Method for producing silicon-containing materials

Abstract

The present invention provides a method for producing an etched silicon-containing material, which comprises, in a first step, depositing silicon in the pores and on the surface of the porous particles by thermal decomposition of a silicon precursor on the porous particles to form a silicon-containing material, and in a second step, removing a portion of the deposited silicon of the silicon-containing material by etching, an etched silicon-containing material producible by this method, and an anode material, an anode, and a lithium-ion battery comprising the etched silicon-containing material producible by this method.

Description

[Technical Field]

[0001] The present invention relates to a method for utilizing silicon-containing materials by removing excess silicon from the particle surface, and to the use of the silicon-containing materials thus obtained as active materials for the anodes of lithium-ion batteries. [Background technology]

[0002] As a storage medium for electrical power, lithium-ion batteries are currently the most practical electrochemical energy storage devices with the highest energy density. They are primarily used in the field of portable electronics, for tools, and for electrically powered transportation such as bicycles, scooters, and automobiles. Graphite-like carbon is currently widely used as the active material for the negative electrode ("anode") of corresponding batteries. However, a drawback is the relatively low electrochemical capacity of such graphite-like carbon, which is theoretically a maximum of 372 mAh per gram of graphite, thus corresponding to only about one-tenth of the electrochemical capacity theoretically achievable with lithium metal. An alternative active material for the anode uses the addition of silicon, as described, for example, in EP 1730800 B1, US 10,559,812 B2, US 10,819,400 B2, or EP 3335262 B1. Silicon forms a binary electrochemically active alloy with lithium, which allows very high electrochemically achievable lithium contents of up to 3579 mAh per gram of silicon [M. Obrovac, V. Chevrier Chem. Rev. 2014, 114, 11444].

[0003] The intercalation and deintercalation of lithium ions in silicon suffers from the drawback of a significant volume change, which can reach up to 300% in the case of complete intercalation. Such volume changes impose significant mechanical stresses on silicon-containing active materials, which can ultimately lead to their decomposition. This process, also known as electrochemical polishing, results in the loss of electrical contact between the active material and the electrode structure, thus resulting in a sustained, irreversible loss of the electrode's capacity.

[0004] Furthermore, the surface of the silicon-containing active material reacts with the electrolyte components, resulting in the continuous formation of a passivating protective layer (solid electrolyte interphase interface, SEI). The formed components are no longer electrochemically active. The lithium bound there is no longer available to the system, leading to a significant and continuous loss of battery capacity. Due to the extreme changes in silicon volume during the battery charge / discharge process, the SEI periodically collapses, meaning that the unoccupied surface of the silicon-containing active material is exposed and then undergoes further SEI formation. Because the amount of mobile lithium in a complete cell corresponding to the usable capacity is limited by the cathode material, it is increasingly consumed, and the cell's capacity drops to an unacceptable level from a performance standpoint after just a few cycles.

[0005] The decrease in capacity over the course of multiple charge and discharge cycles is also called fading or continuous loss of capacity and is generally irreversible.

[0006] A series of silicon-carbon composite particles have been described as active materials for the anode of lithium-ion batteries, in which silicon is incorporated into porous carbon particles starting from a gas or liquid precursor.

[0007] For example, US 10,147,950 B2 describes the deposition of silicon from monosilane SiH4 in porous carbon by a CVD ("chemical vapor deposition") or PE-CVD ("plasma-enhanced chemical vapor deposition") process at high temperatures of 300°C to 900°C in a tubular furnace or equivalent furnace type, preferably with particle agitation. This uses a mixture of 2 mol% monosilane and nitrogen as an inert gas. Low concentrations of silicon precursor in the gas mixture lead to very long reaction times. Furthermore, US 10,147,950 B2 discloses several possible combinations of different temperature ranges from 300°C to 900°C and different pressure ranges from 0.01 to 100 bar for carrying out the deposition of silicon on and in porous starting materials.

[0008] US 10,424,786 B1 describes a similar procedure, in which the silicon precursor is introduced as a mixture with an inert gas at a total pressure of 1.013 bar. WO 2012 / 097969 A1 describes the deposition of ultrafine silicon particles in the range of 1 to 20 nm by heating silane as a silicon precursor on a porous carbon support at 200°C to 950°C, in which the silane is diluted with an inert gas to prevent weak agglomeration of the deposited silicon particles or the formation of a thick layer, and the deposition is carried out in the pressure range of 0.1 to 5 bar.

[0009] Motevalian et al., Ind. Eng. Chem. Res. 2017, 56, 14995, describe the deposition of silicon layers at high pressure, but not in the presence of a porous matrix. Again, the silicon precursor used, in this case monosilane SiH4, is present only in low concentrations of up to 5 mol% in the total gas volume.

[0010] The above methods have several significant drawbacks. Silicon precursors are usually used at low absolute and partial pressures, and therefore at low concentrations. This requires long reaction times to achieve a high silicon content in silicon-containing materials, since otherwise thick Si layers would form on the outside of the particles. These thick silicon layers are detrimental in that they come into contact with the electrolyte and, during cycling, lead to a high degree of structuring of the particle surface, combined with continuous regeneration of the SEI. Furthermore, optimal adjustment of the process parameters requires accurate knowledge of all reaction parameters, which must usually be determined empirically. In addition, the porous matrices used exhibit a certain range of variation in their pore and particle size distribution, making it impossible to eliminate over-infiltration by the silicon precursor, which results in a thick silicon layer. For productivity reasons, if infiltration occurs at a relatively high concentration of Si precursor and / or at a relatively high temperature, a thick Si layer will also form. During these empirical studies, the production of batches of materials with unfavorable product characteristics is inevitable. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] European Patent No. 1730800 [Patent Document 2] U.S. Patent No. 10,559,812 [Patent Document 3] U.S. Patent No. 10,819,400 [Patent Document 4] European Patent No. 3335262 [Patent Document 5] U.S. Patent No. 10,147,950 [Patent Document 6] U.S. Patent No. 10,424,786 [Patent Document 7] International Publication No. 2012 / 097969 [Non-patent literature]

[0012] [Non-Patent Document 1] M.Obrovac, V.Chevrier Chem.Rev.2014, 114, 11444 [Non-patent document 2] Motevalian et al., Ind. Eng. Chem. Res. 2017, 56, 14995 Summary of the Invention [Problem to be solved by the invention]

[0013] Against this background, the objective was to find a method for utilizing batches of materials with unfavorable product properties that would allow the use of silicon-containing materials as active materials in anodes of lithium-ion batteries with high cycling stability. [Means for solving the problem]

[0014] The present invention provides a method for producing an etched silicon-containing material, comprising: In a first step, silicon is deposited in the pores and on the surface of the porous particles by thermal decomposition of a silicon precursor on the porous particles to form a silicon-containing material; In a second step, a portion of the deposited silicon of the silicon-containing material is removed by etching off.

