Composite powder used in negative electrode of battery and battery comprising such composite powder

Abstract

A composite powder for use in the negative electrode of a storage battery, the composite powder comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum, wherein the D band and D' band, both corresponding to the contribution of the carbon matrix material, have a focal length at 1330 cm⁻¹. ‑1 With 1360cm ‑1 Maximum intensity I between D and at 1600cm ‑1 With 1620cm ‑1 Maximum intensity I between D ', where the ratio I D / I D It is at least equal to 0.9 and at most equal to 4.0.

Description

[0001] Technical Field and Background Technology

[0002] This invention relates to composite powders suitable for use in the negative electrode of a storage battery, and storage batteries comprising such composite powders.

[0003] Lithium-ion (Li-ion) batteries are currently the best-performing batteries and have become the standard for portable electronic devices. Furthermore, these batteries are rapidly gaining popularity in other industries such as automotive and electrical storage. The key advantage of these batteries is the combination of high energy density and excellent 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 artificial 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 70% 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-based particles, both the silicon-based 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, US 2019 / 0198863 mentions such composite powders, disclosing an anodic active material comprising a composite of a Si-based or Sn-based material and a carbon-based material, wherein the D peak (1360 cm⁻¹) is... -1 Up to 1370cm -1 Peak intensity (I) D ) relative to the D' peak of carbon-based materials (1620 cm⁻¹) -1 Up to 1625cm -1 Peak intensity (I) D' Raman spectral peak intensity ratio (I) D / I D' The value ranges from 4.5 to 10.

[0013] GB 2563455 discloses a particulate material composed of multiple composite particles, wherein the composite particles contain multiple silicon nanoparticles dispersed within a conductive carbon matrix, and the contribution of the conductive carbon matrix to the Raman spectrum of the particulate material is characterized by a large G band and a significant D band. GB 2563455 does not mention the existence of the D' band, nor does it mention the intensity ratio of the D band and the D' band, respectively. D / I D' Related technical effects.

[0014] WO 2022074031 discloses a carbon-based material powder containing dispersed silicon-based subparticles. WO2022074031 does not disclose any Raman data.

[0015] EP 3113261 discloses a negative electrode material for a non-aqueous electrolyte secondary battery, comprising a conductive powder consisting of silicon-based active material particles coated with a conductive carbon film, wherein the conductive carbon film exhibits a peak intensity ratio of 1.1 or less.D / l G , where l D It is the peak intensity of the D band, l G This refers to the peak intensity of the G band. The D and G bands are determined by the Raman spectra of the conductive carbon film. EP 3113261 does not mention the existence of the D' band, nor does it mention the intensity ratios of the D and D' bands, respectively. D / I D' Related technical effects.

[0016] WO 2010 / 065739 discloses an article comprising a carbon-containing matrix having a Raman spectrum with up to four bands, namely at approximately 1360 cm⁻¹. -1 (D belt), approximately 1580cm -1 (G belt), approximately 1620cm -1 (D' band) and approximately 2660cm -1 At (DP band). WO2010 / 065739 does not mention the intensity ratio I compared to D band and D' band respectively. D / I D' The related technical effects were not mentioned, nor were silicon-based particles embedded in a carbon-containing matrix.

[0017] 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.

[0018] The object of the present invention is to provide a composite powder comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded therein, which, when used as the negative electrode of a battery, has the advantage of allowing a combination of high capacity and long cycle life. Summary of the Invention

[0019] This objective is achieved by providing a composite powder according to the invention, which, once used as the negative electrode of a battery, allows for a combination of high capacity and long cycle life, as demonstrated by Examples 1 to 3 compared with Counterexamples 1 to 3. Detailed Implementation

[0020] 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, which will become apparent from consideration of the following detailed description and the accompanying drawings.

[0021] In a first aspect, the present invention relates to a composite powder for use in the negative electrode of a storage battery, the composite powder comprising composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum obtained by Raman scattering, wherein the D band and D' band, both corresponding to contributions from the carbon matrix material, have a focal length of 1330 cm⁻¹. -1 With 1360cm -1 Maximum intensity I between D and at 1600cm -1 With 1620cm -1 Maximum intensity I between D' , where ratio I D / I D' It is at least equal to 0.9 and at most equal to 4.0.

[0022] Maximum strength I D Preferably at 1330cm -1 With 1359cm -1 Between, more preferably at 1330cm -1 With 1357cm -1 Between, or even more preferably at 1330cm -1 With 1355cm -1 Between, and the maximum intensity I D' Preferably at 1600cm -1 With 1619cm -1 Between, more preferably at 1600cm -1 With 1617cm -1 Between, or even more preferably at 1600cm -1 With 1615cm -1 between.

