Powders containing carbon matrix particles and composite powders containing such powders for use in the negative electrode of a storage battery.

Abstract

A powder containing carbon matrix particles, wherein silicon-based subparticles are dispersed in the carbon matrix particles, wherein the particles have a harmonic mean of their average Vickers hardness value and their average elastic modulus value, the hardness value and elastic modulus value being measured by nanoindentation and expressed in MPa, the harmonic mean being greater than or equal to 7000 MPa and less than or equal to 20000 MPa.

Description

[0001] Technical Field and Background Technology

[0002] The present invention relates to a powder containing carbon matrix particles, a composite powder containing such powder, the use of such composite powder in the negative electrode of a storage battery, and a storage battery including such a negative electrode.

[0003] Lithium-ion (Li-ion) batteries are currently the best-performing batteries and have become the standard for portable electronic devices. Furthermore, these batteries have penetrated other industries such as automotive and energy storage, experiencing rapid growth. The advantages of this type of battery are a combination of high energy density and good power performance.

[0004] Li-ion batteries typically contain multiple so-called Li-ion cells, which in turn contain a positive electrode (also called a cathode), a negative electrode (also called an anode), and a separator immersed in an electrolyte. The most commonly used Li-ion batteries for portable applications are developed using electrochemically active materials, such as lithium cobalt oxide or lithium cobalt nickel manganese oxide for the cathode and natural or synthetic graphite for the anode.

[0005] It is known that one of the important limiting factors affecting battery performance, especially battery energy density, is the active material in the anode. Therefore, in order to improve energy density, the use of silicon-containing electrochemical active materials in the negative electrode has been studied in recent years.

[0006] In this field, the performance of batteries containing Si-based electrochemically active powders is generally quantified by the so-called cycle life of the entire cell, which is defined as the number of times, or cycles, a battery containing such materials can be charged and discharged before reaching 80% of its initial discharge capacity. Therefore, most work on silicon-based electrochemically active powders focuses on improving this cycle life.

[0007] A disadvantage of using silicon-based electrochemical active materials in the anode is their large volume expansion during charging, which can reach up to 300% when lithium ions (e.g., through alloying or intercalation) are fully incorporated into the anode active material (a process commonly known as lithiation). This large volume expansion of the silicon-based material during lithium incorporation can induce stress in the silicon particles, which can then lead to mechanical degradation of the silicon material. Due to the cyclical repetition during charging and discharging in Li-ion batteries, this repeated mechanical degradation of silicon-based electrochemical active materials can shorten battery life to unacceptable levels.

[0008] Furthermore, a negative effect associated with silicon is the potential formation of a thick SEI (solid electrolyte interface) on the anode. The SEI is a complex reaction product of the electrolyte and lithium, leading to the loss of lithium that can participate in the electrochemical reaction, and thus resulting in poor cycle performance—that is, capacity loss per charge-discharge cycle. A thick SEI can further increase the battery's resistance, thereby limiting its ability to charge and discharge at high currents.

[0009] In principle, SEI formation is a self-terminating process that stops once a "passivation layer" forms on the surface of the silicon-based material. However, due to the volume expansion of the silicon particles, both the silicon particles and the SEI may be damaged during discharge (lithiation) and recharge (delithiation), thereby releasing new silicon surfaces and causing the initiation of a new SEI formation.

[0010] To address the aforementioned drawbacks, composite powders are typically used. In these composite powders, nanoscale silicon-based particles are mixed with at least one component suitable for protecting the silicon-based particles from electrolyte decomposition and accommodating volume changes. Such a component may be a carbon-based material, preferably forming the matrix.

[0011] Composite powders typically contain additional graphite particles to adjust their specific capacity to a practical level, between 500 mAh / g and 1500 mAh / g.

[0012] For example, such composite powders are mentioned in EP 2600446, which discloses a powder comprising a silicon and a metal alloy matrix. US 2018 / 0269483 discloses a pre-lithiated silicon-containing material comprising silicon core particles and a lithium coating. WO2016 / 061216 discloses a composite powder comprising silicon disposed within pores of a conductive support matrix. WO2017 / 040299 discloses a composite powder comprising silicon deposited into the pore volume of a porous support material. WO 2019 / 137797 discloses a composite powder comprising composite particles having a size-dependent silicon content within at least a portion of a size range from d10 to d90.

[0013] Despite the use of such composite powders, there is still room for improvement in the performance of batteries containing Si-based electrochemically active powders. Specifically, existing composite powders do not allow for the simultaneous achievement of high capacity and long cycle life, which is essential, especially for batteries used in electric vehicles.

[0014] The object of the present invention is to provide a stable electrochemically active powder comprising carbon-based matrix material particles in which silicon-based subparticles are dispersed. Once used as the negative electrode in a Li-ion battery, this powder has the advantage of allowing a combination of high capacity and long cycle life. Summary of the Invention

[0015] This objective is achieved by providing a powder according to embodiment 1, which, once incorporated into a composite powder for use in the negative electrode of a battery according to embodiment 4, allows for a combination of high capacity and long cycle life, as demonstrated in embodiments 1 to 5, compared to counterexamples 1 to 3.

[0016] This invention relates to the following embodiments:

[0017] Implementation Plan 1

[0018] In a first aspect, the present invention relates to a powder of carbon-based matrix material particles, said particles comprising silicon-based subparticles dispersed therein, said particles having a harmonic mean value HM calculated according to formula (1).

[0019]

[0020] Where H is the average Vickers hardness value of the carbon-based material particles, and E is the average elastic modulus value of the carbon-based material particles, both H and E are measured by nanoindentation and expressed in MPa. The powder is characterized in that HM is greater than or equal to 7000 MPa and less than or equal to 20000 MPa. Preferably, HM is greater than or equal to 7500 MPa and less than or equal to 18540 MPa. More preferably, HM is greater than or equal to 8000 MPa and less than or equal to 17060 MPa.

[0021] The term "powder containing carbon-based matrix material particles with silicon-based subparticles dispersed therein" refers to a powder in which the carbon-based particles are on average larger than the silicon-based subparticles because they contain the latter. Carbon-based matrix material particles are typically in the micrometer range, while silicon-based subparticles are typically in the nanometer range.

