A composite powder for use in the negative electrode of a battery

Abstract

The present invention relates to a composite powder for use in a negative electrode of a battery, the composite powder comprising composite particles, said composite particles comprising a carbonaceous matrix material and silicon-based particles embedded therein, said composite powder having X-ray diffraction and Raman spectroscopy spectra with particular peaks and bands positions and intensity ratios.

Description

[0001] A COMPOSITE POWDER FOR USE IN THE NEGATIVE ELECTRODE OF A BATTERY

[0002] TECHNICAL FIELD AND BACKGROUND

[0003] The present invention relates to a composite powder suitable for use in the negative electrode of a battery.

[0004] Lithium ion (Li-ion) batteries are currently the best performing batteries and already became the standard for portable electronic devices. In addition, these batteries now rapidly gain ground in other industries such as automotive and electrical storage. Enabling advantages of such batteries are a high-energy density combined with a good power performance.

[0005] A Li-ion battery typically contains a number of so-called Li-ion cells, which in turn contain a positive electrode, also called cathode, a negative electrode, also called anode, and a separator which are immersed in an electrolyte. The most frequently used Li-ion cells for portable applications are developed using electrochemically active materials such as lithium cobalt oxide or lithium nickel manganese cobalt oxide for the cathode and a natural or artificial graphite for the anode.

[0006] It is known that one of the important limitative factors influencing a battery's performance and in particular a battery's energy density is the active material in the anode. Therefore, to improve the energy density, the use of electrochemically active materials comprising silicon, in the negative electrode, has been investigated over the past years.

[0007] In the art, the performance of a battery containing silicon-based materials is generally quantified by a so-called cycle life of a full-cell, which is defined as the number of times or cycles that a cell comprising such material can be charged and discharged until it reaches 70% of its initial discharge capacity. Most works on silicon-based materials are therefore focused on improving said cycle life.

[0008] A drawback of using a silicon-based material in an anode is its large volume expansion during charging, which is as high as 300% when the lithium ions are fully incorporated, e.g. by alloying or insertion, in the anode's active material - a process often called lithiation. The large volume expansion of the silicon-based materials during lithium incorporation may induce stresses in the silicon-based particles, which in turn could lead to a mechanical degradation of the silicon material. Repeated periodically during charging and discharging of the Li-ion battery, the repetitive mechanical degradation of the silicon-based material may reduce the life of a battery to an unacceptable level.

[0009] Further, a negative effect associated with silicon-based materials is that a thick SEI, a Solid-Electrolyte Interface, may be formed on the anode. A SEI is a complex reaction product of the electrolyte and lithium, which leads to a loss of lithium availability for electrochemical reactions and therefore to a poor cycle performance, which is the capacity loss per charging-discharging cycle. A thick SEI may further increase the electrical resistance of a battery and thereby limit its ability to charge and discharge at high currents.

[0010] In principle, the SEI formation is a self-terminating process that stops as soon as a 'passivation layer' has formed on the surface of the silicon-based material.

[0011] However, because of the volume expansion of silicon-based particles, both silicon- based particles and the SEI may be damaged during discharging (lithiation) and recharging (delithiation), thereby freeing new silicon surface and leading to a new onset of SEI formation.

[0012] To solve the above-mentioned drawbacks, composite powders are usually used. In these composite powders, nano-sized silicon-based particles are mixed with at least one component suitable to protect the silicon-based particles from electrolyte decomposition and to accommodate volume changes. Such a component may be a carbon-based material, preferably forming a matrix.

[0013] The composite powders usually additionally contain graphitic particles, to adjust their specific capacity to a practical level, between 500 mAh / g and 2000 mAh / g.

[0014] Despite the use of such composite powders, there is still room for improvement of the performance of batteries containing silicon-based materials. In particular, the existing composite powders do not allow achieving both a high capacity and a long cycle life, which is essential, in particular for the batteries of the electric vehicles.

[0015] It is an objective of the present invention to provide a composite powder comprising composite particles, said composite particles comprising a carbon matrix material with silicon-based particles embedded therein, said composite powder which once used in the negative electrode of a battery, is advantageous in that it allows achieving a high capacity combined to a long cycle life. SUMMARY OF THE INVENTION

[0016] This objective is achieved by providing a composite powder according to the invention, said composite powder, which once used in the negative electrode of a battery, allows to achieve a long cycle life, while keeping a high specific capacity, as demonstrated in Examples 1 to 3 compared to Counterexamples 1 and 2.

[0017] DETAILED DESCRIPTION

[0018] In the following detailed description, preferred embodiments are described in detail to enable practice of the invention. Although the invention is described with reference to these specific preferred embodiments, it will be understood that the invention is not limited to these preferred embodiments. To the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description and accompanying drawings.

[0019] In a first aspect, the present invention concerns a composite powder for use in a negative electrode of a battery, the composite powder comprising composite particles, the composite particles comprising a carbonaceous matrix material with silicon-based particles embedded therein, the composite powder having:

[0020] - a silicon peak, which is an X-ray diffraction peak assigned to silicon having a maximum intensity Isi at a 20cu peak position between 28.0° and 29.0°, and

[0021] - one or more carbon peaks, which are X-ray diffraction peaks assigned to carbon having each a maximum intensity at 20cu peak positions between 24.0° and 27.0°, with Ic being the highest of the one or more carbon peaks' maximum intensities, and

[0022] - a ratio Isi / Ic superior to 10, the peak positions and maximum intensities being measured via a peak fitting of the X-ray diffraction pattern.

[0023] The peak positions and maximum intensities are preferably measured via a peak fitting of the X-ray diffraction pattern using Voigt functions, resulting in a fitting quality R2at least equal to 0.995, preferably at least equal to 0.997 and more preferably at least equal to 0.998. Preferably 1 Voigt curve is used to fit the silicon peak and 1 Voigt curve for each of the carbon peak(s) present in the X-ray diffraction pattern. For example 1 Voigt curve for the amorphous carbon peak, resulting for example from the presence of carbon matrix material, and 1 Voigt curve for the crystalline carbon peak, resulting for example from the presence of graphite or graphene particles in the composite powder.

[0024] Preferably, the composite particles consist of a carbon matrix material with silicon nanoparticles embedded therein. By "carbonaceous matrix material and silicon- based particles embedded therein", it is meant that the composite particles are, on average, larger in size than the silicon-based particles, since they comprise these latter. The composite particles are typically of micrometric size, while the silicon- based particles are typically of nanometric size. It is also meant that the surface of the silicon-based particles is covered with the carbonaceous matrix material for at least 50% of the surface and preferably that the silicon-based particles are completely covered with the carbon matrix material, to ensure a proper protection against the reaction with the electrolyte during cycling. In other words, the silicon- based particles and the carbon matrix material are not just mixed together, since a proper coverage of the surface of the silicon-based particles cannot be obtained that way. This can be visually confirmed based on the analysis of one or several SEM images of cross-sections of composite particles, comprising the silicon-based particles.

