A POWDER FOR USE IN THE NEGATIVE ELECTRODE OF A BATTERY, A METHOD FOR PREPARING SUCH A POWDER AND A BATTERY COMPRISING SUCH A POWDER

Abstract

A silicon-based powder suitable for use in a negative electrode of a battery. The silicon-based powder comprises silicon-based particles and non-silicon-based particles. The silicon-based particles have a number-based particle size distribution with a d.sub.S50 value, being at most 200 nm. The silicon-based powder has an oxygen content of at most 20% by weight and comprises one or more elements M from a group of metals that have a Standard Gibbs free energy of formation at a temperature T of the oxide from their zerovalent state which is lower than the Standard Gibbs free energy of formation at the same temperature T of SiO.sub.2 from zerovalent silicon. The temperature T is equal to or higher than 573K and lower than 1373K. The content of said one or more elements M in the silicon-based powder is at least 0.10% of the content of Si by weight in said silicon-based powder.

Claims

1-14. (canceled)

15. A silicon-based powder suitable for use in a negative electrode of a battery, the silicon-based powder comprising silicon-based particles and non-silicon-based particles, the silicon-based particles having a number-based particle size distribution with a d.sub.S50 value, the d.sub.S50 value being at most 200 nm, the silicon-based powder having an oxygen content of at most 20% by weight, the silicon-based powder comprising one or more elements M from a group of metals that have a Standard Gibbs free energy of formation at a temperature T of the oxide from their zerovalent state which is lower than the Standard Gibbs free energy of formation at the same temperature T of SiO.sub.2 from zerovalent silicon, the temperature T being equal to or higher than 573K and lower than 1373K, the content of said one or more elements M in the silicon-based powder being at least 0.10% of the content of Si by weight in said silicon-based powder and at most 5.0% of the content of Si by weight in said silicon-based powder, the one or more elements M being present in the non-silicon-based particles.

16. A silicon-based powder according to claim 15, wherein the silicon-based particles have a surface layer with an average molar composition SiO.sub.x with 0≤x<1.

17. A silicon-based powder according to claim 15, wherein, when considering all elements except oxygen, the content of said one or more elements M in said non-silicon-based particles is at least 60% by weight.

18. A silicon-based powder according to claim 15, wherein said non-silicon-based particles have a number-based particle size distribution with a d.sub.NS50 value, the d.sub.NS50 value being at most 500 nm.

19. A silicon-based powder according to claim 15, wherein the content of said one or more elements M in said silicon-based powder is at least 0.40% of the content of Si by weight in said silicon-based powder.

20. A silicon-based powder according to claim 15, wherein the group of said one or more elements M comprises Zr.

21. A silicon-based powder according to claim 15, wherein, when considering all elements except oxygen, the Si content is at least 90% by weight.

22. A silicon-based powder according to claim 15, said powder having a volumetric particle size distribution having an average primary particle size d.sub.av, d.sub.av being larger than or equal to 17 nm and smaller than or equal to 172 nm.

23. A method for preparing the silicon-based powder according to claim 15, comprising the steps of: a. providing a powder comprising silicon-based particles, having a volumetric particle size distribution with a d.sub.VS50 value, the d.sub.VS50 value being at most 200 nm, and having a surface layer with an average molar composition SiO.sub.x with 0<x<2, preferably 0<x<1, b. providing a M-based powder comprising M-based particles of one or more elements M from a group of metals that have a Standard Gibbs free energy of formation at a temperature T of the oxide from their zerovalent state which is lower than the Standard Gibbs free energy of formation at the same temperature T of SiO.sub.2 from zerovalent silicon, the temperature T being equal to or higher than 573K and lower than 1373K, the M-based particles having a volumetric particle size distribution with a d.sub.M50 value, the d.sub.M50 value being at most 500 nm, c. mixing the silicon-based powder with the M-based powder to obtain an intermediate mixture, d. milling the intermediate mixture, whereby a final mixture of silicon-based particles and M-based particles is obtained, e. performing a heat treatment of the final mixture under protective atmosphere at a temperature equal to or higher than 573K and lower than 1373K, followed by a cooling step to room temperature.

24. A composite powder suitable for use in a negative electrode of a battery, wherein the composite powder comprises composite particles, the composite particles comprising a matrix material and a silicon-based powder according to claim 15, the particles of said silicon-based powder being embedded in the matrix material.

25. A composite powder according to claim 24, wherein the composite powder also contains graphite particles.

26. A composite powder according to claim 24, the composite powder having an average silicon content being at least 5% by weight and at most 60% by weight.

