SiOC COMPOSITE ELECTRODE MATERIAL

Abstract

A SiOC composite material in microparticulate form, wherein the microparticles are formed, in whole or in part, of an amorphous SiOC matrix with Si ranging from 20 wt % to 60 wt %, O from 20 wt % to 40 wt % and C from 10 wt % to 50 wt %, based on the total weight of the SiOC matrix, wherein amorphous or crystallized silicon particles are embedded within the SiOC matrix and wherein the microparticles are of core/coating structure with a core formed of the amorphous SiOC matrix and coated with at least one amorphous carbon layer; and to a method for producing such SiOC composite material. It also relates to an electrode active material, an electrode and a battery, especially a lithium-ion battery, including the aforementioned SiOC composite material.

Claims

1. A SiOC composite material in microparticulate form, wherein the microparticles are formed, in whole or in part, of an amorphous SiOC matrix, with Si ranging from 20 wt % to 60 wt %, O from 20 wt % to 40 wt % and C from 10 wt % to 50 wt %, based on the total weight of the SiOC matrix, wherein amorphous or crystallized silicon particles are embedded within said SiOC matrix and wherein the microparticles are of core/coating structure with a core formed of said amorphous SiOC matrix and coated with at least one amorphous carbon layer.

2. The SiOC composite material according to claim 1, wherein the microparticles have an average particle size ranging from 1 μm to 100 μm.

3. The SiOC composite material according to claim 1, having a Brunauer Emmett Teller specific surface area ranging from 1 m2/g to 100 m2/g.

4. The SiOC composite material according to claim 1, wherein the microparticles have a spherical shape.

5. The SiOC composite material according to claim 1, for which an adsorption isotherm of nitrogen specified in IUPAC is classified in TYPE III.

6. The SiOC composite material according to claim 1, wherein crystallized silicon particles are embedded in said SiOC matrix, the crystallized silicon having a cubic crystalline structure.

7. A method for producing a SiOC composite material in microparticulate form, comprising at least the following steps, in that order, of: (i) providing a product consisting of at least one silicon-containing polymer in admixture with amorphous or crystallized silicon particles; (ii) pyrolysing the product of step (i) to yield an amorphous SiOC matrix with Si ranging from 20 wt % to 60 wt %, O from 20 wt % to 40 wt % and C from 10 wt % to 50 wt %, based on the total weight of the SiOC matrix, wherein amorphous or crystallized silicon particles are embedded within said SiOC matrix; (iii) processing the pyrolysis product obtained in step (ii) into a powder form with an average particle size ranging from 1 μm to 100 μm; and (iv) forming an amorphous carbon coating on the surface of the particles of the powder obtained in step (iii) to obtain the desired SiOC composite material of core/coating structure.

8. The method according to claim 7, wherein the silicon-containing polymer is a polysilsesquioxane.

9. The method according to claim 7, wherein said amorphous or crystallized silicon particles have an average size ranging from 2 nm to 2 μm.

10. The method according to claim 7, wherein the product in step (i) is prepared by mixing at least one silicon-containing polymer in a solid state with a crystallized or amorphous silicon powder.

11. The method according to claim 7, wherein the product in step (i) is prepared by addition of a crystallized or amorphous silicon powder to silicon-containing polymer dissolved in a solvent, followed by spray drying or evaporation of the solvent.

12. The method according to claim 7, wherein the product in step (i) is prepared by synthesizing the silicon-containing polymer by a sol-gel method in the presence of a crystallized or amorphous silicon powder.

13. The method according to claim 7, wherein the product is pyrolysed in step (ii) by heating at a rate ranging from 1° C./min to 30° C./min, to a temperature in the range of 600° C. to 1,400° C., notably with the heating duration at final temperature ranging from 5 minutes to 10 hours.

14. The method according to claim 7, wherein the carbon coating is formed in step (iv) by: (a) coating the particles with at least one organic carbon precursor containing no silicon atoms and being able to be transformed into carbon during a pyrolysis process; and then (b) pyrolysing said coated particles to obtain the carbon coating.

15. The method according to claim 14, wherein the said carbon precursor is chosen from polyvinylidene difluoride, sucrose, chlorinated polyethylene, polyvinyl chloride, polyethylene, phenolic resin, polyethylene oxide, pitch, polyvinyl alcohol, polystyrene, carboxymethyl cellulose or a salt thereof, alginic acid, oxalic acid including sodium or potassium salt, polyacrylic acid or a salt thereof, polyacrylonitrile and polyvinyl fluoride.

16. (canceled)

17. An electrode active material comprising at least a SiOC composite material as defined in claim 1 or as obtained according to a method comprising at least the following steps, in that order: (i) providing a product consisting of at least one silicon-containing polymer in admixture with amorphous or crystallized silicon particles; (ii) pyrolysing the product of step (i) to yield an amorphous SiOC matrix with Si ranging from 20 wt % to 60 wt %, O from 20 wt % to 40 wt % and C from 10 wt % to 50 wt %, based on the total weight of the SiOC matrix, wherein amorphous or crystallized silicon particles are embedded within said SiOC matrix; (iii) processing the pyrolysis product obtained in step (ii) into a powder form with an average particle size ranging from 1 μm to 100 μm; and (iv) forming an amorphous carbon coating on the surface of the particles of the powder obtained in step (iii) to obtain the desired SiOC composite material of core/coating structure.

