Method for manufacturing carbon-coated silicon particles

Abstract

The subject of this invention is a method for producing unaggregated, carbon-coated silicon particles by preparing a dry mixture by mixing silicon particles with polyacrylonitrile in solid form, the silicon particles having an average particle size d50 of 1 to 15 pm and containing <10 wt% carbon and >90 wt% silicon based on the total weight of the carbon-coated silicon particles, characterized in that the polyacrylonitrile in solid form in the dry mixture undergoes thermal decomposition with the formation of a gaseous carbon precursor, and the gaseous carbon precursor thus formed is carbonized in the presence of the silicon particles by a CVD (chemical vapor deposition) technique.

Description

Technical Field

[0001] This invention relates to a method for producing carbon-coated silicon particles and also to a method for producing lithium-ion batteries. Background Technology

[0002] Among commercially available electrochemical energy storage components, rechargeable lithium-ion batteries currently possess the highest specific energy, reaching up to 250 Wh / kg. The anode material used in practice is currently primarily graphite carbon. However, graphite has a relatively low theoretical electrochemical capacity of 372 mAh / g, corresponding to only about one-tenth of the theoretically achievable electrochemical capacity with lithium metal. In contrast, silicon has the highest known lithium-ion storage capacity at 4199 mAh / g. Disadvantageously, silicon-containing electrode active materials undergo extreme volume changes of up to approximately 300% when charged or discharged with lithium. This volume change results in strong mechanical stress on the active material and the entire electrode structure, which leads to loss of electrical contacts through electrochemical wear, and thus electrode damage and capacity loss. Furthermore, the surface of the silicon anode material used reacts with the electrolyte components to continuously form a passivation protective layer (solid electrolyte interface; SEI), which leads to irreversible loss of mobile lithium.

[0003] To address these issues, numerous studies have recommended carbon-coated silicon particles as active materials for the anodes of lithium-ion batteries. For example, Liu, Journal of The Electrochemical Society, 2005, 152(9), pp. A17198–A1725, describes carbon-coated silicon particles with a high carbon content of 27% by weight. Ogumi, Journal of The Electrochemical Society, 2002, 149(12), pp. A1598–A1603, describes silicon particles coated with 20% by weight carbon. JP2002151066 reports carbon content ranging from 11% to 70% by weight for carbon-coated silicon particles. Yoshio, Chemistry Letters, 2001, pp. 1186–1187 describes coated particles containing 20% ​​by weight carbon and having an average particle size of 18 µm. The carbon coating has a layer thickness of 1.25 µm. Disclosed by N.-L. Wu, Electrochemical and Solid-State Letters, 8(2), 2005, pages A100 to A103, are carbon-coated silicon particles having a carbon content of 27% by weight.

[0004] JP2004-259475 teaches a method for coating silicon particles with a non-graphite carbon material and optionally graphite, followed by carbonization, with the coating process repeated multiple times during carbonization. Furthermore, JP2004-259475 reports the use of non-graphite carbon materials and any graphite in suspension form for surface coatings. Such process measures are known to result in aggregated carbon-coated silicon particles. US8394532 also produces carbon-coated silicon particles from dispersions. For the starting material (based on silicon), 20% carbon fiber by weight is specified.

[0005] EP1024544 relates to silicon particles having a surface completely covered by a carbon layer. However, it only specifically discloses aggregated carbon-coated silicon particles, as illustrated by examples of the average particle size of reference silicon and products. As carbon precursors, EP1024544 mentions polymers such as phenolic resins, imide resins, resins of aromatic sulfonates, pitch or tar, or alternative low molecular weight hydrocarbons such as benzene, toluene, naphthalene, phenol, methane, ethane, or hexane. EP2919298 teaches a method for producing Si / C composite materials from a mixture comprising silicon particles and a predominantly polymer (such as polyvinyl chloride), wherein the polymer is first melted and then pyrolyzed, and finally the pyrolysis product is ground, resulting in aggregated particles. US2016 / 0104882 relates to composite materials in which multiple silicon particles are embedded in a carbon matrix. Therefore, these individual carbon-coated silicon particles are in the form of aggregates.

[0006] US2009 / 0208844 describes silicon particles with a carbon coating comprising a conductive, elastic carbon material, specifically expanded graphite. This document discloses silicon particles with expanded graphite particles attached to their surface in granular form by the carbon coating. No process-related references for producing non-aggregated carbon-coated silicon particles can be found in US2009 / 0208844. US2012 / 0100438 contains porous silicon particles with a carbon coating; however, it makes no specific statement regarding the production of the coating or the carbon-to-silicon ratio in the particles. WO2018 / 082880, for the production of carbon-coated silicon particles, describes a CVD (chemical vapor deposition) method in which a hydrocarbon having 1 to 10 carbon atoms is used as the carbon precursor, and the silicon particles remain in motion during the CVD process. Alternatively, in WO2014 / 082880, a dry mixture of silicon particles and a polymeric carbon precursor is heated until the polymeric carbon precursor is completely melted, and only at this point is the molten polymeric carbon precursor carbonized. For the production of anodes, EP1054462 teaches that current collectors are coated with silicon particles and binders and then carbonized.

[0007] In this context, one objective is to provide a method for modifying silicon particles, thereby enabling the use of active materials for the anode of lithium-ion batteries, wherein the method enables the lithium-ion batteries to have high initial reversible capacity and, in addition, stable electrochemical behavior and minimal decrease (degradation) of reversible capacity in subsequent cycles. Summary of the Invention

[0008] This invention provides a method for producing non-aggregated carbon-coated silicon particles by means of a dry mixture of mixed silicon particles and polyacrylonitrile in solid form, the silicon particles having an average particle size d from 1 to 15 µm. 50 It contains ≤10 wt% carbon and ≥90 wt% silicon (each based on the total weight of the silicon particles coated with these carbons), characterized in that the polyacrylonitrile present in solid form in the dried mixture is thermally decomposed to form a gaseous carbon precursor, and the gaseous carbon precursor thus formed is carbonized in the presence of silicon particles by a CVD process (chemical vapor deposition).

[0009] The non-aggregated carbon-coated silicon particles produced according to the present invention are also referred to below as carbon-coated silicon particles.

[0010] Surprisingly, the method according to the invention provides non-agglomerated carbon-coated silicon particles. Surprisingly, only negligible (if any) adhesion or sintering of the different particles and thus the occurrence of agglomeration are present. This is even more surprising because sticky carbonaceous materials can be present at high temperatures during carbonization, and these can lead to particle agglomeration. Surprisingly, despite this, non-agglomerated carbon-coated silicon particles are obtained according to the invention.

[0011] The silicon particles used in the method according to the invention have a volume-weighted particle size distribution, wherein the diameter percentile d 50 Preferably 1 to less than 15µm, particularly preferably 2 to less than 10µm and most preferably 3 to less than 8µm (measured using the Horiba LA950 measuring instrument described below for carbon-coated silicon particles).

[0012] Silicon particles are preferably non-agglomerated, and particularly preferably non-clustered. Agglomeration refers to spherical or very large spherical primary particles, for example, initially formed during the gas-phase process of silicon particle production, coalescing to form aggregates during the reaction process in the gas-phase phase. Agglomerates or primary particles can also form agglomerates. Agglomerates are loose aggregates of aggregates or primary particles. Using commonly employed kneading or dispersing methods, agglomerates can easily break down back into aggregates. Using these methods, aggregates cannot or can only partially decompose into primary particles. As a result of their formation, aggregates and agglomerates inevitably have particle shapes that are completely different from the preferred silicon particles. The statements made regarding carbon-coated silicon particles are similarly applicable to silicon particles in determining agglomeration.

[0013] The silicon particles preferably have a splintery particle shape.

