of reactors A, B or C operated vertically is characterized by the use of a conveying screw. For reactors A, B or C operated horizontally, the preferred configuration is one stirring device or two or more stirring devices that mix the bed material by a rotational movement, for example by a main stirrer shaft. For reactors A, B or C operated vertically, the preferred stirring device is selected from helical stirrers, spiral stirrers, anchor stirrers or general stirring devices that convey the bed material in the axial direction or in the radial direction or in both the axial and radial directions. The wall gap can be reduced by additional scrapers on the stirring device. In addition to the mobile stirring device, reactors A, B or C can also have rigid internal components, such as baffles.

[0111] The materials suitable for configuring reactors A, B or C include in principle any material that exhibits the necessary mechanical strength and resistance under the respective process conditions. In terms of chemical resistance, reactors A, B or C can consist of both suitable solid materials and chemically resistant (pressure-resistant) materials in which the medium-contacting parts have a special coating or plating.

[0112] The cascade reactor system is a connected system of at least two reactors. There is no upper limit to the number of reactors. The number of reactors A, B and C relative to one another and their size, shape, material and configuration can be different. The reactors can be connected directly to one another or spatially separated from one another and fed through mobile storage containers. It is also conceivable for two or more reactors B to be connected to one another and for each reaction step to be carried out in a separate reactor B.

[0113] The silicon precursor and the silicon-free precursor are preferably gaseous, liquid, solid (e.g. sublimable), or a composition of substances optionally consisting of substances in different states of matter. In one variant of the process, the silicon precursor is fed directly into the porous particle bulk in the reactor, for example from below or from the side or by means of a special stirrer.

[0114] The silicon precursor is preferably selected from silicon-hydrogen compounds such as monosilane (SiH4), disilane (Si2H6) and higher linear, branched or cyclic homologues, neopentasilane (Si5H 12 ), hexamethylcyclotrisilane (Si6H 12chlorosilanes, such as trichlorosilane (HSiCl3), dichlorosilane (H2SiCl2), chlorosilane (H3SiCl), tetrachlorosilane (SiCl4), hexachlorodisilane (Si2Cl6) and higher linear, branched or cyclic homologues such as 1,1,2,2-tetrachloroethyldisilane (Cl2HSi-SiHCl2), chlorinated and partially chlorinated oligomeric silanes and polysilanes, methylchlorosilanes, such as trichloromethylsilane (MeSiCl3), dichlorodimethylsilane (Me2SiCl2), trimethylchlorosilane (Me3SiCl), tetramethylsilane (Me4Si), methyldichlorosilane (MeHSiCl2), methenylchlorosilane (MeH2SiCl), methylsilane (MeH3Si), dimethylchlorosilane (Me2HSiCl), dimethylsilane (Me2H2Si), trimethylsilane (Me3SiH) and mixtures of said silicon compounds.

[0115] In particular, the silicon precursor is selected from the group consisting of silane, disilane, trichlorosilane, dichlorosilane, methylsilane and mixtures thereof.

[0116] Other reactive components which can be present in the reaction gas include hydrogen or a hydrocarbon 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 ethylene, acetylene, propylene, methylacetylene, butene, butyne (1 -butyne, 2-butyne), isoprene, butadiene, divinylbenzene, vinylacetylene, cyclohexadiene, cyclooctadiene, cyclic unsaturated hydrocarbons, such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, cyclohexadiene, cyclopentadiene, dicyclopentadiene or norbornadiene, aromatic hydrocarbons, such as benzene, toluene, p-xylene, m-xylene, o-xylene, styrene (vinylbenzene), ethylbenzene, diphenylmethane or naphthalene, other aromatic hydrocarbons, such as phenol, o-cresol, m-cresol, p-cresol, umbeliferone, nitrobenzene, chlorobenzene, pyridine, anthracene and phenanthrene, laurene, geraniol, thujanol, norbornane, borneol, isoborneol, borneol, camphor, limonene, terpinene, pinene, pinane, carene, phenol, aniline, anisole, furan, furfural, furfuryl alcohol, hydroxymethylfurfural, bis-hydroxymethylfuran and mixed fractions containing a plurality of such compounds, such as mixed fractions from natural gas condensates, petroleum distillates, coke oven condensates, product streams from fluidized bed catalytic crackers (FCC), steam crackers or Fischer-Tropsch synthesis plants, or more generally from hydrocarbon-containing material streams from wood, natural gas, petroleum and coal processing.

[0117] The porous particles used in the process according to the application are preferably selected from amorphous carbon in the form of hard carbon, soft carbon, meso carbon, microbeads, natural or synthetic graphite, single- and multi-walled carbon nanotubes and graphene, oxides such as silicon dioxide, aluminium oxide, silicon-aluminium mixed oxides, magnesium oxide, lead oxide and zirconium oxide, carbides such as silicon carbide and boron carbide, nitrides such as silicon nitride and boron nitride, and other ceramic materials such as can be described by the following component formula:

[0118] Al a B b C c Mg d N e O f Si g wherein 0 < a, b, c, d, e, f, g < 1, wherein at least two of a to g are > 0 and a*3 + b*3 + c*4 + d*2 + g*4 > e*3 + f*2.