[0025] As already mentioned, a negative effect associated with silicon is that a thick SEI, a Solid-Electrolyte Interface, may be formed on the anode, in particular on the silicon-based particles. Since the silicon-based particles are affected by a large volume variation during the lithiation / delithiation process in the battery, the SEI which has already formed might break again, leading to a continuous consumption of lithium and thereby to a dramatic drop of the cycle life of the battery. Protecting the surface of the silicon-based particles with the carbonaceous matrix material, at least partially, is an efficient solution against the continuous formation of the SEI and the loss in cycle life.

[0026] The silicon-based particles embedded in the carbonaceous matrix material preferably either form agglomerates of a size smaller than 1 pm or do not for agglomerates at all. Hence, the silicon-based particles are preferably in contact only with each other and / or with the carbonaceous matrix material.

[0027] The silicon-based particles may have any shape, e.g. substantially spherical but also irregularly shaped, rod-shaped, plate-shaped, etc. In the silicon-based particles, the silicon is present in its majority as silicon metal, to which minor amounts of other elements may have been added to improve properties, or which may contain some impurities, such as oxygen or traces of metals. When considering a representative number of silicon-based particles, for example not less than 10 distinct silicon-based particles, the average silicon content in such a silicon-based particle is 70 weight % or more, preferably 80 weight % or more, and more preferably 90 weight % or more with respect to the total weight of the silicon-based particle. This can for example be determined by an elemental mapping analysis of a cross-section of a composite particle, comprising numerous cross-sections of silicon-based particles, using a high resolution FEG-SEM microscope. Furthermore, the silicon-based particles typically have a surface layer comprising SiOx with 0<x<2, and preferably 0<x<l.

[0028] The composite powder according to the invention comprises a carbonaceous matrix material having specific properties which are advantageous, for example in terms of elasticity to accommodate for the volumetric expansion of silicon, without suffering from damages such as cracks during the consecutive cycles of charge / discharge in a battery, resulting in a shorter cycle life. Those properties are difficult to define and to measure, but the inventors have discovered that the X-ray diffraction method could allow to differentiate between a composite powder according to the invention, having a desired carbonaceous matrix material and a composite powder having a less suitable carbonaceous matrix material.

[0029] Preferably the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities is at 20cu peak position superior to 24.0°, more preferably superior to 24.2°, even more preferably superior to 24.4°, particularly preferably superior to 24.6°. Preferably the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities is at 20cu peak position inferior to 26.4°, more preferably inferior to 26.0°, even more preferably inferior to 25.6°, particularly preferably inferior to 25.2° and even more particularly preferably inferior to 25.0°. The composite powder according to the invention preferably has a carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities at 20cu peak position between 24.0° and 26.0°, more preferably between 24.2° and 25.6°, even more preferably between 24.2° and 25.4° and particularly preferably between 24.2° and 25.2°. The carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities, as previously defined, preferably has a full width at half maximum (FWHM), at least equal to 2.0° (20cu), preferably at least equal to 3.0° (20cu), more preferably at least equal to 4.0° (20cu), even more preferably at least equal to 5.0° (20cu). In other words, it is preferable for the composite powder according to the invention to have a carbon peak in X-ray diffraction having the highest intensity Ic of the one or more carbon peaks' maximum intensities, as previously defined, which is broad, thereby excluding composite powders comprising graphite particles, graphene particles or similar types of crystalline carbon particles, since they are known for having a narrow carbon peak in X-ray diffraction at 20cu peak position between 26.0° and 27.0° and a full width at half maximum (FWHM), inferior to 1.0° or 2.0° (20cu).

[0030] It is to be noted that, in particular when X-ray diffraction peaks overlap with each other, it is necessary to perform a profile fitting or peak fitting operation, using any software capable of such an operation, such as, but not limited to, Origin, to define the exact peak position, the maximum intensity and the full width at half maximum of each peak. An example of such profile fitting or peak fitting operation is provided in the section "X-Ray diffraction" in the Analytical Methods and is illustrated in Figure 2A) and 2B). The peak fitting is preferably done using Voigt functions. Preferably 1 Voigt curve is used to fit the silicon peak and 1 Voigt curve for each of the carbon peak(s) present in the X-ray diffraction pattern. For example 1 Voigt curve for the amorphous carbon peak, resulting for example from the presence of carbon matrix material, and 1 Voigt curve for the crystalline carbon peak, resulting for example from the presence of graphite or graphene particles in the composite powder. To be acceptable, a profile fitting or peak fitting should result in a R2score of at least 0.995, preferably at least 0.997, more preferably at least 0.998.

[0031] Furthermore, unless mentioned otherwise, the position of a peak is meant to be the position at which the peak has its maximum intensity.

[0032] As already mentioned, the composite powder according to the invention has a silicon peak in X-ray diffraction having a maximum intensity Isi at 20cu peak position between 28.0° and 29.0° and one or more carbon peaks having each a maximum intensity at 20cu peak positions between 24.0° and 27.0°, with Ic being the highest of the one or more carbon peaks' maximum intensities. The inventors have discovered that for the composite powder according to the invention, the ratio Isi / Ic is superior to 10, preferably superior to 12, more preferably superior to 15, even more preferably superior to 20, particularly preferably superior to 25 and even more particularly preferably superior to 30. A composite powder comprising crystalline carbon, in particular graphite and / or graphene particles, would likely translate into a ratio Isi / Ic, as previously defined, inferior to 10, which is not desired. The ratio Isi / Ic is preferably inferior to 200, more preferably inferior to 100.

[0033] In another embodiment according to the first aspect of the invention, the composite powder has an interplanar spacing determined using Bragg's law applied to the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities at 20cu between 24.0° and 27.0°, also commonly referred to as d-spacing, which is at least equal to 3.40 A, preferably at least equal to 3.45 A, more preferably at least equal to 3.50 A, particularly preferably at least equal to 3.55 A. Braag's law is known as n = 2d sin 0, where n is the diffraction order (n = l is first order, n = 2 is second order, etc.), A is the wavelength of the X-rays (for example A = 1.5406 A for a Cu anticathode), 0 is the diffraction angle and d is the interplanar spacing (in A). For example, the interplanar spacing of ideal graphite, calculated from the 002 diffraction peak at about 26.5° (20cu) is approximately 3.35 A.