[0014] The silicon particles are preferably based on elemental silicon. Elemental silicon should be understood to preferably mean high purity and / or polycrystalline silicon and / or a mixture of polycrystalline and amorphous silicon, optionally containing a small proportion of foreign atoms (e.g., B, P, As).

[0015] These silicon particles preferably contain ≥95 wt%, more preferably ≥98 wt%, particularly preferably ≥99 wt%, and most preferably ≥99.5 wt% silicon. The wt% figures are based on the total weight of the silicon particles, and particularly on the total weight of the silicon particles minus their oxygen content. The proportion of silicon in the silicon particles in this invention can be determined according to EN ISO 11885:2009 using an Optima 7300DV measuring instrument from PerkinElmer by ICP (Inductively Coupled Plasma) optical emission spectroscopy.

[0016] Silicon particles typically contain silicon oxide. The silicon oxide is preferably located on the surface of the silicon particles. Silicon oxide can be formed, for example, during the production of silicon particles by grinding or during storage in air. Such oxide layers are also known as native oxide layers.

[0017] Silicon particles typically have an oxide layer, particularly a silicon oxide layer, on their surface, with a thickness preferably from 0.5 to 30 nm, particularly preferably from 1 to 10 nm, and most preferably from 1 to 5 nm (measured by, for example, HR-TEM (high-resolution transmission electron microscopy)).

[0018] Based on the total weight of the silicon particles (determined using a LecoTCH-600 analyzer), the silicon particles preferably contain 0.1% to 5.0% by weight, more preferably 0.1% to 2% by weight, particularly preferably 0.1% to 1.5% by weight, and most preferably 0.2% to 0.8% by weight of oxygen.

[0019] The surface of silicon particles may be covered with an oxide layer or other inorganic and organic groups. Particularly preferred silicon particles have Si-OH or Si-H groups or covalently bonded organic groups, such as alcohols or alkenes, on their surface.

[0020] Preferred polycrystalline silicon particles. The polycrystalline silicon particles have a crystallite size preferably ≤200 nm, more preferably ≤100 nm, even more preferably ≤60 nm, particularly preferably ≤20 nm, most preferably ≤18 nm, and most preferably all ≤16 nm. The crystallite size is preferably ≥3 nm, particularly preferably ≥6 nm, and most preferably ≥9 nm. According to the Scherrer method, the full width at half maximum (FWHM) of the diffraction reflections belonging to Si(111) is at 2... At 28.4°, the crystallite size was determined by X-ray diffraction pattern analysis. The preferred standard for the X-ray diffraction pattern of silicon is SRM640C (single-crystal silicon), a NIST X-ray diffraction standard reference material.

[0021] Silicon particles can be produced, for example, by a grinding process, such as wet grinding or preferably dry grinding. Jet mills, such as opposed jet mills, or impact mills, planetary ball mills, or stirred ball mills, are preferred. Wet grinding is typically carried out in a suspension containing an organic or inorganic dispersing medium. This can include the use of established methods, such as those described in patent application DE102015215415.7.

[0022] Polyacrylonitrile (PA) is typically based on at least 10 acrylonitrile monomer units. PA can exist, for example, in the form of powder or granular materials. The melting point of PA is known to be 300°C. o C. Below 300 o At temperatures of C, polyacrylonitrile is typically in solid form. According to the invention, polyacrylonitrile in solid form is thermally decomposed without an intermediate melting stage, for example, by appropriate heat treatment or by omitting a holding stage within the melting range of polyacrylonitrile.

[0023] In addition to polyacrylonitrile, one or more other polymers or other hydrocarbon compounds may optionally be used as carbon precursors in the method according to the invention. Preferably, ≥70 wt% and particularly preferably ≥90 wt% of the total weight of carbon precursors used in total are polyacrylonitrile. Most preferably, no other carbon precursors are used besides polyacrylonitrile.

[0024] The method according to the invention uses a dry mixture comprising polyacrylonitrile and silicon particles. In the dry mixture, the silicon particles and polyacrylonitrile typically exist in parallel with each other, particularly as separate particles or granules. The dry mixture preferably does not contain any agglomerates containing silicon particles and polyacrylonitrile, and particularly does not contain any aggregates containing silicon particles and polyacrylonitrile. The dry mixture is preferably in powder form.

[0025] Based on the total weight of the dried mixture, the dried mixture contains preferably 20% to 99% by weight, more preferably 50% to 98% by weight, even more preferably 60% to 95% by weight, particularly preferably 70% to 90% by weight, and most preferably 75% to 85% by weight.

[0026] Based on the total weight of the dried mixture, the dried mixture contains preferably 1% to 80% by weight, more preferably 2% to 50% by weight, even more preferably 5% to 40% by weight, particularly preferably 10% to 30% by weight, and most preferably 15% to 25% by weight. The total amount of polyacrylonitrile is typically chosen to achieve the desired degree of carbon deposition.

[0027] In addition, the dried mixture may contain one or more other components, such as conductive additives, such as graphite, conductive carbon black, graphene, graphene oxide, graphene nanosheets, carbon nanotubes, carbon fibers, or metal particles such as copper. Preferably, conductive additives are not present.

[0028] The dried mixture typically contains no solvent. The method according to the invention is generally carried out in the absence of solvent. However, this does not preclude the starting materials used from containing any residual amount of solvent, for example, due to their production.

[0029] Preferably, the dried mixture, particularly the silicon particles and / or polyacrylonitrile, contains ≤2 wt%, particularly preferably ≤1 wt%, and most preferably ≤0.5 wt% of solvent.

[0030] Examples of solvents include inorganic solvents such as water, or organic solvents, particularly hydrocarbons, ethers, esters, nitrogen-functionalized solvents, sulfur-functionalized solvents, alcohols such as ethanol and propanol, benzene, toluene, dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and dimethyl sulfoxide.

[0031] Silica particles and polyacrylonitrile can be mixed in a conventional manner to prepare a dry mixture, such as by mechanical mixing, for example at a temperature of 0 to 50 °C. o C, preferably 15 to 35 oAt temperatures of C, standard mixers can be used, such as pneumatic mixers, freefall mixers (e.g., container mixers, conical mixers, drum mixers, gyroscope mixers, tumbling mixers, or displacement mixers), as well as impeller mixers (e.g., drum mixers and screw mixers). Mixing can also be accomplished using mills commonly used for this purpose, such as planetary ball mills, stirred ball mills, or drum mills. Typically, starting with silicon particles and polyacrylonitrile in solid form, solvents are not used in the production of the dried mixture, and especially not the aforementioned solvents. Therefore, the dried mixture is typically not produced by spray drying.

[0032] The thermal decomposition of polyacrylonitrile preferably occurs at ≥350°C. o C. Exceptionally preferred ≥360 o C and the optimal value is ≥370 o The thermal decomposition of polyacrylonitrile is carried out at a temperature of C. Preferably, the temperature is ≤500°C. o C. Specific preference ≤450 o C and the optimal value ≤ 400 o The decomposition can be carried out at a temperature of C. Alternatively, the thermal decomposition can also be carried out within a temperature range from the temperatures described above up to the upper limit of the carbonization temperature further mentioned below. The decomposition temperature can be determined by thermogravimetric analysis (TGA).

[0033] During the thermal decomposition of polyacrylonitrile, various decomposition products can be formed, such as acrylonitrile, acetonitrile, vinyl acetonitrile, HCN, and / or NH3. These decomposition products are typically present in gaseous form under the conditions used for the decomposition of polyacrylonitrile.

[0034] Preferably, the dried mixture is rapidly heated until the polyacrylonitrile begins to thermally decompose. Preferably, the temperature of the dried mixture is continuously increased until thermal decomposition occurs. Before thermal decomposition begins, the heated dried mixture is preferably not held at a constant temperature, especially not within the range from the melting point to the temperature at which the polyacrylonitrile begins to thermally decompose.