[0022] The term "silicon-based subparticles dispersed in the matrix material" refers to silicon-based subparticles that form agglomerates smaller than 1 μm or do not form agglomerates at all, and are mostly, preferably entirely, covered by the matrix material. Therefore, in the powder according to embodiment 1, the silicon-based subparticles are preferably in contact only with each other and / or with the matrix material.

[0023] Silicon-based subparticles can have any shape, such as substantially spherical, but can also have irregular shapes, rod-like, plate-like, etc. In silicon-based subparticles, silicon exists primarily in the form of metallic silicon, where trace amounts of other elements may have been added to improve properties, or some impurities such as oxygen or trace metals may be present. When taking into account all elements except oxygen, the average silicon content in such silicon-based subparticles relative to the total weight of the silicon-based subparticles is preferably 80% by weight or more, and more preferably 90% by weight or more.

[0024] For the purpose of illustrating in a non-limiting manner the determination of the average Vickers hardness value H and the average elastic modulus value E of the carbon-containing matrix material particles of the powder according to Embodiment 1, as well as the calculated harmonic average value HM, a procedure based on nanoindentation is provided below.

[0025] 1. First, the powder to be analyzed is embedded in resin to obtain a sample, and then the surface of the sample is polished to obtain a sample with a polished surface.

[0026] 2. The obtained sample with a polished surface was then analyzed using nanoindentation, allowing visualization of several regions containing particles. In each of these regions, contrast and brightness settings were adjusted to easily visualize the carbon-based matrix material particles in which silicon-based subparticles were dispersed. Due to their different chemical compositions, the differences in brightness allowed for easy differentiation between particles and subparticles.

[0027] 3. Depending on the particle size, perform one or more indentations on several carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0028] 4. In summary, at least 100 indentations are performed on at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0029] 5. For each indentation, determine the Vickers hardness and elastic modulus, and then calculate the average Vickers hardness and average elastic modulus for each of at least 10 different particles.

[0030] 6. Finally, calculate the harmonic mean HM using the following formula:

[0031]

[0032] Wherein H is the average Vickers hardness value of at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed, and E is the average elastic modulus value of at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0033] The hardness value in Implementation Scheme 1 corresponds to Vickers hardness, however it can be easily converted to any other type of hardness via well-known mathematical formulas.

[0034] Implementation Plan 2

[0035] In the second embodiment according to embodiment 1, the carbon-containing matrix material particles have an average Vickers hardness value H of at least 4000 MPa and at most 12000 MPa, and at least 28 × 10⁻⁶ MPa. 3 MPa and at most 60×10 3The average elastic modulus E is measured in MPa. Preferably, the carbon-based material particles have an average Vickers hardness H of at least 4000 MPa and at most 11000 MPa, and a minimum elastic modulus of 28 × 10⁻⁶ MPa. 3 MPa and at most 59 × 10 3 The average elastic modulus E is measured in MPa. More preferably, the carbon-based material particles have an average Vickers hardness H of at least 4000 MPa and at most 10000 MPa, and a minimum elastic modulus E of at least 28 × 10⁻⁶ MPa. 3 MPa and at most 58 × 10 3 The average elastic modulus E is measured in MPa.

[0036] Implementation Plan 3

[0037] In a third embodiment according to embodiment 1 or 2, the powder has a silicon content S expressed as a weight percentage (wt%), wherein 20 wt% ≤ S ≤ 70 wt%. In other words, the carbon-based matrix material particles in which silicon-based subparticles are dispersed have an average silicon content S, wherein 20 wt% ≤ S ≤ 70 wt%. Preferably, the silicon content S is greater than or equal to 25 wt% and less than or equal to 60 wt%, more preferably, the silicon content S is greater than or equal to 30 wt% and less than or equal to 50 wt%.

[0038] Powder with too low a silicon content will result in an excessively low specific capacity and will therefore prevent the battery from achieving a high energy density. Furthermore, since silicon subparticles significantly contribute to the average Vickers hardness of the carbon-based matrix material particles, if the amount of silicon subparticles is too low, the minimum HM value of 7000 MPa according to Embodiment 1 may not be achieved. On the other hand, powder with too high a silicon content will result in an excessively low amount of carbon-based matrix material and therefore an excessively low "carbon / Si from matrix" ratio. Consequently, the silicon subparticles will only be partially covered by the carbon-based matrix material, leading to increased SEI formation and thus a reduced average coulombic efficiency and shortened cycle life. Additionally, an excessively high amount of silicon subparticles may result in an excessively high average Vickers hardness of the carbon-based matrix material particles, and thus an HM value higher than the maximum value of 20000 MPa, preferably 18540 MPa, and more preferably 17060 MPa according to Embodiment 1.

[0039] Implementation Plan 4

[0040] In the fourth embodiment, a composite powder for a negative electrode of a storage battery comprises the powder described in any one of embodiments 1 to 3.

[0041] The term "composite powder for the negative electrode of a battery" refers to an electrochemically active powder containing electrochemically active particles, which can store and release lithium ions during the lithiation and delithiation processes of the negative electrode of the battery. Such powders can be equivalently referred to as "active powders."

[0042] The inventors have observed that the composite powder according to embodiment 4 is better able to withstand the adverse consequences of the presence of silicon-based subparticles in the carbon-based matrix material particles, namely, cracking in the matrix material, excessive SEI formation, and shortened cycle life, which are primarily caused by the large volume expansion of the silicon-based subparticles during lithium doping. This capability is attributed to the presence of carbon-based matrix material powder according to any one of embodiments 1 to 3 in the composite powder, thereby imparting a combination of hardness and elasticity properties to the carbon-based matrix material particles. Due to its elastic properties, the carbon-based matrix material can deform under the volume expansion of the silicon-based subparticles, while due to its hardness properties, this deformation is limited and thus ensures limited and somehow controlled negative electrode expansion. This allows the use of negative electrode materials with high capacity while keeping the impact of volume expansion on cycle life at an acceptable level.

[0043] Without elastic properties, the carbon-based matrix material will fracture under the pressure generated by the volume expansion of the silicon-based subparticles. Without hardness properties, the carbon-based matrix material will expand like the silicon-based subparticles, leading to unacceptable expansion of the negative electrode. In both cases, this will shorten the battery life to an unacceptable level.

