A POWDER OF CARBONACEOUS MATRIX PARTICLES AND A COMPOSITE POWDER, FOR USE IN THE NEGATIVE ELECTRODE OF A BATTERY, COMPRISING SUCH A POWDER
20240010495 · 2024-01-11
Inventors
Cpc classification
C01B32/05
CHEMISTRY; METALLURGY
C01P2002/08
CHEMISTRY; METALLURGY
C01P2004/51
CHEMISTRY; METALLURGY
International classification
Abstract
A powder of carbonaceous matrix particles with silicon-based sub-particles dispersed therein, wherein the particles have a harmonic mean value of their average Vickers hardness value and their average elastic modulus value, both values of hardness and elasticity being measured by nanoindentation and expressed in MPa, being superior or equal to 7000 MPa and inferior or equal to 20000 MPa.
Claims
1-15. (canceled)
16. A powder of carbonaceous matrix material particles, said particles comprising silicon-based sub-particles dispersed therein, said particles having a harmonic mean value HM calculated according to the formula (1),
17. The powder of claim 16, wherein said particles of carbonaceous matrix material have an average Vickers hardness value H of at least 4000 MPa and at most 12000 MPa and an average elastic modulus value E of at least 2810.sup.3 MPa and at most 6010.sup.3 MPa.
18. A powder according to claim 16, having a silicon content S expressed in weight percent (wt %), wherein 20 wt %S70 wt %.
19. A composite powder for use in a negative electrode of a battery, said composite powder comprising the powder of claim 16.
20. The composite powder of claim 19, wherein at least 70% by number of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, present in said composite powder, comprise particles having a harmonic mean value HM calculated according to the formula (1),
21. A composite powder according to claim 19, further comprising crystalline carbonaceous particles, the crystalline carbonaceous particles being physically distinct from the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein.
22. A composite powder according to claim 21, wherein the crystalline carbonaceous particles are graphite particles.
23. A powder according to claim 16, wherein the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein have a number-based size distribution with a d.sub.C50, the d.sub.C50 being larger than or equal to 1 m and smaller than or equal to 25 m.
24. A composite powder according to claim 19, wherein the silicon-based sub-particles have a number-based size distribution with a d.sub.Si50, the d.sub.Si50 being larger than or equal to 40 nm and smaller than or equal to 150 nm.
25. A composite powder according to claim 19, having a silicon content A expressed in weight percent (wt %), wherein 10 wt %A60 wt %.
26. A composite powder according to claim 19, having a silicon content A and an oxygen content C, both expressed in weight percent (wt %), wherein C0.15A.
27. A composite powder according to claim 19, wherein when considering all elements except oxygen, the silicon-based sub-particles contain at least 90% by weight of silicon.
28. A composite powder according to claim 19, having a BET surface area which is at most 10 m.sup.2/g.
29. A composite powder according to claim 19, wherein the particles of carbonaceous matrix material with silicon-based particles dispersed therein are non-porous.
30. A battery comprising a composite powder according to claim 19.
31. A composite powder according to claim 19, wherein the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein have a number-based size distribution with a d.sub.C50, the d.sub.C50 being larger than or equal to 1 m and smaller than or equal to 25 m.
Description
DETAILED DESCRIPTION
[0067] 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 considering the following detailed description.
Analytical Methods Used
Determination of the Si Content
[0068] The Si content of the powders or the composite powders in the examples and the counterexamples is measured by X-Ray Fluorescence (XRF) using an energy dispersive spectrometer. This method has an experimental random error of +/0.3 wt % Si.
[0069] In the case where the powder of carbonaceous matrix material particles with silicon-based sub-particles dispersed therein is comprised in a composite powder, it might be difficult to measure the silicon content S of said powder by XRF. In that case, an analysis by Scanning electron microscopy with Energy Dispersive X-Ray Spectrometry (SEM-EDS) might be preferable. This allows to measure the silicon content in a given particle. An analysis of 10 particles of matrix material is sufficient to obtain an average silicon content value S of the powder.
Determination of the Oxygen Content
[0070] The oxygen content of the powders and composite powders in the examples and the counterexamples 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 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 Carbon Content
[0071] The carbon content of the powders and composite powders in the examples and the counterexamples 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 CO.sub.2. After conversion of an eventual presence of CO into CO.sub.2, all produced CO.sub.2 is finally detected by an infrared detector. The signal is finally converted into a carbon content.
