Process for Preparing Electroactive Materials for Use in Metal-Ion Batteries

Abstract

The invention relates to a process for preparing silicon-containing composite particles in a fluidized bed. Porous conductive particles having a defined particle size and pore structure are combined with a particulate additive having defined particle size, density and BET surface area. The combined porous conductive particles and particulate additive are subjected to chemical vapour infiltration in a fluidised bed to cause deposition of silicon in the pores of the porous conductive particles.

Claims

1. A process for preparing silicon-containing composite particles in a fluidized bed, the process comprising the steps of: (a) providing a plurality of porous conductive particles comprising micropores and/or mesopores, wherein: (i) the D.sub.50 particle diameter of the porous conductive particles is in the range from 1 to 30 μm; (ii) the total pore volume of micropores and mesopores as measured by gas adsorption is in the range from 0.4 to 2.2 cm.sup.3/g; (iii) the PD.sub.50 pore diameter as measured by gas adsorption is no more than 10 nm; (b) combining the porous conductive particles with a particulate additive in the form of a particulate material having a D.sub.50 particle diameter in the range from 40 to 300 μm, particle density in the range from 1.3 to 6 g/cm.sup.3 and BET surface area of no more than 200 m.sup.2/g, wherein the mass ratio of the porous conductive particles to the particulate additive is from 95:5 to 70:30; and (c) passing a fluidizing gas comprising a silicon precursor gas through the combined porous conductive particles and particulate additive at a gas velocity effective to cause fluidization of the combined porous conductive particles and particulate additive, and at a temperature effective to cause deposition of silicon in the pores of the porous conductive particles.

2. A process according to claim 1, wherein the porous conductive particles are porous carbon particles.

3. A process according to claim 1 or claim 2, wherein the porous conductive particles have a D.sub.50 particle diameter of at least 1.5 μm, or at least 2 μm, or at least 3 μm, or at least 4 μm, or at least 5 μm.

4. A process according to any preceding claim, wherein the porous conductive particles have a D.sub.50 particle diameter of no more than 25 μm, or no more than 20 μm, or no more than 18 μm, or no more than 15 μm, or no more than 12 μm, or no more than 10 μm.

5. A process according to any preceding claim, wherein the porous conductive particles have a D.sub.10 particle diameter of at least 0.2 μm, or at least 0.5 μm, or at least 0.8 μm, or at least 1 μm, or at least 1.5 μm, or at least 2 μm.

6. A process according to any preceding claim, wherein the porous conductive particles have a D.sub.99 particle diameter of no more than 40 μm, or no more than 30 μm, or no more than 25 μm, or no more than 20 μm.

7. A process according to any preceding claim, wherein the porous conductive particles have a particle size distribution span of 5 or less, or 4 or less, or 3 or less, or 2 or less, or 1.5 or less.

8. A process according to any preceding claim, wherein the porous conductive particles have a total volume of micropores and mesopores of at least 0.45 cm.sup.3/g, or at least 0.5 cm.sup.3/g, or at least 0.55 cm.sup.3/g, or at least 0.6 cm.sup.3/g, or at least 0.65 cm.sup.3/g, or at least 7 cm.sup.3/g, or at least 0.75 cm.sup.3/g, or at least 0.8 cm.sup.3/g, or at least 0.85 cm.sup.3/g, or at least 0.9 cm.sup.3/g, or at least 0.95 cm.sup.3/g, or at least 1 cm.sup.3/g.

9. A process according to any preceding claim, wherein the porous conductive particles have a total volume of micropores and mesopores of no more than 2 cm.sup.3/g, or no more than 1.8 cm.sup.3/g, or no more than 1.6 cm.sup.3/g, or no more than 1.5 cm.sup.3/g, or no more than 1.45 cm.sup.3/g, or no more than 1.4 cm.sup.3/g, or no more than 1.35 cm.sup.3/g, or no more than 1.3 cm.sup.3/g, or no more than 1.25 cm.sup.3/g, or no more than 1.2 cm.sup.3/g.

10. A process according to any preceding claim, wherein the PD.sub.50 pore diameter of the porous conductive particles is no more than 8 nm, or no more than 6 nm, or no more than 5 nm, or no more than 4 nm, or no more than 3 nm, or no more than 2.5 nm, or no more than 2 nm, or no more than 1.5 nm.