[0015] Surprisingly, this object has been achieved by a method in which silicon applied in excess to the particle surface is essentially removed from said surface in a controlled manner via an etching treatment of the over-infiltrated particles.

[0016] The adverse effects of grain structuring caused by thick Si layers during cycling are surprisingly overcome by the method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The silicon-containing material is preferably composed of silicon-containing particles, which can be obtained, for example, by pyrolyzing one or more silicon precursors in the presence of one or more porous particles, so that silicon is deposited in the pores and on the surface of the porous particles.

[0018] Silicon-containing material can be produced in any desired reactor that is conventional for depositing silicon from silicon precursor.Preferably, reactor is selected from the group including fluidized bed reactor, rotary tubular furnace, which can be oriented in any desired configuration from horizontal to vertical, and fixed bed reactor, which can be operated as open or closed system, for example as pressure reactor.Reactor that can homogeneously mix porous particles and silicon-containing material formed during deposition with silicon precursor is particularly preferred.This is advantageous for the deposition of silicon in the pores and on the surface of porous particles as homogeneous as possible.Most preferred reactor is fluidized bed reactor, rotary tubular furnace or pressure reactor, particularly fluidized bed reactor or pressure reactor.

[0019] The silicon precursors used contain at least one reactive component that can react under selected conditions, e.g., thermal treatment, to give silicon. The reactive component is preferably monosilane SiH4, disilane Si2H6, and higher linear, branched, or cyclic homologs, neopentasilane Si5H. 12 , cyclohexasilane Si6H 12the silicon-hydrogen compounds 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-tetrachlorodisilane Cl2HSi-SiHCl2, chlorinated and partially chlorinated oligo- and polysilanes such as chlorine-containing silanes such as trichloromethylsilane MeSiCl3, dichlorodimethylsilane Me2SiCl2, chlorotrimethylsilane Me3SiCl, tetramethylsilane Me4Si, dichloromethylsilane MeHSiCl2, chloromethylsilane MeH2SiCl, methylsilane MeH3Si, chlorodimethylsilane Me2HSiCl, dimethylsilane Me2H2Si, trimethylsilane Me3SiH, methylchlorosilanes, or mixtures of the listed silicon compounds.

[0020] The reactive component may also contain further reactive constituents, such as dopants based on compounds containing boron, nitrogen, phosphorus, arsenic, germanium, iron or nickel, which dopants are preferably selected from the group comprising ammonia NH3, diborane B2H6, phosphane PH3, germanium GeH4, arsine AsH3, iron pentacarbonyl Fe(CO)5 and nickel tetracarbonyl Ni(CO)4.

[0021] Further reactive constituents which may be present in the reactive component include hydrogen, hydrocarbons, for example 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 or butene, 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-, m-, o-xylene, styrene (vinylbenzene), ethylbenzene, Diphenylmethane or naphthalene, further aromatic hydrocarbons such as phenol, o-, m-, p-cresol, cymene, nitrobenzene, chlorobenzene, pyridine, anthracene or phenanthrene, myrcene, geraniol, thioterpineol, norbornane, borneol, isoborneol, bornane, camphor, limonene, terpinene, pinene, pinane, carene, phenol, aniline, anisole, furan, furfural, furfuryl alcohol, hydroxymethylfurfural, bishydroxymethylfuran and mixed fractions containing many such compounds, such as those from natural gas condensates, petroleum distillates or coke oven condensates, mixed fractions from the product streams of fluid catalytic crackers (FCC), steam crackers or Fischer-Tropsch synthesis plants, or more generally hydrocarbon-containing material streams from wood, natural gas, petroleum and coal processing.

[0022] The process for Si deposition is preferably carried out in an inert gas atmosphere, such as a nitrogen or argon atmosphere.

[0023] This process can be carried out in a conventional manner requiring routine adjustments that are common to those skilled in the art, as is otherwise customary for the deposition of silicon from silicon precursors.

[0024] The porous particles for the method according to the invention are preferably selected from the group comprising amorphous carbon in the form of hard carbon, soft carbon, mesocarbon microbeads, natural or synthetic graphite, single-walled and multi-walled carbon nanotubes and graphene, oxides such as silicon dioxide, aluminum oxide, silicon-aluminum mixed oxide, magnesium oxide, lead oxide and zirconium oxide, carbides such as silicon carbide and boron carbide, nitrides such as silicon nitride and boron nitride, and also other ceramic materials as may be described by the following 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, at least two coefficients a~g>0, and a*3+b*3+c*4+d*2+g*4≧e*3+f*2.

[0025] The ceramic material may be, for example, a binary, ternary, quaternary, pentanary, hexanary or heptanary compound. Ceramic materials having the following formula are preferred: 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 (wherein x = 0.1 to 20 and z = 0.1 to 20, and x*3+4≧z*3) Boron nitride oxide BN z O r (wherein z=0.1 to 1 and r=0.1 to 1, and 3≧r*2+z*3) Boron Carbonitride Oxide B x CN z O r (wherein x = 0.1 to 2, z = 0.1 to 1, and r = 0.1 to 1, and x*3+4≧r*2+z*3) Silicon carboxide Si x COz (wherein x = 0.1 to 2 and z = 0.1 to 2, and x*4+4≧z*2) Silicon carbonitride Si x CN z (wherein x = 0.1 to 3 and z = 0.1 to 4, and x*4+4≧z*3) Silicon boron carbonitride Si w B x CN z (wherein w=0.1 to 3, x=0.1 to 2, and z=0.1 to 4, and w*4+x*3+4≧z*3) Silicon borocarbonate Si w B x CO z (wherein w=0.10 to 3, x=0.1 to 2, and z=0.1 to 4, and w*4+x*3+4≧z*2) Silicon borocarbonitride 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, and z=0.1 to 3, and v*4+w*3+4≧x*3+z*2) and Aluminum borosilicocarbonitride oxide Al u B v Si x CN w O z (wherein 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, and u*3+v*3+x*4+4≧w*3+z*2).