[0119] The ceramic material can for example be a binary, ternary, quaternary, quinary, sexinary or septinary compound. Preferred ceramic materials are those having the following component formula:

[0120] Non-stoichiometric boron nitride BN z wherein z = 0.2 to 1,

[0121] Non-stoichiometric carbon nitride CN z wherein z = 0.1 to 4 / 3,

[0122] Boron carbonitride B x CN z wherein x = 0.1 to 20 and z = 0.1 to 20, wherein x*3 + 4 > z*3,

[0123] Boron oxynitride BN z O r wherein z = 0.1 to 1 and r = 0.1 to 1, wherein 3 > r*2 + z*3,

[0124] Boron oxycarbonitride B x CN z O r wherein x = 0.1 to 2, z = 0.1 to 1 and r = 0.1 to 1, wherein: x*3 + 4 > r*2 + z*3,

[0125] Silicon oxycarbide Si x CO z wherein x = 0.1 to 2 and z = 0.1 to 2, wherein x*4 + 4 > z*2,

[0126] Silicon oxycarbide Si x CN zWhere x = 0.1 to 3 and z = 0.1 to 4, and x*4 + 4 ≥ z*3,

[0127] Boron carbonitride Si w B x CN z Where w = 0.1 to 3, x = 0.1 to 2 and z = 0.1 to 4, and w*4 + x*3 + 4 ≥ z*3,

[0128] Boron carbide silicon oxide Si w B x CO z Where w = 0.10 to 3, x = 0.1 to 2 and z = 0.1 to 4, and w*4 + x*3 + 4 ≥ z*2,

[0129] Boron, carbon, nitrogen, silicon oxynitride (Si) v B w CN x O z Where v = 0.1 to 3, w = 0.1 to 2, x = 0.1 to 4 and z = 0.1 to 3, and v*4 + w*3 + 4 ≥ x*3 + z*2 and

[0130] Borosilicate carbon nitrogen aluminum oxide Al u B v Si x CN w O z , where u = 0.1 to 2, v = 0.1 to 2, w = 0.1 to 4, x = 0.1 to 2 and z = 0.1 to 3, where u*3+v*3+x*4+4≥w*3+z*2.

[0131] The porous particles are preferably amorphous carbon selected from hard carbon, soft carbon, mesophase carbon, microspheres, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes, graphene and mixtures thereof.

[0132] Porous particles preferably have a density of 0.1 to 7 g / cm³. 3 And a concentration of 0.3 to 3 g / cm³ is particularly preferred. 3 The density, determined by helium density measurement, is used. This is beneficial for increasing the volumetric capacity (mAh / cm³) of lithium-ion batteries. 3 ).

[0133] Diameter percentile d of the volume-weighted particle size distribution of porous particles 50 Preferably ≥0.5μm, particularly preferably ≥1.5μm, and most preferably ≥2μm. Percentile diameter d 50 Preferably ≤20μm, more preferably ≤12μm and most preferably ≤8μm.

[0134] The preferred diameter percentile of the volume-weighted particle size distribution of porous particles is in d.10 ≥ 0.2 pm and d 90 ≤ 20.0 pm, particularly preferably between d 10 ≥ 0.4 pm and d 90 ≤ 15.0 pm and most preferably between d 10 ≥ 0.6 pm and d 90 ≤ 12.0 pm.

[0135] The diameter percentile d 10 is preferably ≤ 10 pm, particularly preferably ≤ 5 pm, especially preferably ≤ 3 pm and most preferably ≤ 2 pm. The diameter percentile d 10 is preferably ≥ 0.2 pm, particularly preferably ≥ 0.5 pm and most preferably ≥ 1 pm.

[0136] The diameter percentile d 90 is preferably ≥ 4 pm and particularly preferably ≥ 8 pm. The diameter percentile d 90 is preferably ≤ 18 pm, more preferably ≤ 15 pm and most preferably ≤ 13 pm.

[0137] The width d 90 - d 10 is preferably ≤ 15.0 pm, more preferably ≤ 12.0 pm, particularly preferably ≤ 10.0 pm, especially preferably ≤ 8.0 pm and most preferably ≤ 4.0 pm.

[0138] The width d 90 - d 10 is preferably ≥ 0.6 pm, particularly preferably ≥ 0.8 pm and most preferably ≥ 1.0 pm.

[0139] The volume-weighted particle size distribution of the porous particles can be determined according to ISO 13320 by static laser light scattering using the Mie model and a Horiba LA 950 measuring device with ethanol as dispersion medium for the porous particles.

[0140] The porous particles are preferably in the form of individual particles. For example, the particles can be discrete or aggregated. The porous particles are preferably non-aggregated and preferably non-agglomerated. Aggregation generally means that primary particles are initially formed during the preparation of the porous particles and the primary particles grow together and / or the primary particles are connected to each other, for example by covalent bonds, and in this way form aggregates. The primary particles are generally discrete particles. Aggregates or discrete particles can form agglomerates. Agglomerates are loose accumulations of aggregates or primary particles which are connected to each other by, for example, van der Waals interactions or hydrogen bonds. Aggregated aggregates can easily be broken apart again into aggregates by common kneading and dispersing processes. By such processes only the aggregates can be partially broken down into primary particles, if at all. The presence of porous particles in the form of aggregates, agglomerates or discrete particles can be visually observed, for example, using a conventional scanning electron microscope (SEM). In contrast, static light scattering methods for determining the particle size distribution or particle diameter of the matrix particles cannot distinguish between aggregates and agglomerates.