11. A process according to any preceding claim, wherein the volumetric ratio of micropores to mesopores is from 90:10 to 55:45, or from 90:10 to 60:40, or from 85:15 to 65:35.

12. A process according to any preceding claim, wherein the porous conductive particles have a BET surface area of at least 750 m.sup.2/g, or at least 1,000 m.sup.2/g, or at least 1,250 m.sup.2/g, or at least 1,500 m.sup.2/g.

13. A process according to any preceding claim, wherein the porous conductive particles have a BET surface area of no more than 4,000 m.sup.2/g, or no more than 3,500 m.sup.2/g, or no more than 3,250 m.sup.2/g, or no more than 3,000 m.sup.2/g.

14. A process according to any preceding claim, wherein the porous conductive particles have a particle density in the range from 0.35 to 1.2 g/cm.sup.3.

15. A process according to any preceding claim, wherein the particulate additive is selected from silicon dioxide; sand; aluminosilicates; metal oxides such as titanium dioxide, zirconium dioxide, aluminium oxide, and yttrium oxide; carbonates, nitrides, carbides, mineral powders, zeolites, solid electrolytes, ceramics, glass, carbon and mixtures thereof.

16. A process according to any preceding claim, wherein the particulate additive has a D.sub.50 particle diameter of at least 50 μm, or at least 60 μm, or at least 70 μm, or at least 80 μm, or at least 90 μm, or at least 100 μm.

17. A process according to any preceding claim, wherein the particulate additive has a D.sub.50 particle diameter of no more than 280 μm, or no more than 260 μm, or no more than 240 μm, or no more than 220 μm, or no more than 200 μm.

18. A process according to any preceding claim, wherein the particulate additive has a D.sub.10 particle diameter of at least 40 μm, or at least 50 μm, or at least 60 μm, or at least 70 μm, or at least 80 μm.

19. A process according to any preceding claim, wherein the particulate additive has a D.sub.1 particle diameter that is at least 5 μm more than the D.sub.99 particle diameter of the porous conductive particles.

20. A process according to any preceding claim, wherein the particulate additive has a particle density of at least 1.5 g/cm.sup.3, or at least 1.8 g/cm.sup.3, or at least 2 g/cm.sup.3, or at least 2.2 g/cm.sup.3, or at least 2.5 g/cm.sup.3.

21. A process according to any preceding claim, wherein the particulate additive has a particle density of no more than 5.8 g/cm.sup.3, or no more than 5.5 g/cm.sup.3, or no more than 5.2 g/cm.sup.3, or no more than 5 g/cm.sup.3, or no more than 4.8 g/cm.sup.3, or no more than 4.5 g/cm.sup.3, or no more than 4.2 g/cm.sup.3, or no more than 4 g/cm.sup.3.

22. A process according to any preceding claim, wherein the particulate additive has a BET surface area of no more than 150 m.sup.2/g, or no more than 120 m.sup.2/g, or no more than 100 m.sup.2/g, or no more than 80 m.sup.2/g, or no more than 60 m.sup.2/g, or no more than 40 m.sup.2/g, or no more than 20 m.sup.2/g.

23. A process according to claim 1, wherein the mass ratio of the porous conductive particles to the particulate additive is from 95:5 to 75:25; or from 92:8 to 80:20; or from 90:10 to 82:18; or from 90:10 to 85:15.

24. A process according to any preceding claim, wherein the temperature in step (c) is in the range from 400 to 1,250° C., or from 400 to 1000° C., or from 400 to 800° C., or from 400 to 750° C., or from 400 to 700° C., or from 400 to 650° C., or from 400 to 600° C., or from 400 to 550° C., or from 400 to 500° C., or from 400 to 450° C., or from 450 to 500° C.

25. A process according to any preceding claim, wherein the fluidizing gas comprises the silicon precursor gas and an inert carrier gas, optionally wherein the inert carrier gas is selected from nitrogen and argon.

26. A process according to any preceding claim, wherein the silicon precursor gas is selected from silane (SiH.sub.4), silane derivatives (e.g. disilane, trisilane and tetrasilane), and trichlorosilane (SiHCl.sub.3).

27. A process according to any preceding claim, wherein the fluidizing gas comprises from 0.5 to 20 vol %, or from 1 to 10 vol %, or from 1 to 5 vol % of the silicon precursor gas.