27. A composite powder according to claim 24, the composite powder having a BET specific surface area equal to or lower than 5 m.sup.2/g.

28. A battery comprising the silicon-based powder of claim 15.

Description

DETAILED DESCRIPTION

[0066] 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. But to the contrary, the invention includes numerous alternatives, modifications and equivalents as will become apparent from consideration of the following detailed description.

Analytical Methods Used

Determination of the Si and Zr Contents

[0067] The Si and Zr contents of the powders in the examples and the counterexamples are measured by X-Ray Fluorescence (XRF) using an energy 20 dispersive spectrometer.

Determination of the Oxygen Content

[0068] The oxygen contents of the powders in the examples and the counterexamples are determined by the following method, using a LECO TC600 oxygen-nitrogen analyzer. A sample of the powder 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 CO.sub.2 gas. These gases are guided into an infrared measuring cell. The observed signal is recalculated to an oxygen content.

Determination of the Specific Surface Area (BET)

[0069] The specific surface area is measured with the Brunauer-Emmett-Teller (BET) method using a Micromeritics Tristar 3000 BET Surface Area Analyzer. 2 g of the powder to be analyzed is first dried in an oven at 120° C. for 2 hours, followed by N.sub.2 purging. Then the powder is degassed in vacuum at 120° C. for 1 hour prior to the measurement, in order to remove adsorbed species.

Determination of the Electrochemical Performance

[0070] The electrochemical performance of the powders in the examples and the counterexamples is determined by the following method. For the powders according to Embodiments 1 to 9, since it is necessary to avoid any contact with air or oxygen, in order not to re-oxidize the silicon-based particles, the whole preparation of the electrode and the cell is done inside a glove-box containing dry argon (<3 ppm H.sub.2O and <3 ppm O.sub.2). For the composite powders, since the silicon-based particles are embedded in a protective matrix, the preparation of the electrode may be done in air.

[0071] The powders to be tested are first sieved using a 45 μm sieve. They are then mixed with carbon black, optionally with carbon fibers and with a binder. In the case of the silicon-based powders according to Embodiments 1 to 9, the binder is Polyvinylidene fluoride (PVDF) dissolved in N-Methyl-2-pyrrolidone (NMP) at a concentration of 8 wt % PVDF in NMP. The composition of the electrode is 50 weight parts powder/25 weight parts carbon black/25 weight parts PVDF.

[0072] In the case of the composite powders, the binder is sodium carboxymethyl cellulose (CMC) binder dissolved in water at a concentration of 2.5 wt %. The composition of the electrode is 89 weight parts composite powder/1 weight parts carbon black/2 weight parts carbon fibers/8 weight parts CMC.

[0073] In both cases, the 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 μm 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 cm.sup.2 circle 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 1M LiPF6 dissolved in EC/DEC 1/1+2% VC+10% FEC solvents.

[0074] 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”. [0075] Cycle 1: [0076] Rest 6 h [0077] CC lithiation to 10 mV at C/10, then CV lithiation until C/100 [0078] Rest 5 min [0079] CC delithiation to 1.5 V at C/10 [0080] Rest 5 min [0081] From cycle 2 on: [0082] CC lithiation to 10 mV at C/2, then CV lithiation until C/50 [0083] Rest 5 min [0084] CC delithiation to 1.2 V at C/2 [0085] Rest 5 min

[0086] 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, for which reducing the amount of oxygen present in the electrochemically active material has a beneficial effect.

[0087] To reach a desired cell capacity, a battery manufacturer needs to compensate the irreversible loss at the initial cycle caused by the anode, using additional cathode material, which represents a significant additional cost and a loss of energy density. Thus, even a little gain obtained for the CE at the initial cycle, multiplied by millions of cells produced, is significant.

Determination of the Particle Size Distribution

[0088] The number-based particle size distribution of the silicon-based particles and/or of the non-silicon-based particles comprised in the silicon-based powders and the composite powders according to the invention is determined via an electron microscopy analysis (SEM or TEM) of a cross-section of the silicon-based powder (or the composite powder), combined with an image analysis.

[0089] To do this, a cross-section of the silicon-based powder (or the composite powder), comprising multiple cross-sections of silicon-based particles and non-silicon-based particles, is prepared following the procedure detailed hereafter.

[0090] 500 mg of the powder to be analyzed is embedded in 7 g 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 (or TEM).

[0091] The size of a silicon-based particle (or a non-silicon-based particle) is considered to be equivalent to the maximum straight-line distance between two points on the perimeter of a discrete cross-section of that silicon-based particle (or non-silicon-based particle), also called d.sub.max.

