High-performance silicon-based materials for lithium-ion battery anodes

Abstract

The subject of the present invention is an amorphous silicon carbon composite particle comprising, as elements of the particle, a silicon content of 85-99.63% by weight, a carbon content of 0.3-15% by weight, and a hydrogen content of at least 0.07% by weight, the elements adding up to 100% by weight, wherein the carbon content in a subsurface region of the particle, starting at the surface and extending from the surface to at least 30 nm in a direction towards the centre of the particle, is at least 3% by weight higher than in a central region of the particle, the central region being the remainder of the particle and directly connected to the subsurface region.

Description

[Technical Field]

[0001] The subject of the present invention is an amorphous silicon carbon composite particle comprising the elements silicon, carbon and hydrogen, wherein the silicon and carbon contents vary gradually from the center to the surface of the particle, with the silicon content increasing from the surface to the center of the amorphous particle and the carbon content decreasing from the surface to the center.

[0002] The use of silicon-based materials can increase the energy density of lithium-ion batteries by at least 20% compared to conventional graphite-based anodes. However, silicon-containing anodes are prone to rapid decomposition due to the drastic volume changes of the lithiation / delithiation reactions during cycling. This challenge has motivated the development of silicon-based materials with different structures to minimize this decomposition during lithiation / delithiation in silicon-based anodes and to pursue higher capacity and longer cycle life for batteries, especially lithium-ion batteries (LIBs).

[0003] Therefore, the active electrode materials of the anode and cathode are: E cell =C cell U cell (1) [In the formula, C cell is the total cell capacity, and U cell is the nominal voltage of the cell], E cell plays an important role in maximizing the total specific energy of the C cell =1 / (1 / C c +1 / C a +1 / Qm) (2) [In the formula, C c and C aIt can be calculated as follows: where Q is the specific capacity of the cathode (positive electrode, i.e., the electrode operating at the higher electrode potential) and the anode (electrode operating at the lower potential), and 1 / Qm is the specific mass (g / AH) of the inactive battery elements (electrolyte, separator, additives, current collector, casing, etc.). Therefore, to maximize the energy stored in the cell, it is necessary to maximize the reversible specific capacity and the difference in operating potential between the cathode and anode (usually achieved by selecting a cathode with a high potential). High-capacity, high-rate capacity electrodes, and high-potential cathodes enable the production of smaller LIBs.

[0004] The prior art anode material used in LIBs is graphite, which has a fairly low specific capacity of approximately 370 mAh / g. Lithium, on the other hand, is known to form alloys with many elements, including silicon. Compounds that are stable at room temperature, have the highest specific and volumetric capacities, and have an appropriate operating potential (i.e., the potential of the anode material must be low enough to maintain a large potential difference between the cathode and anode, but above that of metallic lithium to minimize Li plating during fast charging), and are preferably non-toxic and abundant.

[0005] Lithium metal is essentially Li / Li + It has the lowest potential and the highest specific capacity of 3862 mAh / g, but in liquid organic electrolytes, lithium is not homogeneously coated and forms Li deposits with high surface area (e.g., dendrites), which pose a high safety risk. Among known alloying elements, silicon has the highest specific capacity: full lithiation of silicon near room temperature corresponds to a specific capacity of about 3600 mAh / g. 15 This results in the formation of the Si4 phase.

[0006] A serious problem with the combination of silicon and lithium as an anode material is its extremely large volume expansion of about 300% (for comparison, graphite expansion upon lithiation is limited to about 10%).

[0007] Volume expansion / contraction during lithiation / delithiation leads to the destruction of (coarse) particles and subsequent decrepitation of the electrode, loss of electrical contact between the particles and the current collector, and repeated destruction of the so-called solid electrolyte interphase (SEI), i.e., the passive layer formed as a result of electrolyte decomposition on the particle surface, which leads to continuous consumption of electrolyte and continuous lithium loss, both of which necessitate a rapid capacity decline and cell failure. The destruction of silicon poses an obstacle to the use of bulk silicon and coarse silicon powder as anode materials in LIBs.

[0008] This behavior is due to the amorphous lithiated Li x Si shell (a-Li x The migration of crystalline silicon (c-Si, where x is close to 3.4) from the surface towards the unlithiated crystalline Si core, resulting in cracks at the particle surface, can be explained by the strong non-uniform stresses that arise as a result of the amorphization of the solid state that occurs upon initial lithiation of crystalline silicon (c-Si) material. In amorphous silicon (a-Si), lithiation occurs through the separation of the unlithiated a-Si phase and the amorphous a-Li x This is also driven by the migration of a sharp phase boundary between the a-Si and Si phases (x ≈ 2.5–3.75), but in contrast to c-Si, the hydrostatic stress of a-Si is smaller, and therefore a higher stability can be expected for amorphous silicon materials.

[0009] The capacity loss of the Si-based electrode is due to the crystalline c-Li 15 This leads to the formation of the Si4 phase. 15 Avoiding the formation of Si4 allows for more stable cycling.

[0010] c-Li 15 The suppression of Si4 formation is achieved by particles containing an active Si phase and an inactive matrix phase, such as Si-transition metal or Si-SiO x(x≦2) alloys [DSM Iaboni and MN Obrovac, J. Electrochem. Soc. 163 (2016) A255]. However, the inactive phase is disadvantageous because it significantly reduces the specific capacity of the material and / or can irreversibly trap Li during the first cycle, i.e., significantly reducing the first cycle coulombic efficiency (CE).

[0011] Therefore, an object of the present invention was the design of silicon-based materials that undergo minimal degradation during lithiation / delithiation, resulting in higher capacity and longer cycle life batteries. Another object of the present invention is therefore to prevent the formation of harmful crystalline Li over a certain period of time during use in those batteries. 15 The goal was to design a material that suppresses the formation of the Si4 phase. A further objective was to provide a silicon-based material with a high specific capacity in the first cycle and subsequent cycles. A further objective was to provide a silicon-based material with a high first cycle coulombic efficiency. A further objective was to provide a silicon-based material that allows for a higher silicon content, particularly in the matrix material of an anode, such as a graphite anode, without compromising its cyclability. In addition, the silicon-based material should be manufacturable in a large-scale, cost-effective process.

[0012] The silicon carbon particles of the present invention comprise silicon alloyed with carbon, and in particular the carbon content of the particles is typically in a range that allows for the formation of an amorphous silicon phase alloyed with carbon, and in particular the carbon is believed to be at least partially distributed on an atomic scale or as small domains of carbon atoms in the amorphous silicon. The silicon carbon particles of the present invention are believed to be present with atomically distributed carbon in amorphous silicon, particularly silicon carbon composites.

[0013] Additionally, certain carbon contents may not be present as alloys with silicon. Furthermore, depending on the synthesis conditions, certain hydrogen contents may be present, particularly on the surface of the silicon-carbon particles. The silicon-carbon composite particles of the present invention combine the electrical conductivity and cyclability of carbon with the high capacity of silicon, which has a beneficial effect on the performance of the particles in battery applications.

[0014] A specific carbon content in the amorphous silicon carbon composite particles of the present invention stabilizes the amorphous phase and inhibits the formation of a crystalline phase over a period of time at high temperatures. Furthermore, it has been found that higher carbon content silicon carbon composite particles can further inhibit the formation of a crystalline phase at high temperatures. For example, while amorphous silicon (pure amorphous silicon, Si-Am) fully converts to the crystalline silicon phase within one hour after annealing at 690°C, amorphous silicon carbon composite particles resist crystallization at least three to four times longer, depending on the carbon content of the particles. While particles containing 6.3 wt% carbon exhibited 40 wt% crystalline phase, only 20 wt% of the particles of the present invention, at a carbon content of 14.2 wt%, underwent partial phase conversion from the amorphous state to the crystalline state. Thus, the degree of crystallization can be correlated with the carbon content (see Figure 4b).

