A METHOD FOR PRODUCING A CARBON-SILICON COMPOSITE MATERIAL POWDER, AND A CARBON-SILICON COMPOSITE MATERIAL POWDER

Abstract

The present disclosure relates to a method for producing a carbon-silicon composite material powder, comprising: providing a carbon-containing precursor, which is lignin; providing at least one silicon-containing active material; melt-mixing at least said carbon-containing precursor and said silicon-containing active material(s) to a melt-mixture; providing said melt-mixture in a non-fibrous form and cooling the melt- mixture to provide an isotropic intermediate composite material; subjecting said isotropic intermediate composite material to a thermal treatment, wherein said thermal treatment comprises a carbonization step to provide a carbon-silicon composite material, and subjecting said carbon-silicon composite material to pulverization to provide said carbon-silicon composite material powder. The present disclosure also relates to a carbon-silicon composite material powder obtainable by the method, a negative electrode for a non-aqueous secondary battery, such as a lithium-ion battery, comprising the carbon-silicon composite material powder, and use of the carbon-silicon composite material powder in a negative electrode of a non-aqueous secondary battery.

Claims

1. A method for producing a carbon-silicon composite material powder comprising: providing a carbon-containing precursor, wherein the carbon-containing precursor comprises lignin; providing at least one silicon-containing active material; melt-mixing at least two components to a melt-mixture, wherein said carbon-containing precursor constitutes one component and each silicon-containing active material constitutes one component, and wherein said melt-mixing is performed at a temperature between 120-250° C.; providing said melt-mixture in a non-fibrous form and cooling said melt-mixture in said non-fibrous form so as to provide an isotropic intermediate composite material; subjecting said isotropic intermediate composite material to a thermal treatment, wherein said thermal treatment comprises a carbonization step so as to provide a carbon-silicon composite material, and subjecting said carbon-silicon composite material to pulverization so as to provide said carbon-silicon composite material powder.

2. The method according to claim 1, wherein the carbon-containing precursor comprises Kraft lignin.

3. The method according to claim 1, wherein the lignin is provided in particulate form.

4. The method according to claim 1, wherein the silicon-containing active material is selected from a group consisting of: elemental silicon, a silicon suboxide, a silicon-metal alloy, or a silicon-metal carbon alloy.

5. The method according to claim 1, wherein the silicon-containing active material is provided in particulate form.

6. The method according to claim 1, wherein the carbon-containing precursor is mixed with 0.5-30 wt-% of said at least one silicon-containing active material in the melt-mixing step.

7. The method according to claim 1, wherein the method further comprises a step of: providing at least one dispersing additive and wherein the components melt-mixed in the melt-mixing step include said at least one dispersing additive.

8. The method according to claim 7, wherein said dispersing additive is selected from a group consisting of: monoethers, polyethers, mono-alcohols, polyalcohols, amines, polyamines, carbonates, polycarbonates, monoesters, polyesters, and polyether fatty acid esters.

9. The method according to claim 8, wherein said dispersing additive is selected from a group consisting of: polyethylene oxide and branched polyether fatty acid esters.

10. The method according to claim 7, wherein the carbon-containing precursor is mixed with 0.5-30 wt-% of said at least one silicon-containing active material and 0.5-10 wt-% of said dispersing additive in the melt-mixing step.

11. The method according to claim 1, wherein the method further comprises a step of: providing graphite particles, or carbon particles, or both, wherein the components melt-mixed in the melt-mixing step include said graphite particles, or said carbon particles or both.

12. The method according to claim 1, wherein the melt-mixing is performed by kneading, compounding, or extrusion.

13. The method according to claim 1, wherein the method further comprises a step of: pre-mixing at least two of said components to be melt-mixed before said melt-mixing step.

14. The method according to claim 13, wherein said pre-mixing is performed by dry mixing, dry milling, wet milling, melt-mixing, solution mixing, spray-coating, spray-drying, dispersion mixing, or combinations thereof.