[0141] The porous particles can have any morphology, i.e. for example, fragmented, flaky, spherical or needle-shaped, wherein preferably fragmented or spherical particles. The morphology can be characterized, for example, by the sphericity ψ or the sphericity S. According to the definition of Wadell, the sphericity ψ is the ratio of the surface area of a sphere having the same volume to the actual surface area of the object. In the case of a sphere, ψ is 1. According to this definition, the sphericity ψ of the porous particles used in the process according to the application is preferably from 0.3 to 1.0, particularly preferably from 0.5 to 1.0 and most preferably from 0.65 to 1.0.

[0142] The sphericity S is the ratio of the circumference of an equivalent circle having the same area A of the projection of the particle onto a surface to the measured projection circumference U: In the case of ideal circular particles, the S value is 1. For the porous particles used in the process according to the application, the sphericity S is preferably from 0.5 to 1.0 and particularly preferably in the range from 0.65 to 1.0, based on the percentiles S 10 to S 90 . The determination of the sphericity S is carried out, for example, using an optical microscope with reference to a micrograph of an individual particle, or in the case of particles < 10 pm, preferably by graphical evaluation using image analysis software such as ImageJ using a scanning electron microscope.

[0143] The porous particles preferably have a gas accessible pore volume of > 0.2 cm 3 / g, particularly preferably > 0.6 cm 3 / g and most preferably > 1.0 cm 3 / g. This facilitates the achievement of high capacity LIBs. The gas accessible pore volume is determined by gas adsorption measurement with nitrogen according to DIN 66134.

[0144] The porous particles are preferably open-pored. Open-pored generally means that the pores are connected to the surface of the particle, for example by channels, and can preferably exchange substances, in particular gaseous compounds, with the environment. This can be demonstrated by gas adsorption measurements (analysis according to Brunauer, Emmett and Teller, "BET") i.e. the specific surface area. The specific surface area of the porous particles is preferably > 50 m 2 / g, particularly preferably > 500 m 2 / g and most preferably > 1000 m 2 / g. The BET surface area is determined according to DIN 66131 (using nitrogen).

[0145] The pores of the porous particles can have any diameter, i.e. typically in the range of macropores (greater than 50 nm), mesopores (2-50 nm) and micropores (less than 2 nm). The porous particles can be used in any mixture of different pore types. It is preferred to use porous particles having less than 30% macropores based on the total pore volume, particularly preferably no macropores, and very particularly preferably porous particles having at least 50% of the pores having a mean pore diameter of less than 5 nm. Very particularly preferred are porous particles which exclusively have pores having a pore diameter of less than 2 nm (determination method: pore diameter distribution in the mesopore range is determined according to DIN 66134 according to BJH (gas adsorption); pore diameter distribution in the micropore range is determined according to DIN 66135 according to Horvath-Kawazoe (gas adsorption); pore diameter distribution in the macropore range is evaluated according to DIN ISO 15901-1 by mercury porosimetry).

[0146] It is preferred that the gas inaccessible pore volume of the porous particles is less than 0.3 cm 3 / g and particularly preferably less than 0.15 cm 3 / g. This can also be used to increase the capacity of the LIB. The gas inaccessible pore volume can be determined using the following equation:

[0147] Gas inaccessible pore volume = 1 / pure material density - 1 / skeleton density.

[0148] The pure material density is the theoretical density of the porous particles, based on the phase composition or density of the pure substance (density of the material as if it had no closed porosity). Density data for pure substances can be found by the person skilled in the art, for example in the ceramic data portal of the National Institute of Standards and Technology (NIST, https: / / srdata.nist.gov / CeramicDataPortal / scd). For example, the pure material density of silicon oxide is 2.203 g / cm 3 , and the pure material density of boron nitride is 2.25 g / cm 3The density of pure silicon nitride is 3.44 g / cm³. 3 The density of pure silicon carbide is 3.21 g / cm³. 3 The skeletal density is the actual density of porous particles (accessible to gas) determined by the helium specific gravity method.

[0149] Porous particles are commonly used as raw materials for preparing silicon composite materials. Preferably, silicon is absent in the pores of the porous particles and on the surface of the porous particles, that is, in particular, silicon obtained by depositing silicon precursors is absent.

[0150] The diameter percentile d of the volume-weighted particle size distribution of a silicon composite material obtained by depositing silicon in the pores and on the surface of porous particles using the method according to the invention. 50 It can be within the range of 0.5μm to 20μm. 50 The value is preferably at least 1.5 μm, and particularly preferably at least 2 μm. Diameter percentile d 50 Preferably, the thickness is up to 13 μm, and particularly preferably up to 8 μm.

[0151] The preferred silicon composite material has a volume-weighted particle size distribution with a diameter percentile in d. 10 ≥0.2μm and d 90 Between ≤20.0μm, with particular preference given to d 10 ≥0.4μm and d 90 ≤15.0μm, especially in d 10 ≥0.6μm and d 90 Between ≤12.0μm.