[0015] Silicon alloyed with carbon and / or silicon combined with the carbon content of silicon carbon particles can form amorphous Li x Si, x=2.5~3.75, especially amorphous Li 15 Crystalline Li from Si4 phase 15 It is believed to suppress the formation of Si4.

[0016] The reason for this behavior may be the altered atomic environment in the amorphous silicon carbon composite particles. The addition of carbon disturbs the local atomic environment in the amorphous phase, thus increasing the local atomic environment of the crystalline c-Li. 15 It can suppress the conversion to Si4 modification.

[0017] For amorphous silicon carbon composite particles, especially those containing carbon distributed on an atomic scale or in domains of carbon atoms in amorphous silicon, it has been observed that particle stability increases with increasing carbon content.

[0018] It is further preferred that the silicon carbon composite particles have no detectable aromatic bonds. The broad signal observed in CPMAS (Figure 2a: 13 C-CP / MAS) is purely due to instrumental background. Hydrogen, carbon or oxygen contents are always given as weight % or atomic %.

[0019] A particular advantage of the method of the present invention is the one-step synthesis, which makes it suitable for scale-up. Furthermore, heterogeneity during synthesis due to mixing particularities does not play a role in the method of the present invention.

[0020] The subject of the present invention is a silicon content of 85 to 99.63% by weight, a carbon content of 0.3 to 15% by weight, in particular a carbon content atomically distributed in amorphous silicon, and a hydrogen content of at least 0.04% by weight, preferably at least 0.05% by weight, and Optionally, silicon carbon composite particles containing elements with an oxygen content of 0-1 wt. %, the elements adding up to 100 wt. %, and the carbon content at the surface, particularly at a subsurface region of the particle starting at 0 nm and extending from the surface to at least 30 nm in a direction towards the center of the particle, is at least 3 wt. % higher than in a central region of the particle, the central region being the remainder of the particle and directly connected to the subsurface region.

[0021] According to a preferred embodiment of the invention, the carbon content at the surface, and in particular in the subsurface region of the particle starting at 0 nm and extending from the surface towards the center of the particle for at least 30 nm, is between 5% and 15% by weight, preferably between 6% and 13% by weight, relative to the remaining elements totalling 100% by weight in the subsurface region of the particle.

[0022] According to a preferred embodiment of the invention, the ratio of carbon content to silicon content, as a weight ratio, in the surface, especially in the subsurface region of the particle starting at 0 nm and extending from the surface to at least 30 nm towards the particle's center is 1:1 to 1:11, especially 1:5 to 1:11, preferably 1:5 to 2:21. Optionally, the ratio of carbon content to silicon content in the central region of the particle is 1:8 to 1:20, preferably 1:11 to 1:20, the central region being the remainder of the particle and directly connected to the subsurface region.

[0023] In addition, the ratio of silicon to carbon (Si / C) in the silicon-carbon composite particles total is greater than 5, preferably greater than 5.6.

[0024] Further, optionally, the specific surface area of ​​the particles is between 3 and 35 m 2 / g, especially 3-12m 2 / g, preferably 4 to 9 m 2 / g.

[0025] In the most preferred embodiment of the present invention, the primary particles have an average particle size of less than 300 nm, in particular less than 250 nm. The primary particles may be agglomerated and / or aggregated; preferably, the primary particles are agglomerated but not sintered, and the agglomerate size is 150-1500 nm, in particular 250-700 nm. Preferably, about 10-90%, in particular 80-90%, of the particles are not sintered.

[0026] The surface of the particle is located at zero nanometer (0 nm). Preferably, the particle comprises amorphous silicon with atomically distributed carbon, the atomically distributed carbon decreasing from the surface of the particle towards the center of the particle.

[0027] In particular, silicon carbon composite particles comprising a silicon content of 85-97 wt. %, a carbon content of 1.05-15 wt. %, and a hydrogen content of at least 0.05 wt. % to 5 wt. %, and optionally an oxygen content of 0-1 wt. %, the elements totaling 100 wt. %, and optionally the particles have a specific surface area of ​​3-35 m. 2 / g, especially 3-10m 2 / g, preferably 4 to 9 m 2 / g of silicon carbon composite particles are preferred.

[0028] Also, silicon carbon composite particles comprising a silicon content of 85-95 wt. %, a carbon content of 1.03-15 wt. %, and a hydrogen content of at least 0.07 wt. % to 5 wt. %, and optionally an oxygen content of 0-1 wt. %, the elements totaling 100 wt. %, and optionally the particles have a specific surface area of ​​3-35 m. 2 / g, especially 3-10m 2 / g, preferably 4 to 9 m 2 Also preferred are silicon carbon composite particles having a pore size of 0.1 / g.

[0029] According to a further object of the present invention, there is provided silicon carbon composite particles comprising a silicon content of 85 to 92.93% by weight, a carbon content of 7 to 15% by weight, and a hydrogen content of at least 0.07% to 5% by weight, and optionally an oxygen content of 0 to 1% by weight, the elements adding up to 100% by weight, the particles being particularly preferably 98% to 100% amorphous particles, and optionally the particles having a specific surface area of ​​3 to 35 m 2 / g, especially 3-10m 2 / g, preferably 4 to 9 m 2 Also preferred are silicon carbon composite particles having a pore size of 0.1 / g.

[0030] Silicon carbon composite particles comprising a silicon content of 85-97 wt. %, a carbon content of 2.5-15 wt. %, and a hydrogen content of at least 0.1 wt. % to 5 wt. %, and optionally an oxygen content of 0-1 wt. %, the elements totaling 100 wt. %, and optionally the particles have a specific surface area of ​​3-35 m. 2 / g, especially 3-10m 2 / g, preferably 4 to 9 m 2 More preferred are silicon carbon composite particles having a SiO 2 content of 1000 ppm / g.

[0031] According to a further particularly preferred subject of the present invention, silicon carbon composite particles are provided which contain a silicon content of 93.5 to 92.93% by weight, a carbon content of 0.7 to 1.5% by weight, preferably 1.0 to 1.5% by weight, and a hydrogen content of at least 0.07% to 5% by weight, and optionally an oxygen content of 0 to 1% by weight, the elements adding up to 100% by weight, the particles being particularly preferably 98% to 100% amorphous particles, and optionally the particles have a specific surface area of ​​3 to 35 m 2 / g, especially 3-10m 2 / g, preferably 4 to 9 m 2 Also preferred are silicon carbon composite particles having a pore size of 0.1 / g.

[0032] By definition, the particle center is located at half the width of each particle's diameter, and spherical particles are preferred, with the carbon content gradually decreasing from the surface to the center. The same applies to non-spherical particles, where at least two diameters are selected to locate the center.

[0033] It is particularly preferred that the silicon carbon composite particles have an amorphous content of more than 90%, in particular more than 98%, and more preferably up to 100%. In this regard, it is preferred that the silicon carbon composite particles are from 95% or 97% to 100% amorphous. It is particularly preferred that the silicon carbon composite particles are from 98% to 100%, most preferably from 99% to 100% amorphous. The amorphous content is measured by X-ray powder diffraction (XRPD).

[0034] The preferred atomic concentrations (atomic %) in the three parts of the particle are: - the surface, especially the subsurface of the particle, starting at 0 nm and extending from the surface towards the centre for at least 30 nm; - a central region of the particle, which is the remainder of the particle and directly connected to the subsurface region, and which comprises a core region with a diameter of 60 nm at the center of the particle and a peripheral region between the core region and the surface region, in which the silicon to carbon concentration (atomic %) in the core region is 51 / 31 to 71 / 15, particularly 52 / 27 to 69 / 16, and in which the silicon to carbon concentration (atomic %) in the peripheral region is 46 / 36 to 69.8 / 17, particularly 50.6 / 32.4 to 64.4 / 19.6. In particular, it is preferred that the core region of the particle comprises carbon atomically distributed in amorphous silicon.

[0035] In a preferred embodiment of the present invention, the silicon carbon composite particles are chlorine-free, in particular the chlorine content is less than 0.7 ppm by weight, preferably less than 0.4 ppm by weight, more preferably between 0.01 ppb and 0.4 ppm by weight.