[0023] Preferably, the composite particles consist of a carbon matrix material and silicon-based particles embedded therein.

[0024] The term "composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material" refers to composite particles with an average size larger than silicon-based particles because they contain silicon-based particles. Composite particles are typically micrometer-sized, while silicon-based particles are typically nanometer-sized.

[0025] The term "silicon-based particles embedded in the carbon matrix material" means that at least 50% of the surface of the silicon-based particles is covered by the carbon matrix material, preferably at least 75%, and preferably the silicon-based particles are completely covered by the carbon matrix material to ensure proper prevention of reaction with the electrolyte during cycling. In other words, the silicon-based particles and the carbon matrix material are not simply mixed together, as this would not achieve adequate coverage of the silicon-based particle surface.

[0026] Silicon-based particles embedded in a carbon matrix material either form agglomerates with a size less than 1 µm or do not form agglomerates at all. Therefore, in the composite powder according to the invention, the silicon-based particles are preferably in contact only with each other and / or with the carbon matrix material.

[0027] Silicon-based particles can have any shape, such as being substantially spherical, but can also have irregular shapes, rod-like shapes, plate-like shapes, etc. In silicon-based particles, 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 particles relative to the total weight of the silicon-based particles is preferably 80% by weight or more, and more preferably 90% by weight or more.

[0028] In the Raman spectra of graphite materials, such as the composite powder according to the invention, the most prominent feature is the so-called characteristic that typically appears at about 1580 cm⁻¹. -1 G-band at approximately 1350cm -1 The D band at approximately 1610cm -1 The D' zone at approximately 2700 cm -1 The G' band (also known as the 2D band) at that location. Figure 1 A diagram illustrating a typical Raman spectrum of a graphite material with four different bands is shown.

[0029] The presence of the G-band is characteristic of the in-plane vibrational modes involved in sp2 hybridized carbon. The D and D' bands are defect-induced Raman features, which are not visible in highly crystalline carbon materials with few defects. The intensity of the D and G bands is greater than that of the I-band. D / I G It is commonly used to characterize the amount of defects in graphite materials.

[0030] However, within the framework of this invention, the inventors noted that another strength ratio (i.e., the I of the D-band and the D'-band) D / I D' There is a surprising direct correlation between ) and battery performance, as presented in other parts of this article.

[0031] The inventor believes that, I D / I D' It is a good indicator of defect concentration and its type, such as edge, vacancy, boundary defects, or defects associated with changes in carbon hybridization, for example, from sp 2 Change to sp 3 .

[0032] Ratio I D / I D'A value above 4.0 is undesirable because it indicates an excessively high concentration of defects in the carbon matrix material, which could be detrimental, for example, to the electronic conductivity of the composite particles. Furthermore, this could also indicate that the defects are of a "more destructive" type, such as those associated with sp... 3 Those hybridization-related factors are considered detrimental to the cycle life of batteries.

[0033] Ratio I D / I D' A value below 0.9 is also undesirable, as it indicates that the defect concentration in the carbon matrix is ​​too low, which could be detrimental, for example, to the ionic conductivity of the composite particles.

[0034] In other words, with ratio I D / I D' The associated technical effect reaches its maximum between 0.9 and 4.0.

[0035] In another embodiment of the first aspect of the invention, ratio I D / I D' Preferably at least equal to 1.0, more preferably at least equal to 1.2, even more preferably at least equal to 1.4, particularly preferably at least equal to 1.6, even more particularly preferably at least equal to 1.8, and most preferably at least equal to 2.0. Ratio I D / I D' Preferably at most 3.8, more preferably at most 3.6, particularly preferably at most 3.4, even more particularly preferably at most 3.2, and most preferably at most 3.0. In other words, with ratio I D / I D' The associated technical effects reach their maximum between versions 2.0 and 3.0.

[0036] In another embodiment of the first aspect of the invention, the carbon matrix material is soft carbon. Soft carbon corresponds to an arrangement of small, disordered graphite domains that can be converted into graphite when heated to a temperature of 3000°C, as opposed to hard carbon, which is non-graphitizable.

[0037] Soft carbon exhibits higher electronic conductivity compared to hard carbon and is therefore preferred. Furthermore, the disordered aggregation of small graphite domains results in nanopores within the matrix material, leading to reduced volume expansion during lithiation of the anode in particles containing primarily graphite or graphene matrix materials compared to particles containing primarily graphite or graphene matrix materials. This reduced volume expansion extends the battery's cycle life.

[0038] In another embodiment of the first aspect of the invention, the composite powder has a silicon content S expressed as a weight percentage (wt%), wherein 10 wt% ≤ S ≤ 60 wt%, and preferably wherein 20 wt% ≤ S ≤ 50 wt%.