[0152] Diameter percentile d of volume-weighted particle size distribution of silicon composite materials 10 Preferably ≤10μm, particularly preferably ≤5μm, especially preferably ≤3μm, and most preferably ≤1μm. Percentile diameter d 10 Preferably ≥0.2μm, particularly preferably ≥0.4μm and especially ≥0.6μm.

[0153] Diameter percentile d of volume-weighted particle size distribution of silicon composite materials 90 Preferably ≥5μm, and particularly preferably ≥10μm. Diameter percentile d 90 Preferably ≤20μm, particularly preferably ≤15μm, and especially ≤12μm.

[0154] Width d of the volume-weighted particle size distribution of silicon composite materials 90 -d 10 The particle size distribution width d of silicon can be ≤15.0 μm, preferably ≤12.0 μm, particularly preferably ≤10.0 μm, especially ≤8.0 μm, and even more preferably ≤4.0 μm. 90 -d10 Preferably > 0.6 pm, particularly preferably > 0.8 pm and in particular > 1.0 pm.

[0155] The particles of the silicon composite are preferably in particulate form. The particles can be discrete or aggregated. The silicon composite is preferably non-aggregated and preferably non-agglomerated. The terms discrete, aggregated and non-aggregated have been defined above in relation to the porous particles. The presence of the silicon composite in the form of aggregates or agglomerates can be observed, for example, using a conventional scanning electron microscope (SEM).

[0156] The silicon composite can have any morphology, i.e. be divided into fragments, be in the form of flakes, be spherical or needle-shaped, with fragmented or spherical particles being preferred.

[0157] The sphericity ψ according to Wadell is the ratio of the surface area of a sphere having the same volume to the actual surface area of the object. In the case of a sphere, ψ is 1. According to this definition, the sphericity ψ of the silicon composite obtainable by the process according to the application is preferably from 0.3 to 1.0, particularly preferably from 0.5 to 1.0 and most preferably from 0.65 to 1.0.

[0158] The sphericity S is the ratio of the circumference of an equivalent circle having the same area A of the projection of the particle onto the surface to the measured projection circumference U: In the case of ideal circular particles, the value of S is 1. For the silicon composite obtainable by the process according to the application, the sphericity S is preferably in the range from 0.5 to 1.0 and particularly preferably in the range from 0.65 to 1.0, based on the percentile S 10 to S 90 . The determination of the sphericity S is carried out, for example, using an optical microscope with reference to a micrograph of an individual particle, or, in the case of particles smaller than 10 pm, preferably using a scanning electron microscope (SEM) by graphical evaluation using image analysis software such as Image J.

[0159] The cycle stability of the LIB can be further improved by the morphology, the material composition, in particular the specific surface area or the internal porosity of the silicon composite.

[0160] If the porous particles comprise a silicon compound, for example in the form of silicon dioxide, the above data in % by weight of silicon obtained by deposition from the silicon precursor can be determined by subtracting the silicon mass of the porous particles determined by elemental analysis from the silicon mass of the silicon composite determined by elemental analysis and dividing the result by the mass of the silicon composite.

[0161] The volume of the silicon deposited in the porous particles can be determined by the mass fraction of the silicon obtained by deposition from the silicon precursor in the total mass of the silicon composite divided by the density of the silicon (2.336 g / cm3).3 ) derived.

[0162] The pore volume P of the silicon composite can be derived from the sum of the gas accessible and the gas inaccessible pore volume. The Gurvich gas accessible pore volume of the silicon composite can be determined according to DIN 66134 by nitrogen gas adsorption measurement.

[0163] The gas inaccessible pore volume of the silicon composite can be determined according to the following formula as described above: Gas inaccessible pore volume = 1 / skeleton density - 1 / pure material density.

[0164] The pore volume P of the silicon composite is preferably in the range of 0 vol.% to 400 vol.%, particularly preferably in the range of 100 vol.% to 350 vol.% and especially preferably in the range of 200 vol.% to 350 vol.%, based on the volume of silicon present in the silicon composite and obtained from the deposition of the silicon precursor.

[0165] The porosity of the silicon composite can be gas accessible or gas inaccessible. The volume ratio of the gas accessible porosity to the gas inaccessible porosity of the silicon composite can generally be in the range of 0 (no gas accessible porosity) to 1 (all porosity is gas accessible). The volume ratio of the gas accessible porosity to the gas inaccessible porosity of the silicon composite is preferably in the range of 0 to 0.8, particularly preferably in the range of 0 to 0.3 and especially preferably in the range of 0 to 0.1.

[0166] 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 silicon composite can also comprise any mixture of different pore types. Preferably, it comprises at most 30% of macropores based on the total pore volume. Particularly preferred is a silicon composite which has no macropores and very particularly preferred is a silicon composite which has pores with an average pore diameter of less than 5 mm based on the total pore volume of at least 50%. The silicon composite is especially preferred to comprise exclusively pores with a diameter of at most 2 nm.

[0167] The silicon composite comprises a silicon structure which has 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 (determination method: SEM and / or high resolution transmission electron microscopy (HR-TEM)).

[0168] The silicon composite preferably comprises a silicon layer having a layer thickness of less than 1000 nm, particularly preferably less than 100 nm, in particular less than 5 nm (determined by SEM and / or HR-TEM). The silicon composite can also comprise silicon in the form of particles. The diameter of the silicon particles is preferably at most 1000 nm, particularly preferably less than 100 nm, in particular less than 5 nm (determined by SEM and / or HR-TEM). Here, the graph of the silicon particles preferably relates to the circumferential diameter of the particles in the micrograph.