[0036] According to one aspect of the present invention, the silicon carbon composite particles have an average primary particle size of less than 300 nm, in particular less than 250 nm. Typically, the carbon silicon composite particles have a primary particle size of 30 nm to 250 nm, preferably 80 nm to 150 nm. Optionally, the particles may form agglomerates, with the primary particle agglomerate size preferably being less than 1500 nm. The particles are obtained or formed in a gas stream containing a precursor silane and a gas stream containing a precursor olefinic hydrocarbon at a reaction temperature ranging from 400°C to 700°C, particularly 400°C to 670°C, and preferably 490°C to 640°C, within a time frame of 500 milliseconds to 20 seconds, and optionally formed in an inert gas stream in a tube. In particular, silicon carbon particles are obtained in a reaction zone located within the inert gas stream in the tube, optionally having a temperature of 400°C to 670°C, preferably 430°C to 650°C. Optionally, the reaction mixture is quenched with an inert gas having a lower temperature than the reaction mixture, and the silicon carbon composite particles are collected. According to a further aspect of the present invention, preferably, the particles do not form agglomerates, i.e., the particles are not sintered into agglomerates upon their formation.

[0037] In a further aspect of the invention, the particles may have a content of silicon, in particular amorphous silicon comprising hydrogen, SiH species and / or (poly-[SiH]), optionally the hydrogen content in the particles is at least 0.05% by weight, elements totalling 100% by weight, in particular the hydrogen content in the particles is at least 0.1% by weight, preferably 0.3% by weight, particularly preferably at least 0.5% by weight.

[0038] According to a further aspect of the invention, the swelling in volume of the particles caused by lithiation is less than 250%, preferably less than 300%, and preferably less than 230%, compared to particles without lithiation, in particular at a specific capacity of at least 3000 mAh / g.

[0039] Preferably, the particles are spherical particles, at least 10% by weight of the particles have a ratio of first diameter to second diameter of 0.9 to 1.1, and the first and second diameters are arranged perpendicular to each other.

[0040] The surface area of ​​the particles in the powder is 3 to 35 m 2 / g, especially 3-15m 2 / g, especially 5-9m 2 / g range, 6-8m 2 / g is preferred.

[0041] According to a further aspect of the present invention, the content of metals other than silicon in the silicon carbon particles is preferably less than 10 ppm by weight, particularly less than 7 ppm by weight, and the metals may be selected from Al, Ca, Fe, Co, Zn, Na, Mg, and K. Most preferably, the content of metals in the silicon carbon composite particles is less than 7 ppm by weight. In addition, the content of halogens may be less than 0.7 ppm by weight, preferably less than 0.4 ppm by weight, and more preferably 0.01 ppm to 0.4 ppm by weight.

[0042] According to a further aspect of the invention, the reactivity with the electrolyte, defined as the ratio of the lithiation capacity at cycle (x) to the delithiation capacity at cycle (x-1), is preferably less than 1.02, and by definition, the reactivity with the electrolyte is in principle greater than 1, meaning that a reaction with the electrolyte occurs; the closer this value is to 1, the lower the reactivity with the electrolyte.

[0043] Furthermore, silicon-carbon composite particles are preferred in which the silicon content of the particle gradually increases from the subsurface region of the particle, starting at the surface, particularly at 0 nm, and extending from the surface to 30 nm in a direction toward the center of the particle, with the central region continuing to the subsurface region. The carbon content is at least 3 wt. %, particularly at least 4 wt. % to 20 wt. % of the total carbon content of the particle, and gradually decreases from the surface to the center of the particle, particularly carbon being carbon atomically distributed in amorphous silicon. The center of the particle is particularly preferred, with the carbon content decreasing from the surface to the center of the particle, located at half the width of the particle's diameter. In particular, the subsurface region of the particle includes the surface of the particle at a distance of 0 nm to 30 nm in a direction toward the particle's diameter.

[0044] Additionally, it is preferred that the silicon content of the particles is at least 0.5% to 30% by weight higher, preferably 2.5% to 20% by weight higher, more preferably 4 to 10% by weight higher, in the central region of the particles than in the subsurface region of the particles, and that the central region is connected to the subsurface region, and that the subsurface region of the particles starts at the surface, particularly at 0 nm, and extends up to 30 nm in the direction from the surface towards the center of the particles.

[0045] Particularly preferred embodiments of the present invention include particles having a silicon content that is at least 0.5 wt % and optionally 30 wt % higher in the central region of the particle than in the sub-surface region of the particle, preferably at least 0.7 wt % higher, more preferably 1.5 wt % to 20 wt % higher, more preferably 2.0 wt % to 15 wt % higher, and in particular the silicon content is at least 2.5 wt % to 10 wt % higher, especially 2.5 wt % to 5 wt % higher, in the central region of the particle than in the sub-surface region of the particle, the central region being connected to the sub-surface region, and the sub-surface region of the particle starting at the surface, in particular at 0 nm, and extending up to 30 nm from the surface in a direction towards the center of the particle.

[0046] In particular, in all cases the subsurface region of the particle includes the surface of the particle at a distance of 0 nm to 30 nm in the direction of the particle's diameter.

[0047] According to a further preferred embodiment of the invention, the carbon content of the particles is at least 3% and optionally 30% by weight higher, in particular 4% to 20% by weight higher, in the subsurface region than in the central region of the particle, the central region being connected to the subsurface region, the subsurface region of the particle starting at the surface, in particular at 0 nm, and extending from the surface to 30 nm in the direction towards the particle's center. It is particularly preferred that the silicon content increases reciprocally with decreasing carbon content.

[0048] According to a further preferred embodiment of the present invention, the carbon content of the particles, i.e., the total carbon content of the particles, is at least 1% to 15% by weight, preferably 2% to 14% by weight, in particular 2% to 10% by weight or 2% to 8% by weight, and particularly preferably 3% to 6% by weight, with the elements of the particles preferably adding up to 100% by weight. According to a further object, the carbon content is preferably 6 to 14% by weight, with the remaining elements adding up to 100% by weight. According to another preferred object, the carbon content is preferably 0.7 to 1.5% by weight, with the remaining elements adding up to 100% by weight.

[0049] Furthermore, the particles may contain an aliphatic hydrocarbon compound content, in particular 0.05% to 5% by weight, in particular 0.05% to 3% by weight, optionally with its carbon content included in the carbon content of the particles. Preferably, the aliphatic hydrocarbon compound contains alkyl and / or alkenyl groups.

[0050] The silicon carbon composite particles according to the present invention preferably have a density of 1.8 to 2.25 g / cm 3 , especially about 2 g / cm 3 (The density of crystalline Si is about 2.3 g / cm 3 (It is).

[0051] According to a further aspect of the invention, the particles of the invention or anodes comprising said particles have a capacity (mAh / g) vs. potential vs. Li / Li +(Volt) curves, the particle curves showing crystalline Li for at least the first cycle, particularly up to at least the 20th cycle, more preferably for at least 100 cycles, particularly during the first cycle of lithiation in secondary cells. 15 Si4(c-Li 15 It does not have a plateau extending from 750 mAh / g to 2000 mAh / g between 0.4 and 0.5 volts due to the formation of Si4).

[0052] According to a further aspect of the invention, the particles or anodes comprising the particles preferably have a capacity (mAh / g) vs. potential vs. Li / Li + It has a delithiation capacity (mAh / g) at 0.6 volts, particularly at least 2500 mAh / g at 0.8 volts, measured as a (volt) curve, on the first cycle, particularly on the first cycle of lithiation in a secondary cell, of at least 2900 mAh / g.

[0053] According to a further aspect of the invention, the swelling ratio of the particle-containing anode caused by lithiation is less than 180%, particularly less than 170%, at a specific capacity of at least 3000 mAh / g compared to the non-lithiated anode. In particular, the swelling ratio of the particle-containing anode in a single-layer laminate full-cell configuration using an NMC111 cathode is less than 180%, particularly less than 170%, at a specific capacity of at least 3000 mAh / g compared to the non-lithiated anode.