[0026] Porous particles are measured by helium pycnometry and have a particle size of 0.1-7 g / cm 3 , and particularly preferably 0.3 to 3 g / cm 3 This is in line with the gravimetric capacity (mAh / cm) of a lithium-ion battery. 3 ) is advantageous in increasing the

[0027] Preferably, amorphous carbon, silicon dioxide, boron nitride, silicon carbide and silicon nitride or mixed materials based on these materials are used as porous particles, particularly preferred is the use of amorphous carbon, boron nitride and silicon dioxide.

[0028] The porous particles preferably have a diameter percentile d of ≧0.5 μm, particularly preferably ≧1.5 μm, most preferably ≧2 μm. 50 The diameter percentile d 50 is preferably ≦20 μm, particularly preferably ≦12 μm, most preferably ≦8 μm.

[0029] The volume-weighted particle size distribution of the porous particles 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, most preferably d 10 ≧0.6μm~d 90 ≦12.0 μm.

[0030] 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 diameter percentile d 10 is preferably ≧0.2 μm, particularly preferably ≧0.5, most preferably ≧1 μm.

[0031] The porous particles preferably have a diameter percentile d of ≧4 μm, particularly preferably ≧8 μm. 90 The diameter percentile d 90 is preferably ≦18 μm, particularly preferably ≦15, most preferably ≦13 μm.

[0032] 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.

[0033] The volume-weighted particle size distribution of the silicon-containing material 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.

[0034] The volume weighted particle size distribution of porous particles can be determined according to ISO 13320 by static laser scattering using the Mie model on a Horiba LA 950 measuring instrument using ethanol as the dispersion medium for the porous particles.

[0035] The particles may be, for example, in an isolated form or in a weakly agglomerated form. The porous particles are preferably not agglomerated, and preferably not agglomerated. Agglomeration generally means that, during the production of the porous particles, primary particles are first formed and then coalesce, and / or the primary particles are connected to each other, for example, via covalent bonds, thus forming agglomerates. The primary particles are usually isolated particles. Aggregates or isolated particles may form agglomerates. Agglomerates are loose accumulations of aggregates or primary particles connected to each other, for example, via van der Waals interactions or hydrogen bonds. Agglomerated agglomerates can be easily broken back into agglomerates by standard kneading and dispersion processes. Agglomerates can only partially, if at all, be broken 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 determining particle size distribution or particle size of matrix particles cannot distinguish between agglomerates and agglomerates.

[0036] The porous particles may have any desired morphology, i.e., for example, crushed, flaked, spherical, or needle-like, with crushed or spherical particles being preferred. The 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 has a value of 1. According to this definition, the porous particles for the method according to the 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.

[0037] Sphericity S is the ratio of the circumference of an equivalent circle having the same area A as the projection of the particle onto the surface to the measured circumference U of this projection.

number

[0038] 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 allows for high-capacity lithium-ion batteries. The gas-accessible pore volume was determined by gas sorption measurements with nitrogen according to DIN 66134.

[0039] The porous particles preferably have open pores. Open pores generally mean that the pores are connected to the surface of the particle, for example, via channels, and are preferably able to exchange mass with the environment, especially gaseous compounds. This can be demonstrated by gas sorption measurements (analysis by Brunauer, Emmett and Teller, "BET"), i.e., specific surface area. The porous particles preferably have a specific surface area of ​​≥ 100 m 2 / g, particularly preferably ≥ 500m 2 / g, particularly preferably ≥ 1000m 2 / g, most preferably ≥ 1500m 2 / g. The BET specific surface area is determined in accordance with DIN 66131 (with nitrogen).

[0040] The pores of the porous particles may have any desired diameter, i.e., generally within the range of macropores (greater than 50 nm), mesopores (2-50 nm), and micropores (less than 2 nm). Porous particles can be used in any desired mixture of different pore types. Preferably, porous particles having less than 30% macropores based on the total pore volume are used, particularly preferably porous particles having no macropores, and very particularly preferably porous particles having at least 50% pores with an average pore diameter of less than 5 nm. Very particularly preferably, the porous particles only have pores with a pore diameter of less than 2 nm (determination method: in the mesopore range, pore size distribution by BJH (gas adsorption) according to DIN 66134 and in the micropore range, pore size distribution by Horvath-Kawazoe (gas adsorption) according to DIN 66135; in the macropore range, pore size distribution is evaluated by mercury porosimetry according to DIN ISO 15901-1).

[0041] Preferably, 0.3 cm 3 / g, particularly preferably less than 0.15 cm 3 The porous particles have a gas-inaccessible pore volume of less than 1 / g. This can also increase the capacity of lithium-ion batteries. The gas-inaccessible pore volume can be determined using the following formula: Gas inaccessible pore volume = 1 / pure material density - 1 / skeletal density.

[0042] Pure material density is the theoretical density of a porous particle based on the phase composition or density of the pure material (the density of the material as if it had no closed pores). Pure material density data can be found by those skilled in the art, for example, at 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 2.20 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 / cm 3 Skeletal density is the actual density of the porous particles (gas accessible) determined by helium pycnometry.

[0043] For clarity, please note that porous particles are different from silicon-containing materials.Porous particles act as the starting material for producing silicon-containing materials.Preferably, there is no silicon located in the pores of porous particles and on the surface of porous particles, more specifically, there is no silicon that is obtained by depositing silicon precursors.

[0044] The silicon-containing material obtainable by depositing silicon in the pores and on the surface of porous particles by the method according to the invention preferably has a diameter percentile d in the range of 0.5 to 20 μm. 50 The particle size distribution has a volume weighted value of d 50 A value of at least 1.5 μm is preferred, and at least 2.0 μm is particularly preferred. Diameter percentile d 50 is preferably at most 13 μm, particularly preferably at most 8 μm.

[0045] The volume weighted particle size distribution of the silicon-containing material 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, most preferably d 10 ≧0.6μm~d 90 ≦12.0 μm.

[0046] The silicon-containing material preferably has a diameter percentile d of ≦10 μm, particularly preferably ≦5 μm, particularly preferably ≦3 μm, most preferably ≦1 μm. 10 The diameter percentile d 10 is preferably ≧0.2 μm, particularly preferably ≧0.4 μm, most preferably ≧0.6 μm.