[0039] Composite powders with a silicon content of less than 10% by weight, preferably less than 20% by weight, will have too limited a specific capacity and therefore will not allow for the achievement of high energy density in batteries. Composite powders with a silicon content of more than 60% by weight, preferably more than 50% 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.

[0040] In yet another embodiment of the first aspect of the invention, the composite powder has a carbon content C expressed as a weight percentage (wt%), wherein 30 wt% ≤ C ≤ 90 wt%.

[0041] 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 particles, leading to increased electrolyte decomposition at the surface of the silicon-based particles and thus increased SEI formation. When the carbon content in the composite powder is greater than 90% by weight, the specific capacity of the composite powder becomes too low.

[0042] In another embodiment of the first aspect of the invention, the composite powder has a silicon content S and an oxygen content N, both expressed as weight percentages (wt%), wherein N ≤ 0.20 × S and preferably wherein N ≤ 0.15 × S.

[0043] Composite powders with excessively high oxygen content will suffer additional irreversible lithium loss due to the formation of lithium silicate (Li2SiO3, Li4SiO4) during the first lithiation of the powder, thereby increasing the initial irreversible capacity loss of batteries containing such composite powders.

[0044] In another embodiment of the first aspect of the invention, the silicon-based particles are characterized by a size distribution based on quantity having a d50, which is greater than or equal to 20 nm and less than or equal to 150 nm.

[0045] With or without image analysis procedures, the number-based size distribution is based on visual analysis of the minimum number of silicon-based particles contained in the composite powder. This minimum number of silicon-based particles is at least 1000 particles. Examples of determining the number-based distribution of silicon-based particles are provided in the "Analytical Methods" section.

[0046] For clarity, a d50 of 100nm would mean, for example, that 50% of at least 1000 silicon-based particles have a size less than 100nm and that 50% of at least 1000 silicon-based particles have a size greater than 100nm.

[0047] Silicon-based particles with a number-based size distribution of d50 below 20 nm are difficult to disperse effectively in carbon-based materials, which may reduce the electronic conductivity of the powder.

[0048] Silicon-based particles with a quantity-based size distribution of d50 greater than 150 nm are more prone to fracture during lithiation, resulting in a significantly shortened cycle life of batteries containing such composite powders.

[0049] It is believed that d50 is not affected by the process of preparing composite powder, which means that the d50 value of the silicon-based powder used as a precursor in the process is the same as the d50 value of the silicon-based particles contained in the composite powder.

[0050] In yet another embodiment of the first aspect of the invention, at least 50% of the surface of the silicon-based particles, preferably at least 75%, is covered by a carbon matrix material. Preferably, the silicon-based particles are completely covered by the carbon matrix material. This can be visually confirmed based on the analysis of one or more SEM images of a cross-section of the composite powder containing the silicon-based particles.

[0051] As already mentioned, a negative effect associated with silicon is the potential formation of a thick SEI (solid-electrolyte interface) on the anode, particularly on silicon-based particles. Due to the large volume changes experienced by silicon-based particles during the lithiation / delithiation process in the battery, the already formed SEI may break down again, leading to continuous lithium consumption and consequently a significant reduction in battery cycle life. Protecting the surface of silicon-based particles at least partially with a carbon-based material is an effective solution to prevent continuous SEI formation and cycle life loss.

[0052] In another embodiment of the first aspect of the invention, the silicon content in the silicon-based particles is at least 80% by weight, and preferably at least 90% by weight.

[0053] Preferably, these silicon-based particles are free of elements other than Si and O to avoid excessively low specific capacity. Silicon-based particles are the main contributor to the specific capacity of the composite powder, and it is preferable that their own capacity is as high as possible, and therefore their silicon content is as high as possible, in this case at least 80% by weight and preferably at least 90% by weight.

[0054] In another embodiment of the first aspect of the invention, the composite powder further comprises graphite and / or graphene particles, but neither the graphite nor the graphene particles are embedded in the carbon matrix material. The phrase "neither the graphite nor the graphene particles are embedded in the carbon matrix material" means that less than 10% of the surface of the graphite and / or graphene particles is covered by the carbon matrix material, preferably less than 5%, and more preferably, their surfaces are not covered by the carbon matrix material at all. This can be visually confirmed based on the analysis of one or more SEM images of the cross-section of the composite powder. In fact, it is advantageous for the graphite and / or graphene particles not to be embedded in the matrix material, because only the silicon-based particles need to be covered with the carbon matrix material, thus requiring less carbon matrix material with high irreversible capacity and low specific capacity.

[0055] However, some contact may exist between the composite particles and the graphite and / or graphene particles, located at their outer surfaces. This is especially desirable to ensure good electronic conductivity of the composite powder, thereby enabling batteries containing the composite powder to achieve high rate performance.