[0169] It is preferred that the amount of coarse silicon in the deposited silicon is less than 3 wt.-%, particularly preferably less than 1 wt.-%, and especially preferably less than 0.1 wt.-%.

[0170] The specific surface area of the silicon composite is preferably at most 100 m 2 / g, particularly preferably less than 30 m 2 / g, and especially preferably less than 10 m 2 / g. The BET surface area is determined according to DIN 66131 (using nitrogen). This can reduce the formation of SEI and increase the initial coulombic efficiency when using the silicon composite as active material for the LIB anode.

[0171] Furthermore, the silicon deposited from the silicon precursor in the silicon composite can comprise a dopant, for example selected from the group consisting of 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 earth elements and combinations thereof. Li and / or Sn are preferred. The content of the dopant in the silicon composite, which can be determined by ICP-OES, is preferably at most 1 wt.-% and particularly preferably at most 100 ppm, based on the total weight of the silicon composite.

[0172] The silicon composite has surprisingly high stability under compressive load and / or shear stress. The compressive load stability and the shear stability are evident, for example, from the fact that the porous structure of the silicon composite, even if it changes under compressive load (for example during compaction of the electrode) and under shear stress (for example during production of the electrode), changes only slightly.

[0173] The silicon composite can optionally contain additional elements such as carbon. Carbon is preferably present in the form of thin layers with a layer thickness of at most 1 pm, preferably less than 100 nm, particularly preferably less than 5 nm and especially preferably less than 1 nm (determined: SEM and HR-TEM). The carbon layers can be present both in the pores and on the surface of the silicon composite. The sequence of the different layers in the silicon composite and their number can also be freely selected by appropriate repetition of the alternating metering of the different precursors. Thus, on the porous particles there can first be a layer of a further material (such as carbon) which is different from the porous particles, and on this a layer of silicon or a layer of silicon particles. On the silicon layer or on the layer of silicon particles there can also be present in turn layers of a further material which can be different from or identical to the material of the porous particles, whether or not a further layer of a material different from the material of the porous particles is present between the porous particles and the silicon layer or the layer composed of silicon particles.

[0174] The silicon composite can contain < 50 wt.-%, preferably < 40 wt.-%, particularly preferably < 20 wt.-% of additional elements. The silicon composite can particularly comprise > 1 wt.-%, especially preferably > 2 wt.-% of additional elements. The figures in wt.-% refer to the total weight of the silicon composite. The silicon composite can also be free of additional elements.

[0175] The silicon composite obtained by the process according to the application is suitable as active material in the negative electrode material of a LIB negative electrode and such a negative electrode is suitable for use in the production of a LIB. All substances and materials required for the production are well known. The production of the components of such a battery and their assembly is carried out by processes familiar in the field of battery production.

[0176] The silicon composite obtained by the process according to the application is characterized by a significantly improved electrochemical behavior and leads to a LIB with high volumetric capacity and excellent performance characteristics. The silicon composite is permeable to lithium ions and electrons, enabling charge transport. With the silicon composite obtained, the SEI in the LIB can be greatly reduced. Furthermore, due to the design of the silicon composite, the SEI is at least to a lesser extent desorbed from the surface of the active material, if at all. All this leads to high cycle stability of a LIB whose negative electrode contains the silicon composite obtainable by the process according to the application.

[0177] The following examples serve to further illustrate the application described herein.

[0178] The characterization was carried out using the following analytical methods and instruments:

[0179] Inorganic analysis / elemental analysis:

[0180] The carbon content recorded in the examples was determined with a Leco CS230 analyzer; the determination of the O and optionally N or H content used a Leco TCH-600 analyzer. The qualitative and quantitative determination of the other specified elements was carried out by ICP (inductively coupled plasma) emission spectroscopy (Optima 7300DV, Perkin Elmer). For this purpose, the samples were subjected to acid digestion (HF / HNO3) in a microwave oven (Microwave 3000 from Anton Paar). The ICP-OES determination is based on ISO 11885 "Water quality - Determination of selected elements by inductively-coupled plasma optical emission spectrometry" (ISO 11885:2007); EN ISO 11885:2009 German version" for the analysis of acidic aqueous solutions, such as acidified drinking water, waste water and other water samples as well as aqua regia extracts of soils and sediments. The silicon determination method used is generally accurate to ± 1 wt.-%.

[0181] Particle size determination:

[0182] The particle size distribution was determined by static laser light scattering using a Horiba LA950 according to ISO 13320. In the preparation of the samples, particular attention must be paid to the dispersion of the particles in the measuring solution to ensure that the results of the measurement are the dimensions of individual particles and not of agglomerates. The particles were dispersed in ethanol for the determination. Before the determination, the dispersion can be sonicated at 250 W for 4 minutes in a Hielscher UIS250v laboratory ultrasound device with LS24d5 ultrasonic generator, if necessary.

[0183] BET surface area determination:

[0184] The specific surface area of the materials was determined by the BET method by nitrogen gas adsorption using a Sorptomatic 199090 instrument (Porotec) or a SA-9603MP instrument (Horiba) (determination using nitrogen according to DIN ISO 9277:2003-05).

