Process for producing a silicon-carbon composite

Abstract

Process for producing a silicon-carbon composite powder in which a) a gas stream A containing at least one starting compound of silicon selected from the group consisting of SiH.sub.4, Si.sub.2H.sub.6 and Si.sub.3H.sub.8, and b) a gas stream B containing at least one starting compound of carbon selected from the group consisting of methane, ethane, propane, ethylene and acetylene
are reacted in a hot wall reactor at a temperature of less than 900° C., the reaction mixture is cooled or allowed to cool and the pulverulent reaction product is separated from gaseous materials.

Claims

1. A process for producing a silicon-carbon composite powder, the process comprising: feeding a) a gas stream A comprising at least one silicon starting compound selected from the group consisting of SiH.sub.4, Si.sub.2H.sub.6 and Si.sub.3H.sub.8, and b) a gas stream B comprising at least one carbon starting compound selected from the group consisting of methane, ethane, propane, ethylene and acetylene into a hot wall reactor at a temperature of less than 900° C., to form a reaction mixture, cooling the reaction mixture or allowing the reaction mixture to cool, and separating a pulverulent reaction product, to obtain the silicon-carbon composite powder, wherein the gas stream B is fed into the hot wall reactor after the gas stream A.

2. The process of claim 1, wherein the gas stream A and the gas stream B are fed into the hot wall reactor simultaneously, either separately or in a mixture comprising the gas stream A and the gas stream B.

3. The process of claim 1, wherein an Si/C volume fraction in the silicon-carbon composite powder is in a range of 30:1 to 1:30.

4. The process of claim 1, wherein the silicon starting compound is SiH.sub.4 and the carbon starting compound is acetylene.

5. The process of claim 1, further comprising: feeding at least one inert gas selected from the group consisting of argon and helium into the hot wall reactor.

6. The process of claim 1, wherein there is a laminar flow through the hot wall reactor.

7. A lithium-ion battery anode comprising a silicon-carbon composite powder, having an Si/C volume fraction in a range of 20:1 to 1:10 and comprising silicon particles having an average diameter of 300 nm or less, wherein a surface of the silicon particles is at least partly encapsulated with an amorphous, carbon-comprising layer having an average layer thickness of less than 200 nm.

8. The lithium-ion battery anode of claim 7, wherein the silicon particles are amorphous.

9. The lithium-ion battery anode of claim 7, wherein the amorphous, carbon-comprising layer comprises at least one species selected from the group consisting of an aliphatic, an aromatic and a graphitic species.

Description

EXAMPLES

Example 1

(1) 20 vol % of SiH.sub.4 and 3 vol % of acetylene are introduced as a homogeneous mixture into the core of a tubular hot wall reactor via a nozzle. In addition, argon is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 700° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(2) The particle size and particle morphology of the pulverulent solid are investigated by transmission electron microscopy (TEM). The median particle size is 260 nm. The particles have a virtually spherical shape.

(3) The silicon and carbon content is measured at selected points by energy dispersive x-ray analysis (EDX) in the TEM. A high carbon content of 90-95 at % is measured at the particle edge. The particle centre has an Si:C atom concentration ratio of 60:40. It is to be noted that during acquisition of the EDX spectrum of the particles a signal for both the particle core and the particle surface is measured. The high carbon content at the particle edge and the relatively low carbon content upon EDX measurement at the particle centre indicate the formation of a silicon-carbon composite powder where the surface of the particles is encapsulated with a carbon-containing layer.

(4) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to the Rietveld refinement the pulverulent solid contains predominantly an amorphous phase (85 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition to the amorphous phase 15 vol % of nanocrystalline silicon is found.

Example 2

(5) 20 vol % of SiH.sub.4 and 3.2 vol % of ethylene are introduced as a homogeneous mixture into the core of a tubular hot wall reactor via a nozzle. In addition, argon is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 650° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(6) The particle size and particle morphology of the pulverulent solid are investigated by transmission electron microscopy (TEM). The median particle size is 150 nm. The particles have a virtually spherical shape.

(7) The silicon and carbon content is measured at selected points by energy dispersive x-ray analysis (EDX) in the TEM. A high carbon content of 80-83 at % is measured at the particle edge. The particle centre has an Si:C atom concentration ratio of 35:65. The high carbon content at the particle edge and the relatively low carbon content upon EDX measurement at the particle centre indicate the formation of a silicon-carbon composite powder where the surface of the particles is encapsulated with a carbon-containing layer.

(8) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to the Rietveld refinement the pulverulent solid contains predominantly an amorphous Si phase (96 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition, 4 vol % of nanocrystalline silicon is found.