[0044] Implementation Plan 5

[0045] In the fifth embodiment according to embodiment 4, at least 70% by weight of the carbon-containing matrix material particles in the composite powder, in which silicon-based subparticles are dispersed, are composed of the particles according to embodiment 1.

[0046] Alternatively, at least 70% by weight of the carbon-based matrix material particles in the composite powder, in which silicon-based subparticles are dispersed, are composed of particles according to embodiment 2 or 3.

[0047] An example of determining this percentage-based quantity of particles is provided in the "Analytical Methods" section.

[0048] Implementation Plan 6

[0049] In a sixth embodiment according to embodiment 4 or 5, the composite powder further comprises crystalline carbon particles that are physically different from carbon matrix material particles in which silicon-based subparticles are dispersed.

[0050] Specifically, the crystalline carbon-containing particles are not embedded in the carbon-containing matrix material particles. This can be visually confirmed based on the analysis of one or more SEM images of the cross-section of the composite powder. The fact that the crystalline carbon-containing particles are not embedded in the carbon-containing matrix material particles is advantageous for at least two reasons: (i) only the silicon-based subparticles need to be covered by the matrix material, thus requiring less matrix material with high irreversible capacity and low specific capacity, and (ii) the matrix material particles with silicon-based subparticles but without crystalline carbon-containing particles are smaller than those with other crystalline carbon-containing particles, resulting in less volume expansion.

[0051] However, some contact may exist between the two types of particles, located on their outer surfaces. This is even preferred to ensure that the composite powder has good electronic conductivity, thereby enabling batteries containing the composite powder to have high rate performance.

[0052] Crystalline carbon particles act as spacers between carbonaceous matrix material particles in which silicon-based subparticles are dispersed, thereby preventing these carbonaceous matrix material particles from agglomerating into aggregated composite powder. Without such spacers, the agglomerated composite powder may require mechanical treatment, such as grinding steps, for use in the negative electrode of a battery. This can weaken the integrity of the matrix material, leading to a decrease in the Vickers hardness and elastic modulus of the carbonaceous matrix material particles in which silicon-based subparticles are dispersed, and ultimately resulting in reduced performance of the battery containing such agglomerated composite powder.

[0053] The presence of crystalline carbon-containing particles in the composite powder can be determined, for example, by X-ray diffraction analysis. This method is described in the "Analytical Methods" section.

[0054] Implementation Plan 7

[0055] In the seventh embodiment according to embodiment 6, the crystalline carbon-containing particles are graphite particles.

[0056] Implementation Plan 8

[0057] In the eighth embodiment according to any one of embodiments 1 to 7, the carbon-based matrix material particles in which silicon-based subparticles are dispersed have d C The size distribution based on the number of 50, the d C 50 is greater than or equal to 1 μm, preferably greater than or equal to 5 μm and less than or equal to 25 μm, preferably less than or equal to 20 μm.

[0058] With or without the aid of image analysis procedures, the quantity-based size distribution is based on visual analysis of the minimum number of carbon-based matrix material particles contained in a powder or composite powder, in which silicon-based subparticles are dispersed. This minimum number of particles is at least 100 particles. Examples of determining the quantity-based fraction of particles are provided in the "Analytical Methods" section.

[0059] For clarity, for example, 10μm d c 50 here would mean that at least 50% of the carbon matrix material particles in which silicon-based subparticles are dispersed have a size of less than 10 μm, and at least 50% of the carbon matrix material particles in which silicon-based subparticles are dispersed have a size of greater than 10 μm.

[0060] Having d c Carbon-based matrix material particles with a number-based size distribution of less than 1 μm or even less than 5 μm, in which silicon-based subparticles are dispersed, may have excessively high specific surface areas, and thus increase the surface area for reaction with electrolytes and the formation of SEI, which is disadvantageous for the reasons previously explained. c Carbon matrix material particles with a number-based size distribution greater than 25 μm or even greater than 20 μm, in which silicon-based subparticles are dispersed, may be more prone to cracking during lithium absorption due to their size, resulting in a shortened cycle life of batteries containing such particles.

[0061] Implementation Plan 9

[0062] In the ninth embodiment according to any one of embodiments 1 to 8, the silicon-based subparticles are characterized by having d Si The size distribution based on the number of 50, the d Si 50 is greater than or equal to 40nm and less than or equal to 150nm.

[0063] With or without the aid of image analysis procedures, the quantity-based size distribution is based on visual analysis of the minimum number of silicon-based subparticles contained in the powder or composite powder. This minimum number of silicon-based subparticles is at least 1000 particles. Examples of determining the quantity-based fraction of particles are provided in the "Analytical Methods" section.

[0064] For clarity, for example, 100nm d Si 50 here would mean that 50% of at least 1000 silicon-based subparticles have a size of less than 100 nm, and 50% of at least 1000 silicon-based subparticles have a size of greater than 100 nm.

[0065] Having d SiSilicon-based subparticles with a size distribution below 40 nm are difficult to disperse effectively in matrix materials, which may reduce the electronic conductivity of the powder.

[0066] Having d Si Silicon-based subparticles with a size distribution greater than 150 nm are more prone to cracking during lithiation, resulting in a significantly shorter cycle life for batteries containing such powders.

[0067] It is believed that d Si 50 is unaffected by the method used to prepare the powder or composite powder, which means that the d of the silicon-based powder used as a precursor in the method is not affected. Si 50 value and d of silicon-based subparticles contained in the powder Si 50 value and d of silicon-based subparticles contained in the composite powder Si The values ​​are all 50.

[0068] Implementation Plan 10

[0069] In the tenth embodiment according to any one of embodiments 4 to 9, the composite powder has a silicon content A expressed as a weight percentage (wt%), wherein 10 wt% ≤ A ≤ 60 wt%.

[0070] Composite powders with a silicon content of less than 10% by weight will have too limited a specific capacity and therefore will not allow for the achievement of high energy densities in batteries. Composite powders with a silicon content of more than 60% by weight will be excessively affected by the volume expansion associated with this high silicon content, and will therefore lead to a shortened cycle life of the battery.

[0071] The composite powder also has a carbon content B expressed as a weight percentage (wt%), wherein 30 wt% ≤ B ≤ 88.5 wt%.