[0185] Skeleton density:

[0186] The skeleton density, i.e. the density of the porous solid based on the volume of the pore space accessible only to the external gas, was determined by He pycnometry according to DIN 66137-2.

[0187] Gas accessible pore volume:

[0188] Gurvich gas accessible pore volume was determined by nitrogen gas adsorption measurements according to DIN 66134.

[0189] Thermogravimetric analysis (TGA) and determination of the crude silicon:

[0190] The reactivity of the powder towards oxygen was determined by TGA measurements in pure oxygen at a temperature window of 25-1000 °C using a heating rate of 5 K / min.

[0191] Conversion:

[0192] The conversion is calculated as the quotient of the amount of substance (in mol) of the starting material which has been converted to the amount of substance (in mol) of the starting material (reactant) used. The conversion indicates how many of the used SiH4molecules have been converted to Si at a specific time. The conversion is variable and can change over the course of the flow.

[0193]

[0194] The overall conversion indicates how much silicon has been deposited in relation to the metered silicon over the entire process.

[0195] Production:

[0196] The production describes how much % weight of silicon has been metered in one hour. It is calculated from the silicon content (target silicon content) of the product taken out (in % weight) in relation to the deposition time of all stages (in hours).

[0197] Examples

[0198] These examples were used to produce silicon composites with a silicon proportion of 47 to 49 % by weight.

[0199] The used SiH4with a quality of 4.0 was obtained from Linde GmbH.

[0200] In all examples, amorphous carbon was used as the porous starting material:

[0201] - specific surface area = 1636 m 2 / g

[0202] - pore volume = 0.76 cm 2 / g

[0203] - average volume-weighted particle size D 50 = 6.4 pm

[0204] Proportion of deposited silicon based on the target content:

[0205] 0.1% to 50% of the target content is to be deposited during a stage A, or up to 50% of the target content is to be deposited in total during two or more stages A.

[0206] The proportion of silicon deposited during one stage A or during regular operation based on the target content represents the relative proportion of silicon deposited in the respective stage. For example, a target silicon content of 48% by weight of the composite corresponds to a relative proportion of 100% of the deposited Si. 50% of Si deposited during a stage A corresponds to a target silicon content of 24% by weight in the composite.

[0207] Fine silicon and coarse silicon in the sample are determined by the reaction of silicon with oxygen to form SiO2 using TGA measurements. The distinguishability of the different silicon species can be due to the fact that thin silicon layers have a higher reactivity towards oxygen compared to thick layers or silicon particles. The result of this is that in TGA measurements, even at low temperatures (400-655 °C), thin silicon layers react (mass increase) and thick layer / coarse silicon structures only react at temperatures above 700 °C. Ideally, a silicon-containing composite to be used as an anode active material does not show a mass increase in a TGA measurement in an oxygen-containing atmosphere at temperatures above 800 °C. This method further allows the determination of the content of elemental silicon. Silicon that has previously been oxidized and passivated due to contact with air no longer participates in the reaction and is therefore not taken into account in the TGA measurement.

[0208] The residual mass (mred) from the TGA method and the mass difference (mdiff) resulting from the oxidation of coarse silicon are required to calculate the coarse silicon present. Using the molar mass of O2 (32 g / mol) and the molar mass of SiO2 (60.08 g / mol), the proportion of coarse silicon in the deposited silicon can now be calculated using the following equation:

[0209]

[0210] Comparative Example 1 : Preparation of a silicon composite in a suitable reactor.

[0211] 2.2 g of porous carbon particles (specific surface area = 1636 m 2 / g; Gurvich pore volume = 0.76 cm 3 / g, average volume-weighted particle size D 502.2 g of porous carbon particles (specific surface area = 1636 m2 / g; Gurvich pore volume = 0.76 cm3 / g, average volume-weighted particle size D = 6.40 pm) in a quartz glass boat were loaded into a tubular reactor. After inertization with nitrogen, the reactor was heated to 410 °C. After reaching this temperature, a silicon precursor (50% SiH4in N2, 10 NL / h) was passed into the reactor. The decomposition of SiH4in the exhaust gas stream was monitored by means of a thermal conductivity detector to provide the reaction of silicon and was quantified. After deposition of 2.1 g of silicon, the SiH4gas stream was switched to a pure nitrogen stream and the heating was switched off. The reactor was cooled to room temperature under N2purging and the product was removed.

[0212] Comparative Example 2: Silicon composite is prepared in a suitable reactor.

[0213] 2.2 g of porous carbon particles (specific surface area = 1636 m 2 / g; Gurvich pore volume = 0.76 cm 3 / g, average volume-weighted particle size D 50 = 6.40 pm) in a quartz glass boat were loaded into a tubular reactor. After inertization with nitrogen, the reactor was heated to 380 °C. After reaching this temperature, a silicon precursor (50% SiH4in N2, 10 NL / h) was passed into the reactor. The decomposition of SiH4in the exhaust gas stream was monitored by means of a thermal conductivity detector to provide the reaction of silicon and was quantified. After deposition of 2.1 g of silicon, the SiH4gas stream was switched to a pure nitrogen stream and the heating was switched off. The reactor was cooled to room temperature under N2purging and the product was removed.