[0047] The silicon-containing material preferably has a diameter percentile d of ≧5 μm, particularly preferably ≧10 μm. 90 The diameter percentile d 90 is preferably ≦20 μm, particularly preferably ≦15 μm, most preferably ≦12 μm.

[0048] The volume-weighted particle size distribution of the silicon-containing material preferably has a width d of ≦15.0 μm, particularly preferably ≦12.0 μm, more preferably ≦10.0 μm, particularly preferably ≦8.0 μm, most preferably ≦4.0 μm. 90 -d 10 The volume-weighted particle size distribution of the silicon-containing material preferably has a width d of ≧0.6 μm, particularly preferably ≧0.8 μm, most preferably ≧1.0 μm. 90 -d 10 It has.

[0049] The silicon-containing material is preferably in the form of particles.Particles can be in isolated form or weakly agglomerated form.The silicon-containing material is preferably not agglomerated, and preferably not agglomerated.The terms isolated, agglomerated and non-agglomerated have already been further defined above with respect to porous particles.The existence of the silicon-containing material in the form of agglomerates or weakly agglomerates can be visualized, for example, by using a conventional scanning electron microscope (SEM).

[0050] The silicon-containing material may have any desired morphology, ie, for example, crushed, flaked, spherical, or acicular, with crushed or spherical particles being preferred.

[0051] 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 has a value of 1. According to this definition, the silicon-containing material obtainable by the method according to the 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.

[0052] Sphericity S is the ratio of the circumference of an equivalent circle having the same area A as the projection of the particle onto the surface to the measured circumference U of this projection.

number

[0053] The cycling stability of lithium-ion batteries can be further enhanced by the morphology, material composition, and especially the specific surface area or internal porosity of silicon-containing materials.

[0054] The silicon-containing material contains porous particles in an amount of preferably 10% by weight to 90% by weight, more preferably 20% by weight to 80% by weight, particularly preferably 30% by weight to 60% by weight, and particularly preferably 40% by weight to 50% by weight, based on the total weight of the silicon-containing material.

[0055] The silicon-containing material preferably contains 10 to 90% by weight, more preferably 20 to 80% by weight, particularly preferably 30 to 60% by weight, and particularly preferably 40 to 50% by weight of silicon obtained by deposition from a silicon precursor, based on the total weight of the silicon-containing material (preferably determined by elemental analysis such as ICP-OES).

[0056] When the porous particles comprise a silicon compound, for example in the form of silicon dioxide, the weight percent values ​​stated above can be determined for silicon obtained by deposition from a silicon precursor by subtracting the mass of silicon of the porous particles, as determined by elemental analysis, from the mass of silicon of the silicon-containing material, as determined by elemental analysis, and dividing the result by the mass of the silicon-containing material.

[0057] The volume of silicon present in the silicon-containing material and obtained via deposition from a silicon precursor is determined by the density of silicon (2.336 g / cm 3 The mass fraction of silicon obtained via deposition from a silicon precursor in the total mass of silicon-containing material divided by the mass fraction of silicon obtained via deposition from a silicon precursor.

[0058] The pore volume P of a silicon-containing material is the sum of the gas-accessible pore volume and the gas-inaccessible pore volume. The Gurwitsch gas-accessible pore volume of a silicon-containing material can be determined by gas sorption measurements using nitrogen according to DIN 66134.

[0059] The gas inaccessible pore volume of a silicon-containing material can be determined using the following formula: Gas inaccessible pore volume = 1 / pure material density - 1 / skeletal density.

[0060] The pure material density of silicon-containing material is the theoretical density that can be calculated from the sum of the theoretical pure material densities of the components present in the silicon-containing material multiplied by the weight-related percentage of each of the total materials. For example, in the case of a silicon-containing material in which silicon is deposited on porous particles, this results in: Pure material density = theoretical pure material density of silicon * silicon percentage (wt%) + theoretical pure material density of porous particles * porous particle percentage (wt%).

[0061] The pore volume P of the silicon-containing material is in the range of 0 vol. % to 400 vol. %, preferably in the range of 100 vol. % to 350 vol. %, particularly preferably in the range of 200 vol. % to 350 vol. %, based on the volume of silicon present in the silicon-containing material and obtained from deposition from the silicon precursor.

[0062] The pores present in the silicon-containing material may be gas-accessible or gas-inaccessible. The volume ratio of gas-accessible pores to gas-inaccessible pores in the silicon-containing material can generally be in the range of 0 (no gas-accessible pores) to 1 (all pores are gas-accessible). The volume ratio of gas-accessible pores to gas-inaccessible pores in the silicon-containing material is preferably in the range of 0 to 0.8, particularly preferably in the range of 0 to 0.3, and particularly preferably in the range of 0 to 0.1.

[0063] The pores of the silicon-containing material can have any desired diameter, for example, within the range of macropores (>50 nm), mesopores (2-50 nm), and micropores (<2 nm). The silicon-containing material can also contain any desired mixture of different pore types. Preferably, the silicon-containing material contains up to 30% macropores based on the total pore volume, with silicon-containing materials without macropores being particularly preferred, and silicon-containing materials with at least 50% pores based on the total pore volume having an average pore diameter of less than 5 nm are very particularly preferred. Particularly preferably, the silicon-containing material only has pores with a diameter of up to 2 nm.

[0064] The silicon-containing material preferably has silicon structures with a structure size of at most 1000 nm, more preferably less than 100 nm, particularly preferably less than 5 nm in at least one dimension (determination method: scanning electron microscopy (SEM) and / or high-resolution transmission electron microscopy (HR-TEM)).

[0065] The silicon-containing material preferably comprises a silicon layer having a layer thickness of less than 1000 nm, more preferably less than 100 nm, particularly preferably less than 5 nm (determination method: scanning electron microscope (SEM) and / or high-resolution transmission electron microscope (HR-TEM)). The silicon-containing material may also contain silicon in the form of particles. The silicon particles preferably have a diameter of at most 1000 nm, more preferably less than 100 nm, particularly preferably less than 5 nm (determination method: scanning electron microscope (SEM) and / or high-resolution transmission electron microscope (HR-TEM)). Here, the data on the silicon particles preferably relate to the diameter of the circumference of the particle in the microscopic image.