Determination of the Specific Surface Area (BET)
[0072] The specific surface area is measured with the Brunauer-Emmett-Teller (BET) method using a Micromeritics Tristar 3000. 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
[0073] The electrochemical performance of the composite powders in the examples and the counterexamples is determined by the following method.
[0074] The powders to be evaluated are sieved using a 45 m sieve and 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). These components are mixed in a Pulverisette 7 planetary ball mill for 30 minutes at 250 rpm.
[0075] A copper foil cleaned with ethanol is used as current collector. A 200 m 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 LiPF.sub.6 dissolved in EC/DEC 1/1+2% VC+10% FEC solvents.
[0076] 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. [0077] Cycle 1: [0078] Rest 6 h [0079] CC lithiation to 10 mV at C/10, then CV lithiation until C/100 [0080] Rest 5 min [0081] CC delithiation to 1.5 V at C/10 [0082] Rest 5 min [0083] From cycle 2 on: [0084] CC lithiation to 10 mV at C/2, then CV lithiation until C/50 [0085] Rest 5 min [0086] CC delithiation to 1.2 V at C/2 [0087] Rest 5 min
[0088] 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.
[0089] 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).
[0090] The target in terms of average CE from cycle 5 to cycle 50 is to reach at least 99.6%, preferably at least 99.65% for a cell comprising a composite powder with a specific capacity of 800 f 20 mAh/g.
Determination of the Number-Based Particle Size Distribution
[0091] The number-based particle size distribution of the particles of carbonaceous matrix material and/or of the silicon-based sub-particles particles is determined via an electron microscopy analysis (SEM or TEM) of a cross-section of the powder (or the composite powder), combined with an image analysis.
[0092] To do this, a cross-section of the powder (or the composite powder), comprising multiple cross-sections of particles of carbonaceous matrix material, each of them comprising multiple cross-sections of silicon-based sub-particles, is prepared following the procedure detailed hereunder.
[0093] 500 mg of the powder (or composite 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.
[0094] 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 (30 mm.sup.2, 127 eV). The signals from this detector are treated by the Quantax 800 EDS system from Bruker.
[0095] 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.
[0096] The size of a particle of carbonaceous matrix material (or of a silicon-based sub-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 particle of carbonaceous matrix material (or of a silicon-based sub-particle).
[0097] For the purpose of illustrating, in a non-limitative way, the determination of the number-based particle size distribution of particles of carbonaceous matrix material (or of silicon-based sub-particles), a SEM-based procedure is provided below. [0098] 1. Multiple SEM images of the cross-section of the powder (or the composite powder) comprising the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, are acquired. [0099] 2. The contrast and brightness settings of the images are adjusted for an easy visualization of the cross-sections of the particles of carbonaceous matrix material and the silicon-based sub-particles. Due to their different chemical composition, the difference in brightness allows for an easy distinction between the particles and the sub-particles. [0100] 3. At least 1000 discrete cross-sections of silicon-based sub-particles and at least 100 discrete cross-sections of particles of carbonaceous matrix material, not overlapping, respectively, with another cross-section of a silicon-based sub-particle or another cross-section of a particle of carbonaceous matrix material, 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 sub-particles or of particles of carbonaceous matrix material can be selected from one or more cross-sections of the powder (or the composite powder) comprising the particles of carbonaceous matrix material and the silicon-based sub-particles. [0101] 4. The size of the discrete cross-sections of the silicon-based sub-particles and of the discrete cross-sections of particles of carbonaceous matrix material, are measured using a suitable image analysis software for each of the at least 1000 discrete cross-sections of silicon-based sub-particles and at least 100 discrete cross-sections of particles of carbonaceous matrix material.
[0102] The d.sub.Si10, d.sub.Si50 and d.sub.Si90 values, as well as the d.sub.C10, d.sub.C50 and d.sub.C90 values of, respectively, the number-based particle size distribution of silicon-based sub-particles and of the number-based particle size distribution of particles of carbonaceous matrix material, 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.