[0034] In yet another embodiment according to the first aspect of the invention, the composite powder has a crystallite size determined using Scherrer's equation applied to the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities at 20cu between 24.0° and 27.0°, also commonly referred to as Lc, of less than 10 nm, preferably less than 8 nm, more preferably less than 6 nm, even more preferably less than 5 nm, particularly preferably less than 4 nm, even more particularly preferably less than 3 nm and utterly preferably less than 2 nm. Scherrer's equation is known as D = where

[0035] D is the crystallite size (in nm), K is the shape factor (usually chosen around 0.9), A is the wavelength of the X-rays (for example A = 1.5406 A for a Cu anticathode), [3 is the Full Width at Half Maximum (FWHM) and 0 is the diffraction angle. For example, for the purpose of illustrating, in a non-limitative way, the application of the Scherrer's equation, a powder having a carbon peak at 26.5° (20cu) with a FWHM of 0.89° would have a crystallite size of 9.17 nm.

[0036] In another embodiment according to the first aspect of the invention, the inventors have discovered that the Raman spectroscopy method could also allow to differentiate between a composite powder according to the invention, having a desired carbonaceous matrix material and a composite powder having a less suitable carbonaceous matrix material. In particular, the composite powder according to the invention has a Raman spectrum, wherein a band A attributed to silicon has a maximum intensity IA between 480 and 540 cm and bands B, C and D attributed to the carbonaceous matrix material have a maximum intensity between 1300 cm and 1360 cm4, between 1560 cm4and 1620 cm4and between 2670 cm-1and 2730 cm’1respectively, whereby the ratio IA / ID is between 6 and 30, the ratio IA / IB is between 0.3 and 1.0, the ratio ID / IB is less than 0.10 and the ratio IB / IC is between 0.95 and 1.25.

[0037] The ratio IA / ID is preferably at least equal to 8, more preferably at least equal to 10 and particularly preferably at least equal to 12. The ratio IA / ID is preferably at most equal to 25, more preferably at most equal to 20 and particularly preferably at most equal to 16. The ratio IA / ID is preferably between 8 and 16, more preferably between 10 and 16.

[0038] The ratio IA / IB is preferably at least equal to 0.4, more preferably at least equal to 0.5. The ratio IA / IB is preferably at most equal to 0.9, more preferably at least equal to 0.8 and particularly preferably at least equal to 0.7. The ratio IA / IB is preferably between 0.4 and 0.7.

[0039] The ratio ID / IB is preferably at least equal to 0.02, more preferably at least equal to 0.03, even more preferably at least equal to 0.04 and particularly preferably at least equal to 0.05. The ratio ID / IB is at most equal to 0.08, more preferably at most equal to 0.07, even more preferably at most equal to 0.06 and particularly preferably at most equal to 0.05. The ratio I D / I B is preferably between 0.03 and 0.08.

[0040] The ratio IB / IC is preferably at least equal to 1.00, preferably at least equal to 1.05. The ratio IB / IC is preferably at most equal to 1.30, more preferably at most equal to 1.25, even more preferably at most equal to 1.20 and particularly preferably at most equal to 1.15. The ratio IB / IC is preferably between 1.00 and 1.20. The composite powder according to the invention has a silicon content at least equal to 40 weight percent (wt%), preferably at least equal to 45 wt% and particularly preferably at least 50 wt%. The composite powder according to the invention also has a silicon content at most equal to 80 weight percent, preferably at most equal to 70 wt%, relative to the total weight of the powder. With the necessity to move from thermic vehicles to clean vehicles, in particular to electric vehicles, the main objective to get acceptance from the users is to achieve driving ranges of at least 500-600 km. Since the size and weight of battery packs cannot be extended infinitely, it is necessary to produce batteries with higher energy densities and thus to produce anode materials with higher specific capacities, therefore with higher silicon contents. Preferably, said specific capacity should be at least equal to 1400 mAh / g, more preferably at least equal to 1600 mAh / g and even more preferably at least equal to 1800 mAh / g. However, because a high specific capacity also implies more swelling and more mechanical deformations during the charge / discharge cycles, it is preferable to limit the specific capacity of the composite powder to at most 2400 mAh / g, more preferably at most 2200 mAh / g and even more preferably at most 2000 mAh / g.

[0041] In another embodiment according to the first aspect of the invention, the composite powder has a BET surface area which less than 5 m2 / g. It is important for the composite powder to have a low BET specific surface area, to decrease the surface of electrochemically active particles in contact with the electrolyte, in order to limit the SEI formation, which consumes lithium, and thus to limit the loss in cycle life of a battery containing such a composite powder. The lower BET is obtained by removing the spacer particles from the manufacturing process of the composite powder. The BET surface area is preferably less than 4 m2 / g, more preferably less than 3 m2 / g and particularly preferably less than 2 m2 / g.

[0042] In yet another embodiment according to the first aspect of the invention, the composite powder has a silicon content and an oxygen content, both relative to the total weight of the composite powder, whereby the ratio of the oxygen content to the silicon content is less than 0.20 and preferably less than 0.15. A composite powder having a too high oxygen content would suffer from an additional irreversible consumption of lithium by the formation of lithium silicate ( LizSiOs, Li4SiO4) during the first lithiation of the powder, thus increasing the initial irreversible capacity loss of a battery containing such a composite powder.

[0043] In another embodiment according to the first aspect of the invention, the composite powder also has a carbon content relative to the total weight of the powder, whereby the ratio of the carbon content to the silicon content is between 0.50 and 1.00. The ratio of the carbon content to the silicon content is at least 0.50, preferably at least 0.60, more preferably at least 0.70 and even more preferably at least 0.80. The ratio of the carbon content to the silicon content is at most 0.90, preferably at most 0.80. The ratio of the carbon content to the silicon content is preferably between 0.60 and 0.90.

[0044] When the ratio of the carbon content to the silicon content in the composite powder is lower than 0.50, the carbonaceous matrix material is not present in an amount sufficient to adequately cover the silicon-based particles, therefore leading to an increased electrolyte decomposition at the surface of the silicon-based particles and thus to an increased SEI formation. When the ratio of the carbon content to the silicon content in the composite powder is higher than 1.00, the specific capacity of the composite powder is too low, since the carbon forming the matrix material has a specific capacity more than 10 times lower than the silicon specific capacity. Furthermore, since the carbonaceous matrix material triggers a high irreversible capacity (low coulombic efficiency at first cycle), it is preferable for the composite powder to contain only the amount of carbonaceous matrix material that is necessary to cover the silicon-based particles.

