PREDOMINANTLY AMORPHOUS SILICON PARTICLES AND USE THEREOF AS ACTIVE ANODE MATERIAL IN SECONDARY LITHIUM ION BATTERIES

Abstract

A method for manufacturing predominantly amorphous silicon-containing particles includes a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.05. The particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°. Both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting. The method includes forming a homogeneous gas mixture of a first precursor gas of a silicon containing compound and at least one second precursor gas of a substitution element M containing compound, injecting the homogeneous gas mixture of the first and second precursor gases into a reactor space where the precursor gases are heated to a temperature in the range of from 700 to 900° C. so that the precursor gases react and form particles, and collecting and cooling the particles to a temperature in the range of from ambient temperature up to about 350° C. The relative amounts of the first and the second precursor gases are adapted such that the formed particles obtain an atomic ratio C: Si in the range of [0.005, 0.05).

Claims

1. A method for manufacturing predominantly amorphous silicon-containing particles comprising a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.05, and where the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting, wherein the method comprises: forming a homogeneous gas mixture of a first precursor gas of a silicon containing compound and at least one second precursor gas of a substitution element M containing compound, injecting the homogeneous gas mixture of the first and second precursor gases into a reactor space where the precursor gases are heated to a temperature in the range of from 700 to 900° C. so that the precursor gases react and form particles, and collecting and cooling the particles to a temperature in the range of from ambient temperature up to about 350° C., wherein the relative amounts of the first and the second precursor gases are adapted such that the formed particles obtain an atomic ratio C: Si in the range of [0.005, 0.05).

2. The method according to claim 1, wherein the first precursor gas is: Silane (SiH.sub.4), disilane (Si.sub.2H.sub.6), trichlorosilane (HCl.sub.3Si), or a mixture thereof.

3. The method according to claim 1, wherein the second precursor gas is chosen from: methane (CH.sub.4), ethane (C.sub.2H.sub.6), propane (C.sub.3H.sub.8), ethene (C.sub.2H.sub.4), ethyne (C.sub.2H.sub.2), alkanes, alkenes, alkynes, or mixtures thereof.

4. The method according to claim 1, wherein the relative amounts of the first and the second precursor gases are adapted such that the formed particles obtain an atomic ratio C: Si in the range of [0.01, 0.04], preferably in the range of [0.01, 0.03], and most preferably in the range of [0.01, 0.02].

5. The method according to claim 1, wherein the homogeneous gas mixture of the first and second precursor gases is preheated to a temperature in the area of from 400 to 500° C. prior to insertion in the reactor space, and then further heated after injection into the reactor space to a temperature in the range of from 740 to 850° C., preferably in the range of from 780 to 830° C., and most preferably in the range of from 790 to 820° C.

6. The method according to claim 1, wherein the gas mixture also comprises hydrogen, nitrogen, a noble gas like Helium, Neon, Argon, or any other gas that will not chemically react with the precursor gases at the temperatures specified.

7. The method according to claim 1, wherein the relative amounts of the first and the second precursor gases are adapted by regulating the flow rates of the first and second precursor gases being injected into the reactor and applying a mass spectrometer to measure the composition of the off-gas exiting the reactor to determine the fraction of the injected first and second precursor gas being converted to particles, and apply this information to deduce the atomic ratio C: Si in the formed particles and regulate the feed rates of the first and second precursor gases to obtain the intended atomic ratio C: Si in the particles being produced.

8. A method according to claim 1, wherein the method further comprises the step of depositing a 0.05-3 nm, preferably a 0.2 to 1 nm thick layer of carbon onto the surface of the condensed particles.

9. Predominantly amorphous silicon-containing particles, wherein the particles comprises a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.02, and the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting.

10. Predominantly amorphous silicon-containing particles according to claim 9, wherein the particles comprises a compound of formula: S.sub.(1−x)C.sub.x, where 0.01≤x<0.02.