Determination of the Presence of Pores in the Particles of Carbonaceous Matrix Material
[0103] The same method of electron microscopy analysis of a cross-section of the powder (or the composite powder) is used. For each of the at least 100 discrete cross-sections of particles of carbonaceous matrix material, the fraction of the total area occupied by pores (or cross-sections of pores) over the total area occupied by the particle(s) (or cross-section of particle(s)) is determined using a suitable image analysis software and the average value of these fractions is calculated. As mentioned earlier, if the average value of these fractions is lower than 0.01, the particles are considered to be non-porous.
Determination of the Presence of Crystalline Carbonaceous Particles in the Composite Powder
[0104] The determination of the presence of crystalline carbonaceous particles in the composite powder is done, performing an X-ray diffraction (XRD) analysis of the composite powder. The following method is used.
[0105] XRD measurements are performed on a Panalytical 'X Pert Pro system with CuK1 and CuK2 radiation, =0.15418 nm, with a step size of 0.017 2, scan rate of 34 minutes (2064 seconds) and measuring from 5 to 90 2 on a flattened surface of about 2 cm.sup.3 powder material at least, using the ICDD database, PDF-4+, for the identification of present compounds. The XRD peak having a maximum at 2.sub.Cu between 26 and 27 corresponds to the (002) reflection of graphitic carbon, which results from diffraction of X-rays from inter-plane graphene layers. The background is first subtracted from the raw XRD data. The 2.sub.Cu values at half maximum intensity on the left side and the right side of the C(002) peak are then determined. The Full Width at Half Maximum (FWHM) value is the difference between these two 2.sub.Cu values. The FWHM value is normally determined using the program provided with the X-Ray diffractometer. A manual calculation may be used as well. If the calculated FWHM value is inferior or equal to 0.52, the presence of crystalline carbonaceous particles in the composite powder is confirmed.
Determination of the Vickers Hardness and Elasticity Modulus by Nanoindentation
[0106] The Vickers hardness values and elastic modulus values of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, comprised in the powders and composite powders are determined using a Nanoindentation Tester NHT.sup.3 with the following test conditions and parameters: [0107] Test atmosphere: Air [0108] Temperature: 22 C. [0109] Humidity: 40% [0110] Indenter Type: Berkovich [0111] Loading Type: Linear [0112] Maximum Load: 5 [mN] [0113] Pause at Max Load: 10 [s] [0114] Loading/Unloading Rate: 30 [mN/min]
[0115] The number of indents performed on each particle of carbonaceous matrix material with silicon-based sub-particles embedded therein, varies depending on their size: for small particles, having a size below 20 m, only one indent per particle is performed, whereas for particles which are large enough, a matrix of various indents was performed. For example, matrices of 44, 45 or 66 indents are performed on the particles for which it is possible. The distance between the indents is set to 10 m. All the results are obtained using the Oliver & Pharr method with supposed sample ratio of 0.3 for elastic modulus calculation.
[0116] The procedure comprises the following steps: [0117] 1. The powder (or composite powder) to be analyzed is first embedded in a resin to obtain a sample, the surface of said sample further being polished to obtain a sample with a polished surface, following the method described earlier. [0118] 2. The obtained sample with a polished surface is then analyzed by nanoindentation; several areas comprising particles are visualized. In each of them, the contrast and brightness settings are adjusted for an easy visualization of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein. Due to their different chemical composition, the difference in brightness allows for an easy distinction between the particles of matrix material comprising or not silicon-based sub-particles. [0119] 3. Depending on the size of the particles, one or several indents are performed on several particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein. [0120] 4. In total, at least 100 indents are performed on at least 10 different particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein. [0121] 5. For each indent, the Vickers hardness value and elastic modulus value are determined, then the average Vickers hardness value and the average elastic modulus value of each of the at least 10 different particles, are calculated. [0122] 6. Finally, the harmonic mean value HM is calculated according to the following formula:
wherein H is the average Vickers hardness value of the at least 10 different particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein comprised in the powder (or the composite powder) and E is the average elastic modulus value of the at least 10 different particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein comprised in the powder (or the composite powder).