28. A process according to any preceding claim, wherein the porous conductive particles and particulate additive are combined upstream of the fluidized bed reactor.

29. A process according to any of claims 1 to 27, wherein the porous conductive particles and particulate additive are introduced separately into the fluidized bed reactor.

30. A process according to any preceding claim, further comprising one or more of: (i) mechanical vibration of the fluidized bed; (ii) acoustic vibration of the fluidized bed; and (iii) pulsed flow of the fluidizing gas.

31. A process according to any preceding claim, further comprising the step of separating the composite particles from some or all of the particulate additive.

32. A process according to any preceding claim, which is a continuous process.

33. A composition comprising or consisting of silicon-containing composite particles obtainable by a process according to any one of the preceding claims.

34. An electrode comprising silicon-containing composite particles obtainable by a process according to any one of claims 1 to 32.

35. A rechargeable metal-ion battery comprising an electrode according to claim 34.

Description

EXAMPLE 1

[0101] A fluidized bed reactor was fabricated with a 0.95 cm (⅜″) stainless steel gas inlet and 60 mm outside diameter (O.D.) tubular section with length of 520 mm. A stainless steel expanded head was fabricated with an O.D. of 100 mm. The reactor was suspended from a frame and a vertically-oriented tube furnace was positioned such that the hot zone ran from the conical section to ¾ of the length of the cylindrical section (approx. 380 mm long). A flanged lid was built for the top with tapped ports for thermocouples, gas outlet and powder dosing. The furnace was dosed with 50 g of a pre-mixed mixture of porous carbon particles (BET surface area 1673 m.sup.2/g, total pore volume: 0.77 cm.sup.3/g, micropore volume 73 vol %, D.sub.1 0.86 μm, D.sub.10 1.86 μm, D.sub.50 5.1 μm, D.sub.98 12.5 μm particle density 0.82 g/cm.sup.3) and silica particles (BET 32.3 m.sup.2/g, D.sub.1 54.4 μm, D.sub.10 70.6 μm, D.sub.50 106 μm, D.sub.98 190 μm, particle density 1830 kg/m.sup.3) in the ratio 3:1 by weight (i.e. 25 wt % of silica).

[0102] The minimum fluidization velocity was determined with a cold-flow pressure-drop test with nitrogen as an inert gas, ramping gas flow rate between 1 to 2.5 L/min. Once minimum fluidizing velocity was determined, the inert gas flow rate was held constant at or above the minimum fluidising velocity. The furnace was ramped to the desired reaction temperature under constant inert gas flow rate. After stabilizing at a target temperature between 450-500° C., the fluidizing gas was switched from pure nitrogen to 1.25 vol % monosilane in nitrogen. The reaction progress was monitored by measuring pressure drop and furnace temperature difference between top and bottom. The gas flow rate was adjusted throughout the run to maintain a pressure drop consistent with continued fluidization and minimum temperature difference between the top and bottom of the bed of less than 40° C. was maintained.

[0103] The reaction was run for 12 hours. Once the reaction time was complete, the fluidizing gas was then switched to pure nitrogen whilst maintaining fluidisation, this purge lasted 30 minutes. Then the furnace was ramped to ambient temperature over several hours. On reaching ambient temperature, the furnace atmosphere was switched to air gradually over a period of hours. The sample was finally unloaded through the gas feed tube at the bottom as a grey free flowing powder. The silica particles were then removed from the silicon-carbon composite particle product by using a 20 μm sieve.

[0104] The results of ICP-OES analysis show that the silicon-carbon composite particle product contained 51.3 wt % of silicon with minimal coarse silicon (Z<5 wt %). The Si:C ratio was therefore approximately 1:1. The BET surface area of the product was 156 m.sup.2/g.

Example 2

[0105] The process of Example 1 was repeated except that the reactor was dosed with 50 g of the porous carbon particles alone, without any silica particles. It was found that a significant amount of the carbon material was elutriated from the reactor (exited the reactor before the deposition process was complete). After deposition was completed the resulting composite powder (excluding the elutriated material) was analysed and found to comprise an excess loading of silicon at 80.6 wt % and a large value of coarse silicon (Z>10 wt %). The BET of the product was 29 m.sup.2/g. Agglomeration of composite particles was also observed in SEM images.