[0035] The dried mixture can be heated by discontinuous or preferably continuously increasing the temperature. For example, the dried mixture can be introduced into a preheated furnace for discontinuous heating. Continuous heating may involve heating at a constant or variable heating rate, but is typically at a positive heating rate. The heating rate is preferably 1-1000. o C / minute, preferably 1-100 o C / minute, optimal value is 1-10 o C / min. In alternative embodiments, this heating rate is preferably from 1 to 20. o C / minute, Special Selection 1 to 15 oC / minute and optimally 1 to 10 o The heating rate is in the range of C / min. In another alternative embodiment, the heating rate is preferably 10 to 1000. o C / minute, preferably 20 to 500 o C / minute, optimal value 50 to 100 o C / minute.

[0036] In the execution of the method according to the invention, polyacrylonitrile is generally not in liquid or molten form, preferably not even partially in liquid or molten form. Typically, melting of polyacrylonitrile does not occur substantially or does not occur significantly before or during the thermal decomposition of polyacrylonitrile. The proportion of molten polyacrylonitrile in the execution of the method according to the invention is preferably based on the total weight of all polyacrylonitrile used, ≤20 wt%, more preferably ≤10 wt%, and particularly preferably ≤5 wt%. Preferably, the polyacrylonitrile in solid form is heated to ≥350°C. o Decomposition occurs at a temperature of C, wherein ≤10 wt%, particularly ≤5 wt%, of the total weight of polyacrylonitrile used is melted. Particularly preferred is decomposition by heating to ≥350°C. o Temperature C will decompose polyacrylonitrile, which exists in solid form, before or during decomposition. Most preferably, the polyacrylonitrile does not melt before or during decomposition. Also most preferably, the polyacrylonitrile does not melt at all during the execution of the method according to the invention. This decomposition behavior can be determined by thermogravimetric analysis (TGA).

[0037] Based on the polyacrylonitrile used (as determined by thermogravimetric analysis (TGA)), at the start of carbonization, the polyacrylonitrile has decomposed to a degree preferably ≥10 wt%, more preferably ≥30 wt%, even more preferably ≥40 wt%, particularly preferably ≥50 wt%, and most preferably ≥60 wt%.

[0038] In the carbonization process according to the CVD method of the present invention, a gaseous carbon precursor formed from polyacrylonitrile decomposes and coats silicon particles with carbon, resulting in carbon-coated silicon particles. As is customary, the gaseous carbon precursor decomposes on the hot surface of the silicon particles, accompanied by carbon deposition.

[0039] The thermal decomposition of polyacrylonitrile and the carbonization of the gaseous carbon precursor formed from polyacrylonitrile can be carried out sequentially or preferably simultaneously. Thermal decomposition and carbonization are preferably carried out simultaneously, preferably in the same furnace or reactor.

[0040] Carbonization is preferably higher than 500 o C to 1400 o C. Particularly preferred 700 o C to 1200 oC and most preferably 900 o C to 1100 o Carbonization is carried out at a temperature of C. Advantageously, carbonization can also be carried out at a low temperature. The carbonization temperature can be determined by thermogravimetric analysis (TGA). Preferably, the carbonization temperature is greater than or equal to the thermal decomposition temperature of polyacrylonitrile.

[0041] The preferred heating rate is 1-1000 o C / minute, preferably 1-100 o C / minute, optimal value is 1-10 o C / min. Heating rate represents the temperature rise per unit time. In alternative embodiments, this heating rate is preferably 1 to 20 °C / min. o C / minute, Special Selection 1 to 15 o C / minute and optimally 1 to 10 o The heating rate is in the range of C / min. In another alternative embodiment, the heating rate is preferably between 10 and 1000. o C / minute, preferably 20 to 500 o C / minute, optimal value 50 to 100 o Within the range of C / minute.

[0042] Furthermore, different heating rates or intervals can be used, along with a stepwise process without a heating rate. For intervals without a heating rate, the reaction mixture is preferably maintained at a certain temperature or within a certain temperature range for a certain period of time. Intervals without a heating rate advantageously last, for example, from 30 min to 24 h, preferably from 1 h to 10 h, and particularly preferably from 2 h to 4 h. Preferably, the interval is from 500... o C to 1200 o C. Special Selection 700 o C to 1100 o C and the optimal choice is 900. o C to 1000 o There are no intervals with no heating rate within the temperature range of C. Below the carbonization temperature, there are preferably no intervals with no heating rate. Cooling can be performed actively or passively, steadily or in stages.

[0043] The duration of thermal decomposition and / or carbonization is guided, for example, by the temperature selected for this purpose and the desired layer thickness of the carbon coating on the silicon particles. Thermal decomposition and / or carbonization preferably lasts from 30 min to 24 h, more preferably from 1 h to 10 h, and particularly preferably from 2 h to 4 h. The method is preferably carried out at a pressure of 0.5–2 bar.

[0044] The thermal decomposition and / or carbonization can be carried out in conventional furnaces, such as tubular furnaces, calcining furnaces, rotary kilns, belt furnaces, chamber furnaces, retort furnaces, or fluidized bed reactors. Heating can be achieved by convection or induction, or by means of microwaves or plasma. Carbonization is preferably carried out in the same apparatus in which thermal decomposition also occurs.

[0045] Thermal decomposition and / or carbonization can be carried out under continuous mixing of the reaction mixture, or preferably statically, i.e., without mixing.

[0046] Components existing in solid form are preferably non-fluidized. This reduces technical complexity.

[0047] The preparation, thermal decomposition, and / or carbonization of the dry mixture can be carried out under aerobic or preferably anaerobic conditions. In particular, thermal decomposition and / or carbonization are preferably carried out under anaerobic conditions. An inert gas atmosphere, such as nitrogen or preferably argon, is particularly preferred. The inert gas atmosphere may optionally contain a proportion of a reducing gas, such as hydrogen. The inert gas atmosphere may be static above the reaction medium or flow through the reaction mixture in the form of a gas stream.

[0048] The silicon particles are preferably coated with carbon in a single coating process. The carbon-coated silicon particles are preferably not subjected to further carbon coating operations.

[0049] The carbon-coated silicon particles obtained according to the present invention can be directly sent for their further use, such as for the production of electrode materials, or alternatively, oversize or undersize can be removed by sorting techniques (sieving, sifting). Preferably, there is no mechanical post-processing or sorting, especially no grinding.

[0050] The carbon-coated silicon particles are preferably in the form of separated particles or loose aggregates, but not in the form of aggregates of carbon-coated silicon particles. Aggregates are clusters of multiple carbon-coated silicon particles. Aggregates are assemblies of carbon-coated silicon particles. Aggregates can be separated into individual carbon-coated silicon particles, for example, using kneading or dispersing methods. Aggregates cannot be separated into individual particles in this way without damaging the carbon-coated silicon particles. However, this does not preclude the individual cases in which aggregates of carbon-coated silicon particles are formed to a lesser extent in the method according to the invention.

[0051] For example, the presence of carbon-coated silicon particles in aggregate form can be visualized using scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Comparison of SEM and TEM images of uncoated silicon particles with corresponding images of carbon-coated silicon particles is particularly suitable for this purpose. Static light scattering methods used to determine particle size distribution or particle size alone are not suitable for determining the presence of aggregates. However, if the carbon-coated silicon particles have a particle size significantly larger than the size of the silicon particles used to prepare them within the range of measurement accuracy, this points to the presence of aggregated carbon-coated silicon particles. The above-described methods are particularly preferably used in combination.

[0052] The carbon-coated silicon particles exhibited a preferred degree of aggregation of ≤40%, more preferably ≤30%, even more preferably ≤20%, particularly preferably ≤15%, and most preferably ≤10%. The degree of aggregation was determined by sieve analysis. The degree of aggregation corresponded to the volume-weighted particle size distribution (d) of the corresponding particle composition analyzed, after dispersion in ethanol and simultaneous ultrasonic treatment without passing through a sieve with a mesh size of ≤10. 90 The percentage of particles that do not pass through a sieve with a mesh size of 20µm, which is twice the value.