[0056] Furthermore, graphite particles act as spacers between composite particles, preventing them from agglomerating into aggregated powder. Without such spacers, the aggregated powder might require mechanical treatment, such as grinding steps, for use in the negative electrode of a battery. This could weaken the integrity of the matrix material and ultimately lead to reduced performance in batteries containing such aggregated powder.

[0057] Alternatively, the composite powder may also contain exfoliated graphite, expanded graphite, and / or graphene nanosheets, which, for the same reasons described above, are not embedded in the matrix material.

[0058] Since these graphite materials may affect the Raman spectra of the composite powder, their contributions should be removed to obtain a ratio I that only includes the contribution of the carbon matrix material. D / I D' In particular, their contributions to the D and D' bands. The procedure is explained in more detail in the "Analytical Methods" section.

[0059] In yet another embodiment of the first aspect of the invention, the composite powder has a density of up to 10 μm. 2 / g and preferably at most 8m 2 / g BET surface area.

[0060] Preferably, 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 SEI and thus limiting the cycle life loss of batteries containing such composite powders.

[0061] In another embodiment of the first aspect of the invention, the composite particles have a volume-based particle size distribution including D10, D50 and D90, wherein 1 μm ≤ D10 ≤ 10 μm, 5 μm ≤ D50 ≤ 25 μm and 10 μm ≤ D90 ≤ 40 μm.

[0062] For clarity, D50 of 15µm, for example, means that 50% by volume of the composite particles are smaller than 15µm, while 50% by volume of the composite particles are larger than 15µm.

[0063] Matrix material particles with a volume-based size distribution of D50 less than 5 μm may have an excessively high specific surface area, thereby increasing the surface area for reaction with the electrolyte and the formation of the SEI, which is disadvantageous for the reasons previously explained. Matrix material particles with a volume-based size distribution of D50 greater than 25 μm may be more prone to cracking during lithium absorption due to their size, resulting in a shortened cycle life of batteries containing such particles.

[0064] In a second aspect, the present invention relates to a negative electrode for a storage battery, preferably a lithium-ion storage battery, comprising a composite powder according to the invention. The negative electrode typically also comprises conductive additives, such as carbon black, graphite particles, graphene particles, carbon nanotubes, or mixtures thereof. The content of the conductive additives is between 0% by weight and 10% by weight, particularly 0.1% by weight to 5% by weight, relative to the total weight of the negative electrode layer (excluding the current collector).

[0065] The negative electrode typically also includes a binder or a mixture of binders. Specific examples of binders include polysaccharides, lithium polyacrylate (Li-PAA), sodium polyacrylate (Na-PAA), potassium polyacrylate (K-PAA), polyacrylic acid (H-PAA), sodium carboxymethyl cellulose (Na-CMC), and styrene-butadiene rubber (SBR). The binder is added to improve the cohesiveness of the various components of the negative electrode, its mechanical strength in the current collector, or even its flexibility. The binder accounts for 1% to 15% by weight, particularly 2% to 10% by weight, relative to the total weight of the negative electrode layer (excluding the current collector). Examples of negative electrode fabrication are provided in other sections of this document.

[0066] Finally, the present invention also relates to a storage battery, preferably a lithium-ion storage battery, comprising a negative electrode according to the invention, and thus comprising a composite powder according to the invention, prepared as previously defined or as previously disclosed.

[0067] The battery according to the invention more specifically includes a negative electrode (anode), a positive electrode (cathode), and an electrolyte, preferably a non-aqueous electrolyte, according to the invention. Examples of the positive electrode include those selected from LiCoO2 and LiNi. 0,6 Mn0,2 Co 0,2 O2, LiNi 0,8 Mn 0,1 Co 0,1 O2, LiNi 0,8 Co 0,15 Al 0,05 O2, Li 1,2 Ni 0,2 Mn 0,6 Positive electrode active materials include O2, LiFePO4, etc. The electrolyte can preferably be a non-aqueous electrolyte solution, a non-aqueous polymer electrolyte, or even a solid electrolyte. Specific examples include organic electrolyte solutions obtained by dissolving lithium salts such as LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, CH3SO3Li, CF3SO3Li, etc., in non-aqueous solvents such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, γ-butyrolactone, etc.; gel polymer electrolytes containing polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, etc.; and solid polymer electrolytes containing polymers having ethylene oxide bonds. Additionally, additives that induce decomposition reactions during the initial charging of the lithium-ion battery can be added to the electrolyte solution. Specific examples of additives include vinylene carbonate (VC), biphenyl, propanesulfonate lactone (PS), fluoroethylene carbonate (FEC), and vinylsulfonate lactone (ES). The amount added is preferably not less than 0.1% by weight and not more than 20% by weight relative to the total weight of the electrolyte. Attached Figure Description

[0068] Figure 1 Illustration of the Raman spectrum of graphite materials

[0069] Figure 2 Raman spectra of composite powder E1 with peak fitting

[0070] The analytical methods used

[0071] Determination of silicon content

[0072] The silicon content of the composite powder was measured using energy-dispersive X-ray fluorescence (XRF) spectroscopy. This method has an experimental random error of + / - 0.3 wt% Si.