[0123] Further, the number-based percentage of particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, consisting of particles according to Embodiment 1 can be calculated. As an illustration, we take a composite powder for which the results obtained by nanoidentation are presented in Table 1:
TABLE-US-00001 TABLE 1 Average Vickers Average elastic Harmonic Particle Number of hardness modulus mean number indents (MPa) (10.sup.3 MPa) (MPa) 1 1 4850 27.3 8237 2 20 5150 28.3 8714 3 1 3810 30.1 6764 4 1 5020 26.3 8431 5 16 4980 27.1 8414 6 36 5030 28.3 8542 7 1 5060 28.0 8571 8 1 5110 27.4 8614 9 1 5090 27.8 8605 10 30 5050 27.6 8538 Average values 4915 (=H) 28.0 (=E)
[0124] In that case, the average Vickers hardness value H is equal to 4915 MPa and the average elastic modulus value E is equal to 28.010.sup.3 MPa, resulting in a mean harmonic value HM of 8354 MPa. Only 1 out of 10 particles (particle number 3) does not have a harmonic mean superior or equal to 7000 MPa and inferior or equal to 20000 MPa, therefore the number-based percentage of particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, present in this illustrative composite powder, and consisting of particles according to embodiment 1, is equal to 90%.
Experimental Preparation of Counter Examples and Examples
Example 1 (E1), According to the Invention
[0125] To produce the powder of Example 1, a silicon-based 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 45 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 17 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 l/h of a N.sub.2/O.sub.2 mixture containing 1 mole % oxygen.
[0126] The specific surface area (BET) of the obtained silicon powder is measured to be 89 m.sup.2/g. The oxygen content of the obtained silicon powder is measured to be 8.4 wt %. The number-based particle size distribution of the silicon powder is determined to be: d.sub.Si10=54 nm, d.sub.Si50=106 nm and d.sub.Si90=175 nm.
[0127] Then, a dry blend is made of 100 g of the obtained silicon-based powder and 308 g of a petroleum-based pitch powder having a softening point of 230 C. The blend is fed under a nitrogen flow at a feed rate of 1000 g/h into a twin-screw extruder, operated at a temperature of 300 C.
[0128] The mixture of the silicon-based powder in pitch thus obtained is cooled to room temperature and, once solidified, pulverized and sieved on a 400-mesh sieve, to produce an intermediate powder.
[0129] 20 g of the intermediate powder are then put in a quartz crucible in a tube furnace, heated up at a heating rate of 3 C./min to 1020 C., kept at that temperature for two hours and then cooled. All this is performed under argon atmosphere.
[0130] 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 powder of Example 1.
[0131] The key synthesis parameters are summarized in Table 2.
[0132] The total Si content in this powder is measured to be 30.4 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 resulting from the carbonization of the pitch over the silicon content in the powder is around 2. The oxygen content of this powder is measured to be 3.0 wt %. The specific surface area (BET) of the obtained powder is measured to be 3.5 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 18.4 m.
[0133] The nanoidentation analysis performed on 12 particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, corresponding to a total of 114 indents, results in an average Vickers hardness value H of 5250 MPa and an average elastic modulus value E of 38.510.sup.3 MPa, which corresponds to a HM value of 9240 MPa. The number-based percentage of particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein, analyzed in the powder of Example 1, and having a harmonic mean value superior or equal to 7000 MPa and inferior or equal to 20000 MPa is 100%.
[0134] The average fraction of the total area occupied by pores (or cross-sections of pores) over the total area occupied by the particle(s) (or cross-section of particle(s)), observed by SEM analysis, using a suitable image analysis software is equal to 0.002 (0.2%).
[0135] These values are reported in Table 3.
Example 2 (E2), According to the Invention
[0136] To produce the composite powder of Example 2 (E2), 20 g of the intermediate powder obtained in Example 1 are mixed with 12.5 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.
[0137] A thermal after-treatment is further given to the obtained mixture of the intermediate powder 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 1020 C., kept at that temperature for two hours and then cooled. All this is performed under argon atmosphere.
[0138] The fired product is finally manually crushed in a mortar and sieved over a 325-mesh sieve to form a final powder.
[0139] The total Si content in this composite powder is measured to be 18.6 wt % by XRF. The oxygen content of this powder is measured to be 1.8 wt %. The specific surface area (BET) of the obtained powder is measured to be 3.9 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 16.6 m.
[0140] Additional physical properties are reported in Table 3.