[0072] When the carbon content in the composite powder is less than 30% by weight, the amount of carbon-containing matrix material present is insufficient to completely cover the silicon-based subparticles, leading to increased electrolyte decomposition at the surface of the silicon-based subparticles and thus increased SEI formation. When the carbon content in the composite powder is higher than 88.5% by weight, the specific capacity of the composite powder becomes too low.

[0073] Implementation Plan 11

[0074] In the eleventh embodiment according to any one of embodiments 4 to 10, the composite powder has a silicon content A and an oxygen content C, both expressed as a weight percentage (wt%), wherein C ≤ 0.15 × A.

[0075] Composite powders with excessively high oxygen content will suffer additional irreversible lithium loss due to the formation of lithium oxide (Li2O) during the first lithiation of the powder, thereby increasing the initial irreversible capacity loss of batteries containing such composite powders.

[0076] Implementation Plan 12

[0077] In the twelfth embodiment according to any one of embodiments 1 to 11, the silicon-based subparticles contain at least 90% by weight of Si when taking into account all elements except oxygen.

[0078] The content of elements other than oxygen (such as metal elements) in silicon-based subparticles exceeding 10% by weight will excessively reduce the specific capacity of powders and / or composite powders, and is therefore undesirable.

[0079] Implementation Plan 13

[0080] In the thirteenth embodiment according to any one of embodiments 4 to 12, the BET surface area of ​​the composite powder is at most 10 m². 2 / g and preferably at most 5m 2 / g.

[0081] Importantly, the composite powder has a low BET specific surface area to reduce the surface area of ​​the electrochemically active particles in contact with the electrolyte, thereby limiting the formation of the lithium-consuming solid electrolyte interphase (SEI) and thus limiting the irreversible capacity loss of batteries containing such composite powders.

[0082] Implementation Plan 14

[0083] In the fourteenth embodiment according to any one of embodiments 1 to 13, the carbon-based matrix material particles in which silicon-based particles are dispersed are non-porous.

[0084] This is based on visual analysis of at least 100 cross-sections of a carbonaceous matrix material particle in which silicon-based particles are dispersed, preferably using a scanning electron microscope (SEM) with the assistance of an image analysis program. The particle is considered non-porous if, on average, less than 1% of the area of ​​the at least 100 cross-sections of the particle is occupied by pores (or cross-sections of pores). In other words, the particle is considered non-porous if the average fraction of the total area occupied by pores (or cross-sections of pores) to the total area occupied by the at least 100 cross-sections of the carbonaceous matrix material particle in which silicon-based particles are dispersed is less than 0.01.

[0085] Implementation Plan 15

[0086] In the fifteenth embodiment, the invention finally relates to a storage battery comprising a composite powder according to any one of embodiments 4 to 14. Detailed Implementation

[0087] In the following detailed description of preferred embodiments to practice the invention, preferred embodiments are described in detail. Although the invention has been described with reference to these specific preferred embodiments, it should be understood that the invention is not limited to these preferred embodiments. Rather, the invention includes many alternatives, modifications, and equivalents that will become apparent upon consideration of the following detailed description.

[0088] The analytical methods used

[0089] Determination of Si content

[0090] In the examples and counterexamples, energy-dispersive spectroscopy was used to measure the Si content of powders or composite powders via X-ray fluorescence (XRF). This method has an experimental random error of + / - 0.3 wt% Si.

[0091] In the case of composite powders containing carbonaceous matrix material particles in which silicon-based subparticles are dispersed, it may be difficult to measure the silicon content S of the powder by XRF. In such cases, analysis can preferably be performed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). This allows for the measurement of the silicon content in a given particle. Analysis of 10 particles of the matrix material is sufficient to obtain the average silicon content value S of the powder.

[0092] Determination of oxygen content

[0093] The oxygen content of powders and composite powders in the examples and counterexamples was determined using a LECO TC600 oxygen-nitrogen analyzer by the following method. The powder sample to be analyzed was placed in a sealed tin container, which itself was placed in a nickel basket. The basket was then placed in a graphite crucible and heated to above 2000°C using helium as the carrier gas. The sample thus melted, and oxygen reacted with the graphite in the crucible to produce CO or CO2 gas. These gases were directed into an infrared measurement cell. The observed signal was recalculated as the oxygen content.

[0094] Determination of carbon content

[0095] The carbon content of the powders and composite powders in the examples and counterexamples was determined using a Leco CS230 carbon-sulfur analyzer by the following method. The samples were melted in a ceramic crucible in a high-frequency furnace under a constant oxygen flow. The carbon in the sample reacted with oxygen and left the crucible as CO or CO2. After the final CO was converted to CO2, all the resulting CO2 was finally detected by an infrared detector. This signal was ultimately converted into carbon content.

[0096] Determination of specific surface area (BET)

[0097] Specific surface area was measured using a Micromeritics Tristar 3000 via the Brunauer-Emmett-Teller (BET) method. First, 2 g of the powder to be analyzed was dried in an oven at 120°C for 2 hours, followed by purging with N2. Then, prior to measurement, the powder was degassed under vacuum at 120°C for 1 hour to remove adsorbed substances.

[0098] Measurement of electrochemical performance

[0099] The electrochemical properties of the composite powders in the examples and counterexamples were determined by the following methods.

[0100] The powder to be evaluated was sieved using a 45 μm sieve and mixed with carbon black, carbon fibers, and sodium carboxymethyl cellulose binder in water (2.5 wt%). The ratio used was 89 parts by weight of composite powder / 1 part by weight of carbon black (C65) / 2 parts by weight of carbon fibers (VGCF) and 8 parts by weight of carboxymethyl cellulose (CMC). These components were mixed in a Pulverisette 7 planetary ball mill at 250 rpm for 30 minutes.

[0101] Copper foil cleaned with ethanol was used as the current collector. A 200 μm thick layer of the mixed components was coated onto the copper foil. The coated copper foil was then dried in a vacuum at 70 °C for 45 minutes. A 1.27 cm current collector was stamped into the dried coated copper foil. 2 The disc is used as an electrode in a button cell that uses lithium metal as the counter electrode. The electrolyte is 1M LiPF6 dissolved in EC / DEC 1 / 1 + 2% VC + 10% FEC solvent.