[0053] Volume-weighted particle size distribution d of carbon-coated silicon particles and silicon particles used as starting material 50 The resulting differences also indicate that the carbon-coated silicon particles do not aggregate. The volume-weighted particle size distribution d of the carbon-coated silicon particles... 50 The volume-weighted particle size distribution d of silicon particles used as starting material for the production of carbon-coated silicon particles. 50 The difference formed is preferably ≤5µm, particularly preferably ≤3µm and most preferably ≤2µm.

[0054] These carbon-coated silicon particles have a volume-weighted particle size distribution, where the diameter percentile d 50 Preferably ≥2µm, particularly preferably ≥3µm, and most preferably ≥4µm. The dm of carbon-coated silicon particles. 50 The preferred value is ≤10µm, the more preferred value is ≤8µm, and the most preferred value is ≤6µm.

[0055] Carbon-coated silicon particles have a volume-weighted particle size distribution, where d 90 The preferred value is ≤40µm, and the most preferred value is d. 90 ≤30µm, a very special preferred size d 90 ≤10µm.

[0056] Carbon-coated silicon particles have a volume-weighted particle size distribution, where d 10 The preferred value is ≥0.5µm, and the particularly preferred value is d. 10 ≥1µm and optimal d 10 ≥1.5µm.

[0057] The particle size distribution of carbon-coated silicon particles can be bimodal or multimodal, and preferably unimodal, particularly narrow. The volume-weighted particle size distribution of the carbon-coated silicon particles has a preferred... 3. More preferably 2.5. Special Selection 2 and optimal selection Width of 1.5 (d) 90 -d 10 ) / d 50 .

[0058] The volume-weighted particle size distribution of carbon-coated silicon particles was determined by static laser scattering using a Mie model equipped with a Horiba LA950 measuring instrument and ethanol as the dispersion medium.

[0059] The carbon coating of the carbon-coated silicon particles has an average layer thickness preferably in the range of 1 to 100 nm, particularly preferably 150 nm (measured by scanning electron microscopy (SEM) and / or transmission electron microscopy (TEM)).

[0060] Carbon-coated silicon particles typically have a preferred size of 0.1-10 μm. 2 / g, with a particularly preferred concentration of 0.3-8m 2 / g and the optimal value is 0.5-5m 2 / g BET surface area (determined with nitrogen according to DIN ISO 9277:2003-05).

[0061] The carbon coating can be porous and is preferably non-porous. The carbon coating has a porosity preferably ≤2% and particularly preferably ≤1% (total porosity is determined by subtracting the quotient of [apparent density (determined by xylene pycnometry according to DIN 51901) and skeleton density (determined by He pycnometry according to DIN 66137-2)] from 1).

[0062] The carbon coating of the carbon-coated silicon particles is preferably impermeable to liquid media such as aqueous or organic solvents or solutions, especially aqueous or organic electrolytes, acids or alkalis.

[0063] Typically, the silicon particles are not inside the pores. The carbon coating is usually located directly on the surface of the silicon particles.

[0064] Carbon coatings are typically in the form of a film or are not usually granular or fibrous. Typically, carbon coatings do not contain any particles or fibers, such as carbon fibers or graphite particles.

[0065] In carbon-coated silicon particles, the silicon particles are partially or preferably entirely embedded in carbon. The surface of the carbon-coated silicon particles is partially or preferably entirely composed of carbon.

[0066] Carbon may exist in the carbon coating in an amorphous form or preferably in a partially or completely crystalline form.

[0067] Typically, each carbon-coated silicon particle contains silicon particles (measured by scanning electron microscopy (SEM) and / or transmission electron microscopy (TEM)).

[0068] Carbon-coated silicon particles can take on any desired shape, and are preferably splintery.

[0069] The carbon-coated silicon particles preferably contain 0.1% to 8% by weight, more preferably 0.2% to 5% by weight, even more preferably 0.3% to 3% by weight, and particularly preferably 0.5% to 1% by weight of carbon. The carbon-coated silicon particles preferably contain 92% to 99.9% by weight, more preferably 93% to 99% by weight, even more preferably 95% to 99% by weight, and particularly preferably 96% to 99% by weight of silicon particles. The above percentages by weight are based on the total weight of the carbon-coated silicon particles in each case.

[0070] Based on the total weight of the carbon-coated silicon particles, the carbon-coated silicon particles have a nitrogen content of preferably 0% to 5% by weight, particularly preferably 0.1% to 3% by weight, and most preferably 0.1% to 1% by weight (determined by elemental analysis). The nitrogen is preferably present in the form of heterocyclic rings (e.g., as pyridine or pyrrole units (N)). This is also advantageous for the cycle stability of lithium-ion batteries.

[0071] The carbon coating may have an oxygen content of, for example, ≤5 wt%, preferably ≤2 wt%, and particularly preferably ≤1 wt%. In addition to the main components mentioned, other chemical elements may be present, for example, as controlled additions or concurrent impurities: such as 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, and rare earth elements; their content is preferably ≤1 wt% and particularly preferably ≤100 ppm. The wt% figures above are based on the total weight of the carbon coating in each case.

[0072] Furthermore, the carbon-coated silicon particles may contain one or more conductive additives, such as graphite, conductive carbon black, graphene, graphene oxide, graphene nanosheets, carbon nanotubes, carbon fibers, or metal particles such as copper. Based on the total weight of the carbon-coated silicon particles, the carbon-coated silicon particles preferably contain ≤10 wt%, and particularly preferably ≤1 wt%, of conductive additives. Most preferably, no conductive additives are present.

[0073] Carbon-coated silicon particles are suitable as active materials, for example, as anode materials for lithium-ion batteries.

[0074] The present invention further provides a method for producing lithium-ion batteries by using carbon-coated silicon particles obtained by the method according to the invention as the anode active material in the production of the anode for lithium-ion batteries. Lithium-ion batteries typically include a cathode, anode, separator, and electrolyte.

[0075] Preferably, the cathode, anode, separator, electrolyte, and / or another reservoir located in the battery casing contain one or more inorganic salts selected from the group consisting of: nitrates (NO3-). - ), nitrite (NO2) - ), azide (N3) - ), phosphate (PO4) 3- ), carbonates (CO3) 2- ), borates and fluorides (F - The inorganic salts are alkali metals, alkaline earth metals, and ammonium salts. They are particularly preferred to be present in the electrolyte and / or especially in the anode. Particularly preferred inorganic salts are nitrates (NO3). - ), nitrite (NO2) - ), azide (N3) - Alkali metal salts, alkaline earth metal salts and ammonium salts; lithium nitrate and lithium nitrite are preferred.

[0076] The concentration of the inorganic salt in the electrolyte is preferably 0.01 to 2 mol, particularly preferably 0.01 to 1 mol, even more preferably 0.02 to 0.5 mol, and most preferably 0.03 to 0.3 mol. In each case, based on the surface area of ​​the anode, cathode, and / or diaphragm, the loading of the inorganic salt in the anode, cathode, and / or diaphragm, especially the anode, is preferably 0.01-5.0 mg / cm³. 2 The preferred concentration is 0.02-2.0 mg / cm³. 2 The optimal concentration is 0.1-1.5 mg / cm³. 2 .

[0077] The anode, cathode, or diaphragm preferably contains 0.8% to 60%, particularly preferably 1% to 40% by weight, and most preferably 4% to 20% by weight of inorganic salts. In the case of the anode, these figures refer to the dry weight of the anode coating; in the case of the cathode, they refer to the dry weight of the cathode coating; and in the case of the diaphragm, they refer to the dry weight of the diaphragm.