[0066] Furthermore, the silicon deposited from the silicon precursor in the silicon-containing material may contain a dopant selected from the group including, 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, or combinations thereof. Lithium and / or tin are preferred. The content of the dopant in the silicon-containing material is preferably at most 1 wt%, particularly preferably at most 100 ppm, based on the total weight of the silicon-containing material, as can be determined by ICP-OES.

[0067] Silicon-containing materials generally exhibit surprisingly high stability under compressive load and / or shear stress. The compressive load stability and shear stability of silicon-containing materials are evident, for example, from the fact that silicon-containing materials have little, if any, change in their porous structure in SEM under compressive load (e.g., during electrode compression) and shear stress (e.g., during electrode preparation).

[0068] The silicon-containing material may optionally contain additional elements such as carbon. Preferably, the carbon is in the form of a thin layer with a layer thickness of at most 1 μm, preferably less than 100 nm, particularly preferably less than 5 nm, and very particularly preferably less than 1 nm (measurable by SEM or HR-TEM). The carbon layer can be present here both in the pores and on the surface of the silicon-containing material. The order of different layers in the silicon-containing material is also arbitrary. Thus, first, a layer of an additional material different from the porous particle, such as carbon, may be present on the porous particle, and then a layer of silicon or silicon particles may be present on top of it. Similarly, regardless of whether a layer of a material different from the material of the porous particle is present between the porous particle and the silicon layer or layer made of silicon particles, a layer of an additional material may be present on the silicon layer or layer of silicon particles, which may be different from or identical to the material of the porous particle.

[0069] The silicon-containing material preferably contains ≦50 wt%, particularly preferably ≦40 wt%, particularly preferably ≦20 wt% of additional elements.The silicon-containing material preferably contains ≧1 wt%, particularly preferably ≧3 wt%, particularly preferably ≧2 wt% of additional elements.The weight percentage refers to the total weight of the silicon-containing material.In an alternative embodiment, the silicon-containing material does not contain any additional elements.

[0070] In the second step, some of the deposited silicon from the silicon-containing material is removed by etching off. Here, excess silicon, also known as coarse silicon, is removed. Fine silicon is desired and remains on and within the etched silicon-containing material.

[0071] Preferably, the amount of excess silicon in the deposited silicon after etching is less than 3% by weight, particularly preferably less than 1% by weight, particularly preferably less than 0.1% by weight.

[0072] The fine and coarse silicon in a sample can be determined by TGA measurement based on the reaction of silicon with oxygen to form SiO2. The distinguishability of different silicon species can be explained by the fact that thin silicon layers show a higher reactivity to oxygen than thick layers or Si particles. This has the consequence that thin Si layers react (gain in mass) even at low temperatures (400-650°C), while thick layers / coarse silicon structures only show a reaction at temperatures above 700°C. Ideally, silicon-containing composites used as anode active materials show no mass increase in TGA measurements in oxygen-containing atmospheres at temperatures above 800°C. This method also allows for the determination of the elemental silicon content. Silicon previously oxidized and passivated by contact with air no longer participates in the reaction and is therefore not considered in the TGA measurement.

[0073] To calculate the coarse silicon present, the residual mass (mres) from the TGA method and the mass difference (mdiff) due to oxidation of the coarse silicon are required. Using the molar mass of O (32 g / mol) and the molar mass of SiO (60.08 g / mol), the percentage of coarse silicon in the deposited silicon can be calculated by the following formula:

number

[0074] If it is desired to calculate the excess silicon of the material, the percentage of coarse silicon must be multiplied by the percentage of deposited silicon of the material.

[0075] Silicon can be removed from surfaces industrially in many ways. Liquid or gaseous etching media are particularly suitable for this purpose. For liquid etching media, on the one hand, wet chemical routes based on HF under oxidizing conditions (for example, HNO3 and acetic acid - HNA, as a mixture with CP4) have been established, while on the other hand, basic solutions such as KOH, tetramethylammonium hydroxide (TMAH), NaOH, LiOH, CsOH, NH4OH, Mg(OH)2, Ca(OH)2, Ba(OH)2, ethylenediamine (ED) are also used. A Wet chemical treatments using solutions containing ethylenediaminetetraacetic acid (ETA) have also been established. These wet chemical etching procedures can be carried out at room temperature (25°C), but can also be carried out at elevated temperatures below the boiling point of the solution to accelerate the reaction. In addition to increasing the temperature, energy can also be introduced into the system via microwave or ultrasonic treatment. Etching processes below room temperature (<25°C) are also contemplated.

[0076] In addition to wet-chemical etching processes, etching processes via the gas phase are also known, in which, for example, XeF2 or SF6 can be used as gaseous etching medium and a plasma is induced.

[0077] Etching can be carried out either iteratively (starving of etching medium) while monitoring the content of rough silicon, or by adjusting the etching to the amount of rough silicon (calculated amount of etching medium).

[0078] After etching, the etched silicon-containing material is preferably washed with a washing medium, preferably water.

[0079] After washing, the etched silicon-containing material is preferably separated from the washing medium and dried.

[0080] The etched silicon-containing material is preferably at most 80 m 2 / g, particularly preferably 30m 2 / g, particularly preferably less than 10m2 / g。 The BET specific surface area is determined according to DIN 66131 (using nitrogen). Therefore, when the silicon-containing material is used as an active material for the anode of a lithium-ion battery, SEI formation can be reduced and the initial coulomb efficiency can be increased.

[0081] The present invention further provides the use of the etched silicon-containing material as an active material in an anode material for a lithium-ion battery anode, and the use of such an anode for manufacturing a lithium-ion battery.

[0082] The anode material is preferably based on a mixture comprising an etched silicon-containing material obtainable by the method according to the invention, one or more binders, optionally graphite as further active material, optionally one or more further conductive components, and optionally one or more additives.

[0083] The use of an additional conductive component in the anode material can reduce the contact resistance within the electrode and between the electrode and the current collector, thereby improving the current-carrying capacity of the lithium-ion battery according to the invention. Preferred additional conductive components are, for example, conductive carbon black, carbon nanotubes or metal particles, such as copper.

[0084] The anode material preferably contains 0% to 95% by weight, particularly preferably 0% to 40% by weight, and most preferably 0% to 25% by weight of one or more further conductive components, based on the total weight of the anode material.