[0102] All button cells were cycled using a high-precision battery tester (Maccor 4000 series) with the procedure described below, where “CC” stands for “constant current” and “CV” stands for “constant voltage”.

[0103] • Loop 1:

[0104] Let stand for 6 hours

[0105] ○ Lithification was performed at C / 10, followed by CC lithiation to 10mV, and then CV lithiation up to C / 100.

[0106] Let it stand for 5 minutes

[0107] ○ Delithiation to 1.5V under C / 10 conditions

[0108] Let it stand for 5 minutes

[0109] • Starting from loop 2:

[0110] ○ Lithification was performed at C / 2 with CC up to 10mV, followed by CV lithiation up to C / 50.

[0111] Let it stand for 5 minutes

[0112] ○Delithiation under C / 2 conditions to 1.2V

[0113] Let it stand for 5 minutes

[0114] The coulombic efficiency (CE) of a coin cell is calculated for both the initial and subsequent cycles. CE is the ratio of the capacity upon delithiation to the capacity upon lithiation at a given cycle. The initial cycle is the most critical for CE because the SEI formation reaction has a significant impact on CE. Typically, for silicon-based powders, the CE at the initial cycle can be as low as 80% (or even lower), corresponding to a substantial 20% irreversible capacity loss in the coin cell. The goal is to achieve at least 90% CE at the initial cycle.

[0115] For subsequent cycles, although the coulombic efficiency (CE) will typically increase to over 99%, technicians will realize that subtle differences in coulombic efficiency per cycle can have a significant cumulative effect after the battery is expected to continue for hundreds or thousands of charge-discharge cycles. For example, a battery with an initial capacity of 1 Ah and an average CE of 99.8% will have 0.8 Ah of remaining capacity after 100 charge-discharge cycles, which is 60% higher than a battery with an average CE of 99.5% (0.5 Ah of remaining capacity).

[0116] For batteries containing composite powder with a specific capacity of 800±20 mAh / g, the target is to achieve an average CE of at least 99.6%, preferably at least 99.65%, from cycle 5 to cycle 50.

[0117] Determination of particle size distribution based on quantity

[0118] The number-based particle size distribution of carbon-based matrix material particles and / or silicon-based subparticles is determined by electron microscopy (SEM or TEM) analysis of cross-sections of powders (or composite powders) combined with image analysis.

[0119] For this purpose, the cross-sections of the powder (or composite powder) are prepared according to the procedure detailed below, including multiple cross-sections of carbon-based matrix material particles, wherein each cross-section includes multiple cross-sections of silicon-based subparticles.

[0120] 500 mg of the powder (or composite powder) to be analyzed was embedded in 7 g of resin (Buehler EpoxiCure 2), which consisted of a mixture of 4 parts epoxy resin (20-3430-128) and 1 part epoxy curing agent (20-3432-032). The resulting 1” diameter sample was dried over at least 8 hours. The sample was then mechanically polished first using a Struers Tegramin-30 until a maximum thickness of 5 mm was achieved, followed by further polishing at 6 kV for approximately 6 hours using an ion beam polisher (Jeol SM-09010 cross-section polisher) to obtain a polished surface. Finally, a carbon coating was applied to the polished surface using a Cressington 208 carbon coating machine for 12 seconds of carbon sputtering to obtain the sample to be analyzed by SEM, also known as a “cross-section”.

[0121] Then, an Xflash5030-127 (30mm) EDS detector from Bruker was used. 2 The prepared cross-section was analyzed using a JEOL FEG-SEM JSM-7600F (127 eV). The signal from this detector was processed by a Bruker Quantax 800EDS system.

[0122] Magnification is achieved by applying a 15 kV voltage at a working distance of a few millimeters. The value is reported as an image from backscattered electrons when added to an image from an optical microscope.

[0123] The size of a carbon-based material particle (or silicon-based subparticle) is considered to be equivalent to the maximum straight-line distance between two points on the periphery of a discrete cross-section of the carbon-based material particle (or silicon-based subparticle).

[0124] For the purpose of illustrating in a non-limiting manner the number-based particle size distribution of carbon-based matrix material particles (or silicon-based subparticles), SEM-based procedures are provided below.

[0125] 1. Obtain multiple SEM images of the cross-section of a powder (or composite powder) containing carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0126] 2. Adjust the image contrast and brightness settings to easily visualize the cross-sections of carbon-based matrix material particles and silicon-based subparticles. Due to their different chemical compositions, the difference in brightness allows for easy differentiation between particles and subparticles.

[0127] 3. Using suitable image analysis software, select at least 1000 discrete cross-sections of silicon-based subparticles and at least 100 discrete cross-sections of carbon-based matrix material particles from one or more of the acquired SEM images, respectively, such that they do not overlap with another cross-section of the silicon-based subparticles or another cross-section of the carbon-based matrix material particles. These discrete cross-sections of the silicon-based subparticles or carbon-based matrix material particles can be selected from one or more cross-sections of a powder (or composite powder) containing both carbon-based matrix material particles and silicon-based subparticles.

[0128] 4. For each of at least 1000 discrete cross sections of the silicon-based subparticles and at least 100 discrete cross sections of the carbon-based matrix material particles, measure the dimensions of the discrete cross sections of the silicon-based subparticles and the discrete cross sections of the carbon-based matrix material particles using appropriate image analysis software.

[0129] Then, the d values ​​of the number-based particle size distribution of silicon-based subparticles and the number-based particle size distribution of carbon-based matrix material particles, as determined by the method described above, are calculated accordingly. Si 10. d Si 50 and d Si 90 value and d C 10. d C 50 and d C 90 values. These quantity-based granular distributions can be easily converted into weight- or volume-based granular distributions using well-known mathematical formulas.

[0130] Determining the presence of pores in carbon-based matrix material particles

[0131] The same method is used for electron microscopy analysis of cross-sections of powders (or composite powders). For each of at least 100 discrete cross-sections of carbon-matrix material particles, the fraction of the total area occupied by pores (or the cross-sections of pores) out of the total area occupied by particles (or the cross-sections of particles) is determined using suitable image analysis software, and the average of these fractions is calculated. As previously stated, if the average of these fractions is less than 0.01, the particle is considered non-porous.