[0078] The anode material of a fully charged lithium-ion battery is preferably only partially lithiated. Therefore, it is preferred that the anode material of the present invention, particularly carbon-coated silicon particles, is only partially lithiated in a fully charged lithium-ion battery. "Fully charged" refers to the state in which the anode material of the battery has its maximum lithium load. Partial lithiation of the anode material means that the maximum lithium absorption capacity of the silicon particles in the anode material has not been exhausted. The maximum lithium absorption capacity of the silicon particles generally corresponds to the chemical formula Li. 4.4 Si, and therefore 4.4 lithium atoms per silicon atom. This corresponds to a maximum specific capacity of 4200 mAh per gram of silicon.

[0079] In a lithium-ion battery, the ratio of lithium atoms to silicon atoms (Li / Si ratio) at the anode can be adjusted, for example, by the flow of charge. The degree of lithiation of the anode material, or the silicon particles present in the anode material, is proportional to the amount of charge that has flowed. In this variant, during the charging process of the lithium-ion battery, the anode material's capacity for lithium is not completely depleted. This results in partial lithiation of the anode.

[0080] In a preferred alternative variant, the Li / Si ratio of the lithium-ion battery is adjusted through cell balancing. In this case, the lithium-ion battery is designed such that the lithium absorption capacity of the anode is preferably greater than the lithium release capacity of the cathode. The effect of this is that, in a fully charged battery, the lithium absorption capacity of the anode is not completely depleted, meaning that the anode material is only partially lithium-ionized.

[0081] In the case of partial lithiation according to the present invention, the Li / Si ratio in the anode material under fully charged state of the lithium-ion battery is preferably ≤2.2, particularly preferably ≤1.98, and most preferably ≤1.76. The Li / Si ratio in the anode material under fully charged state of the lithium-ion battery is preferably ≥0.22, particularly preferably ≥0.44, and most preferably ≥0.66.

[0082] Based on a capacity of 4200mAh per gram of silicon, the capacity utilization of silicon in the anode material of the lithium-ion battery is preferably ≤50%, particularly preferably ≤45%, and most preferably ≤40%.

[0083] The degree of lithiation of silicon, or the capacity of silicon to lithium (Si capacity utilization α), can be determined, for example, as described on page 11, line 4 to page 12, line 25 of WO17025346, especially using the formula for Si capacity utilization α given therein and in the headings “Determination of Delithiation Capacity β” and “Determination of Si-Delithiation Capacity ω”. Si "[Weight ratio of Si ω]" Si[The determination of] ("by reference") is supplementary information.

[0084] The use of carbon-coated silicon particles produced according to the present invention in lithium-ion batteries unexpectedly leads to improved cycle behavior. Such lithium-ion batteries exhibit small irreversible capacity loss in the first charge cycle and stable electrochemical behavior with only slight decay in subsequent cycles. Therefore, the carbon-coated silicon particles of the present invention can achieve small initial capacity loss and also small continuous capacity loss in lithium-ion batteries. Overall, the lithium-ion batteries of the present invention have very good stability. This means that even under multiple cycles, almost no fatigue occurs, for example, due to mechanical damage to the anode material or SEI of the present invention.

[0085] These effects can be further enhanced by adding inorganic salts such as lithium nitrate to the electrolyte.

[0086] In the method according to the invention, carbon is advantageously deposited onto silicon particles with high selectivity. Pure carbon particles or carbon fibers form to a lesser extent as byproducts. This increases yield and also reduces the effort required to separate the carbon particles from the carbon-coated silicon particles. Preferably, based on the total weight of the gaseous carbon precursor formed from polyacrylonitrile, ≥50 wt%, particularly preferably ≥60 wt%, and most preferably ≥70 wt% of carbon is deposited onto the silicon particles (determination method: elemental analysis). Here, the carbon coating is advantageously attached to the silicon particles via covalent bonds.

[0087] Since thermal decomposition and / or carbonization can also be carried out statically (i.e., without fluidization, stirring, or other constant mixing of the reaction mixture), the method of the present invention can be configured in a technically simple manner. Special equipment can be omitted. All of these have significant advantages, especially when the method is scaled up. Furthermore, the method of the present invention is easier to handle compared to conventional CVD methods because it does not require the handling of carbon-containing gases such as ethylene, and therefore has lower safety requirements. Overall, the method of the present invention can be carried out inexpensively because the production of the dried mixture is simply a mixing of these starting materials, and therefore solvents or other conventional drying steps (such as spray drying) are thus unnecessary.

[0088] By eliminating the holding stage for the melt of polyacrylonitrile, the amount of time required can be reduced, space-time yield can be increased, and energy can be saved.

[0089] Surprisingly, the carbon-coated silicon particles produced according to the present invention can be used to obtain lithium-ion batteries that, in addition to the aforementioned advantageous cycling behavior, also have high volumetric energy density.

[0090] Furthermore, the carbon-coated silicon particles produced according to the present invention advantageously possess high electrical conductivity and high resistance to corrosive media (e.g., organic solvents, acids, or alkalis). Using the carbon-coated silicon particles according to the present invention can also reduce the internal resistance of lithium-ion batteries.

[0091] Furthermore, the carbon-coated silicon particles produced according to the invention are unexpectedly stable in water, particularly in aqueous ink formulations for lithium-ion battery anodes. This means that hydrogen evolution, which occurs under such conditions with conventional silicon particles, can be reduced. This enables the processing of the aqueous formulation without foaming, provides stable electrode slurries, and produces particularly uniform and bubble-free anodes. In contrast, silicon particles used as starting materials in the method according to the invention release a relatively large amount of hydrogen in water.

[0092] The advantageous effects of using aggregated carbon-coated silicon particles, for example when using solvents or drying methods not according to the invention or CVD methods not according to the invention, cannot be achieved or cannot be achieved to the extent described in the invention.

[0093] The following examples are used to further illustrate the present invention.

[0094] Unless otherwise stated, the following (comparative) examples were tested in air at ambient pressure (1013 mbar) and room temperature (23°C). o C) Proceed under these conditions. Use the following methods and materials.

[0095] Carbonization:

[0096] Carbonization was performed using 1200 from Carbolite GmbH o The C-zone tube furnace (TFZ12 / 65 / 550 / E301) uses cascaded control including type N sample thermocouples. The temperature is based on the internal temperature of the tube furnace at the thermocouple location. In each case, the starting material to be carbonized is weighed into one or more combustion boats (QCS GmbH) made of quartz glass and introduced into a working tube made of quartz glass. The setup and process parameters for carbonization are reported in the respective embodiments.

[0097] CVD reactor:

[0098] The 1000 used is from Carbolite GmbH oThe C CVD reactor (HTR11 / 150) consists of a quartz glass drum located within an electrically heated rotary kiln with a ceramic liner, where the temperature is controlled. The heating rate along the reaction zone is 10-20 K / min; the heated drum has a uniform temperature distribution within the reaction zone. The temperature is based on the target internal temperature of the drum at the thermocouple location.

[0099] The glass drum is thermally insulated from ambient air with the furnace lid closed. During the process, the glass drum rotates (315°, oscillation frequency 6-8 / min) and has protrusions in its walls, which ensure additional mixing of the powder. A gas conduit is connected to the quartz glass drum. A bypass allows the opening of a bubbling container (whose temperature is controlled by a thermostat) to generate precursor vapors. The resulting byproducts and purge gases are drawn into the opposite exhaust pipe. The setup and processing parameters for chemical vapor deposition vary depending on the precursor used.

