PROCESS FOR THE PREPARATION OF SiOx HAVING A NANOSCALE FILAMENT STRUCTURE AND USE THEREOF AS ANODE MATERIAL IN LITHIUM-ION BATTERIES

Abstract

A process for the preparation of nanofilament particles of SiO.sub.x in which x is between 0.8 and 1.2, the process comprising: a step consisting of a fusion reaction between silica (SiO.sub.2) and silicon (Si), at a temperature of at least about 1410° C., to produce gaseous silicon monoxide (SiO); and a step consisting of condensation of the gaseous SiO to produce the SiO.sub.x nanofilament particles. The process may also comprising using carbon.

Claims

1. Process for the preparation of nanofilament particles of SiO.sub.x in which x is between 0.8 and 1.2, the process comprising: a step comprising a fusion reaction between silica (SiO.sub.2), silicon (Si) and, optionally a source of carbon, at a temperature of at least about 1410° C., to produce gaseous silicon monoxide (SiO); and a step comprising condensation of the gaseous SiO to produce the SiO.sub.x nanofilament particles.

2. Process according to claim 1, wherein the fusion reaction is between silica (SiO.sub.2), silicon (Si) and a source of carbon (C).

3. Process according to claim 1, wherein the SiO.sub.2 is in solid form and the Si is in liquid form.

4. Process according to claim 1, wherein the fusion step is performed in an induction furnace, an electric arc furnace or a submerged arc furnace.

5. Process according to claim 1, wherein the condensation step is performed in a low temperature area of a furnace, the gaseous SiO being moved to the low temperature area by a vector gas selected from the group consisting of inert gas, oxidant gas, reduction gas, volatile hydrocarbon and combinations thereof.

6. (canceled)

7. Process according to claim 1, wherein the fusion step is performed under vacuum.

8. Process according to claim 1, wherein the fusion step is performed under inert atmosphere which is of Ar, He or N.sub.2.

9. (canceled)

10. Process according to claim 1, wherein the temperature at the fusion step is between about 1450 and about 1700° C.

11. Process according to claim 2, wherein the source of carbon is selected from the group consisting of graphite, charcoal, petroleum coke, charcoal, wood or a combination thereof.

12. Process for the preparation of nanofilament particles of SiO.sub.x in which x is between 0.8 and 1.2, the process comprising the following steps: introducing liquid silicon (Si) in a furnace and bringing the temperature to at least about 1410° C.; introducing solid silica (SiO.sub.2) in the furnace while agitating the mixture and producing gaseous silicon monoxide (SiO); and moving the gaseous SiO to a low temperature area of the furnace using a vector gas, and condensing to yield the SiO.sub.x nanofilament particles.

13. Process according to claim 12, further comprising introducing a source of carbon is in the furnace prior to bringing the temperature to at least about 1410° C.

14. (canceled)

15. Process according to claim 12, wherein the furnace is an induction furnace, and the agitation stems from a magnetic field produced by the furnace.

16. Process according to claim 12, wherein the step of introducing the solid silica in the furnace is accompanied by a purge process during which oxygen present is eliminated.

17. Process according to claim 13, wherein the furnace is a submerged arc furnace.

18-23. (canceled)

24. Process according to claim 1, wherein x is about 1.

25. Process according to claim 1, wherein the SiO.sub.2 is in a form which is quartz, quartzite or a combination thereof.

26. Process according to claim 1, wherein the SiO.sub.x particles are in spherical agglomerates consisting of nanofilaments, each agglomerate having a diameter of about 2 to 10 μm.

27. Process according to claim 26, wherein the nanofilaments each has a diameter of about 50 nm, and the spherical agglomerates are linked together by spheres each having a diameter of about 100 to 150 nm.

28. Process according to claim 1, wherein the nanofilament SiO.sub.x particles obtained comprise at least one of: amorphous SiO.sub.2, crystalline Si and SiC.

29. Nanofilament particles of SiO.sub.x obtained by the process as defined in claim 1.

30. Material comprising nanofilament particles of SiO, in which x is between 0.8 and 1.2 obtained by a process comprising: a step comprising a fusion reaction between silica (SiO.sub.2), silicon (Si), and, optionally, a source of carbon (c), at a temperature of at least about 1410° C., to produce gaseous silicon monoxide (SiO); and a step comprising condensation of the gaseous SiO to produce the SiO, nanofilament particles.

31. A method comprising fabricating an anode with nanofilament particles of SiO.sub.x obtained by the process as defined in claim 1.