[0092] For the purpose of illustrating, in a non-limitative way, the determination of the number-based particle size distribution of silicon-based particles (or non-silicon-based particles), a SEM-based procedure is provided below. [0093] 1. Multiple SEM images of the cross-section of the silicon-based powder (or the composite powder) comprising the silicon-based particles and the non-silicon-based particles are acquired. [0094] 2. The contrast and brightness settings of the images are adjusted for an easy visualization of the cross-sections of the silicon-based particles and the non-silicon-based particles. Due to their different chemical composition, the difference in brightness allows for an easy distinction between the two types of particles and, in case of a composite powder, with the matrix. [0095] 3. At least 1000 discrete cross-sections of silicon-based particles and at least 100 discrete cross-sections of non-silicon-based particles, not overlapping with another cross-section of a silicon-based particle or a non-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 or non-silicon-based particles can be selected from one or more cross-sections of the powder comprising the silicon-based particles and the non-silicon-based particles. [0096] 4. d.sub.max values of the discrete cross-sections of the silicon-based particles and the non-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 and each of the at least 100 discrete cross-sections of non-silicon-based particles.

[0097] The d.sub.S10, d.sub.S50 and d.sub.S90 values of the number-based particle size distribution of silicon-based particles and the d.sub.NS10, d.sub.NS50 and d.sub.NS90 of the number-based particle size distribution of non-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.

[0098] Alternatively, the volume-based particle size distribution of the silicon-based powder may be determined by centrifugal sedimentation with the Centrifugal Photosedimentometer DC20000 (CPS Instruments, Inc, USA).

[0099] The instrument is equipped with a hollow polycarbonate disc with an internal radius of 4.74 cm. Rotational speed is set to 20000 rpm which corresponds to a centrifugal acceleration force of approx. 1.9×10.sup.5 m/s.sup.2.

[0100] The disc is filled with 16 ml of a linear density gradient (10 to 5%) of Halocarbon 1.8 (chlorotrifluoroethylene-PCTFE) in 2-butoxyethylacetate (casrn112-07-2). As reference material—to calculate the sedimentation constant—diamond particles with a mean diameter of 0.52 μm and a specific density of 3.515 g/cm.sup.3 are used.

Sample Preparation:

[0101] A 10 wt % suspension in Isopropanol of the powder to be analyzed is prepared using ultrasound (Branson sonifier 550W). The suspension is diluted with butoxyethylacetate to a final concentration of 0.05 weight % silicon. 0.050 ml of the resulting sample is injected in the disc and light absorbance is recorded as a function of time at a wavelength of 470 nm.

[0102] The resulting time-absorbance curve is converted to a particle size distribution (mass or volume) with a build-in algorithm (DCCS software) and using the following parameters: [0103] Spin fluid density: 2.33 g/cm.sup.3 [0104] Spin fluid refractive index: 1.482 [0105] Silicon density: 2.33 g/cm.sup.3 [0106] Silicon refractive index: 4.49 [0107] Silicon adsorption coefficient: 17.2 K

[0108] The volume-based particle size distribution of the composite powders is determined by Laser Diffraction Sympatec (Sympatec-Helos/BFS-Magic 1812), following the user instructions. The following settings are used for the measurement: [0109] Dispergen system: Sympatec-Rodos-M [0110] Disperser: Sympatec-Vibri 1227 [0111] Lens: R2 (0.45-87.5 μm range) [0112] Dispersion: Pressured air at 3 bars [0113] Optical concentration: 3-12% [0114] Start/stop: 2% [0115] Time base: 100 ms [0116] Feed rate: 80% [0117] Aperture: 1.0 mm

[0118] It must be noted that feed rate and aperture settings can vary in function of the optical concentration.

[0119] The d.sub.VS10, d.sub.VS50 and d.sub.VS90 values of the volume-based particle size distributions of the silicon-based powder and the d.sub.C10, d.sub.C50 and d.sub.C90 values of the volume-based particle size distributions of the composite powder, determined using the methods described above, are then calculated.

Analysis of the Particles Comprising the One or More Elements M

[0120] The localization of the particles comprising the one or more elements M is done based on SEM-EDS (Energy-dispersive X-ray spectroscopy) microscopy analysis with a mapping of Si, 0, C and M elements.

[0121] The cross-section is prepared following the procedure previously described and is then analyzed using a FEG-SEM JSM-7600F from JEOL equipped with an EDS detector Xflash 5030-127 from Bruker (30 mm.sup.2, 127 eV). The signals from this detector are treated by the Quantax 800 EDS system from Bruker.

[0122] The enlargements are generated by applying a voltage of 15 kV 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.