[0045] In another embodiment according to the first aspect of the invention, the composite powder comprises composite particles comprising silicon-based particles. The silicon-based particles are characterized by a number-based size distribution having a d50, the d50 being larger than or equal to 20 nm and smaller than or equal to 100 nm. The d50 of the silicon-based particles is preferably at least equal to 30 nm, more preferably at least equal to 40 nm. The d50 of the silicon-based particles is preferably at most equal to 90 nm, more preferably at most equal to 80 nm. For the sake of clarity, a d50 of 60 nm for example, would here mean that 50% in number of the at least 1000 silicon-based particles have a size smaller than 60 nm and that 50% in number of the at least 1000 silicon-based particles have a size larger than 60 nm.

[0046] The number-based size distribution is based on a visual analysis, with or without assistance of an image analysis program, of a minimum number of silicon-based particles comprised in the composite powder. This minimum number of silicon- based particles is at least 1000 particles. An example of a determination of a number-based distribution of Si-based particles is provided in the "Analytical methods" section. Silicon-based particles having a number-based size distribution with a d50 lower than 20 nm are very difficult to disperse efficiently in the carbon matrix material, which may decrease the electronic conductivity of the powder. Silicon-based particles having a number-based size distribution with a d50 larger than 100 nm are more subject to fractures during their lithiation, causing a dramatic reduction of the cycle life of a battery containing such a composite powder. Likewise, the silicon-based particles are characterized by a number-based size distribution having a d90, the d90 being larger than or equal to 40 nm and smaller than or equal to 140 nm. The d90 of the silicon-based particles is preferably at least equal to 50 nm, more preferably at least equal to 60 nm. The d90 of the silicon-based particles is preferably at most equal to 120 nm, more preferably at most equal to 100 nm. It is considered that the d50 and d90 values are not affected by the process of making the composite powder, which means that the d50 and d90 values of the silicon-based powder used as precursor in the process is the same as the d50 and the d90 values of the silicon-based particles comprised in the composite powder.

[0047] In another embodiment according to the first aspect of the invention, the carbonaceous matrix material comprised in the composite powder according to the invention, is soft carbon. Soft carbon corresponds to an arrangement of small disordered graphitic domains that can be converted to graphite upon heating at a temperature of 3000°C, in opposition to hard carbon which is not graphitizable. Soft carbon shows a higher electronic conductivity compared to hard carbon and is therefore preferable. Furthermore, thanks to its disordered collection of small graphitic domains, which leads to the presence of nanovoids in the matrix material, the volumetric expansion of a particle comprising a matrix material mostly comprising soft carbon, during the lithiation of the anode, is reduced compared to a particle comprising a matrix material mostly comprising graphite or graphene. A reduced volumetric expansion will lead to a longer cycle life in a battery.

[0048] In another embodiment according to the first aspect of the invention, the composite particles have a volume-based particle size distribution having a DIO, a D50 and a D90, with 1 pm < DIO < 10 pm, 5 pm < D50 < 20 pm and 10 pm < D90 < 30 pm. For the sake of clarity, a D50 of 15 pm for example, would here mean that 50% in volume of the composite particles have a size smaller than 15 pm and that 50% in volume of the composite particles have a size larger than 15 pm.

[0049] Composite particles having a volume-based size distribution with a D50 smaller than 5 pm, may have a too high specific surface and thus increase the surface of reaction with the electrolyte and the formation of SEI, which is disadvantageous for the reasons previously explained. Composite particles having a volume-based size distribution with a D50 larger than 20 pm, may, due to their size, be more susceptible to suffer from the formation of fractures during the lithium uptake, thus leading to a reduced cycle life of the battery containing such particles.

[0050] In another embodiment according to the first aspect of the invention, the carbonaceous matrix material is obtained by carbonization at a temperature above 800°C, preferably above 900°C, of one, or a mixture of several of the following carbon precursors: polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, coal- tar pitch, petroleum pitch, lignin, and a resin. The carbon precursor, when heated at a temperature above 800°C, preferably has a carbon yield at least equal to 40 wt% - meaning that 40 wt% of the carbon precursor has decomposed into carbon and 60 wt% of the carbon precursor has decomposed into gases - more preferably at least equal to 50 wt% and particularly preferably at least equal to 60 wt%.

[0051] The weight ratio "carbon precursor / silicon" is at least equal to 0.6, more preferably at least equal to 0.8 and even more preferably at least equal to 1.0. The weight ratio "carbon precursor / silicon" is at most equal to 2.0, preferably at most equal to 1.8, more preferably at most equal to 1.6, even more preferably at most equal to 1.4 and particularly preferably at most equal to 1.2.. "silicon" here needs to be understood as the chemical element silicon, independent from its oxidation state. The carbonaceous matrix material obtained after a heat treatment of the carbon precursor above 800 or 900°C typically having a specific capacity of 200- 300 mAh / h, i.e. at least 10 times lower than the specific capacity of silicon, it is preferable to keep the weight ratio "carbon precursor / silicon" as low as possible, but still high enough to have a full embedment and a full coverage of the silicon- based particles in the carbonaceous matrix material. This in order to avoid a direct contact between the silicon-based particles and the liquid electrolyte, triggering the formation of an unstable SEI layer and a decrease of the cycle life of a battery comprising such a composite powder.

[0052] In a second aspect, the present invention concerns a negative electrode for a battery, preferably a lithium-ion battery, comprising the composite powder according to the invention. The negative electrode typically also comprises electronically conductive additives, such as carbon black, graphite particles, graphene particles, carbon nanotubes, or a mixture thereof. The content of electronically conductive additives is comprised between 0% and 10% by weight, in particular from 0.1% to 5% by weight, relative to the total weight of the negative electrode layer (excluding the current collector).

[0053] The negative electrode typically also comprises 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), styrene-butadiene rubber (SBR). The binder(s) is / are added to improve the cohesion of the various components of the negative electrode, its mechanical strength on the current collector or even its flexibility properties. The binder(s) represent from 1% to 15% by weight, in particular from 2% to 10% by weight, relative to the total weight of the negative electrode layer (excluding the current collector). An example of a negative electrode preparation is provided elsewhere in this document.