[0073] Determination of oxygen content

[0074] The oxygen content of the composite powder was determined using a LECO TC600 oxygen / nitrogen analyzer as follows: 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 the 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.

[0075] Determination of carbon content

[0076] The carbon content of the composite powder was determined using a Leco CS230 carbon-sulfur analyzer via the following method: The sample was melted in a ceramic crucible within a high-frequency furnace under a constant oxygen flow. The carbon in the sample reacted with oxygen and exited the crucible as CO or CO2. After the final CO was converted to CO2, all the resulting CO2 was detected by an infrared detector. This signal was then converted into the carbon content.

[0077] Determination of specific surface area (BET)

[0078] The specific surface area of ​​the composite powder was measured using a Micromeritics Tristar 3000 and 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 in a vacuum at 120 °C for 1 hour to remove adsorbed substances.

[0079] Measurement of electrochemical performance

[0080] The electrochemical properties of the composite powders in the examples and counterexamples were determined by the following methods.

[0081] The powder to be evaluated was sieved using a 45µm 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.

[0082] Copper foil cleaned with ethanol was used as the current collector. A 200µm 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 1.27cm² disc was stamped from the dried coated copper foil and used as an electrode in a coin cell that uses lithium metal as the counter electrode. The electrolyte was 1M LiPF6 dissolved in EC / DEC 1 / 1 + 2% VC + 10% FEC solvent.

[0083] 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”.

[0084] • Loop 1:

[0085] o Let it sit for 6 hours

[0086] o is lithiated by CC to 10mV at C / 10, and then lithiated by CV until C / 100.

[0087] Let it sit for 5 minutes.

[0088] At C / 10, CC delithiation occurs to 1.5V.

[0089] Let it sit for 5 minutes.

[0090] • Starting from loop 2:

[0091] o is lithiated by CC at C / 2 to 10mV, and then lithiated by CV until C / 50.

[0092] Let it sit for 5 minutes.

[0093] At C / 2, CC delithiation occurs to 1.2V.

[0094] Let it sit for 5 minutes.

[0095] 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.

[0096] 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).

[0097] 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 99.5%, preferably at least 99.55%, from cycle 5 to cycle 50.

[0098] Determination of particle size distribution based on quantity

[0099] The number-based particle size distribution of silicon-based particles was determined by electron microscopy (SEM or TEM) analysis of the cross-section of the composite powder combined with image analysis.

[0100] To this end, the cross-sections of the composite powder, including multiple cross-sections of the composite particles, are prepared according to the procedure detailed below, wherein each cross-section includes multiple cross-sections of silicon-based particles.

[0101] 500 mg of the 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 with a 12-second carbon sputtering process to obtain the sample to be analyzed by SEM, also known as a "cross-section".

[0102] The prepared cross-sections were then analyzed using a JEOL-based FEG-SEM JSM-7600F equipped with a Bruker Xflash 5030-127 (30 mm², 127 eV) EDS detector. The signal from this detector was processed by a Bruker-based Quantax 800 EDS system.

[0103] 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.

[0104] The size of a silicon-based particle is considered to be equal to the maximum straight-line distance between two points on the periphery of a discrete cross-section of the silicon-based particle.

[0105] For the purpose of illustrating the determination of number-based particle size distribution of silicon-based particles in a non-limiting manner, SEM-based procedures are provided below.

[0106] 1. Obtain multiple SEM images of the cross-section of a composite powder containing composite particles in which silicon-based particles are dispersed.

[0107] 2. Adjust the image's contrast and brightness settings to easily visualize the cross-sections of the composite particles and silicon-based particles. Due to their different chemical compositions, the difference in brightness can easily distinguish between the two types of particles.

[0108] 3. Using suitable image analysis software, select at least 1000 discrete cross-sections of silicon-based particles from one or more acquired SEM images that do not overlap with another cross-section of the silicon-based particles. These discrete cross-sections of the silicon-based particles can be selected from one or more cross-sections of a composite powder containing composite particles and silicon-based particles.

[0109] 4. For each of at least 1000 discrete cross-sections of the silicon-based particle, use appropriate image analysis software to measure the dimensions of the discrete cross-sections of the silicon-based particle.