[0123] To determine whether oxygen is bound to the elements M or Si, the oxidation state(s) of the elements M or Si is determined by X-Ray Photoemission Spectrometry (XPS) analysis using a PHI Quantera SXM spectrometer equipped with a focused monochromatized Al Kα radiation. The take-off angle used is 45°, the depth of analysis is lower than 10 nm and the spot diameter is 200 μm. The sensitivity limits are between 0.1% and 0.5% atomic. MultiPak software is used for data treatment.

[0124] The XPS analysis also allows determining the average molar composition, i.e. the average value of x, x′ in the SiO.sub.x and SiO.sub.x′ surface layer respectively and the average value of y and y′ in the MO.sub.y and MO.sub.y′ surface layer respectively, and to estimate the thickness of those surface layers.

[0125] Alternatively, a TEM-EELS (Electron Energy Loss Spectroscopy) equipment or a Nuclear Magnetic Resonance (NMR) equipment may be used for the same purpose.

EXPERIMENTAL PREPARATION OF COUNTEREXAMPLES AND EXAMPLES

Example 1 (E1), According to the Invention

[0126] To produce the silicon-based powder from Example 1, a silicon powder is first obtained by applying a 60 kW radio frequency (RF) inductively coupled plasma (ICP), using argon as plasma gas, to which a micron-sized silicon powder precursor is injected at a rate of circa 50 g/h, resulting in a prevalent (i.e. in the reaction zone) temperature above 2000K. In this first process step, the precursor becomes totally vaporized. In a second process step, an argon flow of 18 Nm.sup.3/h is used as quench gas immediately downstream of the reaction zone in order to lower the temperature of the gas below 1600K, causing a nucleation into metallic submicron silicon powder. Finally, a passivation step is performed at a temperature of 100° C. during 5 minutes by adding 100 I/h of a N.sub.2/O.sub.2 mixture containing 1 mole % oxygen.

[0127] The specific surface area (BET) of the obtained silicon powder is measured to be 83 m.sup.2/g. The oxygen content of the obtained silicon powder is measured to be 8.7 wt %. The particle size distribution of the silicon powder is determined to be: d.sub.VS10=63 nm, d.sub.VS50=113 nm, d.sub.VS90=205 nm and d.sub.avS=119 nm.

[0128] This silicon powder is then mixed, inside a glove box (dry Ar atmosphere, <3 ppm H.sub.2O and <3 ppm 02) to avoid oxygen contamination, in a Fritsch Pulverisette 7 planetary ball-mill, with a zirconium powder (American Elements, average particle size 50 nm-100 nm), using a rotation speed of 600 rpm, stainless steel balls with a size adapted to the jar, a ball-to-powder mass ratio (BPR) of 20:1 and a milling time of 240 minutes. The weight of zirconium powder is 0.0913% of the weight of the silicon powder, so that the content by weight of Zr is 0.1% of the content by weight of Si present in the resulting mixture.

[0129] The resulting mixed powder is further given a heat treatment, in an oven placed in the glove-box (dry Ar atmosphere, <3 ppm H.sub.2O and <3 ppm 02) at 773 K for 2 hrs and subsequently cooled to room temperature.

[0130] Based on a SEM analysis, the average sizes of the silicon particles and the zirconium particles have not been significantly modified during the process. This means that d.sub.VS10, d.sub.VS50, d.sub.VS90, days values and d.sub.S10, d.sub.S50, d.sub.S90, d.sub.av values, respectively, can be considered equal. Similarly, d.sub.M10, d.sub.M50, d.sub.M90 values and d.sub.NS10, d.sub.NS50, d.sub.NS90 values, respectively, can be considered equal.

[0131] The oxygen content of the mixture is measured to be 8.7 wt %, meaning that no additional oxygen intake has occurred. The specific surface area (BET) of the mixture is measured to be 83 m.sup.2/g, meaning that a content of 0.1% of Zr relative to Si does not change the BET value.

[0132] Based on an XPS analysis of the obtained silicon-based powder, the surface of the zirconium particles up to 10 nm deep is fully oxidized, meaning that the zirconium is at an oxidation state+IV. The SEM-EDS analysis of the cross-section of the obtained powder also confirms that oxygen is present in the core of the zirconium particles. Still based on an XPS analysis, the average x value in the SiO.sub.x surface layer of the silicon particles of the obtained silicon-based powder is lower than the average x′ value in the SiO.sub.x′ surface layer of the silicon particles after their production by plasma and before their mixing with the zirconium particles.