[0054] Finally, the present invention also concerns a battery, preferably a lithium-ion battery, comprising a negative electrode according to the present invention, and therefore comprising a composite powder according to the present invention, as previously defined or prepared as previously disclosed. A battery according to the invention more specifically comprises a negative electrode (anode) according to the invention, a positive electrode (cathode) and an electrolyte, preferably a nonaqueous electrolyte. As examples of the positive electrode, mention may be made of the positive electrode active materials selected from LiCoO2, LiNio,6Mno,2Coo,202, LiNio,8Mno,iCoo,i02, LiNio,8Coo,i5Alo,os02, Lii,2Nio,2Mno,e02, LiFePCU, and the like. The electrolyte may be preferably a non-aqueous electrolytic solution, a non-aqueous polymer electrolyte or even a solid electrolyte. Specific examples thereof include an organic electrolytic solution obtained by dissolving lithium salt such as LiCICU, LiPFe, LiAsFe, LiBF4, USO3CF3, CH3SO3 Li, CF3SO3U or the like into a non-aqueous solvent such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), fluoro ethylene carbonate (FEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butylene carbonate, acetonitrile, propionitrile, dimethoxyethane, tetrahydrofuran, y-butyrolactone or the like; a gel polymer electrolyte comprising polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate or the like; and a solid polymer electrolyte comprising a polymer having an ethylene oxide bond. Moreover, an additive which causes a decomposition reaction during initial charge of the lithium ion battery may be added to the electrolytic solution. Specific examples of additives include vinylene carbonate (VC), biphenyl, propane sultone (PS), fluoro ethylene carbonate (FEC), ethylene sultone (ES) or the like. The additive amount thereof is preferably not less than 0.1% by weight and not more than 20% by weight, relative to the total weight of the electrolyte.

[0055] BRIEF DESCRIPTION OF THE FIGURES

[0056] Figure 1: X-ray diffraction pattern of composite powders CE1 and El.

[0057] Figure 2: Peak fitting of the X-ray diffraction pattern of composite powders A) CE1 and B) El.

[0058] Figure 3: Raman spectroscopy spectra of A) composite powder CE1 and B) composite powder E3.

[0059] ANALYTICAL METHODS USED

[0060] Determination of the silicon content

[0061] The silicon content of the composite powders is measured by X-Ray Fluorescence (XRF) using an energy dispersive spectrometer. This method has an experimental random error of + / - 0.3 wt% Si.

[0062] Determination of the oxygen content

[0063] The oxygen content of the composite powders is determined by the following method, using a LECO TC600 oxygen-nitrogen analyzer. A sample of the powder to be analyzed is put in a closed tin capsule that is put itself in a nickel basket. The basket is put in a graphite crucible and heated under helium as carrier gas to above 2000°C. The sample thereby melts and oxygen reacts with the graphite from the crucible to CO or CO2 gas. These gases are guided into an infrared measuring cell. The observed signal is recalculated to an oxygen content.

[0064] Determination of the carbon content

[0065] The carbon content of the composite powders is determined by the following method, using a Leco CS230 carbon-sulfur analyzer. The sample is melted in a constant oxygen flow in a ceramic crucible in a high frequency furnace. The carbon in the sample reacts with the oxygen gas and leaves the crucible as CO or CO2. After conversion of an eventual presence of CO into CO2, all produced CO2 is finally detected by an infrared detector. The signal is finally converted into a carbon content.

[0066] Determination of the specific surface area (BET)

[0067] The specific surface area of the composite powders is measured with the Brunauer- Emmett-Teller (BET) method using a Micromeritics Tristar 3000. 2g of the powder to be analyzed is first dried in an oven at 120°C for 2 hours, followed by N2 purging. Then the powder is degassed in vacuum at 120°C for 1 hour prior to the measurement, in order to remove adsorbed species.

[0068] Determination of the electrochemical performance

[0069] The electrochemical performance of the composite powders in the examples and the counterexamples is determined by the following method.

[0070] The composite powders to be evaluated are sieved using a 45 pm sieve. Then, in a first stage, the composite powders are tested as such, without any dilution with graphite particles, to determine their specific capacity. They are mixed with carbon black, carbon fibers and sodium carboxymethyl cellulose binder in water (2.5 wt%). The ratio used is 89 weight parts composite powder / 1 weight part carbon black (C65) / 2 weight parts carbon fibers (VGCF) and 8 weight parts carboxymethyl cellulose (CMC). All these components are mixed in a Pulverisette 7 planetary ball mill for 30 minutes at 250 rpm. A copper foil cleaned with ethanol is used as current collector. A 200 pm thick layer of the mixed components is coated on the copper foil. The coated copper foil is then dried for 45 minutes in vacuum at 70°C. A 1.27 cm2circle is punched from the dried coated copper foil and used as an electrode in a coin cell using lithium metal as counter electrode. The electrolyte is IM LiPFe dissolved in EC / DEC 1 / 1 + 2% VC + 10% FEC solvents.

[0071] All coin-cells are cycled using a high precision battery tester (Maccor 4000 series) using the procedure described below, where "CC" stands for "constant current" and "CV" stands for "constant voltage".

[0072] • Cycle 1 : o Rest 6h o CC lithiation to 10 mV at C / 10, then CV lithiation until C / 100 o Rest 5 min o CC delithiation to 1.5 V at C / 10 o Rest 5 min

[0073] The capacity obtained for the delithiation at cycle 1 is the specific capacity of the composite powder.

[0074] In a second stage, the composite powders are tested at a lower capacity, i.e. after dilution with graphite particles in a mixture "composite powder + graphite" . The respective weight contents of composite powder and graphite in the mixture "composite powder + graphite" are adjusted such as to obtain a theoretical specific capacity for said mixture of about 550 mAh / g. For example, for a composite powder having a measured specific capacity of 1500 mAh / g and using a theoretical capacity of 350 mAh / g for the graphite, the respective weight contents of composite powder and graphite are respectively 17.4 wt% and 82.6 wt%. The rest of the procedure, anode formulation, cell composition and cell assembling, is kept unchanged.

[0075] The cycling procedure is as follows:

[0076] • Cycle 1 : o Rest 6h o CC lithiation to 10 mV at C / 10, then CV lithiation until C / 100 o Rest 5 min o CC delithiation to 1.5 V at C / 10 o Rest 5 min

[0077] • From cycle 2 on: o CC lithiation to 10 mV at C / 2, then CV lithiation until C / 50 o Rest 5 min o CC delithiation to 1.2 V at C / 2 o Rest 5 min

[0078] The coulombic efficiency (CE) of the coin-cell, being the ratio of the capacity at delithiation to the capacity at lithiation at a given cycle, is calculated for the initial cycle as well as for the subsequent ones. The initial cycle is the most important one in terms of coulombic efficiency, since the reaction of SEI formation has a huge impact on the CE. Typically for a silicon-based powder the coulombic efficiency at the initial cycle can be as low as 80% (or even lower), corresponding to an irreversible capacity loss for the coin-cell of 20%, which is huge. The target is to reach at least 90% CE at the initial cycle.