[0110] Then, the d10, d50, and d90 values ​​of the number-based particle size distribution of the powder, determined using the method described above, are calculated. These number-based particle size distributions can be easily converted into weight- or volume-based particle size distributions using well-known mathematical formulas.

[0111] Determination of particle size distribution based on volume

[0112] The volume-based particle size distribution of the composite powder was determined using a Malvern Mastersizer 2000 laser diffraction particle size analyzer. The following measurement conditions were selected: compression range; effective beam length 2.4 mm; measurement range: 300 RF; 0.01 µm to 900 µm. Sample preparation and measurements were performed according to the manufacturer's instructions.

[0113] Raman spectroscopy

[0114] Raman spectroscopy analysis of the composite powder was performed using a Renishaw inVia Qontor Raman spectrometer with 532 nm laser excitation.

[0115] Perform the following steps to process the acquired spectrum:

[0116] 1. Background is subtracted by removing the contributions of both cosmic rays and the baseline.

[0117] 2. Using suitable software, fit the obtained spectrum with three curves: D-band, G-band, and D'-band, such as... Figure 2 As shown. In the presence of graphite particles, the spectrum of pure graphite is first obtained, and its contribution to the composite powder spectrum is subtracted. In the absence of graphite particles, all D, G, and D' bands must be contributions from the carbon matrix.

[0118] 3. Measurement I D / I D' ratio.

[0119] Experimental preparation of the examples

[0120] Counterexample 1 (CE1) not based on the present invention

[0121] To produce the powder of Counterexample 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 200 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, a 20 Nm³ / h argon flow was used as a quench gas immediately downstream of the reaction zone to lower the gas temperature to below 1600 K, resulting in the nucleation of metallized submicron silicon powder. Finally, a passivation step was performed at 100 °C by adding 100 L / h of an N₂ / O₂ mixture containing 1 mol% oxygen over 5 minutes.

[0122] The specific surface area (BET) of the obtained silicon powder was measured to be 82 m². 2 / g. The oxygen content of the obtained silicon powder was measured to be 7.9% by weight. The number-based particle size distribution of the silicon powder was determined to be: d10 = 52 nm, d50 = 111 nm and d90 = 171 nm.

[0123] Then, a dry blend was prepared from 100g of the obtained silicon powder and 840g of polyvinyl chloride (PVC) with a melting point of 160°C. The blend was heated to 190°C under a nitrogen flow and, after a 60-minute waiting period, mixed under high shear for 30 minutes using a Cowles dissolving mixer operating at 1000 rpm.

[0124] The resulting mixture of silicon powder and PVC was cooled to room temperature, and once solidified, it was ground into powder and sieved through a 400-mesh sieve to produce intermediate powder 1.

[0125] Then, 20g of the obtained intermediate powder 1 was placed in a quartz crucible in a tube furnace and heated to 900°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. In the obtained product, silicon-based particles were dispersed and embedded in a soft carbon matrix produced by the thermal decomposition of PVC.

[0126] Finally, the calcined product was ball-milled at 300 rpm for 1 hour using alumina balls and sieved through a 325-mesh sieve to obtain the powder of Counterexample 1.

[0127] Key synthesis parameters are summarized in Table 1.

[0128] The total Si content in the powder, measured by XRF, was 39.3 wt%, with an experimental error of + / - 0.3 wt%. This corresponds to calculated values ​​based on approximately 84 wt% weight loss of PVC during heating and insignificant weight loss of other components during heating. The calculated ratio of carbon content from the carbonization of the PVC forming the matrix material to the silicon content in the powder was approximately 1.46. The oxygen content of the powder was measured to be 3.4 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.3 m². 2 / g.

[0129] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 5.4 μm, D50 equals 15.8 μm and D90 equals 24.6 μm.

[0130] Then, following the previously described procedure, the powder of counterexample 1 was analyzed using Raman spectroscopy. The result was obtained at 1344 cm⁻¹. -1 The intensity of peak D at 1610 cm⁻¹ is similar to that at 1610 cm⁻¹ -1 The ratio of the intensity of the D' peak at that location is 0.54. This value is reported in Table 2.

[0131] According to Embodiment 1 (E1) of the present invention

[0132] The method for preparing the composite powder in Example 1 (E1) is the same as that for preparing the composite powder in Counterexample 1 (CE1), except that the intermediate powder 1 is heated to 1000°C instead of 900°C.

[0133] The total Si content in the composite powder was determined to be 39.3% by weight using XRF. The oxygen content of the powder was measured to be 3.5% by weight. The specific surface area (BET) of the obtained powder was measured to be 3.2 m². 2 / g.

[0134] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 5.2 μm, D50 equals 16.1 μm and D90 equals 25.2 μm.