11. Predominantly amorphous silicon-containing particles according to claim 9, wherein the particles have an average particle size in the range of from 10 to 200 nm, preferably in the range of from 15 to 150 nm, preferably in the range of from 20 to 100 nm, and most preferably in the range of from 20 to 70 nm.

12. (canceled)

13. Predominantly amorphous silicon-containing particles according to claim 9, wherein the particles are coated with a from 0.05-3 nm, preferably of from 0.2 to 1 nm thick coating of carbon.

14. A negative electrode for a secondary lithium-ion electrochemical cell, comprising: at least one particulate active material, a particulate conductive filler material, binder material, and a current collecting substrate, wherein the at least one particulate active material is embedded in the binder material to form an anode mass which is deposited as an anode mass layer onto the current collecting substrate, the or one of the at least one particulate active material is predominantly amorphous silicon-containing particles, wherein the particles comprises a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.04, and wherein the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting.

15. A negative electrode according to claim 14, wherein the conductive substrate is a foil or a sheet of either graphite, Cu or Al.

16. A negative electrode according to claim 14, wherein the binder is either a styrene butadiene copolymer, a carboxymethylcellulose, an ethylene-propylene-diene methylene (EPDM), a polyacrylic acid (PAA).

17. A negative electrode according to claim 14, wherein the anode mass further comprises a particulate conductive additive material mixed with and embedded together with the particulate active material in the binder material.

18. A negative electrode according to claim 17, wherein the particulate conductive filler material is a carbon black, carbon nanotubes, graphene, or a mixture thereof.

19. A composite particle for use in the negative electrode in a secondary lithium-ion electrochemical cell, wherein the composite particle comprises: a plurality of predominantly amorphous silicon-containing particles, wherein the particles comprises a chemical compound of formula: Si(1−x)CAM, where 0.005≤x<0.04 and where the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting, and a predominantly carbon containing material made by pyrolysis of a carbon rich material.

20. A composite particle for use in the negative electrode in a secondary lithium-ion electrochemical cell, wherein the composite particle comprises: a plurality of predominantly amorphous silicon-containing particles, wherein the particles comprises a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.04, and the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting, and an elastic polymer.

21. A composite particle for use in the negative electrode in a secondary lithium-ion electrochemical cell, wherein the composite particle comprises: a plurality of predominantly amorphous silicon-containing particles, wherein the particles comprises a chemical compound of formula: Si.sub.(1−x)C.sub.x, where 0.005≤x<0.04 and where the particles, when subjected to XRD analysis applying unmonochromated CuKα radiation, exhibit one peak at around 28° and one peak at around 52°, and where both peaks have a Full Width at Half Maximum of at least 5° when using Gaussian peak fitting, and graphene or reduced graphene oxide.

22. Use of a composite particle according to claim 19 in a negative electrode in a secondary lithium-ion electrochemical cell.

Description

LIST OF FIGURES

[0074] FIG. 1 is a diagram showing an XRD-analysis of silicon particles made at three different temperatures.

[0075] FIG. 2 is a diagram showing an XRD analysis of various samples of Si.sub.0.99C.sub.0,01 and Si.sub.0.98C.sub.0,02 made above 800° C. (samples R11_FA, R11_FB, and R11_FC) in nearly the same process as in FIG. 1 and still being fully amorphous.

[0076] FIG. 3 is a diagram showing an XRD analysis of a sample of Si.sub.0.96C.sub.0,04 after heat treatment for two hours at 700° C. (R18-F1 700) and 800° C. (R18-F1 800), respectively. The curves show that Si.sub.0.96C.sub.0,04 stays amorphous even after 2 hours at 800° C.

[0077] FIG. 4 is a diagram showing an XRD analysis of Si.sub.0.92C.sub.0,08 after heat treatment for two hours at 700° C. (R18-F2 700) and 800° C. (R18-F2 800), respectively. The curves show that Si.sub.0.92C.sub.0,08 stays amorphous after 2 hours at 700° C. but starts to crystallize if it is exposed for 2 hours at 800° C.