[0054] According to a further aspect of the invention, the particles or the anode comprising said particles preferably contain crystalline Li 15 Si4(c-Li 15 The particles have a differential capacitance (dQ / dV) versus voltage curve with a peak corresponding to the formation of Si4), whereby the ratio of the area of ​​this peak to the area of ​​the differential capacitance (dQ / dV) in the range between 0.38 and 0.8 V is in the range of 0 to 0.1 for at least the first cycle, particularly up to at least the 20th cycle, and more preferably for at least 100 cycles.

[0055] According to a further aspect of the invention, the particles or an anode comprising said particles have a coulombic efficiency at the silicon carbon composite particles (synonymous with respect to the Si / C powder of the invention) of at least 89% in the first cycle.

[0056] The subject of the present invention is also a method for the preparation of silicon-carbon composite particles, in particular particles obtainable by said method, comprising the steps of: (i) a) a gas stream comprising at least one precursor silane, the precursor silane being monosilane, disilane, trisilane, tetrasilane, pentasilane, hexasilane, heptasilane, octasilane, iso-tetrasilane, iso-pentasilane, neo-pentasilane, cyclopentasilane, cyclohexasilane and / or fully hydrogenated organosilanes containing 1 to 8 silicon atoms and 1 to 10 carbon atoms or a mixture of at least two of the aforementioned silanes; b) a gas stream comprising a precursor hydrocarbon selected from olefinic hydrocarbons and alkynes or a mixture of at least two of the aforementioned hydrocarbons (particularly preferred are gas streams comprising a precursor olefinic hydrocarbon of at least one precursor olefinic hydrocarbon selected from alkenes and cycloalkenes containing 1 to 10 carbon atoms or a mixture of at least two of the aforementioned olefinic hydrocarbons), (ii) reacting in a tubular reactor at a reaction temperature of 400°C to 700°C, preferably 490°C to 670°C, more preferably 490°C to 645°C; (iii) the reaction occurs primarily within a heated tubular inert gas flow for a time frame of 500 milliseconds to 20 seconds, preferably 500 milliseconds to 15 seconds, and optionally (iv) quenching the reaction mixture with an inert gas at a temperature lower than that of the reaction mixture and, optionally, collecting the silicon carbon composite particles. The method includes:

[0057] In particular, the olefinic hydrocarbons and alkynes may be selected from linear, branched and / or cyclic olefinic hydrocarbons and alkynes, such as alkenes, cyclo-alkenes, alkynes and cyclo-alkynes. Generally, the hydrocarbons may include hydrocarbons having 1 to 100 C atoms, preferably 1 to 20 C atoms.

[0058] Optionally, gaseous by-products are also collected.

[0059] The reaction is carried out (ii) in a tubular reactor at a reaction temperature of 400°C to 700°C, preferably 490°C to 670°C, particularly preferably 490°C to 645°C, and most preferably 490°C to 610°C, and (iii) in a heated tubular reactor at a time frame of 500 milliseconds to 20 seconds, preferably 500 milliseconds to 15 seconds, and the reaction is carried out at a pressure of 0.8 to 5 bar. abs. , especially 1 to 3 bar abs. , preferably 1.2 to 3.0 bar abs. It is preferable that the process is carried out in the following manner.

[0060] The reaction temperature is defined as the temperature of the reaction within the heated tubular inert gas flow, particularly within a time frame of 500 milliseconds to 20 seconds, particularly the temperature of the reaction zone.

[0061] According to a particularly preferred method, (iii) the reaction is carried out in a reaction zone located within a heated tubular inert gas stream for a time period of 500 milliseconds to 20 seconds, the heated tubular inert gas stream having an outer and inner circumference, the inner circumference being connected to the reaction zone within the heated tubular inert gas stream, and the radial distance from the inner circumference to the outer circumference of the tubular inert gas stream relative to the radius of the reaction zone within the tubular inert gas stream is in a ratio of 2:1 to 1:10, preferably 1:1 to 1:5. The radius of the reaction zone can change over the reaction time, and in particular, the radius can increase after injection of the precursor gas stream or mixture of precursor streams. Additionally, in (iii), the reaction is carried out in a reaction zone located within a heated tubular inert gas stream for a time period of 500 milliseconds to 20 seconds, and most preferably, the heated tubular inert gas stream has a temperature of about 400 to 520°C when the precursor silane, precursor hydrocarbon, particularly a precursor olefinic hydrocarbon, or mixture thereof is injected into the reaction zone of the tubular reactor. Injecting the precursor toward the center of the tubular inert gas flow confines the reaction to the center of the reactor tube. For very specific reaction conditions, a reaction zone containing at least two reaction sections is formed within the tubular inert gas flow. The first reaction section involves the injection of a gaseous precursor stream containing a precursor silane and a precursor hydrocarbon, particularly a precursor olefinic hydrocarbon, axially into a reaction zone having a temperature of 400°C to 520°C, preferably 430°C to less than 490°C. Here, the reaction zone includes at least two reaction sections along the axis of the tubular reactor, with the second reaction section following the first reaction section. The second reaction section has a reaction temperature of 490°C to 700°C, particularly 490°C to 650°C. The carbon source is not 100% consumed in the reaction.

[0062] The heated tubular inert gas stream has a concentric outer periphery and a concentric inner periphery, the inner periphery being connected to a reaction zone within the heated tubular inert gas stream, and the radial distance from the inner periphery to the outer periphery of the tubular inert gas stream has a ratio of 2:1 to 1:10. Concentricity means having a common center on the longitudinal axis of the tubular reactor.

[0063] a) a gas stream comprising at least one precursor silane of a precursor silane, and b) a gas stream comprising a precursor hydrocarbon, in particular an olefinic hydrocarbon, in a range of 1 to 15 Nm 3 / h volumetric flow rate, especially 1-5 Nm 3 / h, preferably 1.1 to 5 Nm 3 It is further preferred that the precursor silane, the precursor hydrocarbon, in particular the olefinic hydrocarbon, or a mixture thereof is injected into the tubular reactor at a volumetric flow rate of 1 to 15 Nm / h. 3 / h, especially 1-10Nm 3 / h, preferably 1 to 5 Nm 3 / h into the tubular reactor. a) and b) can be mixed before injecting them into the reactor.

[0064] According to a further embodiment, a) a gas stream comprising at least one precursor silane of a precursor silane, and b) a gas stream comprising a precursor hydrocarbon, in particular an olefinic hydrocarbon, is mixed at a concentration of 1 to 15 Nm 3 / h volumetric flow rate, especially 1-5 Nm 3 / h, preferably 1.1 to 5 Nm 3 / h, the ratio of a) to b) is 20:1 to 1:1, preferably 10:1 to 1:1, and optionally the reaction is carried out at a pressure of 1.2 to 3.0 bar. abs. It is held at.

[0065] Furthermore, the reaction is preferably carried out primarily within a heated tubular inert gas flow comprising argon, helium and / or neon, particularly argon, for a time frame of 500 milliseconds to 15 seconds.

[0066] According to a further aspect of the invention, the inert gas is selected from argon, helium, neon and nitrogen, in particular the inert gas stream is selected from argon and / or the inert gas for quenching is selected from nitrogen and argon.

[0067] Inert gas flow: 0.5 to 25 Nm 3 / h, especially 1-10Nm3 / h, especially 2-8Nm 3 / h, and the preferred inert gas is argon.

[0068] A heated tubular inert gas flow of 0.5 to 25 Nm 3 / h, especially 1-10Nm 3 / h, especially 2-8Nm 3 / h and the temperature of the inert gas flow is more preferably between 490° C. and 670° C. A preferred inert gas is argon.