[0214] Examples 1-2: Silicon composite is prepared by the process according to the application with stage A (index A denotes the parameters of stage A).

[0215] 2.2 g of porous carbon particles (specific surface area = 1636 m 2 / g; Gurvich pore volume = 0.76 cm 3 / g, average volume-weighted particle size D 50 = 6.40 pm) in a quartz glass boat were loaded into a tubular reactor. After inertization with nitrogen, the reactor was heated to T A (stage (index) A). After reaching the target temperature, monosilane was passed into the reactor as a mixture with N2(concentration C A , volume flow of silicon precursor VS A ). The decomposition of SiH4in the exhaust gas stream was monitored by means of a thermal conductivity detector to provide the reaction of silicon and was quantified. Once M A [g] of silicon had been deposited, the plant was switched to regular operation (index R): temperature T R , monosilane concentration C R , volume flow of silicon precursor VS R , and a further amount M Rof silicon. The reactor is then cooled to room temperature under N2purging and the silicon composite is removed.

[0216] Table 1 : Experimental parameters for examples 1 to 2 of the application

[0217]

[0218]

[0219] Example 3-4: Preparation of a silicon composite by the process according to the application in two or more stages A.

[0220] 2.2 g of porous carbon particles (specific surface area = 1636 m 2 / g; Gurvich pore volume = 0.76 cm 3 / g, average volume-weighted particle size D 50 = 6.40 pm) in a quartz glass boat are charged into a tubular reactor. After inertization with nitrogen, the reactor is heated to T A1 (stage (index) A1). After the target temperature has been reached, silane is passed into the reactor as a mixture with N2(concentration C A1 , volume flow rate of the silicon precursor VS A1 ). The decomposition of SiH4in the offgas stream is monitored by means of a thermal conductivity detector to provide the reaction of silicon and is quantified. Once M A1 [g] of silicon has been deposited (stage (index) A1), the plant is switched to regular operation: temperature T R , silane concentration C R , volume flow rate of the silicon precursor VS R , and a further amount M R [g] of silicon is deposited in regular operation. Once M R [g] of silicon has been deposited in regular operation (up to this point the target silicon content is M A1 + M R , the set-up is switched again and a new change D (stage (index) A2) is made: temperature T A2 , silane concentration C A2 , volume flow rate of the silicon precursor VS A2 , and a further amount M A2 [g] of silicon is deposited. The reactor is then purged with N2and cooled to room temperature and the product is removed.

[0221] Table 2: Experimental parameters for examples 1 to 2 of the application

[0222]

[0223]

[0224] The reaction conditions for the preparation and the material properties of the silicon composites are summarized in Table 3 below.

[0225] Table 3

[0226]

[0227]

[0228] *non-inventive

[0229] According to the selected parameters M R , M A , T R , T A , C R , C A , VS A and V R , the overall conversion of the silicon precursor and the production throughput of the plant installation can be significantly improved while maximizing the material properties.

[0230] Evaluation of silicon composite particles in electrochemical cells

[0231] Example 5: Silicon composites from Examples 1-4 of the present invention and from comparative examples were tested as anode components in LIBs.

[0232] 29.71 g of polyacrylic acid (dried to constant weight at 85 °C; Sigma-Aldrich, M wA solution of 3.87 g of the neutralized polyacrylic acid and 0.96 g of graphite (Imerys, KS6LC) was first charged into a 50 ml vessel and mixed in a planetary mixer (SpeedMixer, DAC 150 SP) at 2000 rpm. In each case, 3.35 g of the silicon composite from Examples 1 to 5 and Comparative Examples 1 and 2 were added and then stirred for 1 minute at 2000 rpm. Then 1.21 g of the 8% conductive carbon black dispersion and 0.8 g of deionized water were added and incorporated in the planetary mixer at 2000 rpm. Dispersion was then carried out in a dissolver at 3000 rpm for 30 minutes at a constant 20°C. The ink was degassed again in the planetary mixer at 2500 rpm for 5 minutes under vacuum. The final dispersion was then applied to a copper foil (Schlenk Metallfolien, SE-Cu58) having a thickness of 0.03 mm using a drawdown frame (Erichsen, model 360) with a gap of 0.06 mm. The negative electrode coating thus produced was then dried at 50°C and an air pressure of 1 bar for 60 minutes. The average basis weight of the dried negative electrode coating was 2.7 mg / cm 2 and the coating density was 0.8 g / cm 3 .

[0233] Electrochemical studies were carried out using coin cells (CR2032 type, Hohsen Corp.) in a two-electrode arrangement. The electrode coating was used as the counter electrode or negative electrode (Dm= 15 mm). A lithium-nickel-manganese-cobalt oxide (6:2:2) based coating with a content of 94.0% and an average basis weight of 15.9 mg / cm 2 obtained from the 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 M solution of lithium hexafluorophosphate in a 1:4 (v / v) mixture of fluoroethylene carbonate and diethyl carbonate. The cells were assembled in a glove box (<1 ppm H2O, O2); the water content in the dry substance of all components used was below 20 ppm.