18. An electrode comprising an electrode active material as defined in claim 17.

19. The electrode according to claim 18, which is an anode electrode, in particular a lithium-ion battery anode.

20. A battery, comprising an electrode as defined in claim 18.

21. The battery according to claim 20, which is a lithium-ion battery.

Description

FIGURES

[0128] FIG. 1: SEM picture of a SiOC composite powder in accordance with the invention synthetized in example 1;

[0129] FIG. 2: Particle size distribution diagram obtained by laser diffraction measurement of the SiOC composite powder synthetized in example 1;

[0130] FIG. 3: Nitrogen adsorption isotherm of the SiOC composite powder synthetized in example 1;

[0131] FIG. 4: X-ray diffraction pattern of the SiOC composite powder synthetized in example 1;

[0132] FIG. 5: Voltage profile obtained with the battery prepared according to example 7 with the SiOC material synthetized in example 1;

[0133] FIG. 6: Electrochemical performances (capacity v/s number of cycles) of the batteries prepared according to example 7 from the materials synthetized in examples 1 to 6;

[0134] FIG. 7: Electrochemical performances (capacity v/s number of cycles) of the battery prepared from the SiOC composite material synthetized in example 8.

EXAMPLES

Example 1

Preparation of a SiOC Composite Material in Accordance with the Invention

[0135] A sample of 28.850 g of amorphous phenyl-bridged polysilsesquioxane compound and 6.053 g of crystallized silicon were put together in a bowl and milled for 1 hour at a speed of 150 rpm.

[0136] The obtained powder was then pyrolysed under argon atmosphere for 1 hour at 1,000° C.

[0137] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30 minutes.

[0138] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved at 60° C. The obtained mixture was spray-dried at 100° C. and a powder was recovered.

[0139] This powder was heat treated at 200° C. for 16 hours under air, and then pyrolysed at 1,000° C. for 1 hour under argon atmosphere.

Analysis of the Obtained Powder

Elemental Analysis

[0140] The silicon content of the obtained powder is measured by inductively coupled plasma (ICP) emission spectrophotometry. Carbon content is measured by infrared absorption method after combustion in high frequency induction furnace. Oxygen content is measured as carbon monoxide and carbon dioxide by a non-dispersive infrared detector.

[0141] The elemental analysis of the obtained powder thus confirms the presence of Si (32.0 wt %), C (36.7 wt %) and O (31 wt %).

SEM Analysis

[0142] The observation of the powder by Scanning Electron Microscopy (SEM) (FIG. 1) shows that the particles have a spherical shape.

Laser Diffraction Analysis

[0143] The particle size distribution obtained by laser diffraction measurement is represented in FIG. 2. The obtained powder has an average particle size of around 10-20 μm.

TEM Analysis

[0144] The powder is analyzed by transmission electron microscopy (TEM), and element mapping obtained from energy dispersive X-ray spectrometry (EDX) measurement in TEM shows the presence of a carbon coating on the surface of the particles.

Adsorption Isotherm of Nitrogen

[0145] The nitrogen adsorption isotherm of the obtained powder is shown in FIG. 3. This is classified into TYPE III according to IUPAC.

X-Ray Diffraction Analysis

[0146] The X-ray diffraction pattern of the obtained powder is represented in FIG. 4. It reveals a cubic crystalline silicon phase in the final powder coming from the silicon particles trapped in the SiOC amorphous matrix.

BET Specific Surface Area

[0147] The BET specific surface area, measured by the nitrogen adsorption technic, of the obtained powder, is 18 m.sup.2/g.

Example 2 (Comparative Example)

[0148] A sample of 10 g of phenyl-bridged polysilsesquioxane compound was pyrolysed at 1,000° C. for 1 hour under argon atmosphere.

[0149] The recovered sample was then milled at a speed of 400 rpm for 5 min.

[0150] The obtained powder was added to an aqueous solution containing dissolved PVA (62.5 g/L) and dispersed particles of crystallized silicon (27.4 g/L).

[0151] The mixture was spray-dried at 100° C. and a powder was recovered.

[0152] This powder was heat treated at 200° C. for 16 hours under air and then pyrolysed at 1,000° C. for 1 hour under argon atmosphere.

Example 3

Preparation of a SiOC Composite Material in Accordance with the Invention

[0153] A sample of 28.850 g of amorphous phenyl-bridged polysilsesquioxane compound and 6.053 g of crystalized silicon were put together in a bowl and milled for 1 hour at a speed of 150 rpm.

[0154] The obtained powder was then pyrolysed under argon atmosphere for 1 hour at 1,000° C.

[0155] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30 min.

[0156] An amount of 6.25 g of solid PVA was added in the bowl and the mixture was milled for 1 hour at a speed of 150 rpm. A powder was recovered. This powder was heat treated at 200° C. for 16 hours under air, and then pyrolysed at 1,000° C. for 1 hour under argon atmosphere.