Example 3

(9) 20 vol % of SiH.sub.4 and 3.1 vol % of ethane are introduced as a homogeneous mixture into the core of a tubular hot wall reactor via a nozzle. In addition, argon is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 650° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(10) The particle size and particle morphology of the pulverulent solid are investigated by transmission electron microscopy (TEM). The median particle size is 210 nm. The particles have a virtually spherical shape. The silicon and carbon content is measured at selected points by energy dispersive x-ray analysis (EDX) in the TEM. A high carbon content of 84-92 at % is measured at the particle edge. The particle centre has an Si:C atom concentration ratio of 40:60. The high carbon content at the particle edge and the relatively low carbon content upon EDX measurement at the particle centre indicate the formation of a silicon-carbon composite powder where the surface of the particles is encapsulated with a carbon-containing layer.

(11) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to the Rietveld refinement the pulverulent solid contains predominantly an amorphous Si phase (97 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition, 3 vol % of nanocrystalline silicon is found.

Example 4

(12) 20 vol % of SiH.sub.4 and 3.2 vol % of propane are introduced as a homogeneous mixture into the core of a tubular hot wall reactor via a nozzle. In addition, argon is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 650° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(13) The particle size and particle morphology of the pulverulent solid are investigated by transmission electron microscopy (TEM). The median particle size is 200 nm. The particles have a virtually spherical shape.

(14) The silicon and carbon content is measured at selected points by energy dispersive x-ray analysis (EDX) in the TEM. A high carbon content of 97 at % is measured at the particle edge. The particle centre has an Si:C atom concentration ratio of 53:47. The high carbon content at the particle edge and the relatively low carbon content upon EDX measurement at the particle centre indicate the formation of a silicon-carbon composite powder where the surface of the particles is encapsulated with a carbon-containing layer.

(15) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to the Rietveld refinement the pulverulent solid contains predominantly an amorphous Si phase (94 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition, 6 vol % of nanocrystalline silicon is observed.

Example 5

(16) 20 vol % of SiH.sub.4 and 6.3 vol % of methane are introduced as a homogeneous mixture into the core of a tubular hot wall reactor via a nozzle. In addition, a mixture of argon and hydrogen is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 650° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(17) The particle size and particle morphology of the pulverulent solid are investigated by transmission electron microscopy (TEM). The median particle size is 195 nm. The particles have a virtually spherical shape.

(18) The silicon particles are partly encapsulated with a carbon-containing layer.

(19) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to the Rietveld refinement the pulverulent solid contains predominantly an amorphous Si phase (93 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition, 7 vol % of nanocrystalline silicon is observed.

Example 6

(20) 20 vol % of SiH.sub.4 is introduced into the hot wall reactor core of a tubular hot wall reactor via a nozzle and 3.5 vol % of ethylene is introduced into said reactor laterally. In addition, argon is employed as veil gas. There is a laminar flow through the hot wall reactor. A temperature of 650° C. is measured at the reactor outer wall. The pulverulent solid is separated from gaseous substances in a filter and packed under inert conditions via an airlock system.

(21) The particle size and particle morphology of the pulverulent solid are determined by transmission electron microscopy (TEM). The median particle size is 170 nm. The particles have a virtually spherical shape. Silicon and carbon content is measured at selected points by energy dispersive x-ray analysis (EDX) in the TEM. A high carbon content of 99 at % is measured at the particle edge. The particle centre has an Si:C atom concentration ratio of 80:20.

(22) Rietveld refinement of the x-ray diffractograms makes it possible to calculate the proportions of the phases in the pulverulent solid. According to said refinement the pulverulent solid contains predominantly an amorphous Si phase (85 vol %). The amorphous phase is characterized by three broad reflections. These broad reflections, also known as a halo, are characteristic of an amorphous phase. In addition, 15 vol % of nanocrystalline silicon is found.

(23) Input materials and materials properties are summarized in the table.

(24) TABLE-US-00001 TABLE Input materials and materials properties of the silicon-carbon composite powders. Amor- Median C Si:C phous particle particle particle propor- Exam- Input materials diameter.sup.a) edge.sup.b) centre.sup.b) tion.sup.c) ple vol % nm at % at %/at % % 1 20 SiH.sub.4/3 C.sub.2H.sub.2 260 90-95 1.5:1   85 2 20 SiH.sub.4/3 C.sub.2H.sub.4 150 80-83 1:1.85 96 3 20 SiH.sub.4/3.1 C.sub.2H.sub.6 210 84-92 1:1.5  97 4 20 SiH.sub.4/3.2 C.sub.3H.sub.8 200 97 1:1.13 94 5 20 SiH.sub.4/6.3 CH.sub.4 195 — — 93 6 20 SiH.sub.4/3.5 C.sub.2H.sub.4 170 99 4:1   85 .sup.a)TEM; .sup.b)EDX; .sup.c)x-ray diffractometry