15. The method according to claim 1, wherein said carbonization is performed at a temperature of 700-1300° C.

16. The method according to claim 1, wherein said thermal treatment further comprises one or more initial heating steps before said carbonization step, wherein each initial heating step is performed at a temperature of 250-700° C.

17. The method according to claim 16, wherein the method further comprises a pulverization step after said one or more initial heating steps and before said carbonization step.

18. The method according to claim 1, wherein the method further comprises a step of: crushing or pulverization of said isotropic intermediate composite material before said thermal treatment.

19. The method according to claim 1, wherein said carbon-silicon composite material powder comprises powder particles having an average particle size between 5-25 .Math.m.

20. The method according to claim 1, wherein said carbon-silicon composite material powder comprises powder particles, and Wherein said method further comprises a step of: carbon-coating the carbon-silicon composite material powder particles.

21. A carbon-silicon composite material powder obtained by the method according to claim 1.

22. A negative electrode for a non-aqueous secondary battery comprising: the carbon-silicon composite material powder to claim 21.

23. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0094] FIGS. 1a-c are SEM (1a) and SEM-EDX (1b, carbon only), (1c, silicon only) images of a HC/Si composite material powder obtained by initial ball-milling of lignin and silicon as described in Example 2.

[0095] FIGS. 2a-c are SEM (2a) and SEM-EDX (2b, carbon only), (2c, silicon only) images, respectively, of a HC/Si composite material powder with <13 wt-% Si obtained by melt-mixing without dispersing additive as described in Example 3.

[0096] FIGS. 3a-g are SEM (3a-b) and SEM-EDX (3c, carbon only), (3d, silicon only) images and cross-section SEM (3e) and SEM-EDX (3f, carbon only), (3 g, silicon only) images of a HC/Si composite material powder with <13 wt-% Si obtained by melt-mixing with PEO (dispersing additive) as described in Example 4. The elliptical structure / particle on the left side in FIGS. 3e to 3g is not part of the HC/Si sample, but is an artefact from sample preparation, namely the epoxy resin used to fix the HC/Si sample for the cross-sections.

[0097] FIGS. 4a-c are SEM (4a) and SEM-EDX (4b, carbon only), (4c, silicon only) images, respectively, of a pre-carbonized intermediate C/Si composite material powder obtained by melt-mixing with TWEEN 80 (dispersing additive) as described in Example 7.

[0098] FIGS. 5a-c are SEM (5a) and SEM-EDX (5b, carbon only), (5c, silicon only) images, respectively, of a pre-carbonized intermediate C/Si composite material powder obtained by melt-mixing with TWEEN 80 (dispersing additive) as described in Example 8.

[0099] FIG. 6 shows the electrochemical behavior of a HC/Si composite material powder obtained by melt-mixing as described in Example 9.

EXAMPLES

Example 1: Pure Hard Carbon (HC) (Comparative)

[0100] Softwood Kraft lignin was heat-treated in N.sub.2 at 500° C. under N.sub.2 flow using a heating rate of 10° C./min, and a dwell time at 500° C. of 1 hour (initial heating). After cooling to room temperature the obtained cake was crushed. The crushed material was heat-treated at 1000° C. under N.sub.2 using a heating rate of 10° C./min, and a dwell time at 1000° C. of 1 hour (carbonization). After cooling, the carbonised material was milled and classified using a laboratory fluidised bed opposed jet mill and a single-wheel classifier to obtain a carbon powder with an average particle size of 10 .Math.m as measured by laser diffraction.

Example 2: HC/Si Composite Material Powder, Obtained by Ball-Milling (Comparative)

[0101] Softwood Kraft lignin was mixed with Si particles (with a primary particle size of 200 nm) using a laboratory mixer. The mixture was then transferred to a ball-mill and milled at 20 Hz for 3 minutes. The resulting lignin/Si mixture was then heat-treated, milled and classified in the same way as the material in Example 1, yielding a HC/Si composite material powder with an average particle size of 10 .Math.m. FIGS. 1a-c are SEM (1a) and SEM-EDX (1b, carbon only), (1c, silicon only) images of the obtained HC/Si composite material powder.