[0085] The etched silicon-containing material may be present in the anode for a lithium-ion battery to the extent of preferably 5% to 100% by weight, particularly preferably 30% to 100% by weight, and most preferably 60% to 100% by weight, based on all active materials present in the anode material.

[0086] Preferred binders are polyacrylic acid or its alkali metal salts, especially lithium or sodium salts, polyvinyl alcohol, cellulose or cellulose derivatives, polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, polyimides, especially polyamide-imides, or thermoplastic elastomers, especially ethylene-propylene-diene terpolymers. Alkali metal salts of the aforementioned binders, especially lithium or sodium salts, are also particularly preferred. All or, preferably, some of the acid groups of the binder may be in the form of a salt. The binder preferably has a molar mass of 100,000 to 1,000,000 g / mol. Mixtures of two or more binders may also be used.

[0087] The graphite used can typically be natural or synthetic graphite. The graphite particles preferably have a diameter percentile d 10 >0.2μm~d 90 <200 μm.

[0088] Examples of additives are pore formers, dispersants, levelling agents or dopants such as elemental lithium.

[0089] A preferred formulation for the anode material preferably contains 5 wt. % to 95 wt. % silicon-containing material, 0 wt. % to 90 wt. % further conductive component, 0 wt. % to 90 wt. % graphite, 0 wt. % to 25 wt. % binder, and 0 wt. % to 80 wt. % additive, the weight percentages referring to the total weight of the anode material and the percentages of all components of the anode material adding up to 100 wt. %.

[0090] The components of the anode material are preferably processed into an anode ink or paste, preferably using a rotor-stator machine, a high-energy mill, a planetary kneader, an agitator bead mill, a vibrating plate, or an ultrasonic device, in a solvent preferably selected from the group including water, hexane, toluene, tetrahydrofuran, N-methylpyrrolidone, N-ethylpyrrolidone, acetone, ethyl acetate, dimethyl sulfoxide, dimethylacetamide, and ethanol, and mixtures of these solvents.

[0091] The anode ink or paste preferably has a pH of 2 to 8.5 (at 20° C., measured, for example, using a WTW pH340i pH meter equipped with a SenTix RJD probe).

[0092] The anode ink or paste can be applied to a copper foil or another current collector, for example, by a doctor blade. Other coating processes, such as spin coating, roller coating, dip or slot die coating, painting or spraying, can also be used in accordance with the present invention.

[0093] Before coating the copper foil with the anode material according to the invention, the foil can be treated with a commercially available primer, for example based on a polymer resin or silane, which can provide improved adhesion to the copper but which generally has no substantial electrochemical activity itself.

[0094] The anode material is usually dried to a constant weight. The drying temperature depends on the components and solvent used. The drying temperature is preferably between 20°C and 300°C. The layer thickness, i.e., the dry layer thickness of the anode coating, is preferably between 2 and 500 μm.

[0095] Finally, the electrode coating may be calendered to set a defined porosity. The electrode thus produced preferably has a porosity of 15% to 85%, which can be measured by mercury porosimetry according to DIN ISO 15901-1. Preferably, 25% to 85% of the pore volume thus determined is provided by pores with diameters of 0.01 to 2 μm.

[0096] The present invention further provides a lithium-ion battery comprising a cathode, an anode containing an etched silicon-containing material, two conductive connections to the electrodes, a separator, an electrolyte in which the separator and the two electrodes are impregnated, and a housing to contain the above components.

[0097] In the context of the present invention, the term lithium-ion battery also encompasses cells. A cell generally comprises a cathode, an anode, a separator, and an electrolyte. In addition to one or more cells, a lithium-ion battery preferably further comprises a battery management system. A battery management system is generally used to control the battery, for example using electronic circuits, in particular to detect the state of charge, and for over-discharge or over-charge protection.

[0098] Preferred cathode materials for use in accordance with the present invention may be lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide (doped or undoped), lithium manganese oxide (spinel), lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium vanadium phosphate, or lithium vanadium oxide.

[0099] The separator is generally an electrically insulating, ion-permeable membrane, preferably made of polyolefin, such as polyethylene (PE) or polypropylene (PP), or polyester or a corresponding laminate. Alternatively, as is customary in battery manufacturing, the separator may consist of or be coated with a glass or ceramic material. As is known, the separator separates the first electrode from the second electrode, thus preventing a conductive connection (short circuit) between the electrodes.

[0100] The electrolyte is preferably a solution containing one or more lithium salts (=conductive salts) in an aprotic solvent. The conductive salts are preferably selected from the group consisting of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium perchlorate, lithium tetrafluoroborate, lithium imide, lithium methide, lithium trifluoromethanesulfonate, LiCF3SO3, lithium bis(trifluoromethanesulfonimide)LiN(CF3SO2)2, and lithium borate. The concentration of the conductive salt, based on the solvent, is preferably between 0.5 mol / l and the solubility limit of the salt in question. Particularly preferably, the concentration is between 0.8 and 1.2 mol / l.

[0101] The solvents used are preferably cyclic carbonates, propylene carbonate, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxyethane, diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, acetonitrile, organic carbonates or nitriles, used individually or as mixtures thereof.

[0102] The electrolyte preferably contains a film-forming agent such as vinylene carbonate or fluoroethylene carbonate. As a result, it is possible to achieve a significant improvement in the cycling stability of anodes containing etched silicon-containing materials obtained by the method of the present invention. This is mainly due to the formation of a solid-electrolyte interfacial interface on the surface of the active particles. The proportion of the film-forming agent in the electrolyte is preferably between 0.1% and 20.0% by weight.

[0103] In order to best match the actual capacities of the electrodes of a lithium-ion cell to one another, it is advantageous to balance the materials of the positive and negative electrodes with respect to their absolute capacities. Particularly important in this context is the fact that during the first or initial charge / discharge cycle (known as activation) of a secondary lithium-ion cell, a coating layer forms on the surface of the electrochemically active material in the anode. This coating layer, called the "solid electrolyte interphase" (SEI), generally consists primarily of electrolyte decomposition products and a certain amount of lithium, and is therefore no longer available for further charge / discharge reactions. The thickness and composition of the SEI depend on the anode material used and the type and quality of the electrolyte solution used.

[0104] In the case of graphite, the SEI is particularly thin. Graphite typically loses 5% to 35% of its mobile lithium during the first charging step, resulting in a corresponding decrease in the reversible capacity of the battery.