[0234] Electrochemical tests were performed at 20°C. The battery was charged using a 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, until the voltage limit of 4.2V was reached, at which point the current was maintained at a constant voltage until it dropped below 1.2 mA / g (corresponding to C / 100) or 15 mA / g (corresponding to C / 8). Discharge was performed using a constant current (cc) method, with a constant current of 5 mA / g (corresponding to C / 25) in the first cycle and 60 mA / g (corresponding to C / 2) in subsequent cycles, until the voltage limit of 2.5V was reached. The specific current selected was based on the weight of the positive electrode coating. Electrodes were selected to establish a positive to negative capacitance ratio of 1:1.2.

[0235] The electrochemical test results of the LIB full cells of silicon-containing composite materials from Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 4.

[0236] Table 4

[0237]

[0238] *Not a present invention

[0239] Comparative Example 1 exhibited high yield and good conversion of the silicon precursor, but with a crude Si content of 0.6% (Table 3), only low cycle stability was achieved. Comparative Example 2 exhibited good electrochemical performance, but this was only achievable at low conversion rates and yields (Table 4).

[0240] Examples 1-3 of the present invention exhibited higher yields and higher conversion rates compared to Comparative Example 2, while maintaining very good electrochemical performance. In contrast to Comparative Example 1, Examples 1-3 did not provide crude Si and were therefore considered advantageous. By adjusting the temperature and silane concentration, Example 4 achieved better electrochemical performance than Comparative Example 1, while also having a higher conversion rate.

Claims

1. A method for preparing a silicon composite material, comprising thermally decomposing at least one silicon precursor in the presence of porous particles, said porous particles being amorphous carbon selected from: hard carbon, soft carbon, mesophase carbon, microspheres, natural or artificial graphite, single-walled carbon nanotubes and multi-walled carbon nanotubes, graphene and mixtures thereof, wherein silicon is deposited in the pores and on the surface of said porous particles by chemical vapor infiltration and the target silicon content of said silicon composite material is 35% to 60% by weight, wherein the method is carried out under the following conditions in conventional operation: The average temperature T from -300℃ to 500℃ and The concentration of silicon precursor C ranges from -30 vol% to 100 vol%. Its features are, The method includes at least one stage A, in which at least one of parameters T and C is changed Δ relative to normal operation and optionally relative to another stage A, wherein -ΔT = 10℃ to 130℃ and -ΔC = 2% to 70% (volume percentage) The condition is that during stage A, 0.1% to 50% of the target silicon content is deposited, or during two or more stages A, up to 50% of the target silicon content is deposited in total.

2. A method for preparing a silicon composite material, comprising thermally decomposing at least one silicon precursor in the presence of porous particles, said porous particles being amorphous carbon selected from: hard carbon, soft carbon, mesophase carbon, microspheres, natural or artificial graphite, single-walled carbon nanotubes and multi-walled carbon nanotubes, graphene and mixtures thereof, wherein silicon is deposited in the pores and on the surface of said porous particles by chemical vapor infiltration and the target silicon content of said silicon composite material is 35% to 60% by weight, wherein the method is carried out under the following conditions in conventional operation: The average temperature T ranges from -300℃ to 500℃. -30 vol% to 100 vol% concentration of silicon precursor C, and -Based on 1g of the porous particles, the volumetric flow rate VS of the silicon precursor is 0.01NL / h to 20NL / h, and Its features are, The method includes at least one stage A, in which at least one of parameters T, C, and VS is changed Δ relative to normal operation and / or relative to another stage A, wherein -ΔT = 10℃ to 130℃, -ΔC = 2% to 70% (volume percentage) -ΔVS = 0.01NL / h to 10NL / h The condition is that during stage A, 0.1% to 50% of the target silicon content is deposited, or during two or more stages A, up to 50% of the target silicon content is deposited in total.

3. The method according to claim 2, characterized in that, Based on 1g of the porous particles, the VS is 0.01NL / h to 10NL / h in normal operation.

4. The method according to claim 2 or 3, characterized in that, Based on 1g of the porous particles, ΔVS is 0.01NL / h to 5NL / h.

5. The method according to any one of the preceding claims, characterized in that, The target silicon content of the silicon composite material is 40% to 55% by weight.

6. The method according to any one of the preceding claims, characterized in that, The target silicon content is determined during the method by analyzing the composition of the exhaust gas stream using at least one method selected from the following: gas chromatography, mass spectrometry, infrared spectroscopy, and thermal conductivity determination.

7. The method according to any one of the preceding claims, characterized in that, During normal operation, T is between 315℃ and 475℃.

8. The method according to any one of the preceding claims, characterized in that, In normal operation, C is 40% to 100% by volume.

9. The method according to any one of the preceding claims, characterized in that, ΔT ranges from 20℃ to 100℃.

10. The method according to any one of the preceding claims, characterized in that, ΔC ranges from 5% to 60% by volume.

11. The method according to any one of the preceding claims, characterized in that, The change Δ is carried out continuously from the beginning of stage A until its end.

12. The method according to any one of the preceding claims, characterized in that, The method is carried out at a pressure of less than 0.7 MPa.

13. The method according to any one of the preceding claims, wherein it is carried out in a reactor equipped with a close-gap stirrer.

14. The method according to any one of the preceding claims, wherein it is carried out in a cascade reactor system comprising two or more reactors.

15. The method according to any one of the preceding claims, characterized in that, The silicon precursor is selected from silane, silane, trichlorosilane, dichlorosilane, methylsilane, and mixtures thereof.

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