[0079] For the subsequent cycles even though the CE usually increases well over 99%, the skilled person will be aware that even a small difference in coulombic efficiency per cycle, will have, over the hundreds or thousands of charging-discharging cycles a battery is expected to last, a significant cumulative effect. To give an example, a cell with an initial capacity of 1 Ah having an average CE of 99,8% will, after 100 charging-discharging cycles, have a remaining capacity of 0,8 Ah, which is 60% higher than for a cell having an average CE of 99,5% (remaining capacity of 0,5 Ah).

[0080] The target in terms of average CE from cycle 5 to cycle 50 is to reach at least 99.75%, preferably at least 99,80%, and even more preferably at least 99.85% for a cell comprising a composite powder with a specific capacity of 550 ± 10 mAh / g.

[0081] Determination of the number-based particle size distribution

[0082] The number-based particle size distribution of the silicon-based particles is determined via an electron microscopy analysis (SEM or TEM) of a cross-section of the composite powder, combined with an image analysis. To do this, a cross-section of the composite powder, comprising multiple crosssections of composite particles, each of them comprising multiple cross-sections of silicon-based particles, is prepared following the procedure detailed hereunder.

[0083] 500 mg of the composite powder to be analyzed is embedded in 7g of a resin (Buehler EpoxiCure 2) consisting of a mix of 4 parts Epoxy Resin (20-3430-128) and 1 part Epoxy Hardener (20-3432-032). The resulting sample of 1" diameter is dried during at least 8 hours. It is then polished, first mechanically using a Struers Tegramin-30 until a thickness of maximum 5 mm is reached, and then further polished by ion-beam polishing (Cross Section Polisher Jeol SM-09010) for about 6 hours at 6 kV, to obtain a polished surface. A carbon coating is finally applied on this polished surface by carbon sputtering using a Cressington 208 carbon coater for 12 seconds, to obtain the sample, also called "cross-section", that will be analyzed by SEM.

[0084] The prepared cross-section is then analyzed using a FEG-SEM JSM-7600F from JEOL equipped with an EDS detector Xflash 5030-127 from Bruker (30mm2, 127 eV). The signals from this detector are treated by the Quantax 800 EDS system from Bruker.

[0085] The enlargements are generated by applying a voltage of 15kV at a working distance of several millimeters. The images from the backscattered electrons are reported when adding value to the images from the optical microscope.

[0086] The size of a silicon-based particle is considered to be equivalent to the maximum straight-line distance between two points on the perimeter of a discrete crosssection of that silicon-based particle.

[0087] For the purpose of illustrating, in a non-limitative way, the determination of the number-based particle size distribution of silicon-based particles, a SEM-based procedure is provided below.

[0088] 1. Multiple SEM images of the cross-section of the composite powder comprising composite particles with silicon-based particles dispersed therein, are acquired.

[0089] 2. The contrast and brightness settings of the images are adjusted for an easy visualization of the cross-sections of the composite particles and the silicon- based particles. Due to their different chemical composition, the difference in brightness allows for an easy distinction between both types of particles.

[0090] 3. At least 1000 discrete cross-sections of silicon-based particles, not overlapping with another cross-section of a silicon-based particle, are selected from one or several of the acquired SEM image(s), using a suitable image analysis software. These discrete cross-sections of silicon-based particles can be selected from one or more cross-sections of the composite powder comprising the composite particles and the silicon-based particles.

[0091] 4. The size of the discrete cross-sections of the silicon-based particles are measured using a suitable image analysis software for each of the at least 1000 discrete cross-sections of silicon-based particles.

[0092] The dlO, d50 and d90 values of the number-based particle size distribution of silicon-based particles, determined using the method described above, are then calculated. These number-based particle size distributions can be readily converted to a weight- or a volume-based particle size distribution via well-known mathematical equations.

[0093] Determination of the volume-based particle size distribution

[0094] The volume-based particle size distribution of the composite particles is determined with a laser diffraction particle size analyzer Malvern Mastersizer 2000. The following measurement conditions are selected: compressed range; active beam length 2.4 mm; measurement range: 300 RF; 0.01 to 900 pm. The sample preparation and measurement are carried out in accordance with the manufacturer's instructions.

[0095] X-Rav diffraction

[0096] X-ray Diffraction (XRD) analyses are performed with a Panalytical Empyrean system equipped with a copper anode producing Koi and Ko2 X-rays and a wavelength A equal to 0.15406 nm, with a step size of 0.02° 20, a scan rate of 0.25° / min and measuring from 20° to 40° (20cu) on a flattened surface of about 1.5 cm3of powder material. During the measurement the sample rotates at 30 rpm. Peak fitting of the obtained X-ray diffraction pattern is performed using Voigt functions in the Origin program. 1 Voigt curve is used to fit the silicon peak and 1 Voigt curve for each of the carbon peak(s) present in the X-ray diffraction pattern. For example 1 Voigt curve for the broad carbon peak at a 20cu angle between 24.0 and 26.0°, resulting from the presence of low-crystallinity carbon matrix material, and 1 Voigt curve for the narrow carbon peak at a 20cu angle between 26.0°and 27.0°, resulting for example from the optional presence of graphite or graphene particles in the composite powder. Therefore, all X-ray diffraction patterns in the present application are fitted with either 2 or 3 Voigt curves. All peak fittings result in excellent fitting qualities (R2) above 0.998, as reported in Table 2a. For the purpose of illustrating, in a non-limitative way, the peak fitting of the X-ray diffraction patterns and the determination of the peak positions and maximum intensities, the procedure used is provided in more details below.

[0097] The X-ray diffraction data are imported to Origin. Only the data for 20cu angles from 20.0° to 32.0° are kept. The column containing the intensity values (Y axis) are selected, the function "Analysis - Peaks and Baseline - Peak Analyzer" is activated and the Dialog box is opened. The function "Subtract Baseline" is selected as goal and "Straight line" is selected as baseline mode, the baseline is then subtracted. The column containing the subtracted baseline intensities is selected, the function "Analysis - Peaks and Baseline - Multiple Peak Fit" is activated and the Dialog box is opened. "Voigt" is selected as Peak Function. 1 Voigt curve is then manually added for the silicon peak at about 28.45° (20cu), 1 Voigt curve for the broad carbon peak at a 20cu angle between 24.0 and 26.0° and 1 Voigt curve for the narrow carbon peak at a 20cu angle between 26.0°and 27.0°, if this latter is present. The function "Open NLFit" is used and the yO parameter ("offset") boundary is defined as 0 < yo < 50. Alternatively, if exceptionally the fit would not converge it is also possible to manually set yo to 0. Finally, the "Fit" function is used and the peak fitting is performed, resulting in a fitting quality R2at least equal to 0.995, preferably at least 0.998. The resulting peaks positions and maximum intensities are listed. Following this procedure, the standard error on the Isi / Ic ratio is at most about 3-6%.

