Methods for modifying silicon particles

Abstract

The invention relates to methods for producing non-aggregated, modified silicon particles by treating non-aggregated silicon particles which have volume-weighted particle size distributions with diameter percentiles d.sub.50 of 1.0 μm to 10.0 μm at 80° C. to 900° C. with an oxygen-containing gas.

Claims

1. A method for producing nonaggregated, modified silicon particles, comprising: treating nonaggregated reactant silicon particles having a volume-weighted particle size distribution with a diameter percentile d.sub.50 of 3.0 μm to 7.0 μm with an oxygen-containing gas at 80° C. to 900° C. and recovering nonaggregated, modified silicon particles containing 0.1-3.0% by weight of oxygen based on the total weight of the non-aggregated, modified silicon particles, with the proviso that the nonaggregated, modified silicon particles have an oxygen content which is 0.05% to 0.6% by weight greater than the oxygen content of the nonaggregated silicon particles based on the total weight of the silicon particles and have a BET surface area of 0.2 to 8.0 m.sup.2/g.

2. The method of claim 1, wherein the oxygen-containing gas contains 1 to 100 vol % of oxygen based on the total volume of the oxygen-containing gas.

3. The method of claim 2, wherein the treatment with an oxygen-containing gas is carried out at 400° C. to 800° C.

4. The method of claim 2, wherein the treatment with an oxygen-containing gas is carried out at 80° C. to 400° C.

5. The method of claim 1, wherein the oxygen-containing gas contains from 1 to 5 vol. % of oxygen based on the total volume of the oxygen-containing gas.

6. The method of claim 1, wherein the nonaggregated silicon particles contain ≤2.0% by weight of oxygen.

7. The method of claim 1, wherein the nonaggregated, modified silicon particles contain 0.2% to 1.5% by weight of oxygen based on the total weight of the nonaggregated, modified silicon particles.

8. The method of claim 1, wherein the nonaggregated silicon particles are nonagglomerated.

9. The method of claim 1, wherein surfaces of the nonaggregated, modified silicon particles have a silicon oxide layer with an average layer thickness of 2 to 50 nm.

10. The method of claim 1, wherein the nonaggregated, modified silicon particles have a volume-weighted particle size distribution with a diameter percentile d.sub.50 of 5.0 μm to 7.0 μm.

11. The method of claim 1, wherein the nonaggregated silicon particles and/or the nonaggregated, modified silicon particles have BET surface areas of 0.5 to 5.0 m.sup.2/g determined according to DIN 66131 with nitrogen.

12. Nonaggregated, modified silicon particles obtained by the method of claim 1.

13. The nonaggregated, modified silicon particles of claim 12, wherein the nonaggregated, modified silicon particles contain 0.2% to 1.5% by weight of oxygen based on the total weight of the nonaggregated, modified silicon particles.

14. A method for producing an aqueous ink formulations, comprising: mixing nonaggregated, modified silicon particles of claim 12 with one or more binders and water.

15. An anode for lithium-ion batteries, comprising nonaggregated, modified silicon particles prepared by the method of claim 1.

16. The anode for lithium-ion batteries of claim 15, wherein silicon particles in the anode material are only partly lithiated in the fully charged lithium-ion battery.

17. The nonaggregated, modified silicon particles of claim 1, having a BET surface area between 1.0 and 5.0 m.sup.2/g.

18. The nonaggregated, modified silicon particles of claim 1, which are prepared by milling metallurgical grade silicon into particles with sharp-edged fracture surfaces.

19. The nonaggregated, modified silicon particles of claim 1, wherein the oxygen content is from 0.1 to 0.6 wt. % greater than the oxygen content of the reactant silicon particles.

Description

EXAMPLE 1

(1) Production of Si Particles a (Noninventive):

(2) The Si particles A were produced according to the prior art by milling coarse crushed silicon from the production of solar silicon in a fluidized bed jet mill (Netzsch-Condux CGS16 with 90 m.sup.3/h of nitrogen at 7 bar as milling gas). The obtained particles were filled into receptacles under inert gas and stored thus. After removal of the particles in air the analytical data reported in table 1 were obtained.