[0132] Determination of the presence of crystalline carbon-containing particles in composite powder

[0133] The presence of crystalline carbon-containing particles in the composite powder was determined by performing X-ray diffraction (XRD) analysis. The following methods were used.

[0134] Radiation with CuKα1 and CuKα2 (λ = 0.15418 nm) was applied to at least approximately 2 cm on the Panalytical'X Pert Pro system. 3 XRD measurements were performed on a flat surface of the powder material with a step size of 0.017°2θ, a scan rate of 34 minutes (2064 seconds), and 2θ measurements ranging from 5° to 90°. The compounds of this invention were identified using the ICDD database PDF-4+. At 2θ... Cu The XRD peak with a maximum value between 26° and 27° corresponds to the (002) reflection of graphitic carbon, which is generated by X-ray diffraction from interplanar graphene layers. First, the background is subtracted from the original XRD data. Then, the 2θ values ​​at half maximum intensity to the left and right of the C(002) peak are determined. Cu The full width at half maximum (FWHM) is the sum of these two 2θ values. Cu The difference between values. FWHM values ​​are generally determined using the procedure provided with the X-ray diffractometer. Manual calculation is also possible. If the calculated FWHM value is less than or equal to 0.5°2θ, it confirms the presence of crystalline carbonaceous particles in the composite powder.

[0135] Vickers hardness and elastic modulus were determined by nanoindentation method.

[0136] The Vickers hardness and elastic modulus of carbon-based matrix material particles containing silicon-based subparticles dispersed in powders and composite powders were determined using a nanoindentation tester (NHT). 3 The measurements were performed under the following test conditions and parameters:

[0137] Test atmosphere: air

[0138] Temperature: 22℃

[0139] Humidity: 40%

[0140] Indenter type: Berkovich

[0141] Load type: Linear

[0142] Maximum load: 5 mN

[0143] Pause at maximum load: 10 [s]

[0144] Loading / unloading rate: 30 [mN / min]

[0145] The number of indentations performed on each carbon-based matrix material particle containing embedded silicon subparticles varied depending on the particle size: for small particles smaller than 20 μm, only one indentation was performed on each particle, while for sufficiently large particles, matrices of various indentations were performed. For example, 4×4, 4×5, or 6×6 indentation matrices were performed on the particles (which is possible for these particles). The distance between the indentations was set to 10 μm. All results were obtained using the Oliver & Pharr method, where a sample ratio of 0.3 was assumed for the elastic modulus calculation.

[0146] The procedure includes the following steps: :

[0147] 1. First, the powder (or composite powder) to be analyzed is embedded in resin to obtain a sample, and the surface of the sample is further polished according to the previously described method to obtain a sample with a polished surface.

[0148] 2. The obtained sample with a polished surface was then analyzed using nanoindentation, allowing visualization of several regions containing particles. In each of these regions, contrast and brightness settings were adjusted to easily visualize the carbonaceous matrix material particles in which silicon-based subparticles were dispersed. Due to their different chemical compositions, the differences in brightness allowed for easy differentiation of matrix material particles containing or not containing silicon-based subparticles.

[0149] 3. Depending on the particle size, perform one or more indentations on several carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0150] 4. In summary, at least 100 indentations are performed on at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed.

[0151] 5. For each indentation, determine the Vickers hardness and elastic modulus, and then calculate the average Vickers hardness and average elastic modulus for each of at least 10 different particles.

[0152] 6. Finally, calculate the harmonic mean HM using the following formula:

[0153]

[0154] Wherein H is the average Vickers hardness value of at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed, contained in the powder (or composite powder), and E is the average elastic modulus value of at least 10 different carbon-based matrix material particles in which silicon-based subparticles are dispersed, contained in the powder (or composite powder).

[0155] Furthermore, the percentage by quantity of carbon-based matrix material particles (composed of particles according to Embodiment 1) in which silicon-based subparticles are dispersed can be calculated. As an illustration, a composite powder was used, and the results obtained for this composite powder by nanoindentation are presented in Table 1:

[0156]

[0157] In this case, the average Vickers hardness H is 4915 MPa, and the average elastic modulus E is 28.0 × 10⁻⁶ MPa. 3 MPa, resulting in a harmonic average value HM of 8354 MPa. Only one of the 10 particles (particle number 3) does not have a harmonic average value of 7000 MPa or higher and 20000 MPa or lower, thus the percentage by number of the carbon-based matrix material particles in which silicon-based subparticles are dispersed (present in this exemplary composite powder and composed of particles according to embodiment 1) is equal to 90%.

[0158] Preparation of experiments for counterexamples and examples

[0159] According to Embodiment 1 (E1) of the present invention

[0160] To produce the powder of Example 1, silicon-based powder was first obtained by applying 60 kW radio frequency (RF) inductively coupled plasma (ICP) using argon as the plasma gas. A micron-sized silicon powder precursor was injected into the argon gas at a rate of approximately 45 g / h, thereby achieving a general temperature (i.e., in the reaction zone) above 2000 K. In this first process step, the precursor was completely vaporized. In the second process step, 17 Nm... 3 A flow of argon gas at a rate of / h is used as a quenching gas immediately downstream of the reaction zone to lower the gas temperature to below 1600K, thereby causing nucleation of submicron silicon powder. Finally, a passivation step is performed at 100°C by adding 100 l / h of a N2 / O2 mixture containing 1 mol% oxygen over 5 minutes.

[0161] The specific surface area (BET) of the obtained silicon powder was measured to be 89 m². 2 / g. The oxygen content of the obtained silicon powder was measured to be 8.4% by weight. The number-based particle size distribution of the silicon powder was determined as: d Si 10 = 54 nm, d Si 50 = 106 nm and d Si 90 = 175nm.

[0162] Then, a dry blend was prepared from 100g of the obtained silicon-based powder and 308g of petroleum-based pitch powder with a softening point of 230°C. The blend was fed into a twin-screw extruder operating at 300°C under a nitrogen flow at a feed rate of 1000g / h.

[0163] The resulting silicon-based powder mixture in asphalt is cooled to room temperature, and once solidified, it is ground into powder and sieved through a 400-mesh sieve to produce intermediate powder.