[0078] FIG. 5 is a diagram showing an XRD analysis of Si showing that the material is fully crystalline if it is exposed for to 2 hours at 780° C.

[0079] FIG. 6 is a XRD-diagram of a sample with both crystalline and amorphous silicon and where the area under the Bragg peak is marked as dark grey and the area under the broad peak subtracted an area und a linear background is shown as light grey.

[0080] Verification of the Invention

[0081] The invention will be described in further detail by way of example embodiments.

Comparison Example

[0082] Three samples of (pure) silicon particles were made by pre-heating a homogenous gas mixture of 33% silane diluted in hydrogen gas to about 400° C. and introducing the gas into a decomposition reactor and mixing the silane gas with preheated hydrogen gas having a temperature of 710° C., 745° C. and 770° C., respectively. The residence time in the reactor was approximate 1.5 seconds. The resulting silicon particles were rapidly cooled to below 300 C and collected by filtration.

[0083] The sample particles were then analysed by XRD to investigate their atomic structure. The particles made at 710° C. (marked as RTF1 on FIG. 1) has a XRD-curve typical of amorphous silicon, the particles made at 745° C. (marked as RTF2 on FIG. 1) has a XRD-curve indicating some formation of crystalline silicon, while the particles made at 770° C. (marked as RTF3 on FIG. 1) has a XRD-curve typical of crystalline silicon.

Example 1

[0084] An example embodiment of the predominantly amorphous silicon particles according to the invention may be prepared as follows:

[0085] A homogeneous mixture of silane gas and ethene was preheated to about 400° C. and introduced into a reactor chamber. There the homogeneous mixture of silane gas and ethene was further mixed with an inert gas (nitrogen) which was preheated to a temperature giving a temperature in the resulting gas mixture of 810° C. The relative amounts of the gases in the final mixture were approximately 28 mole % silane, 1.5 mole % ethene and the rest (70 mole %) was nitrogen, which gave an atomic ratio of C: Si in the gas mixture of 0.05. The resulting particles, however, had an atomic ratio of C: Si of 0.02, i.e. the particles consisted of predominantly amorphous Si.sub.0.98C.sub.0.02.

[0086] The residence time in the reactor was approximately 1.0 seconds. The exhaust gas and particles exiting the reactor space were thereafter rapidly cooled and collected in a filter. The particles were analysed by XRD to investigate their atomic structure. The result is shown in FIG. 2 as the curve marked with R11_FA. The XRD-curve is typical for silicon having an amorphous molecular structure.

Example 2

[0087] Two more example embodiments of particles were made in the similar way as in example 1, except that the gas mixture was heated to 800° C. in the reactor for material R11_FB and the ethene concentration was reduced by 50% in sample R11_FC in order to make Si.sub.0.99C.sub.0.01. These particle samples were analysed by XRD and the result is shown in FIG. 2 as the curve marked R11_FB and R11_FC, respectively. Both curves are typical for amorphous silicon.

Example 3

[0088] Three more embodiments of particles were made in the similar way as in example 1, except that the gas mixture comprised silane, ethene, ammonia and nitrogen. These samples where characterized using Differential Scanning Calorimetry to determine the crystallization temperature from the energy released during crystallization. The nitrogen content is not as easy to measure as the carbon content for these low inclusions, but based on linear extrapolation from samples with higher nitrogen content, and analysing the gas consumption in the reaction, is was estimated that the particles had compositions Si.sub.x,C.sub.y,N.sub.z of: Si0.sub.0.984C.sub.0.016N.sub.0, Si.sub.0.992,C.sub.008,N.sub.0, and Si.sub.0.976C.sub.0.012N.sub.0.012.

[0089] All these samples showed an increased crystallization temperature as compared to the comparison particles of pure silicon described above, with the sample of estimated composition of Si.sub.0.976C.sub.0.012N.sub.0.012 having the highest crystallization temperature of 794° C. The two other samples showed a crystallinity temperature of being at least 10° C. lower, i.e. somewhat less than 784° C.

REFERENCES

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