(3) Production of Si Particles B (Inventive):

(4) Si particles A (151.90 g) were heated in air at 80° C. for 6 h in a glass dish in a Heraeus, T6060 drying cabinet. After cooling to room temperature the thus obtained modified silicon particles B were removed, reweighed (152.10 g) and analyzed. The stability of the silicon particles in water was analyzed by GC, as specified under the heading “hydrogen evolution (H.sub.2—evolution)”. The results obtained are shown in table 1.

(5) Production of Si Particles C (Inventive):

(6) Silicon particles A (829.2 g, cf. table 1) were introduced into an evaporating dish and placed in a ThermoConcept KK480 calcination furnace. The interior of the furnace was heated to 600° C. for a duration of 6 h, ensuring airflow to the Si bed.

(7) After cooling to room temperature the thus obtained modified silicon particles C were removed, reweighed (832.8 g) and analyzed. The stability of the silicon particles in water was analyzed by GC, as specified under the heading “hydrogen evolution (H.sub.2-evolution)”. The results obtained are shown in table 1.

(8) TABLE-US-00001 TABLE 1 Analytical data of the Si particles and reaction conditions for the oxidation: Si particles A (comparison) Si particles B Si particles C Temperature — 80° C. 600° C. Duration — 6 h 6 h d.sub.10 2.4 μm 2.3 μm 2.3 μm d.sub.50 4.7 μm 4.7 μm 4.8 μm d.sub.90 7.9 μm 7.9 μm 7.9 μm O content 0.16% 0.22% 0.72% d(SiO.sub.2) 2.2 nm 3.1 nm 10.6 nm H.sub.2 evolution 0.29 vol % 0.07 vol % 0.00 vol % (40° C.) H.sub.2 evolution 0.67 vol % 0.26 vol % 0.00 vol % (80° C.) d.sub.50: diameter percentiles d.sub.50 of the volume-weighted particle size distributions of the particles A, B and C; d(SiO.sub.2): calculated average silicon dioxide layer thickness on the surface of the Si particles.

(9) The reactant Si particles show significant H.sub.2 evolution even at 40° C. The inventive products show very little, if any, H.sub.2 evolution at 40° C.

Example 2: Production of Aqueous Ink Formulations

(10) 127.5 g of the respective silicon particles were mixed with 45.5 g of graphite (KS6L from Imerys) and with 100 g of an aqueous LiPAA binder solution (produced from LiOH und polyacrylic acid, m.w. 450 k, Sigma-Aldrich, prod. no. 181285) (4% by weight, pH 6.9) with a planetary mixer (PC Laborsystem LPV 1 G2). After 60 minutes of stirring time at 50 rpm a further 119.5 g of the abovementioned LiPAA binder solution were added and stirred for a further 60 minutes at 100 rpm. For analysis of H.sub.2 evolution 5 g (Si particles A) or 15 g (Si particles B/C) of the respective ink were filled into a headspace vial (20 ml total volume) and stored at room temperature. The composition of the gas space was analysed after the times reported in table 2. The analytical data are summarized in table 2.

(11) TABLE-US-00002 TABLE 2 Hydrogen evolution of aqueous ink formulations: Ink A Ink B Ink C (comparative) (inventive) (inventive) Si particles Si particles A Si particles B Si particles C (comparative) (inventive) (inventive) H.sub.2 evolution 48 vol % 0.00 vol % 0.00 vol % (1 day) (1 day) (7 days) (5 g ink) (5 g ink) (15 g ink) (17 ml gas (17 ml gas space) (7 ml gas space) space)

(12) The comparative ink containing silicon particles A showed severe foaming during processing with the planetary mixer and also severe H.sub.2 evolution even after a short standing time while the inventive inks containing the modified silicon particles B or C showed no H.sub.2 evolution even after prolonged standing times.

(13) Both inventive ink formulations are processable into homogeneous electrode coatings.

(14) The electrode coating comprising Si particles A has a propensity for bursting of the coating, and thus for nonhomogeneous coating, on account of the severe hydrogen evolution.