[0100] Categorization / Filtering:

[0101] C-coated Si powder obtained after carbonization or chemical vapor deposition was wet-screened with water on a stainless steel sieve using an AS200 basic sieve separator (Retsch GmbH) to remove the oversize >20µm. The powdered product (20% solids content) was dispersed in ethanol (Hielscher UIS250V; amplitude 80%, period: 0.75; duration: 30 min) by ultrasonication and applied to a sieve tower with a sieve (20µm). Sieving was performed using an infinite time pre-selection and a water stream passing through at 50%–70% amplitude. The silica-containing suspension discharged from the bottom was filtered through a 200nm nylon membrane, and the filter residue was subjected to 100... o Dry in a vacuum drying oven at 50-80 mbar for a constant weight.

[0102] The obtained C-coated Si particles were characterized using the following analytical methods and equipment:

[0103] Scanning electron microscope (SEM / EDX):

[0104] Microscopic analysis was performed using a Zeiss Ultra55 scanning electron microscope and an energy-dispersive INCA x-field X-ray spectrometer. Prior to analysis, carbon vapor deposition was performed on the samples using a Baltec SCD500 sputtering / carbon coating unit to prevent charging phenomena.

[0105] Transmission electron microscopy (TEM):

[0106] Layer thickness and carbon configuration were analyzed using a Zeiss Libra 120 transmission electron microscope. Samples were prepared either by embedding them in a resin matrix and then sectioning them using a microtome, or directly from powder. This was accomplished by dispersing each sample in approximately 2 ml of isopropanol using a scraper tip with the aid of sonication and applying it to a copper grid. The sample was then heated on a hot plate at 100°C. o Dry on both sides for about 1 minute under C.

[0107] Inorganic analysis / elemental analysis:

[0108] The C content reported in the examples was determined using a Leco CS230 analyzer; for the determination of O and any N content, a Leco TCH-600 analyzer was used. Qualitative and quantitative determinations of other elements in the obtained carbon-coated silicon particles were performed by ICP (Inductively Coupled Plasma) emission spectrometry (Optima 7300DV, from Perkin Elmer). For this purpose, the samples were acid-digested (HF / HNO3) in a microwave (Microwave 3000, from Anton Paar). ICP-OES determination was guided by ISO 11885 "Water quality—Determination of selected elements by inductively coupled plasma emission spectrometry (ICP-OES) (ISO 11885:2007; German version EN ISO 11885:2009)," which is used for the analysis of acidic aqueous solutions (e.g., acidified drinking water, wastewater and other water samples, soil and sediment aqua regia extract)).

[0109] Particle size determination:

[0110] Particle size distribution was determined by static laser scattering using a Horiba LA950 according to ISO 13320. Special attention must be paid to the dispersion of particles in the measurement solution during sample preparation to avoid measuring the size of agglomerates rather than individual particles. The particles to be analyzed were dispersed in ethanol. For this purpose, if necessary, the dispersion was ultrasonically treated for 4 minutes at 250W in a Hielscher UIS250V ultrasonic laboratory instrument with an LS24d5 ultrasonic welding electrode (sonotrode) before measurement.

[0111] Determination of the aggregation degree of C-coated Si particles:

[0112] The degree of aggregation was determined by sieving analysis. Aggregation corresponds to the volume-weighted particle size distribution (d) of the analyzed particulate composition after dispersion in ethanol and simultaneous ultrasonic treatment, where the particle size is the same as the particle size distribution that cannot pass through a sieve. 90 The percentage of particles on the sieve is twice the value.

[0113] BET surface area measurement:

[0114] The specific surface area of ​​the material was measured by the BET method using nitrogen gas adsorption with a Sorptomatic 199090 instrument (Porotec) or an SA-9603MP instrument (Horiba) according to DIN ISO 9277:2003-05.

[0115] Si compactness:

[0116] Si accessibility in liquid media:

[0117] The accessibility of silicon to liquid media in C-coated Si particles was determined by the following test methods on materials with known silicon content (from elemental analysis):

[0118] First, 0.5-0.6 g of C-coated silicon was dispersed ultrasonically in 20 ml of a mixture (NaOH (4M; H2O) and ethanol (1:1 volume)). Then, at 40°C... o Stir at C for 120 minutes. Filter these particles through a 200 nm nylon membrane, wash with water until pH neutral, and then dry in a drying oven at 100°C. o Dry at 50-80 mbar (C). Determine the silicon content after NaOH treatment and compare it with the Si content before testing. Compactness corresponds to the quotient of the Si content (in %) of the sample after alkali treatment to the Si content (in %) of the untreated C-coated particles.

[0119] Determination of powder conductivity:

[0120] The resistivity of C-coated samples was determined using a measurement system from Keithley, 2602 System Source Meter ID 266404, which consists of a pressure chamber (6 mm mold radius) and a hydraulic unit (from Caver, USA, model 3851CE-9; S / N: 130306) under controlled pressure (up to 60 MPa). Detailed Implementation

[0121] Example 1 (Ex.1):

[0122] Silicon particles are produced by grinding:

[0123] Rough Si chips from polycrystalline silicon production were ground using a fluidized bed jet mill (Netzsch-Condux CGS16, with nitrogen at 90 m³ / h at 7 bar as the grinding gas).

[0124] As in Figure 1 The SEM image (7500× magnification) shows that the silicon particles obtained are in the form of individual, non-aggregated, sheet-like particles.

[0125] Elemental composition: Si≥98wt%; C 0.01wt%; H<0.01wt%; N<0.01wt%; O 0.47wt%.

[0126] Particle size distribution: unimodal; D 10 : 2.19µm, D 50 : 4.16µm, D 90 : 6.78µm; (D 90 –D 10 ) / D 50 =1.10; (D) 90 -D 10 = 4.6µm.

[0127] Specific surface area (BET): 2.662 m² 2 / g.

[0128] Si density: 0%.

[0129] Powder conductivity: 2.15µS / cm.

[0130] Example 2 (Ex.2):

[0131] Silicon particles coated from polyacrylonitrile (PAN) C using vapor phase coating:

[0132] 80.00 g of silicon particles (Si) and 20.00 g of polyacrylonitrile (PAN) from Example 1 were mechanically mixed at 80 rpm for 3 hours using a ball mill roller bed (Siemens / Groschopp). The resulting 99.00 g of Si / PAN mixture was then placed in a quartz glass boat (QCS GmbH) and carbonized, considering the following parameters:

[0133] Nitrogen / H2 was used as the inert gas, the N2 / H2 flow rate was 200 ml / min, and the following temperature treatment was performed:

[0134] Heating rate 10 o C / min until the temperature reaches 1000 o C, holding time 3 hours.

[0135] After cooling, 87.00 g of a black powder (carbonization yield 88%) was obtained. The powder was then subjected to wet sieving to remove the oversize. 79.00 g of a powder with a particle size D was obtained. 99 C-coated Si particles <20µm.

[0136] Figure 2 The SEM image (7500× magnification) of the obtained C-coated Si particles is shown. Figure 3 TEM image (40000× magnification).

[0137] Elemental composition: Si≥98wt%; C 0.7wt%; H 0.01wt%; N 0.32wt%; O 0.7wt%.

[0138] Particle size distribution: unimodal; D 10 : 2.71µm, D 50 : 4.57µm, D 90 7.30µm; (D 90 –D 10 ) / D 50 =1.00.

[0139] Clustering degree: 9%.

[0140] Specific surface area (BET): 2.51 m² 2 / g.

[0141] Si density: Approximately 100% (impermeable).

[0142] Powder conductivity: 70820.64µS / cm.

[0143] Comparative Example 3 (CEx.3):

[0144] C-coating of silicon particles by melt coating from polyacrylonitrile (PAN):

[0145] As in Example 2, the difference is that the Si / PAN mixture is subjected to the following temperature treatment in a three-zone tube furnace:

[0146] First: The heating rate is 10 o C / minute, until reaching 300 o The temperature was set at C for 90 minutes, and the N2 / H2 flow rate was 200 ml / min.