32. (canceled)

33. Anode comprising a material as defined in claim 30.

34. Battery comprising an anode as defined in claim 33.

35. Material according to claim 30, wherein the fusion reaction is between silica (SiO.sub.2), silicon (Si) and a source of carbon (C).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0065] FIG. 1 shows a typical aspect of a commercially available SiO material; micrograph taken by an electronic microscope and X-ray diffraction analysis.

[0066] FIG. 2 shows the capacity of the anode when commercially available SiO.sub.x is used, and when a mixture of SiO.sub.x and graphite is used.

[0067] FIG. 3 shows an induction furnace equipped with a graphite crucible.

[0068] FIG. 4 shows nanofilaments of SiO.sub.x obtained by the process of the invention.

[0069] FIG. 5 shows the X-ray diffraction analysis of nanofilament particles of SiO.sub.x obtained by the process of the invention.

[0070] FIG. 6 shows results of cycling formation (electrochemical tests).

[0071] FIG. 7 shows results of cycling stability (electrochemical tests).

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0072] The present invention relates to a process for the preparation of a SiO.sub.x material, wherein x is between about 0.8 to about 1.2; preferably x is about 1. The SiO.sub.x material according to the invention has a nanoscale filament structure (nanofilaments, nano-structured particles).

[0073] The process of the invention comprises the synthesis of SiO.sub.x particles from condensation of gaseous SiO obtained by a high temperature metallurgic process as outlined below.

[0074] A step comprising a fusion reaction between Si(l) and SiO.sub.2(l,s) to produce SiO(g) is performed, under controlled atmosphere. For example, fusion in an induction furnace, a plasma furnace, an electric arc furnace or a submerged arc furnace. The fusion reaction proceeds according to the following reaction:

##STR00003##

[0075] Thereafter, a gas or mixture of gases is used as vector to move SiO(g) in a cold area for the condensation. Nucleation and growth of solid SiO.sub.x nano-structured particles occur during condensation.

[0076] According to an aspect, the fusion step may be replaced by a step of carbothermic reduction of SiO.sub.2 as illustrated by the reaction below. Various source of carbon may be used; for example graphite (FIG. 2), coal, petroleum coke, charcoal, wood or a combination thereof. Silica may be, for example, in a form which is quartz, quartzite or a combination thereof.

SiO.sub.2(l,s)+C(s).fwdarw.SiO(g)+CO(g)

[0077] The gas mixture used as vector to move gaseous SiO may comprise inert gases (for example Ar, He, N.sub.2), oxidant gases (for example air, H.sub.2O, O.sub.2, CO.sub.2), reducing gases (for example CO, H.sub.2, volatiles hydrocarbons) or a combination thereof.

EXAMPLES

[0078] The following examples are provided solely as illustrative embodiments and should not be interpreted, in any way, as limiting the invention.

Example 1

[0079] Metallurgical grade silicon (Si) is melted in an induction furnace equipped with a graphite crucible. The experiment system also comprises a cover for the crucible, a feeding port for feeding argon as vector gas, and a capacitor (FIG. 3).

[0080] Liquid silicon is heated to 1500° C. Silica (SiO.sub.2) is added, at the liquid (Si) surface. The crucible cover is then put in place and the process of feeding argon begins. The induction furnace produces a magnetic field which causes the liquid to rotate, leading to SiO.sub.2(s) being dispersed within Si(l). Once oxygen initially present in the system is completely purged, the side reaction producing silica fume stops (2SiO(g)+O.sub.2(g).fwdarw.2SiO.sub.2(s)) and the reaction producing SiO.sub.x particles begins (SiO(g).fwdarw.SiO(am)). The color of the product changes from white (silica fume, SiO.sub.2) to brown (SiO.sub.x).

[0081] The material obtained is examined using a scanning electron microscope (SEM) under high magnification. SiO.sub.x obtained presents spherical agglomerates having diameters of 2 to 10 μm and a nanoscale fibrous structure. The nanofilaments have a diameter of about 50 nm and are joined together by spheres having diameters of about 100 to 150 nm (FIG. 4).

[0082] According to the X-ray diffraction analysis (FIG. 5), the particles comprise amorphous silica (SiO.sub.2), crystalline silicon (Si) and silicon carbide (SiC) (β form). SiO.sub.x has thus undergone a dismutation reaction leading to a nanometric dispersion of crystalline Si in an amorphous SiO.sub.2 matrix.

