Powder, Electrode and Battery Comprising Such a Powder

Abstract

Powder comprising particles comprising a matrix material and silicon-based domains dispersed in this matrix material, whereby either part of the silicon-based domains are present in the form of agglomerates of silicon-based domains whereby at least 98% of these agglomerates have a maximum size of 3 μm or less, or the silicon-based domains are not at all agglomerated into agglomerates.

Claims

1-15. (canceled)

16. A powder comprising particles comprising a matrix material and silicon-based domains dispersed in the matrix material, wherein either a portion of the silicon-based domains are present in the form of agglomerates of the silicon-based domains and wherein at least 98% of the agglomerates have a maximum size of 3 μm or less, or the silicon-based domains are not at all agglomerated into agglomerates.

17. The powder according to claim 16, wherein the matrix material is a continuous matrix.

18. The powder according to claim 16, wherein at least 98% of the agglomerates of silicon based domains have a maximum size of 2 μm or less.

19. The powder according to claim 16, wherein at least 98% of the agglomerates of silicon based domains have a maximum size of 1 μm or less.

20. The powder according to claim 16, wherein all of the agglomerates of the silicon based domains have a maximum size of 3 μm or less.

21. The powder according to claim 16, wherein the powder contains less than 3 weight % of oxygen.

22. The powder according to claim 16, wherein the powder contains between 2 weight % and 25 weight % of silicon.

23. The powder according to claim 16, wherein the powder has an average particle diameter d.sub.50 of between 1 and 20 microns.

24. The powder according to claim 16, wherein the silicon-based domains have a mass-based average diameter d50 which is less than 500 nm.

25. The powder according to claim 16, wherein the silicon-based domains are silicon-based particles.

26. The powder according to claim 16, wherein the particles of the powder contain at least 90% by weight of said silicon-based domains and said matrix material.

27. The powder according to claim 16, wherein the powder has a BET value of less than 10 m.sup.2/g.

28. The powder according to claim 16, wherein that the particles have a porosity of less than 20 volume %.

29. An electrode for an electrochemical cell comprising the powder of claim 16.

30. A battery containing the electrode of claim 29.

Description

EXAMPLE 1

[0071] A submicron-sized silicon powder was 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 was injected at a rate of 220 g/h, resulting in a prevalent (i.e. in the reaction zone) temperature above 2000K. In this first process step the precursor became totally vaporized followed. In a second process step an argon flow was 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 was 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 0.15 mole % oxygen. The gas flow rate for both the plasma and quench gas was adjusted to obtain submicron silicon powder with an average particle diameter d50 of 80 nm and a d.sub.90 of 521 nm. In the present case 2.5 Nm.sup.3/h Ar was used for the plasma and 10 Nm.sup.3/h Ar was used as quench gas.

[0072] A blend was made of 16 g of the mentioned submicron silicon powder and 32 g petroleum based pitch powder.

[0073] This was heated to 450° C. under N.sub.2, so that the pitch melted, 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.

[0074] The mixture of submicron silicon in pitch thus obtained was cooled under N.sub.2 to room temperature and, once solidified, pulverized and sieved to give a powder with an average particle diameter d.sub.50 of 17.8 μm.

[0075] A SEM microscopic evaluation was performed to determine if the silicon particles in the silicon powder were agglomerated in the resulting composite powder. No agglomerates with a size of 0.5 μm or higher were found.

[0076] The oxygen content of the powder was 0.95 weight %.

[0077] A SEM micrograph is shown in FIGS. 1 and 2, whereby it can be seen that the distribution of the silicon particle throughout the pitch was very homogeneous. In these pictures the white colour indicates silicon particles and the dark colour indicates pitch.

[0078] Graphite (Showa Denko SCMG-AF) was added to the as-dried silicon powder/pitch blend by dry-mixing, to obtain a silicon powder/pitch/graphite mixture with a weight ratio of 1.0:2.0:7.6, respectively.

[0079] 10 g of the obtained mixture was fired in a quartz boat in a tube furnace continuously flushed with argon and heated to 1000° C. at a heating rate of 3° C./min. The sample was kept at 1000° C. for 2 h. The heating was turned off and the sample was allowed to cool to room temperature under argon atmosphere. The sample was removed from the quartz recipient, milled for 15 min in a coffee mill, and sieved to obtain a composite powder having an average particle diameter dm of 13.6 μm. The oxygen content of the obtained composite powder was 0.8 weight %.