[0135] The Raman spectrum of composite powder E1 is as follows Figure 2 As shown. The value is located at 1344cm. -1 The intensity of peak D at 1610 cm⁻¹ is similar to that at 1610 cm⁻¹ -1 The ratio of the intensity of the D' peak at that location is 1.23.

[0136] Counterexample 2 (CE2) not based on the present invention

[0137] To prepare the composite powder of Counterexample 2 (CE2), the same silicon powder as in Counterexample 1 (CE1) was used. A dry blend was prepared from 100 g of silicon powder and 750 g of polyvinyl chloride (PVC) with a melting point of 210 °C. The blend was heated to 240 °C under a nitrogen atmosphere and, after a 60-minute waiting period, mixed under high shear for 30 minutes using a Cowles dissolving mixer operating at 1000 rpm.

[0138] The resulting mixture of silicon powder and PVC is cooled to room temperature, and once solidified, it is ground into powder and sieved through a 400-mesh sieve to produce intermediate powder 2.

[0139] Then, 20g of the obtained intermediate powder 2 was placed in a quartz crucible in a tube furnace and heated to 900°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. In the obtained product, silicon-based particles were dispersed and embedded in a soft carbon matrix produced by the thermal decomposition of PVC.

[0140] Finally, the calcined product was ball-milled at 300 rpm for 1 hour using alumina balls and sieved through a 325-mesh sieve to obtain the powder of Counterexample 2.

[0141] The total Si content in the powder was measured to be 39.2% by weight. This corresponds to a calculated value based on approximately 82% by weight loss of PVC upon heating and insignificant weight loss of other components upon heating. The calculated ratio of carbon content to silicon content resulting from PVC carbonization in the powder is approximately 1.47. The oxygen content of the powder was measured to be 3.4% by weight. The specific surface area (BET) of the obtained powder was measured to be 3.4 m². 2 / g.

[0142] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 5.6 μm, D50 equals 16.4 μm and D90 equals 25.6 μm.

[0143] According to Embodiment 2 (E2) of the present invention

[0144] The method for preparing the composite powder in Example 2 (E2) is the same as that for preparing the composite powder in Counterexample 2 (CE2), except that the intermediate powder 2 is heated to 1000°C instead of 900°C.

[0145] The total Si content in the composite powder was determined to be 39.2 wt% by XRF. The oxygen content of the powder was measured to be 3.6 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.5 m². 2 / g.

[0146] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 4.9 μm, D50 equals 15.6 μm and D90 equals 23.8 μm.

[0147] According to Embodiment 3 (E3) of the present invention

[0148] To prepare the composite powder of Example 3 (E3), the same procedure as for the composite powder of Example 2 (E2) was used, except that 20 g of intermediate powder 2 was mixed with 26 g of graphite. The resulting mixture was placed in a quartz crucible in a tube furnace and heated to 1000°C at a heating rate of 3°C / min and held at that temperature for two hours, followed by cooling. All of this was carried out under an argon atmosphere. In the product obtained, silicon-based particles were dispersed and embedded in a soft carbon matrix produced by the thermal decomposition of PVC. Graphite particles were not embedded in the soft carbon matrix.

[0149] 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 3.

[0150] The ratio of carbon content to silicon content generated from the carbonization of PVC in composite powder E3 is approximately 1.47.

[0151] The total Si content in the composite powder was determined to be 17.0 wt% by XRF. The oxygen content of the powder was measured to be 1.5 wt%. The specific surface area (BET) of the obtained powder was measured to be 3.3 m². 2 / g.

[0152] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 5.2 μm, D50 equals 15.7 μm and D90 equals 24.4 μm.

[0153] Counterexample 3 (CE3) not based on the present invention

[0154] To prepare the composite powder of Counterexample 3 (CE3), the same silicon powder as in Counterexample 1 (CE1) was used. A wet blend was prepared from 100 g of silicon powder and 180 g of a phenolic resin precursor (a mixture of phenol and formaldehyde) with a crosslinking temperature of 100 °C, and mixed under high shear for 30 minutes at 1000 rpm using a Cowles dissolving mixer under a nitrogen flow. The wet blend was then heated to 200 °C for 30 minutes under a nitrogen flow to complete the polymerization reaction.

[0155] The mixture of silicon powder thus obtained in phenolic resin is cooled to room temperature, ground into powder, and sieved on a 400-mesh sieve to produce intermediate powder 3.

[0156] Then, 20g of the obtained intermediate powder 3 was placed in a quartz crucible in a tube furnace and heated to 1000°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. In contrast to the previously obtained composite powder, in the composite powder of counterexample 3, due to the thermal decomposition of the phenolic resin, the silicon-based particles were dispersed and embedded in the hard carbon matrix.