Example 3: HC/Si Composite Material Powder With <13 Wt-% Si, Obtained by Melt-Mixing Without Dispersing Additive

[0102] Softwood Kraft lignin was pre-mixed (dry mixed) with 5 wt-% Si particles (with a primary particle size of 200 nm) using a laboratory mixer. The mixture was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160 ºC for 20 minutes. After cooling to room temperature, a mass of a melt-mixed material (i.e. isotropic intermediate composite material) was obtained in the kneader. The material was then crushed, using a cutting-mill (equipped with a 0.5 mm cut-off sieve). The resulting lignin/Si mixture was then heat-treated, milled and classified according to Example 1, yielding a HC/Si composite material powder with <13 wt-% Si and with an average particle size of 10 .Math.m. FIGS. 2a-c are SEM (2a) and SEM-EDX (2b, carbon only), (2c, silicon only) images, respectively, of the obtained HC/Si composite material powder. It is evident from the SEM-picture (2a), that a high loading of silicon and a high degree of silicon dispersion is obtained.

Example 4: HC/Si Composite Material Powder With <13 Wt-% Si, Obtained by Melt-Mixing With PEO

[0103] Softwood Kraft lignin was pre-mixed (dry mixed) together with 5 wt-% Si particles (primary particle size of 200 nm) and 5 wt-% of PEO (Mw=1500 g/mol) using a laboratory mixer. The mixture was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160 ºC for 20 minutes. After cooling to room temperature, a mass of a melt-mixed material (i.e. isotropic intermediate composite material) was obtained in the kneader. The material was then crushed using a cutting-mill (equipped with a 0.5 mm coarse cut-off sieve). The resulting lignin/Si mixture was then heat-treated, milled and classified in the same way as the material in Example 1, yielding a HC/Si composite material powder with <13 wt-% Si and with an average particle size of 10 .Math.m. FIGS. 3a-g are SEM (3a-b) and SEM-EDX (3c, carbon only), (3d, silicon only) images of the obtained HC/Si composite material powder and cross-section SEM (3e) and SEM-EDX (3f, carbon only), (3 g, silicon only) images of the obtained HC/Si composite material powder. Note that the elliptical structure / particle on the left side in FIGS. 3e to 3g is not part of the HC/Si sample, but is an artefact from sample preparation, namely the epoxy resin used to fix the HC/Si sample for the cross-sections. It is evident from both SEM/SEM-EDX that a high loading of silicon in the matrix is obtained and that silicon is highly uniformly distributed on the surface as well as internally as by cross-section pictures. Also, it is evident from the SEM images of FIGS. 3a-g when compared with the SEM images of FIGS. 2a-2c that the use of a dispersing additive (PEO) results in further improvement of the degree of dispersion of silicon in the carbon matrix.

Example 5: HC/Si Composite Material Powder With 2.0 Wt-% Si, Obtained by Melt-Mixing with PEO

[0104] Softwood Kraft lignin was pre-mixed (dry mixed) with 0.9 wt.% Si particles (with a primary particle size of 200 nm) and 5 wt-% of PEO (Mw=1500 g/mol) using a laboratory mixer. The mixture was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160° C. for 20 minutes. After cooling to room temperature, a mass of a melt-mixed material (i.e. isotropic intermediate composite material) was obtained in the kneader. The material was then crushed using a cutting-mill (equipped with a 0.5 mm cut-off sieve). The resulting lignin/Si mixture was then heat-treated, milled and classified according to Example 1, yielding a HC/Si composite material powder with 2.0 wt-% Si and with an average particle size of 10 .Math.m.