[0069] According to a particularly preferred embodiment, the precursor silane, precursor olefinic hydrocarbon or mixtures thereof are preferably oxidized at a temperature of 3 to 15 Nm. 3 / h, especially at a volumetric flow rate lower than that of a heated tubular inert gas stream, from 1 to 5 Nm 3 / h into the tubular reactor, and in particular, the heated tubular inert gas stream has a temperature of about 400-520°C when the precursor silane, precursor olefinic hydrocarbon, or mixture thereof is injected into the reaction zone of the tubular reactor.

[0070] According to a particularly preferred embodiment, the precursor silane, precursor olefinic hydrocarbon or mixtures thereof are preferably oxidized in a solvent, in particular at 4 to 10 Nm 3 / h, especially at lower volumetric flow rates than the heated tubular inert gas stream, from 1 to 4 Nm 3 / h into the tubular reactor.

[0071] According to a further embodiment, the reaction may be carried out in the presence of hydrogen, in particular the gas stream containing the precursor silane may further contain hydrogen, more preferably from 0.2 to 15 Nm 3 / h, and / or b) the gas stream containing the precursor olefinic hydrocarbon may further contain hydrogen (H2), more preferably 0.2 to 15 Nm 3 / h and / or the heated tubular inert gas stream may further contain hydrogen at a volumetric flow rate of 0.2 to 15 Nm 3The hydrogen may contain hydrogen (H2) at a volumetric flow rate of 0.2 to 15 Nm3 / h. 3 / h, optionally in a mixture with at least one or both precursors and / or in a mixture with an inert gas, preferably into a tubular reactor.

[0072] The present invention also provides an anode, in particular an anode for use in a cell in a secondary lithium-ion battery (LIB), comprising silicon-carbon composite particles, optionally comprising at least a binder, and optionally comprising acetylene black, carbon black, graphite, or a mixture of these elements. A preferred composition of the anode may comprise 2 to 90% by weight, in particular 40 to 65% by weight, of silicon and / or silicon-carbon composite particles, preferably silicon-carbon composite particles, 5 to 97% by weight, 5 to 30% by weight, preferably 0.5 to 25% by weight, of graphite or acetylene black, carbon black, graphite, or a mixture of these elements, and 0.5 to 30% by weight, in particular 5 to 25% by weight, of binder, the composition totaling 100% by weight.

[0073] A typical anode composition may include 10 wt% carbon black, 15 wt% graphite, and 15 wt% polyacrylic acid binder (PAA), totaling 100 wt% silicon carbon composite particles.

[0074] Preferred binders include polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), alginate (Alg), gum arabic (GA), guar gum (GG), chitosan, starch, polyimide, polyethyleneimine (PEI), poly(1-pyrenemethyl methacrylate), poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoate), b-cyclodextrin polymer (b-CDp), PEDOT:PSS:xanthan gum (XG), chitosan-glutaraldehyde (CS-GA), polyvinylidene fluoride (PVDF), or mixtures thereof.

[0075] A further subject of the present invention is a battery, in particular a secondary battery, more preferably a battery for use in a lithium ion battery (LIB), comprising at least one anode, in particular an anode comprising the silicon carbon composite particles of the present invention, preferably amorphous silicon carbon composite particles comprising carbon atomically distributed in amorphous silicon. Furthermore, it is preferred that the battery comprises at least two or more secondary cells, in particular up to 1000 secondary cells.

[0076] Specific embodiments of the present invention are described below without limiting the invention to these specific examples.

[0077] Working Example: Experiment: A tubular reactor made of quartz (length 500 mm or 1000 mm to be heated, diameter 120 mm). Precursor silane and precursor olefinic hydrocarbon were injected into the tubular reactor through a nozzle. Inert gas was injected tubularly around the nozzle of the tubular reactor. A heating element was placed on the outside of the quartz glass reactor and could be controlled along the reactor length. The nozzle was located on the axis of the reactor in the reaction zone of the first reaction section. Unless otherwise stated, the reaction was carried out at 1 bar. abs. So I went.

[0078] Analysis method: Specific surface area measurement The specific surface area was measured by nitrogen absorption using the Brunauer, Emmett and Teller (BET) method (instrument: TriStar II Plus, Micromeretics). Prior to the measurement, the samples were dried under vacuum at 150°C for 20 minutes.

[0079] Carbon, Hydrogen, and Oxygen Content Measurement: The total carbon, hydrogen, and oxygen content is defined as the concentration averaged over the entire powder volume and is measured using elemental analysis by combustion. A Leco CS744 analyzer was used to measure the carbon content. Elemental analysis of oxygen and hydrogen was performed using a Leco ONH836 elemental analyzer. For oxygen and hydrogen content measurements, measurements were performed with and without air contact. For measurements without air contact, samples were filled into capsules in a glove box under a protective atmosphere, sealed, and evacuated from the glove box into transport containers. These transport containers were placed on an attachment, flushed with gas, placed in the analyzer, and passed through an incinerator, after which measurements were performed.

[0080] X-ray Photoelectron Spectroscopy (XPS): Carbon, oxygen, and silicon content are measured by X-ray photoelectron spectroscopy (XPS) using an ESCALAB 250xi ThermoFisher Scientific spectrometer equipped with a monochromated Al Kα source as a function of distance from the surface, using a depth profiling method that reveals subsurface information. The powder is placed on an XPS sample holder, and XPS spectra are collected first from the sample surface. The binding energy is referenced to C1s at 284.6 eV. The sequence of argon ion gun etching and spectrum acquisition is repeated until the desired depth of profiling is reached.

[0081] X-ray diffraction (XRD): The compositional and structural parameters of the layers were measured by Rietveld refinement of X-ray diffraction data collected in the 2-theta range from 15 to 110 °C with steps of 0.05° using a Philips X'Pert Pro diffractometer (Cu Kα radiation) operated at 40 kV and 40 mA.

[0082] Transmission Electron Microscopy (TEM): Structural and powder morphology studies were performed using a transmission electron microscope (TEM). The instruments used included an FEI Tecnai F20 operating at 200 kV and a Cs-corrected JEOL JEM-2200FS TEM / STEM using an accelerating voltage of 200 kV. The nanoparticles were dispersed in ethanol and deposited on a holey carbon TEM sample grid.

[0083] Differential Scanning Calorimetry (DSC): DCS measurements were performed using a Netzsch STA 449 F1 Jupiter TG / DSC to measure the thermal properties of the powders and to determine the characteristic temperatures of phase transformations that occur during heat treatment of the samples. Samples were tested in the temperature range between 30 and 1100 °C with a heating rate of 10 K / min.

[0084] Solid-state NMR: NMR measurements were performed at 400 MHz (H 1 A Bruker Avance III HD spectrometer was used, operating at a frequency of 5 kHz (5 kHz) and equipped with a Bruker CP / MAS probe. The sample was placed in a ZrO rotor (4 mm diameter) and measured at 5 kHz (5 kHz). 29 ) / 9kHz(C 13 ) and a 5-second relaxation delay (C 13 and Si 29 ), 32kHz(Si 29 ) / 29.8kHz(C 13 ) spectral width, and 100 Hz (Si 29 ) / 50Hz(C 13 ) line broadening and Fourier transform were used to obtain the field-induced decay (FID).

[0085] Working Example: Precursor silane and precursor olefinic hydrocarbon were injected into a tubular reactor made of quartz (500 mm or 1000 mm long, 120 mm diameter, heated outside the reactor) through a nozzle located at the reactor axis (see Table 1). Inert gas was tubularly injected around the nozzle of the tubular reactor. In the hot-wall reactor, pure Si powder was obtained by injecting silane into the reactor, but for the synthesis of powdered silicon-carbon composite particles, a mixture of monosilane and ethylene was used as the carbon precursor. The selection of appropriate gas-phase reaction conditions was guided by the intended structural and microstructural design aimed at improving the material's performance in LIB anode applications (see Table 1). [Table 1] [Table 2]

[0086] Lower reaction temperatures (approximately 700°C or less) favor the formation of an amorphous phase. Increasing the temperature to 700°C and above increases the proportion of crystalline Si. At 850°C, fully crystalline Si is obtained under otherwise identical reaction conditions (Si-cr). Figures 1a and 1b show transmission electron microscope (TEM) images of silicon-carbon composite particles, showing that nanoparticles produced at 640°C and 690°C, respectively, are amorphous and form agglomerates without obvious sintering between particles.