[0083] The total amount of oxygen, measured by LECO, shows a similar level of oxygen for commercially available SiO.sub.x and for SiO.sub.x obtained in Example 1.

Example 2

[0084] Metallic silicon is prepared, using a submerged arc furnace, by carbothermic reduction of quartz (SiO.sub.2) with reducing materials such as mineral coal, charcoal or coke petroleum. During the reaction, about 80% of silicon is reduced according to the following global reaction:

##STR00004##

[0085] An intermediate reaction occurs, which is the production of gaseous SiO in the hottest area of the furnace (the arc), according to the following reaction:

SiO.sub.2+C.fwdarw.SiO(g)+CO(g)

[0086] In order to allow for retrieval of a sample of SiO.sub.x, a modification was made to the arc furnace, which consists of creating a longitudinal opening in one of the graphite electrodes. Gaseous SiO leaving the reaction area was sucked through the opening. Gaseous SiO flowing through the electrode condenses once it reaches a colder area, in absence of oxygen, according to the following reaction:

SiO(g).fwdarw.SiO(am).fwdarw.Si(cr)+SiO.sub.2(am)

[0087] SiO.sub.x obtained is fibrous, as in the first synthesis, and presents the same diffractogram as the one obtained for the sample in Example 1: an amount of SiO undergoes dismutation leading to metallic silicon and amorphous quartz; moreover, the carbon-rich atmosphere leads to the production of traces of silicon carbide (SiC).

Example 3

[0088] A composite electrode is fabricated by mixing the active material (SiO.sub.x) with 25% wt of carbon black (Denka black) and 25% wt of binder (sodium alginate, Aldrich) in a solvent consisting of deionized water to obtain a homogenous dispersion, which is then deposited on a current collector made of copper. The electrode is dried for 20 hours under vacuum at 110° C. A button cell of CR2032 format is assembled in a glovebox full of helium. The electrolyte used is LiPF.sub.6 (1M) in a 3:7 (v/v) mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 2% wt vinylene carbonate (VC) (Ube). The counter electrode is a thin film of lithium. The electrochemical tests on the battery are performed by discharge/charge cycling in galvanostatic mode within a potential of 0.005 to 2.5 V at a C/24 speed (FIG. 6). Once the reversible capacity is measured, cycling of the battery is performed in order to measure its stability at a C/6 speed (FIG. 7).

[0089] Although the present invention is described by way of specific embodiments thereof, it is to be understood that various variations and modifications may be linked to these embodiments. The present inventions covers such modifications, uses or adaptations of the invention in general, the principles of the invention including any variation which will become known or conventional in the field of the invention, and which may apply to essential elements indicated above in accordance with the scope of the claims.

[0090] The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.

REFERENCES

[0091] [1] Uday Kasavajjula, Chunsheng Wang, A. John Appleby; Nano- and bulk-silicon-based insertion anodes for lithium-ion secondary cells, Journal of Power Sources 163 (2007) 1003-1039. [0092] [2] Candace K. Chan, Hailin Peng, Gao Liu, Kevin McIlwrath, Xiao Feng Zhang, Robert A. Huggins and Yi Cui; High-performance lithium battery anodes using silicon nanowires, Nature Nanotechnology, vol. 3, January 2008, pp. 31-35. [0093] [3] T. Morita, N. Takami, Nano Si Cluster-SiO—C Composite Material as High-Capacity Anode Material for Rechargeable Lithium, Journal of the Electrochemical Society, 153 (2) A425-A430 (2006). [0094] [4] A. Guerfi, P. Charest, M. Dontigny, J. Trottier, M. Lagacé, P. Hovington, A. Vijh, K. Zaghib; SiO.sub.x-graphite as negative for high energy Li-ion batteries, Journal of Power Sources, Volume 196, Issue 13, 1 Jul. 2011, pages 5667-5673. [0095] [5] U.S. Pat. No. 1,104,384. [0096] [6] H.-D. Klein, F. König, Production, Properties and Application of Silicon Monoxide, in: R. Corriu, P. Jutzi (Eds.), Tailor-made silicon-oxygen compounds-from molecules to materials, Vieweg, Braunschweig, Weiesbaden, 1996, pp. 141-145. [0097] [7] P. Lamontagne, G. Soucy, J. Veilleux, F. Quesnel, P. Hovington, W. Zhu and K. Zaghib; Synthesis of silicon nanowires from carbothermic reduction of silica fume in RF thermal plasma; Phys. Status Solidi A, 1-7 (2014).