[0164] Then, 20g of the intermediate powder was placed in a quartz crucible in a tube furnace and heated to 1020°C at a heating rate of 3°C / min, held at that temperature for two hours, and then cooled. All of this was carried out under an argon atmosphere.

[0165] Finally, the calcined product was ball-milled at 300 rpm for 1 hour using alumina balls and sieved on a 325-mesh sieve to obtain the powder of Example 1.

[0166] Key synthesis parameters are summarized in Table 2.

[0167] The total Si content in the powder, determined by XRF, was 30.4 wt%, with an experimental error of + / - 0.3 wt%. This corresponds to calculated values ​​based on a weight loss of approximately 35 wt% from the asphalt upon heating and insignificant weight losses from other components. The calculated ratio of carbon content to silicon content from asphalt carbonization in the powder was approximately 2. The oxygen content of the powder was measured to be 3.0 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.5 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value of 50 equals 18.4 μm.

[0168] Nanoindentation analysis of 12 carbon-based matrix material particles containing silicon-based subparticles (corresponding to a total of 114 indentations) yielded an average Vickers hardness H of 5250 MPa and an average elastic modulus E of 38.5 × 10⁻⁶ MPa. 3 MPa, which corresponds to an HM value of 9240 MPa. The percentage of carbon-based matrix material particles in which silicon-based subparticles are dispersed (analyzed in the powder of Example 1 and with a harmonic mean greater than or equal to 7000 MPa and less than or equal to 20000 MPa) is 100%.

[0169] Using appropriate image analysis software, SEM analysis showed that the average fraction of the total area occupied by pores (or the cross-section of pores) to the total area occupied by particles (or the cross-section of particles) was 0.002 (0.2%).

[0170] These values ​​are all reported in Table 3.

[0171] According to Embodiment 2 (E2) of the present invention

[0172] To produce the composite powder of Example 2 (E2), 20 g of the intermediate powder obtained in Example 1 was mixed with 12.5 g of graphite on a rotary table for 3 hours. Afterward, the resulting mixture was passed through a mill to depolymerize it. Under these conditions, good mixing was achieved, but the graphite particles did not embed into the pitch.

[0173] The obtained mixture of intermediate powder and graphite was further subjected to thermal post-treatment as follows: the product was placed in a quartz crucible in a tube furnace and heated to 1020°C at a heating rate of 3°C / min, held at that temperature for two hours, and then cooled. All of this was carried out under an argon atmosphere.

[0174] Finally, the roasted product is manually crushed in a mortar and sieved through a 325-mesh screen to form the final powder.

[0175] The total Si content in the composite powder was determined to be 18.6 wt% by XRF. The oxygen content of the powder was measured to be 1.8 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.9 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value 50 equals 16.6 μm.

[0176] Additional physical properties are reported in Table 3.

[0177] According to Embodiment 3 (E3) of the present invention

[0178] To produce the composite powder of Example 3 (E3), the same procedure as that for the composite powder of Example 2 was used, except that the heat treatment was performed at a temperature of 950°C instead of 1020°C.

[0179] The total Si content in the composite powder was determined to be 18.5 wt% by XRF. The oxygen content of the powder was measured to be 1.8 wt%. The specific surface area (BET) of the obtained powder was measured to be 4.2 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value of 50 equals 16.4 μm.

[0180] Additional physical properties are reported in Table 3.

[0181] According to Embodiment 4 (E4) of the present invention

[0182] To produce the composite powder of Example 4 (E4), a new intermediate powder was prepared as in Example 1, except that 100g of the same silicon-based powder was blended with 230g (instead of 308g) of the same pitch powder.

[0183] Then, the composite powder of Example 4 was prepared according to the same procedure as that of Example 2, except that 20g of new intermediate powder was mixed with 20g (instead of 12.5g) of graphite. The ratio of carbon content to silicon content generated by the carbonization of pitch in composite powder E4 was approximately 1.5.

[0184] The total Si content in the composite powder was determined to be 18.3 wt% by XRF. The oxygen content of the powder was measured to be 1.9 wt%. The specific surface area (BET) of the obtained powder was measured to be 4.0 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value 50 equals 16.6 μm.

[0185] Additional physical properties are reported in Table 3.

[0186] According to Embodiment 5 (E5) of the present invention

[0187] To produce the composite powder of Example 5 (E5), a new intermediate powder was prepared as in Example 1, except that the softening point of the asphalt powder used was 270°C (instead of 230°C).

[0188] Then, the composite powder of Example 5 was prepared according to the same procedure as the composite powder of Example 2.

[0189] The total Si content in the composite powder was determined to be 18.4 wt% by XRF. The oxygen content of the powder was measured to be 1.8 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.8 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value of 50 equals 16.7 μm.

[0190] Additional physical properties are reported in Table 3.

[0191] Counterexample 1 (not based on the present invention)

[0192] To produce the composite powder of Counterexample 1 (CE1), a new intermediate powder was prepared as in Example 1, except that the carbon precursor used was lignin instead of petroleum-based pitch. Since the carbon yield of lignin (approximately 50%) is lower than that of pitch (approximately 65%), 100g of the same silicon-based powder was blended with 400g of lignin (instead of 308g of pitch).

[0193] Then, the composite powder of Counterexample 1 was prepared according to the same procedure as the composite powder of Example 2.

[0194] The total Si content in the composite powder was determined to be 18.6 wt% by XRF. The oxygen content of the powder was measured to be 1.9 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.2 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value 50 equals 20.1 μm.

[0195] Additional physical properties are reported in Table 3.

[0196] Counterexample 2 (CE2) not based on the present invention

[0197] To produce the composite powder of Counterexample 2 (CE2), the same procedure as that for the composite powder of Example 2 was used, except that the heat treatment was performed at a temperature of 800°C instead of 1020°C.

[0198] The total Si content in the composite powder was determined to be 18.4 wt% by XRF. The oxygen content of the powder was measured to be 2.0 wt%. The specific surface area (BET) of the obtained powder was measured to be 2.8 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value of 50 equals 25.2 μm.

[0199] Additional physical properties are reported in Table 3.

[0200] Counterexample 3 (CE3) not based on the present invention

[0201] To produce the composite powder of Counterexample 3 (CE3), the same procedure as Counterexample 1 (CE1) disclosed in International Patent Application WO 2019 / 137797 A1 was used. It should be noted that the softening point of the bitumen powder used was 290°C.