[0105] In the case of an anode having an etched silicon-containing active material obtained by the method according to the invention, there is preferably a loss of mobile lithium of at most 30%, particularly preferably at most 20%, most preferably at most 10% in the first charging step, which is much lower than the values ​​described in the prior art such as US 10,147,950 B1.

[0106] All of the substances and materials utilized in the manufacture of such lithium ion batteries as described above are known, and the manufacture of the components of such batteries and their assembly to form the batteries is carried out according to methods known in the art of battery manufacturing.

[0107] The etched silicon-containing material obtained by the method of the present invention is characterized by significantly improved electrochemical behavior, resulting in lithium-ion batteries with high volumetric capacity and excellent performance characteristics. The etched silicon-containing material obtained by the method of the present invention is permeable to lithium ions and electrons, thus enabling charge transport. The SEI in lithium-ion batteries can be significantly reduced by the etched silicon-containing material obtained by the method of the present invention. In addition, due to the design of the etched silicon-containing material obtained by the method of the present invention, the SEI peels off from the surface of the active material, if at all, at least to a much lesser extent. All of this results in high cycle stability of the corresponding lithium-ion battery, the anode of which contains the etched silicon-containing material obtained by the method of the present invention.

[0108] The following examples serve to further elucidate the invention described herein.

[0109] The following analytical methods and instruments were used for characterization:

[0110] <Scanning electron microscopy (SEM / EDX)> Microscopic analysis was performed using a Zeiss Ultra 55 scanning electron microscope and an energy-dispersive Oxford X-Max 80N X-ray spectrometer. Prior to analysis, the samples were subjected to carbon deposition using a Safematic Compact Coating Unit 010 / HV to prevent charging phenomena. Cross sections of the silicon-containing materials were prepared using a Leica TIC 3X ion cutter at 6 kV.

[0111] <Inorganic analysis / elemental analysis> The C content reported in the examples was determined using a Leco CS230 analyzer. For the determination of O and, where appropriate, N or H content, a Leco TCH-600 analyzer was used. Qualitative and quantitative determination of the other reported elements was carried out by ICP (inductively coupled plasma) optical emission spectrometry (Optima 7300 DV, Perikin Elmer). For this purpose, the samples were subjected to acid digestion (HF / HNO3) in a microwave (Microwave 3000, manufactured by Anton Paar). ICP-OES determinations were guided by ISO 11885 ("Water quality - Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES) (ISO 11885:2007), German version of EN ISO 11885:2009"), which is used for the analysis of acidic aqueous solutions (e.g., acidified drinking water, wastewater, and other water samples, as well as aqua regia extracts of soil and sediment).

[0112] <Determination of particle size> In the context of the present invention, the particle size distribution was determined in accordance with ISO 13320 by static laser scattering using a Horiba LA 950. In the preparation of the samples, special attention must be paid to dispersing the particles in the measuring solution to ensure that what is measured is the size of the individual particles and not the size of weakly aggregated particles. For the measurement, the particles were dispersed in ethanol. For this purpose, prior to measurement, if necessary, the dispersion was treated with ultrasound at 250 W for 4 minutes in a Hielscher UIS250v laboratory ultrasonic device equipped with an LS24d5 sonotrode.

[0113] <BET specific surface area measurement> The specific surface area of the material was measured by the BET method (determination according to DIN ISO 9277:2003-05 using nitrogen) by gas adsorption with nitrogen using a Sorptomatic 199090 device (Porotec) or a SA-9603MP device (Horiba).

[0114] <Skeletal Density> The skeletal density, i.e. the density of the porous solid based on the volume of the external gas-accessible pore space only, was determined by He pycnometry according to DIN 66137-2.

[0115] <Gas-accessible pore volume> The Gurwitsch gas-accessible pore volume was determined by gas sorption measurements with nitrogen according to DIN 66134.

[0116] Thermogravimetric analysis (TGA) and determination of coarse silicon The reactivity of the powders towards oxygen was determined by TGA measurements in pure oxygen in the temperature window of 25-1000°C using a heating rate of 5 K / min.

[0117] The following materials and equipment were used in carrying out the examples:

[0118] The SiH4 used, quality 4.0, was obtained from Linde GmbH.

[0119] <Porous particles used> Porous carbon particles with the following characteristics were used: BET specific surface area: 2140m 2 / g Gurvich PV:1.01cm 3 / g [Example]

[0120] Comparative Example 1: Production of over-infiltrated Si / C composite

[0121] <Production of silicon-containing materials using monosilane SiH4 as a silicon precursor>

[0122] In step 1, the autoclave was charged with 10.04 g of porous material and closed. In step 2, the autoclave was first evacuated. Then, 16.6 g of SiH4 was added at a pressure of 15.5 bar. In step 3, the autoclave was heated to a temperature of 420°C over 2.5 hours, and in step 4, this temperature was maintained for 60 minutes. In step 5, the autoclave was cooled to room temperature over 12 hours. After cooling, a pressure of 37.6 bar remained in the autoclave. In step 6, the pressure in the autoclave was reduced to 1 bar, and then purged five times with nitrogen, five times with lean air having an oxygen content of 5%, five times with lean air having an oxygen content of 10%, and then five times with air. In step 7, 22 g of silicon-containing material was isolated in the form of a black, finely divided solid. The silicon content was 57.5% by weight.

[0123] Example 2: (BeS06956) Removal of excess silicon by etching with sodium hydroxide solution in an amount tailored to the coarse silicon content

[0124] First, 0.2 g of NaOH in 99.8 ml of demineralized water was placed in a 250 ml round-bottom flask, and 9 g of the material from Example 1 was gradually added. The resulting suspension was stirred in a water bath at 40 °C for 10 minutes and then passed through a paper filter (filter paper 413, VWR). The powder thus obtained was then suspended in 200 ml of water and again isolated by filtration. This procedure was repeated until the pH of the resulting filtrate was 8.0. The resulting filter cake was dried to constant weight at 80 °C in a drying cabinet.

[0125] The properties of the processed Si composite are shown in Table 1 (excess silicon 0.0 wt%, BET specific surface area 64 m 2 / g). The silicon content was 48.0 wt%.