[0157] Finally, the calcined product was ball-milled at 300 rpm for 1 hour using alumina balls and sieved through a 325-mesh sieve to obtain the powder of Counterexample 1.

[0158] The total Si content in the powder was determined to be 39.2% by weight using XRF. This corresponds to a calculated value based on approximately 25% by weight loss of the phenolic resin upon heating and insignificant weight loss of other components upon heating. The calculated ratio of carbon content to silicon content resulting from the carbonization of the phenolic resin in the powder was approximately 1.47. The oxygen content of the powder was measured to be 3.4% by weight. The specific surface area (BET) of the obtained powder was measured to be 4.2 m². 2 / g.

[0159] The volume-based particle size distribution of the obtained composite particles is as follows: D10 equals 6.2 μm, D50 equals 17.2 μm and D90 equals 26.3 μm.

[0160] Table 1: Summary of synthesis parameters for composite powders E1-E3 and CE1-CE3

[0161]

[0162] Electrochemical evaluation of composite powder

[0163] The prepared composite powders were tested in coin cells according to the procedure specified above. Only the graphite-containing composite powder E3 achieved the target capacity of 800 mAh / g ± 20 mAh / g, while the specific capacity of the other powders was approximately 1380 mAh / g. Therefore, during electrode preparation, composite powders E1, E2, CE1, CE2, and CE3 were mixed with graphite to achieve a capacity of approximately 800 mAh / g for the mixture "composite powder + graphite". The results obtained for the average coulombic efficiency between cycle 5 and cycle 50 are presented in Table 2.

[0164] Comparing the results of the composite powders E1 to E3 according to the present invention with the results of the composite powders CE1 to CE3, it can be seen that for those containing I D / I D' Batteries with composite powder ratios between 0.9 and 4.0, particularly between 1.0 and 3.0, and even more particularly between 1.0 and 2.6, yielded the best results, for reasons that have been previously given.

[0165] Table 2: Performance of button cells containing composite powders E1-E3 and CE1-CE3

[0166]

Claims

1. A composite powder for use in the negative electrode of a storage battery, the composite powder comprising composite particles, the composite particles comprising a carbon matrix material and silicon-based particles embedded in the carbon matrix material, the composite powder having a Raman spectrum, wherein the D band and D' band, both corresponding to contributions from the carbon matrix material, have a focal length at 1330 cm⁻¹. -1 With 1360cm -1 Maximum intensity I between D and at 1600cm -1 With 1620cm -1 Maximum intensity I between D' , where ratio I D / I D' It is at least equal to 0.9 and at most equal to 4.

0.

2. The composite powder according to claim 1, wherein I D / I D' The ratio must be at least 1.0 and at most 3.

0.

3. The composite powder according to claim 1, wherein I D / I D' The ratio must be at least 1.0 and at most 2.

6.

4. The composite powder according to any one of claims 1 to 3, wherein the carbon matrix material is soft carbon.

5. The composite powder according to any one of claims 1 to 3, wherein the composite powder has a silicon content S expressed as a weight percentage (wt%), wherein 10 wt% ≤ S ≤ 60 wt%.

6. The composite powder according to any one of claims 1 to 3, wherein the composite powder has a carbon content C expressed as a weight percentage (wt%), wherein 30 wt% ≤ C ≤ 90 wt%.

7. The composite powder according to any one of claims 1 to 3, wherein the composite powder has a silicon content S and an oxygen content N, both expressed as weight percentages (wt%), wherein N ≤ 0.20 S.

8. The composite powder according to any one of claims 1 to 3, wherein the silicon-based particles are characterized by a size distribution based on quantity having a d50, the d50 being greater than or equal to 20 nm and less than or equal to 150 nm.

9. The composite powder according to any one of claims 1 to 3, wherein at least 50% of the surface of the silicon-based particles is covered by the carbon matrix material.

10. The composite powder according to any one of claims 1 to 3, wherein the silicon content in the silicon-based particles is at least 80% by weight.

11. The composite powder according to any one of claims 1 to 3, wherein the composite powder further comprises graphite and / or graphene particles such that less than 10% of the surface of the graphite and / or graphene particles is covered by the carbon matrix material.

12. The composite powder according to any one of claims 1 to 3, wherein the composite powder has a particle size of at most 10 μm. 2 / g of BET surface area.

13. The composite powder according to any one of claims 1 to 3, wherein the composite particles have a volume-based particle size distribution including D10, D50 and D90, wherein 1 μm ≤ D10 ≤ 10 μm, 5 μm ≤ D50 ≤ 25 μm and 10 μm ≤ D90 ≤ 40 μm.

14. A negative electrode comprising the composite powder according to any one of the preceding claims.

15. A storage battery comprising a negative electrode according to claim 14.

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