Examples 2-5 (E2-E5), According to the Invention

[0133] To produce the silicon-based powders of Examples 2 to 5, the same procedure is used as for Example 1, except that different amounts of zirconium powder are used during the mixing step. These amounts are: 0.4 wt % for Example 2, 1.0 wt % for Example 3, 2.0 wt % for Example 4 and 5.0 wt % for Example 5, whereby these amounts are expressed as percentages compared to the Si amount present in the final silicon-based powder.

Counterexample 1 (CE1), not According to the Invention

[0134] To produce the silicon-based powder of Counter Example 1, the same procedure as for Example 1 is used, except that no zirconium powder is added. In order to ensure maximum comparability between the examples and the counterexample, the mentioned heating step at 773K is nevertheless performed in this procedure.

[0135] All the oxygen contents of the obtained silicon-based powders (E2 to E5 and CE1) are measured to be 8.7 wt %. All the specific surface area (BET) values of the obtained silicon-based powders (E2 to E5 and CE1) range between 82 and 85 m.sup.2/g.

Electrochemical Testing of the Powders

[0136] The produced powders are tested in coin-cells according to the procedure specified above. The following results are obtained:

TABLE-US-00001 TABLE 1 Performance of coin-cells containing powders E1, E2, E3, E4, E5 and CE1 Zr weight content/Si Initial coulombic efficiency Example # weight content (%) (CE) in coin-cell (%) E1 0.1 88.15 E2 0.4 88.29 E3 1.0 88.52 E4 2.0 88.98 E5 5.0 90.28 CE1 0.0 88.11

[0137] It can be seen that there is an increase in the initial coulombic efficiency (CE) with the amount of Zr added for the coin-cells using the silicon-based powders according to the invention (E1 to E5) as anode material.

[0138] This is explained by the fact that partly due to the mixing and partly due to the subsequent heating, part of the oxygen present at the surface of the silicon particles is transferred to the zirconium particles that are present. This reduces the amount of lithium converted to lithium oxide during the initial lithiation of the anode, thereby reducing the initial irreversible capacity loss and increasing the initial coulombic efficiency (CE) of the cell.

Example 6 (E6), According to the Invention

[0139] To produce the composite powder of Example 6, a blend is made, inside the glove-box, of 26 g of the silicon-based powder from Example 4 (E4) and 32 g petroleum-based pitch powder.

[0140] This blend is heated to 450° C. under N.sub.2, so that the pitch melts, and, after a waiting period of 60 minutes, mixed for 30 minutes under high shear by means of a Cowles dissolver-type mixer operating at 1000 rpm.

[0141] The mixture of the silicon-based powder E4 in pitch thus obtained is cooled under N.sub.2 to room temperature and, once solidified, pulverized and sieved on a 400-mesh sieve, to produce an intermediate composite powder.

[0142] 16 g of the intermediate composite powder is then mixed with 24.6 g 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 does not become embedded in the pitch.

[0143] A thermal after-treatment is further given to the obtained mixture of the powder from E4, the pitch and the graphite as follows: the product is put 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 argon atmosphere.

[0144] The fired product is finally manually crushed in a mortar and sieved over a 325-mesh sieve to form a final composite powder.

[0145] The total Si content in this composite powder is measured to be 20.3 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 40 wt % and an insignificant weight loss upon heating of the other components. The oxygen content of this composite powder was measured to be 2.0 wt %. The Zr content of this composite was measured to be 0.41 wt %, which means that the Zr/Si ratio of 2.0% has not changed. The specific surface area (BET) of the obtained composite powder is measured to be 3.6 m.sup.2/g.

Counterexample 2 (CE2), not According to the Invention

[0146] To produce the composite powder of Counter Example 2, the same procedure as for Example 6 is used, except that the powder of Counter Example 1 (CE1) was used instead of the powder of Example 4 (E4). The oxygen content of this composite powder was measured to be 2.0 wt % and the BET value was measured to be 3.5 m.sup.2/g.

Electrochemical Testing of the Composite Powders

[0147] The produced composite powders are tested in coin-cells according to the procedure specified above. The following results are obtained:

TABLE-US-00002 TABLE 2 Performance of coin-cells containing powders E6 and CE2 Zr weight content/Si Initial coulombic efficiency Example # weight content (%) (CE) in coin cell (%) E6 2.0 90.08 CE2 0.0 89.88

[0148] It can be seen that the initial coulombic efficiency (CE) of the coin-cell using the composite powder according to the invention as anode material is significantly higher than the initial coulombic efficiency of the coin-cell using the composite powder not according to the invention. In other words, the advantage observed for the silicon-based powder according to the invention, is kept when the silicon-based powder is integrated in a composite structure.