[0087] The collected silicon-carbon particles were analyzed by XRD to detect the content of silicon, carbon, hydrogen, and oxygen. Furthermore, XRPD confirmed that the particles were produced as 100% amorphous particles at a reaction temperature below 690°C. The results are described below.

[0088] The following diagram details the chemical and physical properties of silicon carbon particles and their electrical properties as materials in anodes. [Brief explanation of the drawings]

[0089] [Figure 1a] FIG. 1 shows amorphous silicon carbon composite particles (Si / C22) produced by gas phase reaction in a hot wall reactor at 640° C. [Figure 1b] FIG. 1 shows amorphous silicon carbon composite particles (Si / C2) produced by gas phase reaction at 690° C. in a hot wall reactor. [Figure 2a] Figure 13C-CP / MAS spectrum 9.091 pp / cm, 914.7 Hz / cm. No aromatic bonds are observed and the broad signal is purely due to instrumental background. [Figure 2b] FIG. 1 shows the 29Si-CP / MAS spectrum, 9.091 ppm / cm, 727.7 Hz / cm. [Figure 3]Figure 3a shows the potential vs. capacity for the first cycle measured at a rate of 0.2 C with a cutoff potential of 0.01-2.5 V vs. Li / Li+ for pure crystalline Si (Alfa Aesar, SSA approximately 28 m / g). Figure 3b shows the potential vs. capacity for the first cycle measured at a rate of 0.2 C with a cutoff potential of 0.01-2.5 V vs. Li / Li+ for amorphous Si (Si-am) produced in a gas-phase reactor at 640 °C. Figure 3c shows the potential vs. capacity for the first cycle measured at a rate of 0.2 C with a cutoff potential of 0.01-2.5 V vs. Li / Li+ for amorphous silicon carbon composite particles (Si / C22) produced in a gas-phase reactor at 640 °C. Figure 3d shows the potential vs. capacity for the first cycle measured at a rate of 0.2 C with a cutoff potential of 0.01-2.5 V vs. Li / Li+ for pure crystalline Si (Alfa Aesar). Figure 3e shows the differential capacity curves dQ / dV obtained during delithiation at a rate of 0.2 C using a cutoff potential of 0.01-2.5 V vs. Li / Li+ for amorphous silicon (Si-am) produced in a gas-phase reactor at 640 °C. Figure 3f shows the differential capacity curves dQ / dV obtained during delithiation at a rate of 0.2 C using a cutoff potential of 0.01-2.5 V vs. Li / Li+ for amorphous silicon (Si-am) produced in a gas-phase reactor at 640 °C. Figure 3f shows the differential capacity curves dQ / dV obtained during delithiation at a rate of 0.2 C using a cutoff potential of 0.01-2.5 V vs. Li / Li+ for amorphous silicon (Si / C22) composite particles produced in a gas-phase reactor at 640 °C. FIG. 3a shows the differential capacity curves dQ / dV obtained during delithiation at a rate of 0.2 C using Li / Li+, and FIG. 3b shows the differential capacity curves dQ / dV obtained during delithiation at a rate of 0.2 C using Li / Li+ in the first and second cycles at a cutoff potential of 0.005-1 V vs. the cutoff potential of 0.005-1 V for amorphous silicon carbon composite particles (Si / C15) produced at 665°C in a gas-phase reactor. [Figure 4a] FIG. 1 shows the X-ray diffraction patterns of silicon and amorphous silicon carbon composite particles with different carbon contents synthesized at 640° C. with a residence time of 5 seconds. [Figure 4b]Figure 1 shows the X-ray diffraction patterns of pure amorphous silicon (Si-am) and amorphous silicon carbon composite powders with different carbon contents (Si / C14: 6.3 wt% C, Si / C17: 14.2 wt%) synthesized at 640 °C for a dwell time of 5 seconds and then annealed at 690 °C for 1 hour. [Figure 4c] FIG. 1 shows XPS carbon concentration depth profiles recorded from pure amorphous silicon (Si-am) and amorphous silicon carbon composite particles with different carbon contents. [Figure 4d] FIG. 1 shows DSC signals collected from amorphous silicon (Si-am) and amorphous silicon carbon composite powders containing 3.5 wt% carbon (Si / C22), 6.3 wt% carbon (Si / C14), and 14.2 wt% carbon (Si / C17). [Figure 5] Figure 1 shows the differential capacity (dQ / dV) area in the range between 0.38 and 0.8 V for pure crystalline Si (from Alfa Aesar), amorphous silicon (Si-am), and amorphous silicon carbon composite particles, and the ratio of the differential capacity peak area corresponding to the formation of crystalline c-Li15Si4, A[c-Li15Si4], to A[c-Li15Si4+a-Si'']. [Figure 6]Figures 6a-d show transmission electron microscopy (STEM) images and energy dispersive spectra (EDS) of silicon obtained from (a) agglomerated amorphous silicon nanoparticles after 270 full (de)lithiation cycles and (b) agglomerated amorphous silicon carbon composite particles after 310 full (de)lithiation cycles, using cutoff potentials of 0.05-1 V vs. Li / Li. The nanoparticles are discarded from the electrodes in the delithiated state. The electrodes contain 60 wt% Si or amorphous silicon carbon composite particles, 15 wt% carbon black, 10 wt% graphite, and 15 wt% polyacrylic acid binder (PAA), respectively. The electrodes are assembled into coin-shaped cells with a pure lithium counter electrode. The electrolyte solution used was a mixture of 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (3:7), 2 wt% vinylene carbonate, and 10 wt% fluoroethylene carbonate (FEC). The anode's first-cycle delithiation capacity was approximately 2900 mAh / g, the first-cycle coulombic efficiency was approximately 90%, and the mass loading was 1.6-1.7 mganode / cm-2. [Figure 7] Coulombic efficiency vs. cycle number and specific capacity vs. cycle number for amorphous silicon carbon composite particles (amorphous Si / C, 100% amorphous) and crystalline silicon (100% crystalline). Delithiation capacity (filled symbols) and Coulombic efficiency (open symbols) for fully crystalline silicon (circle symbols) and amorphous silicon carbon composite particles (square symbols).

[0090] The chemical and physical properties of the silicon carbon particles as materials in the anodes of FIGS. 1 to 7 and their electrochemical properties are described below.

[0091] The silicon carbon particles were analyzed by Rietveld analysis of XRPD, and the silicon, carbon, hydrogen, and oxygen contents were determined by elemental analysis (Table 2). XRPD confirmed that the particles were produced as amorphous particles, with the amount of amorphous phase ranging from 99% to 100% by weight.

[0092] Figures 2a and 2b show the solid-state NMR spectra obtained from silicon-carbon composite particles. 13 C-CP / MAS spectrum 9.091 pp / cm, 914.7 Hz / cm (Fig. 2a) and 29 Not observed by Si-CP / MAS spectrum 9.091 ppm / cm, 727.7 Hz / cm (Fig. 2b); 13 The broad signals in the C-CP / MAS spectra are purely due to instrumental background. 29 Si-CP / MAS (CP: cross polarization) shows a very broad signal extending to about 130 ppm, which according to the literature (Lit: H. Brequel et al., J. of. Materials Synthesis and Processing, 8, 5 / 6, 2000, 369-375) can be assigned to the following fragments, as proposed in Table 3: [Table 3]

[0093] Also, 29 With Si (high performance decoupling), the observed signal is broader, less intense, and shifted to higher field (negative chemical shift). 13 The C-NMR spectrum (CP / MAS, CP: cross polarization) shows a signal at +14 ppm with a Gaussian profile, verifying a pure aliphatic carbon signal. The broad signal is also typical for amorphous systems. Therefore, 29 Si-NMR spectrum and 13Both the C-NMR spectrum and the amorphous silicon carbon composite particles have been shown to be free of crystalline phases and free of polymeric SiC. 29 In the Si-NMR spectrum, there are three very sharp signals at -16 ppm, -20 ppm and 27 ppm. 13 The C-NMR spectrum also has a set of three sharp signals at 27 ppm, 20 ppm, and 15 ppm.