Examples 3 (E3), According to the Invention
[0141] To produce the composite powder of Example 3 (E3), the same procedure as for the composite powder of Example 2 is used, except that the thermal after-treatment is performed at a temperature of 950 C., instead of 1020 C.
[0142] The total Si content in this composite powder is measured to be 18.5 wt % by XRF. The oxygen content of this powder is measured to be 1.8 wt %. The specific surface area (BET) of the obtained powder is measured to be 4.2 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 16.4 m.
[0143] Additional physical properties are reported in Table 3.
Examples 4 (E4), According to the Invention
[0144] To produce the composite powder of Example 4 (E4), a new intermediate powder is prepared, as in the Example 1, except that 100 g of the same silicon-based powder are blended with 230 g (instead of 308 g) of the same pitch powder.
[0145] The composite powder of Example 4 is then prepared following the same procedure as for the composite powder of Example 2, except that 20 g of the new intermediate powder are mixed with 20 g of graphite (instead of 12.5 g). The ratio of carbon content resulting from the carbonization of the pitch over the silicon content in the composite powder E4 is around 1.5.
[0146] The total Si content in this composite powder is measured to be 18.3 wt % by XRF. The oxygen content of this powder is measured to be 1.9 wt %. The specific surface area (BET) of the obtained powder is measured to be 4.0 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 16.6 m.
[0147] Additional physical properties are reported in Table 3.
Examples 5 (E5), According to the Invention
[0148] To produce the composite powder of Example 5 (E5), a new intermediate powder is prepared, as in the Example 1, except that the pitch powder used has a softening point of 270 C. (instead of 230 C.).
[0149] The composite powder of Example 5 is then prepared following the same procedure as for the composite powder of Example 2.
[0150] The total Si content in this composite powder is measured to be 18.4 wt % by XRF. The oxygen content of this powder is measured to be 1.8 wt %. The specific surface area (BET) of the obtained powder is measured to be 3.8 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 16.7 m.
[0151] Additional physical properties are reported in Table 3.
Counter Example 1, not According to the Invention
[0152] To produce the composite powder of Counter example 1 (CE1), a new intermediate powder is prepared, as in the Example 1, except that the carbon precursor used is lignin, instead of petroleum-based pitch. The carbon yield of lignin (50%) being inferior to the one of pitch (65%), 100 g of the same silicon-based powder are blended with 400 g of lignin (instead of 308 g of pitch).
[0153] The composite powder of Counter example 1 is then prepared following the same procedure as for the composite powder of Example 2.
[0154] The total Si content in this composite powder is measured to be 18.6 wt % by XRF. The oxygen content of this powder is measured to be 1.9 wt %. The specific surface area (BET) of the obtained powder is measured to be 3.2 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 20.1 m.
[0155] Additional physical properties are reported in Table 3.
Counter Example 2 (CE2), not According to the Invention
[0156] To produce the composite powder of Counter example 2 (CE2), the same procedure as for the composite powder of Example 2 is used, except that the thermal after-treatment is performed at a temperature of 800 C., instead of 1020 C.
[0157] The total Si content in this composite powder is measured to be 18.4 wt % by XRF. The oxygen content of this powder is measured to be 2.0 wt %. The specific surface area (BET) of the obtained powder is measured to be 2.8 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 25.2 m.
[0158] Additional physical properties are reported in Table 3.
Counter Example 3 (CE3), not According to the Invention
[0159] To produce the composite powder of Counter example 3 (CE3), the same procedure as for Counter example 1 (CE1) disclosed in the International Patent Application WO 2019/137797 A1, is used. It is to be mentioned that the pitch powder used has a softening point of 290 C.
[0160] The total Si content in this composite powder is measured to be 14.7 wt % by XRF. The oxygen content of this powder is measured to be 1.8 wt %. The specific surface area (BET) of the obtained powder is measured to be 3.5 m.sup.2/g. The number-based d.sub.C50 value of the particles of carbonaceous matrix material with silicon-based sub-particles dispersed therein is equal to 14.2 m.
[0161] Additional physical properties are reported in Table 3.