Example 6: HC/Si Composite Material Powder With 4.8 Wt-% Si, Obtained by Melt-Mixing with PEO

[0105] Softwood Kraft lignin was pre-mixed (dry mixed) with 2.0 wt.% Si particles (with a primary particle size of 200 nm) and 5 wt.% of PEO (Mw=1500 g/mol) using a laboratory mixer. The mixture was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160° C. for 20 minutes. After cooling to room temperature, a mass of a melt-mixed material (i.e. isotropic intermediate composite material) was obtained in the kneader. The material was then crushed using a cutting-mill (equipped with a 0.5 mm cut-off sieve). The resulting lignin/Si mixture was then heat-treated, milled and classified according to Example 1, yielding a HC/Si composite material powder with 4.8 wt-% Si and with an average particle size of 10 .Math.m.

Example 7: Pre-carbonized Intermediate C/Si Composite Material Powder Obtained by Melt-Mixing with TWEEN

[0106] Softwood Kraft lignin was pre-mixed (dry mixed) together with 5 wt-% Si particles (primary particle size of 200 nm) in a laboratory mixer. The mixture was then melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160 ºC for 20 minutes, where 5 wt-% of TWEEN 80 was added directly after heating up in the kneader. After cooling to room temperature, a mass of a melt-mixed material (i.e. isotropic intermediate composite material) was obtained in the kneader. The material was then crushed using a cutting-mill (equipped with a 0.5 mm coarse cut-off sieve). The resulting lignin/Si mixture was then heat-treated by initial heating (but without carbonization) according to Example 1 and milled and classified according to Example 1, yielding a pre-carbonized intermediate C/Si composite material powder with an average particle size of 10 .Math.m. FIGS. 4a-c are SEM (4a) and SEM-EDX (4b, carbon only), (4c, silicon only) images, respectively, of the obtained pre-carbonized intermediate C/Si composite material powder. It is evident from both SEM/SEM-EDX that Si is highly uniformly distributed.

Example 8: Pre-carbonized Intermediate C/Si Composite Material Powder Obtained by Melt-Mixing with Teen

[0107] Softwood Kraft Lignin (90 g) was dispersed in water (1 liter), and TWEEN 80 (5 g) was added while mixing with a Ultraturrax mixer for 5 minutes at room temperature. In a next step, nano-silicon (200 nm) was added and mixing continued for another 5 minutes at room temperature. Subsequently, the mixture was filtered and dried at 80° C. in vacuum (10 mbar). Thereafter the sample was melt-mixed using a kneader (HAAKE™ Rheomix OS Lab Mixer equipped with banbury rotors) at a set temperature of 160° C. for 20 minutes and further treated as described in Example 7. FIGS. 5a-c are SEM (5a) and SEM-EDX (5b, carbon only), (5c, silicon only) images, respectively, of the obtained pre-carbonized intermediate C/Si composite material powder. It is evident from both SEM/SEM-EDX that Si is highly uniformly distributed.

Example 9: Electrochemical Behavior of a HC/Si Composite Material Powder Obtained by Melt-Mixing

[0108] Electrodes were prepared from the HC/Si composite material powder of Example 6 or from pure HC of Example 1 and characterized electrochemically as follows: 82 wt-% HC/Si or HC were mixed with 8 wt-% poly(vinylidene fluoride) binder dissolved in 1-methyl-2-pyrrolidone, coated onto Cu foil via a doctor-blade process, and dried. Lab-type 3-electrode cells were built from the HC/Si or HC electrode, a Li metal counter electrode, and a Li metal reference electrode, using glass-fibre separators and 1 M LiPF.sub.6 dissolved in ethylene carbonate : dimethyl carbonate (1:1 by wt.) as electrolyte. The cells were galvanostatically charged and discharged between 5 mV vs. Li/Li.sup.+ and 1.5 V vs. Li/Li.sup.+ using a specific current of 74.4 mA/g(AM), where g(AM) denotes the gram of active material in the electrode. FIG. 6 compares the discharge potential curves of the HC/Si and pure HC materials. By adding Si, the capacity could be increased by approx. 120 mAh/g. The presence of Si and its participation in the charge/discharge process is noticed by the prolongation of the potential plateau below 0.1 V vs. Li/Li.sup.+ and by the appearance of a second potential plateau between 0.4 and 0.5 V vs. Li/Li.sup.+.

[0109] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.