[0147] Afterwards: Heating rate 10 o C / minute, until it reaches 1000 o Temperature C, holding time 3h, N2 / H2 flow rate 200ml / min.

[0148] After cooling, 92.12 g of a black powder (carbonization yield 94%) was obtained. The black powder was then subjected to wet sieving to remove the sieve residue. 87.51 g of a powder with a particle size D was obtained. 99 C-coated Si particles <20µm.

[0149] Elemental composition: Si≥98wt%; C 0.5wt%; H<0.01wt%; N 0.1wt%; O 0.61wt%.

[0150] Particle size distribution: unimodal; D 10 : 2.35µm, D 50 : 4.51µm, D 90 : 8.01µm; (D 90 –D 10 ) / D 50 =1.26.

[0151] Clustering degree: 5%.

[0152] Specific surface area (BET): 2.46 m² 2 / g.

[0153] Si density: Approximately 100% (impermeable).

[0154] Powder conductivity: 50678.78µS / cm.

[0155] Comparative Example 4 (CEx.4):

[0156] Silicon particles coated from polyacrylonitrile (PAN) C using liquid coating:

[0157] 20.00 g of polyacrylonitrile (PAN) was dissolved in 1332 ml of dimethylformamide (DMF) at room temperature. 80.00 g of silicon powder (Si) (D) from Example 1 was dissolved by sonication. 50 =4.16µm) dispersed in the PAN solution (Hielscher UIS 250V; amplitude 80%, period: 0.9; duration: 30min). A B-290 laboratory spray dryer (BÜCHI GmbH) with a B-295 inert loop and a B-296 dehumidifier (BÜCHI GmbH) (nozzle tip 0.7mm; nozzle cap 1.4mm; nozzle temperature 130℃) were used. o The resulting dispersion was spray-dried using a C; N2 gas flow rate of 30; suction device of 100%; and pump of 20%. 58.00 g of brown powder (58% yield) was obtained.

[0158] The 57.50 g of Si / PAN powder thus obtained was placed in a three-zone tube furnace and subjected to temperature treatment as described in Comparative Example 3.

[0159] After cooling, 47.15 g of a black powder (carbonization yield 82%) was obtained, which was then subjected to wet sieving to remove the sieve residue. 39.61 g of a powder with a particle size D was obtained. 99 C-coated Si particles <20µm.

[0160] Elemental composition: Si≥98wt%; C 0.4wt%; N 0.17wt%; O 0.73wt%.

[0161] Particle size distribution: unimodal; D 10 3.69µm, D 50 6.98µm, D 90 : 11.12µm; (D 90 –D 10 ) / D 50 =1.06.

[0162] Clustering degree: 16%.

[0163] Specific surface area (BET): 2.13 m² 2 / g.

[0164] Si density: Approximately 100%.

[0165] Powder conductivity: 56714.85µS / cm.

[0166] Comparative Example 5 (CEx.5):

[0167] C-coating of silicon particles from polystyrene (PS) via vapor phase coating:

[0168] As in Example 2, the difference is that polystyrene (PS) is used instead of polyacrylonitrile.

[0169] After cooling, 80.00 g of a black powder (carburization yield 80%) was obtained, and the residue on the sieve was removed by wet sieving. 75.00 g of C-coated Si particles with a particle size of D99 < 20 µm were obtained.

[0170] Elemental composition: Si≥98wt%; C 0.22wt%; H<0.01wt%; N<0.01wt%; O 0.39wt%.

[0171] Particle size distribution: unimodal; D 10 : 2.73µm, D 50 5.02µm, D 90 : 8.29µm; (D 90 –D 10 ) / D 50 =1.11.

[0172] Clustering degree: 6%.

[0173] Specific surface area (BET): 1.547 m² 2 / g.

[0174] Si density: Approximately 86%.

[0175] Powder conductivity: 4084.782µS / cm.

[0176] Comparative Example 6 (CEx.6):

[0177] C coating of silicon particles from ethylene using vapor phase coating:

[0178] 20.00g of silicon particles (D) from Example 1 were placed at room temperature. 50 The sample (4.16 µm) was transferred to a glass tube in a CVD reactor (HTR11 / 150) from Carbolite GmbH. Following sample introduction, a purging program of process gases was used (10 min argon 3 slm; 3 min ethylene and H2 1 slm each, 5 min argon 3 slm). The reaction zone was heated to 900 °C at a heating rate of 20 K / min. o C. Even during purification and heating, the tube was rotated (315°, oscillation frequency 8 / min) and the powder was mixed. Upon reaching the target temperature, a holding time of 10 minutes was then performed. This CVD coating lasted for a reaction time of 30 minutes, with a total gas flow rate of 3.6 slm and the following gas composition:

[0179] 2 mol of ethylene, 0.3 slm, 8.33% by volume; argon, 2.4 slm, 66.67% by volume; H2, 0.9 slm, 26% by volume.

[0180] After cooling, 15.00 g of a black powder (75% yield) was obtained. The residue on the sieve was removed by wet sieving. 14.50 g of a powder with a particle size D was also obtained. 99 C-coated Si particles <20µm.

[0181] Elemental composition: Si≥94wt%; C 2.54wt%; H<0.01wt%; N<0.01wt%; O 0.10wt%.

[0182] Particle size distribution: unimodal; D 10 : 2.79µm, D 50 5.26µm, D 90 : 8.77µm; (D 90 –D 10 ) / D 50 =1.44.

[0183] Clustering degree: 3%.

[0184] Specific surface area (BET): 2.1 m² 2 / g.

[0185] Si density: Approximately 100% (impermeable).

[0186] Powder conductivity: 818267.37µS / cm.

[0187] Example 7 (Ex.7):

[0188] An anode containing C-coated silicon particles from Example 2 and electrochemical testing in a lithium-ion battery:

[0189] 29.71g polyacrylic acid (at 85) o Dry at C to constant weight; Sigma-Aldrich, M w ~450000 g / mol) and 756.60 g of deionized water were stirred for 2.5 h using a shaker (290 rpm) until the polyacrylic acid was completely dissolved. Lithium hydroxide monohydrate (Sigma-Aldrich) was added in portions to the solution until the pH reached 7.0 (measured using a WTW pH 340i pH meter and a SenTix RJD probe). The solution was then mixed again using a shaker for 4 h.

[0190] Then, 7.00 g of carbon-coated silicon particles from Example 2 were dispersed in a dissolver at a circumferential speed of 4.5 m / s in 12.50 g of neutralized polyacrylic acid solution and 5.10 g of deionized water for 5 min and 12 m / s for 30 min, while simultaneously being kept at 20 o Cooling at C. After adding 2.50 g of graphite (Imerys, KS6LC), the mixture was stirred at a circumferential speed of 12 m / s for another 30 min. After degassing, the dispersion was applied to a copper foil (SchlenkMetallfolien, SE-Cu58) with a thickness of 0.03 mm using a film applicator (Erichsen, model 360) with a gap height of 0.20 mm. The resulting anodic coating was then cooled at 50 °C. o Dry at C and 1 bar air pressure for 60 minutes.

[0191] The average basis weight of the dried anodic coating was 3.01 mg / cm³. 2 The coating density is 1.0 g / cm³. 3 .

[0192] Electrochemical studies were conducted on a coin cell (CR2032 type, Hohsen Corp.) with a 2-electrode arrangement.

[0193] The electrode coating from Example 7 was used as the counter electrode or negative electrode (Dm=15mm); the coating had a content of 94.0% and an average basis weight of 15.9 mg / cm³. 2A lithium-nickel-manganese-cobalt oxide-based 6:2:2 coating (from SEI Corp.) was used as the working or positive electrode (Dm=15mm). Glass fiber filter paper (Whatman, GD type A / E) soaked in 60µl of electrolyte was used as the separator (Dm=16mm). The electrolyte used consisted of a 1.0 mol solution of lithium hexafluorophosphate in a 1:4 (v / v) mixture of ethylene fluorocarbonate and diethyl carbonate. The battery cells were constructed in a glove box (<1ppm H2O, O2); the water content in the dry matter of all components used was less than 20ppm.