[0094] Figure 3a-3g: Potential curves measured on electrodes containing 60 wt% Si or amorphous silicon carbon composite particles, 20 wt% acetylene black, and 20 wt% polyimide binder (PI), respectively; mass loadings were 1.7-1.9 mg anode / cm -2 The electrodes are assembled into coin-shaped cells with a pure lithium counter electrode. The electrolyte solution is a mixture of 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (3:7) with 3 wt% vinylene carbonate. The numbers 1, 3, 10, and 20 correspond to the 1st, 3rd, 10th, and 20th cycles. a-Si' and a-Si'' represent the dQ / dV peaks due to the lithiated amorphous phases of various compositions, while c-Li 15 Si4 is a crystalline c-Li 15 The position of the dQ / dV peak due to the Si4 phase is shown.

[0095] c-Li 15 The electrochemical signature of Si4 formation is a characteristic voltage plateau around 0.42 V in the voltage vs. capacity curve during delithiation, or a corresponding peak at about 0.42 V in the differential capacity curve dQ / dV (Figures 3a, 3b, 3d, and 3e). Both features indicate a first-order phase transformation and consequently a large volume change during the transformation, reducing the stability of the silicon-based particles.

[0096] Both crystalline and amorphous silicon exhibit this plateau / peak at approximately 0.42 V, which is consistent with the c-Li 15The formation of Si4 is shown (Figures 3a, 3b, 3d, and 3e).

[0097] In an electrode containing silicon carbon composite particles (synonymous with amorphous silicon carbon composite particles), c-Li 15 The formation of Si4 is effectively suppressed, as confirmed by the absence of a characteristic voltage plateau in the voltage vs. capacity curves and the absence or only a weak peak at approximately 0.42 V in the differential capacity dQ / dV curves (Fig. 3c, 3f, 3g). Conversely, a clear peak in the differential capacity curve is observed around 0.42 V in amorphous Si (Si-am), with a peak area approximately four times larger than that of amorphous silicon carbon composite particles (Fig. 3e); the peak area is approximately 4 times that of c-Li formed during cycling. 15 Corresponding to the amount of Si4.

[0098] The area of ​​differential capacitance (dQ / dV), A[c-Li], in the range between 0.38 V and 0.8 V was measured for pure crystalline Si (Alfa Aesar), amorphous silicon (Si-am), and amorphous silicon carbon composite particles. 15 Si4+a-Si′′] versus crystalline c-Li 15 The peak area of ​​the differential capacity corresponding to the formation of Si4, A[c-Li 15 The ratio A[c-Li 15 Si4] / A[c-Li 15 The ratio A[c-Li] for amorphous silicon carbon particles is less than 0.1 and remains virtually unchanged during cycling, whereas this ratio is between 0.1 and 0.37 for pure crystalline Si (Alfa Aesar) and amorphous Si (Si-am). The ratio A[c-Li] for amorphous silicon carbon particles (Si / C15) produced at 665 °C 15 Si4] / A[c-Li 15 Si4+a-Si′′] is zero, i.e., crystalline c-Li 15 No formation of Si4 phase is observed (Fig. 3g). [Table 4]

[0099] The first cycle coulombic efficiency (CE) is maintained at a high level of 89.2% in the amorphous silicon carbon composite powder; for comparison, the first cycle CE of Si-am is 90.2% and that of pure crystalline Si (Alfa Aesar) is 77.2% (the corresponding lithiation / delithiation curves are shown in Figure 3).

[0100] Surprisingly, without the addition of FEC, the c-Li 15 The suppression of the formation of the Si4 phase is observed (Figs. 3c and 3f). These silicon carbon composite particle powders have a thickness of about 6 m 2 The low specific surface area (SSA) of the electrode material is a promising strategy for realization in LIBs. The addition of carbon to the silicon-carbon particles of the present invention disrupts the local atomic environment of the amorphous phase, thus forming crystalline c-Li 15 Conversion to Si4 modification is suppressed.

[0101] Therefore, the design of silicon carbon composite particles is 15 This represents a new concept for suppressing Si4 formation.

[0102] Reacting silane with ethylene at 640°C for 5 seconds yields perfect (100%) amorphous silicon-carbon composite particles with a characteristic amorphous halo in the X-ray diffraction pattern (Figure 4a), regardless of the concentrations of silane and ethylene in the gas mixture. Specifically, the intensity of the halo decreases, and the position of the halo shifts to higher diffraction angles as the carbon concentration increases, indicating the formation of a silicon- and carbon-containing amorphous phase.

[0103] To investigate the distribution of carbon within silicon-carbon composite particles (Si / C nanoparticles), carbon XPS spectra were collected from amorphous Si (Si-am) and amorphous silicon-carbon composite particles, and depth profiles were measured using sputtering. Amorphous Si (Si-am) exhibits a low but consistent background carbon concentration, which is typical of samples handled under ambient conditions. In contrast, a clear carbon concentration gradient is observed in silicon-carbon composite particles. The higher the carbon content in the silicon-carbon composite particles, as measured by elemental analysis, the steeper the depth-dependent carbon concentration gradient. Therefore, the structure of silicon-carbon composite particles can be described as C-lean at the particle center and C-rich near the particle surface. This particular Si / C structure in the silicon-carbon composite particles of the present invention is distinctly different from conventional Si+C composites, in which Si is coated by a carbon layer and embedded in a carbon layer.

[0104] The DSC curves of the silicon and silicon-carbon composite powders show several distinct features (Figure 4d). The feature between approximately 400 and 450 °C can be attributed to hydrogen desorption. The exothermic peak at 680 °C is most prominent in samples with no or low carbon content. This peak indicates the crystallization of amorphous silicon, as confirmed by X-ray diffraction analysis of material annealed at 690 °C for 1 h (Figure 4b). Surprisingly, the silicon-carbon composite particles exhibit a broader, less intense exothermic silicon crystallization signal compared to amorphous Si (Figure 4d). In addition to amorphous Si, the silicon-carbon composite particles exhibit an additional exothermic peak between 880 and 920 °C, which can be attributed to the in situ formation of silicon carbide. Rietveld refinement of the X-ray data shown in Figure 4b indicates that pure amorphous Si is fully crystallized after annealing at 690 °C for 1 h. The amount of crystalline phase in the silicon-carbon composite powder after annealing is significantly lower than that in the Si, decreasing from 40 to 20 wt% when the carbon concentration increases from 6.3 to 14.2 wt%, respectively. From the DSC measurements, it can be concluded that carbon is advantageous in suppressing the crystallization of amorphous silicon-based materials, which is particularly important for the realization of silicon-carbon composite particles as anode materials.

[0105] The presence of carbon in the amorphous silicon carbon composite particles alters the dealloying reaction and has a stabilizing effect against degradation of the silicon particles, as qualitatively shown by scanning transmission electron microscopy (STEM) analysis (Figures 6a-6d). Annular dark-field (ADF) scanning transmission electron microscopy (STEM) images and energy dispersive spectroscopy (EDS) of the amorphous silicon carbon composite particles at cutoff potentials of 0.005-1 V vs. Li / Li, respectively. +(The electrodes were cycled to similar degradation in terms of specific capacitance values.) This example demonstrates that the degree of degradation due to dealloying reactions can be reduced in amorphous silicon carbon composite particles, and thus better control or attenuation of surface area changes can be achieved in amorphous silicon carbon composite particle-containing materials.