Example 4

Preparation of a SiOC Composite Material in Accordance with the Invention

[0157] A sample of 10.070 g of amorphous methyl/phenyl (4/1) bridged polysilsesquioxane compound, 1.688 g of crystallized silicon and 20 mL of acetone were put together in a bowl and milled for 1 hour at a speed of 200 rpm.

[0158] The obtained mixture was dried in an oven at 60° C. overnight. The resulting dried product was pyrolysed under argon atmosphere for 5 hour at 1,150° C.

[0159] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 5 min.

[0160] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved at 60° C. The obtained mixture was spray-dried at 100° C. and a powder was recovered.

[0161] This powder was heat treated at 200° C. for 16 hours under air and then pyrolysed at 1050° C. for 1 hour under argon atmosphere.

Example 5

Preparation of a SiOC Composite Material in Accordance with the Invention

[0162] A sample of 8 g of amorphous methyl/phenyl (4/1) bridged polysilsesquioxane compound was put in solution in 200 mL of acetone.

[0163] The solution was heated at 55° C. under magnetic stirring for 10 min. A sample of 1.3 g of crystalized silicon was added to the solution. Acetone was then evaporated with a rotary evaporator.

[0164] The obtained dried product was pyrolysed under argon atmosphere for 5 hour at 1,150° C.

[0165] After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 5 min.

[0166] The obtained powder was added to an aqueous solution containing PVA (62.5 g/L) dissolved at 60° C. The obtained mixture was spray-dried at 100° C. and a powder was recovered.

[0167] This powder was heat treated at 200° C. for 16 hours under air and then pyrolysed at 1,050° C. for 1 hour under argon atmosphere.

Example 6

Preparation of a SiOC Composite Material in Accordance with the Invention

[0168] PhSi(OMe).sub.3 and MeSi(OMe).sub.3 were both dissolved in methanol. Then, a required amount of crystallized silicon was added to the previous mixture. The obtained solution was stirred for several minutes at room temperature. Then, a required amount of hydrochloric acid was added and the solution was stirred for several minutes at 60° C.

[0169] The obtained Si-loaded polysilsesquioxane material was washed and dried before pyrolysis at 1,200° C. for 5 hours under argon. After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30 min.

[0170] An amount of 6.25 g of solid PVA was added in the bowl and the mixture was milled for 1 h at a speed of 150 rpm. A powder was recovered.

[0171] This powder was heat treated at 200° C. for 16 hours under air and then pyrolysed at 1,050° C. for 1 hour under argon atmosphere.

Example 7

Use of the Material as Electrode Active Material

[0172] For each of examples 1 to 3, slurry containing the obtained material, carboxymethyl cellulose (CMC) used as binder and vapor grown carbon fibers (VGCF) used as conductive agent was coated on a 12 μm cupper foil and used as electrode.

[0173] The electrode was used in coin-cell type battery in order to evaluate the electrochemical performance of the material. The other electrode was lithium metal. The two electrodes were separated by a Celgard 2400 separator and the battery was filled with a LiPF.sub.6-containing electrolyte. Electrochemical performances were evaluated at a C-rate of C/10.

Results

[0174] FIG. 5 shows the voltage profile for the first two charge-discharge cycles (obtained from a galvanostatic measurement at a C rate of C/10 between 0.01 and 1.2 V) of the battery prepared with the SiOC material obtained in example 1.

[0175] The electrochemical performances (capacity v/s number of cycles) of the batteries prepared from anode materials of examples 1 to 6 are shown in FIG. 6.

[0176] The anode materials using the SiOC composite materials of the invention (examples 1, 3, 4, 5 and 6) provide high capacity even after more than 20 cycles, whereas the capacity obtained with the electrode material of example 2 not in accordance with the invention deteriorates over time after 20 cycles.

[0177] Thus, the SiOC material of the invention provides a superior anode material for both capacity and cycle durability.

Example 8

Preparation of a SiOC Composite Material in Accordance with the Invention and Use as an Electrode Active Material

[0178] PhSi(OMe).sub.3 and MeSi(OMe).sub.3 were both dissolved in methanol. Then, a required amount of crystallized silicon was added to the previous mixture. The obtained solution was stirred for several minutes at room temperature. Then, a required amount of hydrochloric acid was added and the solution was stirred for several minutes at 60° C.

[0179] The obtained Si-loaded polysilsesquioxane material was washed and dried before pyrolysis at 1,200° C. for 5 hours under argon. After pyrolysis, the sample was recovered and milled at a speed of 400 rpm for 30 min.

[0180] The electrochemical performances (capacity v/s number of cycles) of a battery, prepared as described in previous example 7, from the obtained material are shown in FIG. 7.

REFERENCES

[0181] [1] Fukui et al., Appl. Mater Interfaces, 2010 April (4), 998-1008;

[0182] [2] Fukui et al., Journal of Power Sources, 196 (2011), 371-378;

[0183] [3] Fukui et al., Journal of Power Sources, 243 (2013), 152-158;