[0080] A SEM analysis was done to confirm that the size of the agglomerates had not grown due to the firing step. This was confirmed: No agglomerates with a size of 0.5 μm or higher were observed. No porosity was visually observed.

[0081] The specific surface area of the composite powder measured by the BET method was 1.8 m.sup.2/g

EXAMPLE 2

[0082] 500 g of a submicron-sized silicon powder, obtained as in Example 1, was mixed with 1000 g of petroleum based pitch powder.

[0083] In order to apply high shear, the blend was fed into a Haake process 11 extruder, equipped with a twin screw and heated to 400° C., with the screw running at a rotating speed of 150 rpm. The residence time in the extruder was 30 minutes.

[0084] The obtained extrudate, with silicon well dispersed in the pitch material, was cooled down to less than 50° C. The injection port of the extruder and the container in which the extrudate was collected were shielded from ambient air by flushing with N.sub.2.

[0085] A part of the obtained extrudate was pulverized in a mortar, and sieved to give a powder with an average particle diameter dm of 15.9 μm.

[0086] A SEM microscopic evaluation was performed to determine if the silicon particles in the silicon powder were agglomerated in the resulting composite powder. No agglomerates with a size of 0.5 μm or higher were found.

[0087] The oxygen content of the powder was 0.98%.

[0088] Graphite (Showa Denko SCMG-AF) was added to the resulting silicon powder/pitch blend by dry-mixing, to obtain a silicon powder/pitch/graphite mixture with a weight ratio of 1.0:2.0:7.6, respectively.

[0089] Hereafter, the obtained mixture was fired and sieved as described in Example 1.

[0090] The average particle diameter d.sub.50 of the obtained powder was 14.1 μm and the oxygen content was 0.79%

[0091] A SEM analysis was done to confirm that the size of the agglomerates had not grown due to the firing step. This was confirmed: No agglomerates with a size of 0.5 μm or higher were observed. No porosity was visually observed.

[0092] The specific surface area of the composite powder measured by the BET method was 3.7 m.sup.2/g

COMPARATIVE EXAMPLE 1

[0093] 16 g of a submicron-sized silicon powder, obtained as in Example 1, was dry-mixed with 32 g of petroleum based pitch powder.

[0094] This was heated to 450° C. under N.sub.2, so that the pitch melted, and kept at this temperature for 60 minutes. No shear was applied.

[0095] The mixture of submicron silicon in pitch thus obtained was cooled under N.sub.2 to room temperature and, once solidified, pulverized and sieved to give a composite powder with an average particle diameter dm of 11.2 μm. The oxygen content of the powder was 1.21%.

[0096] A SEM microscopic evaluation was performed to determine if the silicon particles in the silicon powder were agglomerated in the resulting composite powder. The following results were obtained, with all results in μm:

TABLE-US-00001 Maximum size d10 d50 d90 d98 d99 observed 0.7 1.8 2.9 3.6 3.8 5.0

[0097] Graphite (Showa Denko SCMG-AF) was added to the resulting silicon powder/pitch blend by dry-mixing, to obtain a silicon powder/pitch/graphite mixture with a weight ratio of 1.0:2.0:7.6, respectively.

[0098] Hereafter, the obtained mixture was fired and sieved as described in Example 1. The average particle diameter d.sub.50 of the obtained powder was 16 μm, and the oxygen content was 0.9%

[0099] The SEM microscopic evaluation of the silicon particles and agglomerates was repeated on the fired product. The following results were obtained, with all results in pm, showing that significant agglomeration of the silicon nanoparticles had occurred:

TABLE-US-00002 Maximum size d10 d50 d90 d98 d99 observed 0.5 1.7 2.9 3.7 3.9 5.0

[0100] As can be seen the results are similar to the results on the unfired product. SEM images showed porosity, especially between the silicon particles making up an agglomerate of silicon particles.

[0101] The specific surface area measured by the BET method was 8.7 m.sup.2/g

[0102] The electrochemical performance was determined on all products after firing, and is reported in table 1.

TABLE-US-00003 TABLE 1 d98 of silicon d98 of silicon 1.sup.st agglomerates agglomerates discharge Coulombic (μm) (μm) capacity efficiency at Product before firing after firing (mAh/g) cycle 9 (%) Example 1 <0.5 <0.5 645 99.46 Example 2 <0.5 <0.5 646 99.51 Comparative 3.6 3.7 610 99.32 example 1