[0106] The electrochemical capacity and coulombic efficiency of amorphous silicon-carbon composite particles were compared with crystalline silicon material (Si-Cr) (Figure 7). Electrode preparation was as follows: Electrochemical performance was evaluated in a half-cell using lithium metal as the counter electrode. Silicon or silicon-carbon composite particles were mixed with carbon (TIMCAL, carbon black C45) and binder (polyacrylic acid) in a ratio of 80:5:15 weight percent. All components were mixed with an ethanol / water mixture in a centrifugal mixer for approximately 7 minutes to obtain a homogeneous slurry. This slurry was then doctor-bladed onto a copper sheet and dried at 60 °C for 16 hours. The sheet was cut into circular pieces with a diameter of 13 mm. The mass loading was 1 mg / cm. 2 The electrodes were mounted in a glove box in Swagelok T-cells. Lithium foil was used as the counter and reference electrodes. The electrolyte was a mixture of 1 M LiPF6, ethylene carbonate (EC), dimethyl carbonate (DMC), and fluoroethylene carbonate (FEC). Glass fiber material was used as the separator. All electrochemical measurements were performed at 25 °C using a 4000 Battery Tester (Maccor) at specific currents corresponding to 0.05 C, 0.1 C, and 0.5 C.

[0107] The initial capacity is approximately 3500 mAh / g for pure crystalline silicon and approximately 3070 mAh / g for amorphous silicon carbon composite particles. For both materials, the capacity drops to approximately 2200 mAh / g after the second cycle. However, the coulombic efficiency of the amorphous silicon carbon composite particles is high, in contrast to pure crystalline silicon, reaching 85% and 92%, respectively, in the first and second formation cycles, and reaching levels above 99.5% in subsequent cycles. We believe that the high coulombic efficiency is due to reduced formation of a solid electrolyte interphase, particularly due to the carbon content at the particle surface. The high initial capacity is due to the high overall silicon content, indicating good electrical connection of the silicon. The amorphous silicon carbon composite particles exhibit good performance during the first 120 cycles, along with a high specific capacity. After 120 cycles, the capacity is 1700 mAh / g, whereas for pure crystalline silicon the capacity is approximately 415 mAh / g.

[0108] A further modification of the synthesis of silicon-carbon composite particles at low temperatures within a well-defined reaction zone within a tubular inert gas flow, surrounding a precursor silane and a precursor olefinic hydrocarbon at low temperatures of about 490°C to 640°C within a short time frame of 500 milliseconds to 20 seconds, preferably up to 10 seconds, results in highly uniform, spherical silicon-carbon particles with particle sizes of less than 250 nm, preferably 90 to 230 nm. The tubular inert gas flow is, in particular, a laminar inert gas flow. Under very specific reaction conditions, a reaction zone is formed within the tubular inert gas flow at temperatures between 400°C and 670°C, preferably between 430°C and 500°C, and a gas flow containing the precursor silane and the precursor olefinic hydrocarbon is injected into this reaction zone, resulting in 100% amorphous silicon-carbon particles with a carbon content that decreases from the subsurface region toward the center of the particle, which is characterized by the presence of crystalline Li. 15 Highly effective in suppressing the formation of Si4 phase.

Claims

1. 1. A silicon carbon composite particle, the particle comprising: a silicon content of 85 to 99.63 wt. %; a carbon content of 0.3 to 15% by weight, and A hydrogen content of at least 0.04% by weight and an oxygen content of 0-1% by weight Contains elements of 1. A silicon carbon composite particle, wherein the elements total 100% by weight, and the subsurface region of the particle, beginning at the surface and extending at least 30 nm from the surface toward the center of the particle, has a carbon content that is at least 3% by weight higher than that of the central region of the particle, the central region being the remainder of the particle and directly connected to the subsurface region.

2. 2. The silicon carbon composite particles of claim 1, wherein the particles have a chlorine content of less than 0.7 ppm by weight.

3. 3. The silicon-carbon composite particles according to claim 1, wherein the average particle size of the primary particles is less than 300 nm.

4. The particles may contain hydrogen, SiH- species and / or (poly-[SiH ２ 4. Particles according to claim 1, characterized in that they have a content of amorphous silicon comprising:

5. 5. Particles according to claim 1, characterized in that the silicon content of the particles is at least 0.5% to 30% by weight higher in a central region of the particle than in a subsurface region of the particle, the central region being connected to the subsurface region, the subsurface region of the particle starting at the surface and extending up to 30 nm in the direction from the surface towards the center of the particle.

6. 6. The particle of claim 5, wherein the silicon content of the particle is at least 2.0% to 15% by weight higher in a central region of the particle than in a subsurface region of the particle, the central region being connected to the subsurface region, and the subsurface region of the particle starting at the surface and extending up to 30 nm in a direction from the surface towards the center of the particle.

7. 7. Particles according to any one of claims 1 to 6, characterized in that the carbon content of the particles is at least 3% to 30% by weight higher in the subsurface region of the particles than in the central region of the particles, the central region being connected to the subsurface region, the subsurface region of the particles starting at the surface and extending up to 30 nm in the direction from the surface towards the center of the particle.

8. 8. Particles according to claim 1, characterized in that the carbon content of the particles is between 2% and 15% by weight.

9. 9. Particles according to any one of claims 1 to 8, characterized in that the particles have a content of aliphatic hydrocarbon compounds.

10. The particles are crystalline Li １５ Si ４ (c-Li １５ Si ４ 10. The particles according to claim 1, characterized in that they have a differential capacity (dQ / dV) versus voltage curve with a peak corresponding to the formation of dQ / dV (dichloromethane), whereby the ratio of the area of ​​this peak to the area of ​​the differential capacity (dQ / dV) in the range between 0.38 and 0.8 V is in the range of 0 to 0.1, at least during the first cycle.

11. A method for producing silicon carbon composite particles according to any one of claims 1 to 10, comprising: (i) a) a gas stream comprising at least one precursor silane of a precursor silane, comprising monosilane, disilane, trisilane, tetrasilane, pentasilane, hexasilane, heptasilane, octasilane, iso-tetrasilane, iso-pentasilane, neo-pentasilane, cyclopentasilane, cyclohexasilane and / or fully hydrogenated organosilanes containing 1 to 8 silicon atoms and 1 to 10 carbon atoms or a mixture of at least two of the aforementioned silanes; and b) subjecting a gas stream comprising a precursor hydrocarbon selected from olefinic hydrocarbons, alkynes and a mixture of at least two of the aforementioned hydrocarbons to (ii) reacting in a tubular reactor at a reaction temperature of 400°C to 700°C; (iii) The reaction occurs primarily within a heated tubular inert gas flow for a time frame of 500 milliseconds to 20 seconds. A method comprising:

12. 12. The method of claim 11, wherein in (b), the precursor hydrocarbon is at least one precursor olefinic hydrocarbon selected from alkenes and cycloalkenes containing 1 to 10 carbon atoms or a mixture of at least two of the foregoing olefinic hydrocarbons.

13. 13. The method of claim 11 or 12, wherein in (iii), the reaction is carried out in a reaction zone located within a heated tubular inert gas flow for a time frame of 500 milliseconds to 20 seconds.

14. 14. The method of any one of claims 11 to 13, wherein in (iii), the reaction is conducted in a reaction zone located within a heated tubular inert gas stream for a time frame of 500 milliseconds to 20 seconds, the heated tubular inert gas stream having a temperature of about 400 to 520°C when the precursor silane, precursor olefinic hydrocarbon, or mixture thereof is injected into the reaction zone of the tubular reactor.

15. 15. The method according to any one of claims 11 to 14, wherein the inert gas is selected from argon, helium, neon and nitrogen.

16. The heated tubular inert gas flow is 1 to 10 Nm ３ 16. The process according to claim 11, wherein the volume flow rate is 0.1 / h.

17. An anode comprising silicon carbon composite particles according to any one of claims 1 to 10.

18. A battery comprising at least one anode according to claim 17.

Images