[0098] Raman spectroscopy

[0099] The Raman spectroscopy analysis of the composite powders is performed with a WITec alpha300 apyron confocal Raman microscope, using a 532 nm laser excitation and the following settings:

[0100] - Magnification 10 x NA 0.25 - Integration time 10 seconds

[0101] - Accumulations: 5 times

[0102] - Powder: 1.00 mW

[0103] - Grating: 600

[0104] The sample is prepared as follows: the composite powder is placed on a with Al- tape covered microscopic glass plate and crushed with a spatula to a flat surface. The Al-tape has no Raman signal interfering with the Raman spectrum of the composite powder. For every sample, 10 different locations are randomly measured. The result given in Table 2b is the average of the 10 measurements. For each spectrum, a background correction and a normalization to the D peak (at ± 1337 cm-1) is done.

[0105] EXPERIMENTAL PREPARATION OF EXAMPLES

[0106] Counterexample 1 (CE1), not according to the invention

[0107] First, a silicon suspension SI is prepared by wet-milling. 0.1 mm Yttrium-stabilized Zirconia beads are weighed to reach a filling ratio of 80%. The filling ratio is defined as the volume of the grinding beads divided by the volume of the grinding chamber and usually ranges from 60% to 90% depending on the type of mill and rotor used. After weighing the correct amount of beads, they are introduced into the mill, a Buhler MMX1. The mill is then flushed with N2 gas in order to create an inert atmosphere. This is to avoid the creation of a potentially explosive environment (ATEX) when introducing the liquid. All equipment is also grounded.

[0108] Then, the liquid, in this case isopropyl alcohol (IPA), is added to the mill to pre-wet the beads. The amount of liquid depends on the batch size and the solid load of the suspension. In this example, the batch size is 3000 g and the solid load is 30.0 weight%. This amounts to 2100 g of IPA being introduced in the mill. At this point the mill is started to allow the solvent to mix with the beads. The mill is set to circulation mode. 900 g of silicon powder (dgo =10 pm) is then slowly added to the mill. A viscosity-reducing agent is added to the mill together with the silicon powder, in order to limit the increase in viscosity of the suspension during the milling operation, thereby limiting the risks of clogging of the sieves, increased milling time and silicon particles not reaching the desired size.

[0109] The mill is programmed to maintain a power output of 4 kW and the tip speed is varied accordingly. Using 0.1 mm beads, the tip speed varies between 14 m / s and 15 m / s. The milling is continued until a specific energy of 40000 kWh / t is reached. This amounts to approximately 9h of milling. At 40000 kWh / t, a cho particle size of 115 nm is reached for the silicon particles comprised in the suspension. At this point the mill is stopped and the suspension SI is drained. The BET specific surface of the dried silicon particles is also measured to be 122 m2 / g and the oxygen content in the dried silicon particles is measured to be 12.5 wt%.

[0110] Then, a silicon-carbon precursor suspension S2 is prepared by mixing the suspension SI with a carbon precursor capable of fully decomposing into carbon at a temperature above 600°C, in that case petroleum pitch. The petroleum pitch used for producing the composite powder of CE1 has a softening point of 250°C.

[0111] For a batch size of 700 g and a solid load of 20 weight%, 408 g of liquid (IPA), 217 g of silicon-containing dispersion SI (at 30 wt% solid load) and 75 g pitch are weighed. The ratio between the pitch content and the silicon-based particles content, both expressed in weight%, in the suspension S2 (ratio "carbon precursor / silicon") is 1.15. The components are mixed using a dissolver for 15 min at 500 rpm using a 80 mm dispersion disc. 0.3 mm Yttrium-stabilized Zirconia beads are then weighed to achieve a filling ratio of 83%. After weighing, the beads are added to the mill.

[0112] The mill is then flushed with N2 in order to create an inert atmosphere. This to avoid the creation of an ATEX environment when introducing solvent. All equipment is also grounded. The dispersion is added to the mill and milling is initiated. The tip speed is set to 12 m / s and milling is continued in circulation mode until a specific energy of 1000 kWh / t is reached. Afterwards the mill is stopped and the suspension S2 is drained. The solid load is determined using a dry balance.

[0113] Next, the suspension S2 is dried using a lab spray dryer. The dispersion is sprayed using a 2-fluid nozzle into a hot nitrogen gas stream upon which the solvent quickly vaporizes and a "silicon-carbon precursor" powder is collected from the cyclone. The inlet temperature is set to 130°C and the nitrogen flow is 1052 l / h.

[0114] Afterwards, the "silicon-carbon precursor" powder (with petroleum pitch as carbon precursor) is fed under a nitrogen flow at a feed rate of 500g / h into a twin-screw extruder, operated at a temperature of 310°C. The mixture of the silicon-based powder in the carbon precursor thus obtained is cooled under N2 to room temperature and, once solidified, pulverized and sieved on a 400-mesh sieve, to produce an intermediate powder.

[0115] The obtained intermediate powder is then mixed with 16.0 g of graphite, for 3 hours on a roller bench, after which the obtained mixture is passed through a mill to de-agglomerate it. At these conditions good mixing is obtained but the graphite particles do not become embedded in the pitch.

[0116] The obtained mixture is then placed in a quartz crucible in a tube furnace, heated up at a heating rate of 3°C / min to 1000°C, kept at that temperature for two hours and then cooled. All this is performed under an oxygen-free argon atmosphere. In the obtained composite powder, the silicon-based particles are dispersed and embedded in a matrix of soft carbon, resulting from the thermal decomposition of the carbon precursor (the petroleum pitch). Graphite particles are located between the Si / carbon matrix and act as spacer particles.

[0117] The fired product is finally ball-milled with alumina balls for 1 hour at 300 rpm and sieved over a 325-mesh sieve, to obtain the composite powder of Counterexample 1.