[0126] [Examples 3, 4, and 6: Electrochemistry of Comparative Examples 1 and 2, and Comparative Example 5]

[0127] Electrochemical characterization of silicon-containing materials used as active materials in lithium-ion battery anodes

[0128] 29.71 g of polyacrylic acid (dried to constant weight at 85 °C, Sigma-Aldrich, M w Polyacrylic acid (approximately 450,000 g / mol) and 756.6 g of deionized water were stirred on a shaker (290 L / min) for 2.5 hours until the polyacrylic acid was completely dissolved. Lithium hydroxide monohydrate (Sigma-Aldrich) was added in small portions to the solution until the pH reached 7.0 (measured using a WTW pH340i pH meter and a SenTix RJD probe). The solution was then mixed on a shaker for an additional 4 hours.

[0129] 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 in a planetary mixer (SpeedMixer, DAC 150 SP) at 2000 rpm. Then, 3.40 g of the silicon-containing material from Example 1 or Example 2 was added and stirred at 2000 rpm for 1 minute. Subsequently, 1.21 g of an 8% conductive carbon black dispersion and 0.8 g of deionized water were added and charged into the planetary mixer at 2000 rpm. This was followed by dispersion in a dissolver at 3000 rpm for 30 minutes at a constant temperature of 20°C. The ink was again degassed in the planetary mixer at 1500 rpm for 5 minutes. The finished dispersion was then applied to a copper foil (Schlenk Metallfolien, SE-Cu58) having a thickness of 0.03 mm using a film stretching frame (Erichsen, Model 360) with a gap clearance of 0.1 mm. The anode coating thus produced was then dried for 60 minutes at 50°C and 1 bar air pressure. The average basis weight of the dried anode coating was 1.9 mg / cm. 2 and the coating density is 0.9 g / cm 3 It was.

[0130] Electrochemical studies were carried out in a two-electrode button cell (CR2032 type, Hosen). The electrode coating was used as the counter electrode or negative electrode (Dm = 15 mm). The content was 94.0% and the concentration was 15.9 mg / cm.2 A lithium-nickel-manganese-cobalt oxide 6:2:2 based coating (obtained from SEI) with an average basis weight of 1000 kJ / cm2 was used as the working electrode or 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). The water content in the dry matter of all components used was less than 20 ppm.

[0131] Electrochemical testing was performed at 20°C. The cells were charged using the cc / cv (constant current / constant voltage) method at a constant current of 12 mA / g (corresponding to C / 10) for the first cycle and 60 mA / g (corresponding to C / 2) for subsequent cycles. After reaching a voltage limit of 4.2 V, the cells were charged at a constant voltage until the current dropped below 1.2 mA / g (corresponding to C / 100) or 15 mA / g (corresponding to C / 8). The cells were discharged using the cc (constant current) method at a constant current of 12 mA / g (corresponding to C / 10) for the first cycle and 60 mA / g (corresponding to C / 2) for subsequent cycles until a voltage limit of 2.5 V was reached. The specific current selected was based on the weight of the coating on the positive electrode. The ratio of the charge capacity to the discharge capacity of the cell is called the coulombic efficiency. The electrodes were selected to establish a cathode:anode capacitance ratio of 1:1.2.

[0132] Comparative Example 5: Excessive removal of excess silicon by etching with sodium hydroxide solution in an amount tailored to the coarse silicon content

[0133] First, 0.4 g of NaOH in 99.8 ml of demineralized water was placed in a 250 ml round-bottom flask, and 6.05 g of the material from Example 1 was gradually added. The resulting suspension was stirred in a water bath at 40°C for 10 minutes and then passed through a paper filter (filter paper 413, VWR). The powder thus obtained was then suspended in 200 ml of water and again isolated by filtration. This procedure was repeated until the pH of the resulting filtrate was 8.0. The resulting filter cake was dried to constant weight at 80°C in a drying cabinet.

[0134] The properties of the processed Si composite are shown in Table 1 (excess silicon 0.0 wt%, BET specific surface area 170 m 2 / g). The silicon content was 41.6 wt%.

[0135] [Table 1]

Claims

1. 1. A method for producing an etched silicon-containing material, comprising: In the first step, a silicon precursor is pyrolyzed onto the porous particles to form a silicon dioxide film having a thickness of ≥ 100 m, determined according to DIN 66131. ２ depositing silicon in the pores and on the surfaces of the porous particles having a specific surface area of ​​1 / g or more to form a silicon-containing material; In a second step, a portion of the deposited silicon of the silicon-containing material is removed by etching off; the surface area of ​​the etched silicon-containing material is less than 80 m 2 / g; The method wherein the amount of coarse silicon in the deposited silicon after etching is less than 1 wt %.

2. 2. The method of claim 1, wherein a liquid or gaseous etching medium is used in the second step.

3. 3. The method according to claim 1, wherein the etching off is carried out by wet chemical treatment using a basic solution.

4. The basic solution may be KOH, tetramethylammonium hydroxide (TMAH), NaOH, LiOH, CsOH, NH ４ OH, Mg(OH) ２ , Ca(OH) ２ , Ba(OH) ２ , ethylenediamine (EDA).

5. In the second step, a portion of the deposited silicon of the silicon-containing material, referred to as coarse silicon, is removed by etching off, leaving silicon, referred to as fine silicon, on top of the etched silicon-containing material; The method according to any one of claims 1 to 4, wherein before said etching off, the rough silicon to be etched off is determined as follows: The reactivity of the powders towards oxygen was determined and calculated by TGA (thermogravimetric analysis) measurements in pure oxygen in the temperature range 25-1000°C using a heating rate of 5 K / min; (mres) is the residual mass after performing TGA; (mdiff) is the mass difference resulting from oxidation of coarse silicon at temperatures above 700°C; O ２ molar mass (32 g / mol) and SiO ２ Using the molar mass (60.08 g / mol) of the silicon dioxide, the proportion of coarse silicon in the deposited silicon was calculated according to the formula shown in Equation 1: [Equation 1] Silicon in the "coarse silicon" category exhibits a reaction in the TGA above 700°C.

6. The method according to any one of claims 1 to 5, wherein after etching the etched silicon-containing material is washed with a washing medium, separated from the washing medium and dried.

7. 7. The method according to claim 1, wherein amorphous carbon, silicon dioxide, boron nitride, silicon carbide and silicon nitride, or mixed materials based on these materials, are used as porous particles.

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