[0162] Table 2: Summary of the synthesis parameters of the powders E1-E5 and CE1-CE3
TABLE-US-00002 TABLE 2 Presence of Heat treatment Carbon crystalline temperature Ratio C from Example # precursor carbon ( C.) precursor/Si E1 Pitch - 230 C. No 1020 2 E2 Pitch - 230 C. Yes 1020 2 E3 Pitch - 230 C. Yes 950 2 E4 Pitch - 230 C. Yes 1020 1.5 E5 Pitch - 270 C. Yes 1020 2 CE1 Lignin Yes 1020 2 CE2 Pitch - 230 C. Yes 800 2 CE3 Pitch - 290 C. Yes 1000 1.2
[0163] Table 3: Physical properties of the powders E1-E5 and CE1-CE3
TABLE-US-00003 TABLE 3 Nanoindentation properties Fraction of % of surface Average Average particles occupied by Vickers elastic Harmonic with pores vs. Example Hardness H modulus E mean HM 7000 < HM < surface of # (MPa) (10.sup.3 MPa) (MPa) 20000 MPa particles E1 5250 38.5 9240 100 0.001 E2 6430 40.1 11083 100 0 E3 4860 29.2 8333 90 0.001 E4 8230 35.1 13334 100 0 E5 9490 56.1 16234 100 0 CE1 3760 27.9 6627 10 0.025 CE2 3120 22.9 5492 10 0.001 CE3 12950 52.2 20752 40 0
[0164] It can be observed from Table 2 and Table 3 that there are mainly 2 parameters having a strong influence on the HM value. Firstly, the carbon source, for which a comparison between powders E2 and E5 shows an increase of the HM value with an increase of the softening point of the pitch material. This is probably due to the fact that a pitch material with a high softening point comprises larger molecules than a pitch material with a low softening point, which will, even after firing, lead to a higher average Vickers hardness of the particles of carbonaceous matrix material. A comparison between powders E2 and CE1 also illustrates the effect of the type of carbon source, in that case lignin vs. pitch, on the HM value.
[0165] Secondly, the ratio carbon from precursor/Si, for which a comparison between powders E2 and E4 shows an increase of the HM value with a decrease of said ratio. As already mentioned earlier, the silicon sub-particles having a significant contribution to the average Vickers hardness of the particles of carbonaceous matrix material, when the ratio carbon from precursor/Si decreases, the contribution of the silicon sub-particles increases, and the average Vickers hardness increases too. Similarly, the presence of a higher concentration of silicon sub-particles leads to a higher density of the particles of carbonaceous matrix material comprising those latter and therefore to a higher average Vickers hardness and to a higher HM value.
Electrochemical Evaluation of the Powders
[0166] The produced powders and composite powders are tested in coin-cells according to the procedure specified above. All powders and composite powders tested have a specific capacity of 800 mAh/g f 20 mAh/g, except the powder of Counter example 3, which has a specific capacity of 734 mAh/g and the powder of Example 1, which has a specific capacity of 1080 mAh/g. Therefore, the powder of Example 1 is mixed with graphite during the electrode preparation, to achieve a capacity of the mixture powder+graphite of 800 mAh/g. The results obtained for the average coulombic efficiency between cycle 5 and cycle 50 are given in Table 4. Comparing the results of the powders and composite powders from E1 to E5according to the inventionwith the composite powders from CE1 and CE2, it can be seen in E1-E5 that there is an increase in the average coulombic efficiency with the HM value, for the possible reasons that have been previously given. However, when the HM value is larger than 17060 MPa, more so when it is larger than 18540 MPa and even more so when it is larger than 20000 MPa, as it is the case for the composite powder of CE3, the average coulombic efficiency appears to decrease dramatically. This is probably due principally to the high average Vickers hardness of the particles of carbonaceous material with silicon-based sub-particles dispersed therein, being larger than 12000 MPa, thus leading to fractures or cracks in the carbonaceous matrix during the large volume expansion of the silicon-based sub-particles during lithium incorporation, thereby leading to an excessive SEI formation and to a reduced average coulombic efficiency value for the battery.
[0167] Table 4: Performance of coin-cells containing powders and composite powders E1-E5 and CE1-CE3
TABLE-US-00004 TABLE 4 Average coulombic efficiency cycles Example # 5-50 (%) E1 99.64 E2 99.68 E3 99.62 E4 99.75 E5 99.80 CE1 99.57 CE2 99.54 CE3 99.50