[0118] The total Si content in this powder is measured to be 43.9 wt% by XRF, having an experimental error of + / - 0.3 wt%. This corresponds to a calculated value based on a weight loss of the pitch upon heating of circa 35 wt% and an insignificant weight loss upon heating of the other components. The calculated ratio of carbon content (expressed in weight%) resulting from the carbonization of the pitch, forming the matrix material, over the silicon content (expressed in weight%) in the powder is around 0.86. The oxygen content of this powder is measured to be 6.3 wt%. The specific surface area (BET) of the obtained powder is measured to be 5.2 m2 / g. The volume-based particle size distribution of the composite particles obtained has a D10 equal to 5.2 pm, a D50 equal to 15.8 pm and a D90 equal to 24.5 pm. The chemical compositions of composite powder CE1 and all other composite powders are summarized in Table 1 Counterexample 2 (CE2), not according to the invention

[0119] The composite powder of Counterexample 2 (CE2) is produced following the same method as for Counterexample CE1, except that the intermediate powder is mixed with 16.0 g of graphene nanoplatelets, instead of 16.0 g of graphite.

[0120] Example 1 (El), according to the invention

[0121] The composite powder of Example 1 (El) is produced starting from the same suspension SI as for Counterexample CE1. Then the suspension S2 is prepared, for a similar batch size of 700 g and a similar solid load of 20 weight% by mixing 429 g of liquid (IPA), 187 g of silicon-containing dispersion SI (at 30 wt% solid load) and 85 g of pitch. The ratio between the pitch content and the silicon-based particles content, both expressed in weight%, in the suspension S2 (ratio "carbon precursor / silicon") is 1.52. The petroleum pitch used is the same as in Counterexample CE1. The resulting mixture is milled, dried and heat-treated exactly as in Counterexample CE1. No graphite is added.

[0122] Example 2 (E2), according to the invention

[0123] The composite powder of Example 2 (E2) is produced using the same method as for the production of the composite powder of Counterexample 1, except that no graphite is added.

[0124] Example 3 (E3), according to the invention

[0125] The composite powder of Example 3 (3) is produced using the same method as for the production of the composite powder of Example 2, except that the heat-treating temperature is set at 950°, instead of 1000°C.

[0126] Table 1: Chemical compositions of the composite powders E1-E3 and CE1-CE2. The "C matrix" content corresponds to the content of carbon resulting from the thermal decomposition of the carbon precursor (pitch).

[0127] able 2: Values extracted from the X-ray diffraction and Raman spectroscopy analyses for the composite powders E1-E3 and CE1E2.

[0128] Electrochemical evaluation of the composite powders

[0129] The produced composite powders are tested in coin-cells according to the procedure specified above. In a first stage, the composite powders are evaluated as such, i.e. without dilution with graphite particles, to determine their specific capacities. As shown in Table 3, all composite powders have high specific capacities, comprised between 1440 mAh / g and 1610 mAh / g.

[0130] For an easier comparison of their performance, in a second stage, the composite powders are mixed with graphite particles during the electrode preparation, to reach a capacity of the mixture "composite powder + graphite" of around 550±10 mAh / g. The results obtained for the initial coulombic efficiency and the average coulombic efficiency of the coin cells comprising the different composite powders, between cycle 5 and cycle 50, are given in Table 3.

[0131] Comparing the results obtained for the composite powders CE1 and CE2 and El to E3, it can be seen that the best results are obtained for the cells containing composite powders according to the invention.

[0132] Table 3: Performance of coin-cells containing composite powders E1-E4 and CE1

Claims

CLAIMS1.- A composite powder for use in a negative electrode of a battery comprising composite particles, said composite particles comprising a carbonaceous matrix material and silicon-based particles embedded therein, said composite powder having:- a silicon peak, which is an X-ray diffraction peak assigned to silicon having a maximum intensity Isi at a 20cu peak position between 28.0° and 29.0°, and- one or more carbon peaks, which are X-ray diffraction peaks assigned to carbon having each a maximum intensity at 20cu peak positions between 24.0° and 27.0°, with Ic being the highest of the one or more carbon peaks' maximum intensities, and- a ratio Isi / Ic superior to 10, wherein the peak positions and maximum intensities are measured via a peak fitting of the X-ray diffraction pattern.2.- The composite powder according to claim 1, wherein the peak positions and maximum intensities are measured via a peak fitting of the X-ray diffraction pattern with 1 Voigt curve for the silicon peak and 1 Voigt curve for each of the carbon peak(s), said peak fitting having a quality R2at least equal to 0.995.3.- The composite powder according to claim 1 or 2, wherein the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities is at 20cu peak position between 24.0° and 26.0°.

4. The composite powder according to any one of the preceding claims, wherein the carbon peak having the highest intensity Ic of the one or more carbon peaks' maximum intensities has a full width at half maximum, also commonly referred to as FWHM, at least equal to 2.0° (20cu).5.- The composite powder according to any one of the preceding claims, wherein the powder is free of graphite and graphene particles.6.- The composite powder according to any one of the preceding claims, having a silicon content at least equal to 40 weight % and at most equal to 80 weight % relative to the total weight of the powder, and a specific capacity of at least 1400 mAh / g.7.- The composite powder according to any one of the preceding claims, wherein the interplanar spacing determined using Bragg's law applied to the carbon peak having the highest intensity Ic, also commonly referred to as d-spacing, is at least equal to 3.40 A.8.- The composite powder according to any one of the preceding claims, wherein the crystallite size determined using Scherrer's equation applied to the carbon peak having the highest intensity Ic, also commonly referred to as Lc, is less than 10 nm.9.- The composite powder according to any one of the preceding claims, having a Raman spectrum, wherein a band A attributed to silicon has a maximum intensity IA between 480 and 540 cm-1and bands B, C and D attributed to the carbonaceous matrix material have a maximum intensity between 1300 cm and 1360 cm , between 1560 cm4and 1620 cm4and between 2670 cm4and 2730 cm4respectively, whereby the ratio IA / ID is between 6 and 30, the ratio IA / IB is between 0.3 and 1.0, the ratio ID / IB is less than 0.10 and the ratio I B / IC is between 0.95 and 1.25.10.- The composite powder according to claim 9, wherein the ratio ID / IB is between 0.03 and 0.08.11.- The composite powder according to claim 9 or 10, wherein and the ratio IB / IC is between 1.00 and 1.20.12.- The composite powder according to any one of the preceding claims having a silicon content and an oxygen content, relative to the total weight of the powder, whereby the ratio of the oxygen content to the silicon content is less than 0.20, preferably less than 0.15.13.- The composite powder according to any one of the preceding claims having a silicon content and a carbon content, relative to the total weight of the powder, whereby the ratio of the carbon content to the silicon content is between 0.50 and 1.00, preferably between 0.60 and 0.90.14.- The composite powder according to any one of the preceding claims, wherein the silicon-based particles are characterized by a number-based size distribution having a d90, the d90 being larger than or equal to 40 nm and smaller than or equal to 140 nm, preferably smaller than or equal to 120 nm.15.- A battery comprising the composite powder according to any one of the preceding claims.

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