[0202] The total Si content in the composite powder was determined to be 14.7 wt% by XRF. The oxygen content of the powder was measured to be 1.8 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.5 m². 2 / g. The number-based d of carbonaceous matrix material particles in which silicon-based subparticles are dispersed. C The value of 50 equals 14.2 μm.

[0203] Additional physical properties are reported in Table 3.

[0204] Table 2: Summary of synthesis parameters for powders E1-E5 and CE1-CE3

[0205]

[0206] Table 3: Physical properties of powders E1-E5 and CE1-CE3

[0207]

[0208] As can be observed from Tables 2 and 3, two main parameters have a significant impact on the HM value. First, the comparison of powders E2 and E5 for the carbon source shows that the HM value increases with the increase of the softening point of the asphalt material. This may be attributed to the fact that asphalt materials with high softening points contain larger molecules than those with low softening points, which, even after calcination, will lead to a higher average Vickers hardness of the carbon-based material particles.

[0209] The comparison between powder E2 and CE1 also illustrates the effect of the type of carbon source (in this case, lignin versus pitch) on the HM value.

[0210] Secondly, a comparison of the "carbon / Si ratio from the precursor" between powders E2 and E4 shows that the HM value increases as the ratio decreases. As previously mentioned, since silicon subparticles significantly contribute to the average Vickers hardness of carbon-based material particles, the contribution of silicon subparticles increases as the "carbon / Si ratio from the precursor" decreases, and the average Vickers hardness also increases. Similarly, the presence of higher concentrations of silicon subparticles leads to higher densities of carbon-based material particles containing silicon subparticles, and thus results in higher average Vickers hardness and higher HM values.

[0211] Electrochemical evaluation of powder

[0212] The resulting powders and composite powders were tested in coin cells according to the procedure specified above. The specific capacity of all tested powders and composite powders was 800 mAh / g ± 20 mAh / g, except for the powder of Counterexample 3 with a specific capacity of 734 mAh / g and the powder of Example 1 with a specific capacity of 1080 mAh / g. Therefore, the powder of Example 1 was mixed with graphite during electrode preparation to achieve a mixture "powder + graphite" with a capacity of approximately 800 mAh / g. The results obtained for the average coulombic efficiency between cycles 5 and 50 are given in Table 4.

[0213] Comparing the results of the powders and composite powders from E1 to E5 according to the present invention with those from the composite powders from CE1 and CE2, it can be seen in E1-E5 that the average coulombic efficiency increases with the HM value, for possible reasons previously given. However, when the HM value is greater than 17060 MPa, especially when it is greater than 18540 MPa, and even more especially when it is greater than 20000 MPa, as is the case with the composite powder for CE3, the average coulombic efficiency decreases significantly. This may be mainly attributed to the high average Vickers hardness (greater than 12000 MPa) of the carbonaceous material particles in which silicon-based subparticles are dispersed, thus causing cracks or fissures in the carbonaceous matrix during the large volume expansion of the silicon-based subparticles during lithium incorporation, resulting in excessive SEI formation and thus a decrease in the average coulombic efficiency value of the battery.

[0214] Table 4: Performance of button cells containing powdered and composite powders E1-E5 and CE1-CE3

[0215]

Claims

1. A powder of carbon-based matrix material particles, said particles comprising silicon-based subparticles dispersed therein, said particles having a harmonic mean HM calculated according to formula (1), Wherein H is the average Vickers hardness value of the carbon-containing matrix material particles, H is at least 4000 MPa and at most 12000 MPa, and E is the average elastic modulus value of the carbon-containing matrix material particles, E is at least 28 × 10⁻⁶ MPa. 3 MPa and at most 60×10 3 The values ​​H and E are both measured by nanoindentation and expressed in MPa. The powder is characterized in that HM is greater than or equal to 7000 MPa and less than or equal to 20000 MPa.

2. The powder according to claim 1, wherein the powder has a silicon content S expressed as a weight percentage (wt%), wherein 20 wt% ≤ S ≤ 70 wt%.

3. The powder according to claim 1 or 2, wherein the carbon-based matrix material particles in which silicon-based subparticles are dispersed have a d C The size distribution based on the number of 50, the d C 50 is greater than or equal to 1µm and less than or equal to 25µm.

4. A composite powder for use in the negative electrode of a storage battery, said composite powder comprising the powder according to any one of claims 1 to 3.

5. The composite powder according to claim 4, wherein at least 70% by weight of the carbon-containing matrix material particles in which silicon-based subparticles are dispersed are composed of the particles according to claim 1.

6. The composite powder according to claim 4 or 5, wherein the composite powder further comprises crystalline carbon-containing particles, the crystalline carbon-containing particles being physically different from the carbon-containing matrix material particles in which silicon-based subparticles are dispersed.

7. The composite powder according to claim 6, wherein the crystalline carbon-containing particles are graphite particles.

8. The composite powder according to claim 4 or 5, wherein the carbon-containing matrix material particles in which silicon-based subparticles are dispersed have a d C The size distribution based on the number of 50, the d C 50 is greater than or equal to 1µm and less than or equal to 25µm.

9. The composite powder according to claim 4 or 5, wherein the silicon-based subparticles have d Si The size distribution based on the number of 50, the d Si 50 is greater than or equal to 40nm and less than or equal to 150nm.

10. The composite powder according to claim 4 or 5, wherein the composite powder has a silicon content A expressed as a weight percentage (wt%), wherein 10 wt% ≤ A ≤ 60 wt%.

11. The composite powder according to claim 4 or 5, wherein the composite powder has a silicon content A and an oxygen content C, both expressed as a weight percentage (wt%), wherein C ≤ 0.15 × A.

12. The composite powder according to claim 4 or 5, wherein the silicon-based subparticles contain at least 90% by weight silicon when all elements except oxygen are taken into account.

13. The composite powder according to claim 4 or 5, wherein the composite powder has a particle size of at most 10 μm. 2 / g of BET surface area.

14. The composite powder according to claim 4 or 5, wherein the carbon-based matrix material particles in which silicon-based particles are dispersed are non-porous.

15. A storage battery comprising the composite powder according to any one of claims 4 to 14.

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