[0194] Electrochemical tests in 20 o The process was carried out at C. These batteries were charged using the cc / cv method (constant current / constant voltage) at a constant current of 5 mA / g in the first cycle (corresponding to C / 25) and 60 mA / g in subsequent cycles (corresponding to C / 2), and at a constant voltage until the voltage limit of 4.2V was reached, until the current dropped below 1.2 mA / g (corresponding to C / 100) or 15 mA / g (corresponding to C / 8). The batteries were discharged using the cc method (constant current) at a constant current of 5 mA / g in the first cycle (corresponding to C / 25) and 60 mA / g in subsequent cycles (corresponding to C / 2) until the voltage limit of 3.0V was reached. The specific current chosen was based on the weight of the coating on the positive electrode.

[0195] Based on this formulation, lithium-ion batteries operate through cell balancing and partial lithiation of the anode.

[0196] The results of the electrochemical tests are summarized in Table 1.

[0197] Example 8 (Ex.8):

[0198] An anode comprising C-coated silicon particles from Example 2, wherein the electrode is impregnated with lithium nitrate and electrochemically tested in a lithium-ion battery:

[0199] The anode as described in Example 7 was produced using carbon-coated silicon particles from Example 2. The anode was further modified with LiNO3 by the following steps.

[0200] Use 30 µl of ethanol-LiNO3 solution (21.7 mg / ml) 乙醇 The anode with a diameter of 15 mm from Example 7 was then wetted. The impregnated anode was then immersed in 80 °C. o The coating was dried in a drying oven at C for 2 hours and the weight was measured. The amount of LiNO3 applied to the anode was calculated by the weight difference and given as mg of LiNO3 per mg of coating weight (mg / mg). 涂层 ): 0.08 mg / g 涂层 (0.24mg / cm)2 阳极 ).

[0201] As described in Example 7, the impregnated anode was installed in a lithium-ion battery and tested using the same procedure.

[0202] The results of the electrochemical tests are summarized in Table 1.

[0203] Comparative Example 9 (CEx.9):

[0204] An anode containing C-coated silicon particles from Comparative Example 3 and electrochemical tests in a lithium-ion battery:

[0205] As described in Example 7 above, lithium-ion batteries were produced and tested, except that carbon-coated silicon particles from Comparative Example 3 were used.

[0206] The results of the electrochemical tests are summarized in Table 1.

[0207] Comparative Example 10 (CEx.10):

[0208] An anode containing C-coated silicon particles from Comparative Example 4 and electrochemical testing in a lithium-ion battery:

[0209] As described in Example 7 above, lithium-ion batteries were produced and tested, except that carbon-coated silicon particles from Comparative Example 4 were used.

[0210] The results of the electrochemical tests are summarized in Table 1.

[0211] Comparative Example 11 (CEx.11):

[0212] An anode containing C-coated silicon particles from Comparative Example 5 and electrochemical testing in a lithium-ion battery:

[0213] As described in Example 7 above, lithium-ion batteries were prepared and tested, except that carbon-coated silicon particles from Comparative Example 5 were used.

[0214] The results of the electrochemical tests are summarized in Table 1.

[0215] Comparative Example 12 (CEx.12):

[0216] An anode containing C-coated silicon particles from Comparative Example 6 and electrochemical testing in a lithium-ion battery:

[0217] As described in Example 7 above, lithium-ion batteries were produced and tested, except that carbon-coated silicon particles from Comparative Example 6 were used.

[0218] The results of the electrochemical tests are summarized in Table 1.

[0219] Table 1: Test results of (comparative) Examples 7 to 12:

[0220]

[0221] Compared to the lithium-ion batteries from Comparative Examples 9, 10, 11 and 12, the lithium-ion battery from Example 7 according to the present invention unexpectedly exhibits more stable electrochemical behavior and has a relatively high discharge capacity after one cycle.

[0222] The lithium-ion battery with lithium nitrate added according to Example 8 of the present invention unexpectedly exhibited even more stable electrochemical behavior.

Claims

1. A process for producing non-agglomerated carbon-coated silicon particles having an average particle size d 50 and comprising < 10 wt% of carbon and > 90 wt% of silicon, each based on the total weight of the non-agglomerated carbon-coated silicon particles, by producing a dry mixture by mixing silicon particles and polyacrylonitrile present in solid form in the absence of a solvent for producing the non-agglomerated carbon-coated silicon particles. characterized in that thermally decomposing polyacrylonitrile present in the dry mixture in solid form to form a gaseous carbon precursor, and carbonizing the gaseous carbon precursor thus formed in the presence of silicon particles by a CVD method including chemical vapor deposition; no temperature holding level below the carbonization temperature is included in the entire process from the thermal decomposition of polyacrylonitrile to form a gaseous carbon precursor to the CVD method carbonization.

2. The method of claim 1, wherein, The silicon particles and the polyacrylonitrile are present together in the dry mixture as separate particles or granules.

3. The method of claim 1 or 2, wherein, The dry mixture comprises 2 to 50 wt% of polyacrylonitrile, based on the total weight of the dry mixture.

4. The method of claim 1 or 2, wherein, The thermal decomposition of polyacrylonitrile takes place at temperatures ≥ 350 o C.

5. The method of claim 1 or 2, wherein, The proportion of polyacrylonitrile melted in the thermal decomposition and carbonization process is ≤ 20 wt%, based on the total weight of all polyacrylonitrile used, using a determination method of thermal gravimetric analysis.

6. The method of claim 1 or 2, wherein, No polyacrylonitrile is melted in the thermal decomposition and carbonization process.

7. The method of claim 1 or 2, wherein, The non-agglomerated carbon-coated silicon particles exhibit an agglomeration degree of < 40 %, as determined by sieve analysis, wherein the agglomeration degree corresponds to the percentage of particles of a sieve size which is twice the value of the volume-weighted particle size distribution d 90 the volume-weighted particle size distribution d of the respective particle composition analyzed.

8. The method of claim 1 or 2, wherein, The volume-weighted particle size distribution d of the non-agglomerated carbon-coated silicon particles 50 The volume-weighted particle size distribution d of the silicon particles used as starting material for producing the non-agglomerated carbon-coated silicon particles 50 The difference formed is ≤ 5 pm.

9. The method of claim 1 or 2, wherein, Decomposition products are formed in the thermal decomposition of the polyacrylonitrile, the decomposition products being from the group comprising acrylonitrile, acetonitrile, vinylacetonitrile and HCN.

10. The method of claim 1 or 2, wherein, The dry mixture does not comprise any electrically conductive additives selected from the group comprising graphite, electrically conductive carbon black, graphene, graphene oxide, graphene nanoplatelets, carbon nanotubes, carbon fibers and copper.

11. A method for producing a lithium ion battery using the non-agglomerated carbon-coated silicon particles obtained by the method of any one of claims 1 to 10 as anode active material for an anode used in the production of lithium ion batteries.

12. The method of claim 11, wherein, The cathode, anode, separator and / or electrolyte of the lithium ion battery and / or other storage located in the battery housing comprises one or more inorganic salts selected from the group comprising nitrates, nitrites, azides, phosphates, carbonates, borates and fluorides of alkali metals, alkaline earth metals and ammonium. The cathode, anode, separator and / or electrolyte of the lithium ion battery and / or other storage located in the battery housing comprises one or more inorganic salts selected from the group comprising nitrates, nitrites, azides, phosphates, carbonates, borates and fluorides of alkali metals, alkaline earth metals and ammonium.

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