SILICON CARBON COMPOSITE PARTICLES

Abstract

Silicon carbon composite particles and anode materials for use within lithium-ion batteries utilizing the silicon carbon composite particles. Where the silicon carbon composite particles have an alkali metal or alkaline earth metal concentration of 0.05 to 10 wt% and a pH > 7.5.

Claims

1-14. (canceled)

15. Silicon carbon composite particles, comprising: a) an alkali metal or alkaline earth metal concentration of 0.05 to 10 wt%; and b) a pH > 7.5.

16. The silicon carbon composite particles of claim 15, wherein the silicon carbon composite particles have a volume-weighted particle size distribution with diameter percentiles d.sub.50 of 0.5 to 20 .Math.m.

17. The silicon carbon composite particles of claim 15, wherein the silicon carbon composite particles have at least 30 wt% of silicon obtained by silicon infiltration.

18. The silicon carbon composite particles of claim 15, wherein in pores and on the outer surface of the silicon carbon composite particles silicon is present in the form of layers, or in the form of layers formed from silicon particles, having a thickness of at most 1 .Math.m.

19. The silicon carbon composite particles of claim 15, wherein the silicon carbon composite particles have a specific BET surface area of at most 100 m.sup.2/g.

20. The silicon carbon composite particles of claim 17, wherein the silicon carbon composite particles have a pore volume P which is at least 100 vol%, based on the volume of the silicon obtained from silicon infiltration in the silicon carbon composite particles, the pore volume P of the silicon carbon composite particles resulting from the sum total of gas-accessible and gas-inaccessible pore volume.

21. The silicon carbon composite particles of claim 15, wherein the silicon carbon composite particles are used in an anode material of a lithium-ion battery.

22. A process for producing the silicon carbon composite particles, comprising: providing silicon carbon composite particles having an alkali metal or alkaline earth metal concentration of 0.05 to 10 wt% and a pH > 7.5 by silicon infiltration from silicon precursors which are selected from silicon precursors which are liquid or gaseous at 20° C. and 1013 mbar, in the presence of porous carbon particles, wherein the porous carbon particles, by treatment with a basic alkali metal or alkaline earth metal compound in a molar ratio of 100:1 to 5:1, based on the carbon present in the porous carbon particles, have an alkali metal or alkaline earth metal concentration of 0.1 to 20 wt% and a pH of > 7.5.

23. The process of claim 22, wherein the silicon infiltration takes place in a reactor selected from fluidized bed reactors, rotary tube furnaces arranged horizontally through vertically, open or closed fixed-bed reactors, and pressure reactors.

24. The process of claim 22, wherein silicon infiltration is carried out at 280 to 900° C.

25. The process of claim 22, wherein the silicon carbon composite particles are produced by silicon infiltration from silanes selected from monosilane and chlorine-containing silanes.

26. An anode material for a lithium-ion battery, comprising: wherein the anode material comprises the silicon carbon composite particles having an alkali metal or alkaline earth metal concentration of 0.05 to 10 wt% and a pH > 7.5.

27. The anode material for a lithium-ion battery of claim 26, wherein the anode material is coated on a current collector.

Description

EXAMPLES

[0112] The pH values are determined according to ASTM standard number D1512, method A.

Scanning Electron Microscopy (SEM/EDX)

[0113] The microscope studies were carried out using a Zeiss Ultra 55 scanning electron microscope and an Oxford X-Max 80N energy-dispersive X-ray spectrometer. In order to prevent charging phenomena, the samples were vapor-coated with carbon, prior to the study, using a Safematic 010/HV Compact Coating Unit. Cross sections of the silicon-containing materials were produced using a Leica TIC 3X ion cutter at 6 kV.

Inorganic Analysis/Elemental Analysis

[0114] The C contents were determined using a Leco CS 230 analyzer, while a Leco TCH-600 analyzer was used for determining oxygen and nitrogen contents. The qualitative and quantitative determination of other elements, especially the determination of the alkali metals and alkaline earth metals, took place by means of ICP (inductively coupled plasma) emission spectrometry (Optima 7300 DV, from Perkin Elmer). For this purpose the samples underwent acid digestion (HF/HNO.sub.3) in a microwave (Microwave 3000, from Anton Paar). The ICP-OES determination is based on ISO 11885 “Water quality - Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES) (ISO 11885:2007); German version EN ISO 11885:2009”, which is employed for analysis of acidic aqueous solutions (for example, acidified samples of drinking water, wastewater and other waters, aqua regia extracts from soils and sediments).

Particle Size Determination

[0115] The particle size distribution was determined according to ISO 13320 by means of static laser scattering with a Horiba LA 950. In preparing the samples, particular care must be taken here in dispersing the particles in the measuring solution, so as not to measure the size of agglomerates rather than individual particles. For the materials studied here, they were dispersed in ethanol. Accordingly, prior to the measurement, as and where necessary, the dispersion was ultrasonicated for 4 minutes in a Hielscher laboratory ultrasound instrument, model UIS250v with LS24d5 sonotrode, at 250 W.

BET Surface Area Measurement

[0116] The specific surface area of the materials was measured via gas adsorption with nitrogen using a Sorptomatic 199090 instrument (Porotec) or SA-9603MP instrument (Horiba) in accordance with the BET method (determination according to DIN ISO 9277:2003-05 with nitrogen).

Skeletal Density

[0117] The skeletal density, meaning the density of the porous solid based on the volume exclusively of the pore spaces accessible to gas from outside, was determined by means of helium pycnometry according to DIN 66137-2.

Gas-Accessible Pore Volume (Gurvich Pore Volume)

[0118] The gas-accessible pore volume according to Gurvich was determined by gas sorption measurements with nitrogen according to DIN 66134.

[0119] In inventive examples 1 - 6 below and also in comparative example 1, the production and properties of the porous carbon particles used for producing the silicon-carbon composite particles of the invention are described.

[0120] Comparative example 1: Porous carbon particles having an alkali/alkaline earth metal concentration < 0.1 wt% and a pH < 7.5.

[0121] Porous carbon particles having the following properties were used: [0122] BET surface area: 2140 m.sup.2/g [0123] Gurvich PV: 1.01 cm.sup.3/g [0124] Na content: 25 ppm [0125] K content: 115 ppm [0126] pH= 5.4

[0127] Inventive example 1: Treatment of porous carbon particles with 1-molar NaOH solution.

[0128] A 250 ml flask was charged with 20 g of carbon from comparative example 1 and admixed at room temperature with 160 ml of 1M NaOH (aqueous solution). The suspension was then heated to 100° C. and boiled at reflux for 3 hours. After cooling to ambient temperature, the suspension was filtered through a suction filter and the solid product was washed with distilled water until the wash water had a pH of 7. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.6 g of a black solid.

[0129] Inventive example 2: Treatment of porous carbon particles with 1-molar NaOH solution and an additional washing step.

[0130] After treatment of the porous carbon particles as in inventive example 1, the sample was additionally washed with 2 L of distilled water. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.4 g of a black solid.

[0131] Inventive example 3: Treatment of porous carbon particles with 1-molar NaOH solution at room temperature.

[0132] A 250 ml flask was charged with 20 g of carbon from comparative example 1 and admixed at room temperature with 160 ml of 1 M NaOH (aqueous solution). The suspension was then stirred at room temperature for 1 h and subsequently filtered through a suction filter, and the solid product was washed with distilled water until the wash water had a pH of 7. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.5 g of a black solid.

[0133] Inventive example 4: Treatment of porous carbon particles with NaOH solution at room temperature without washing.

[0134] A 250 ml flask was charged with 20 g of carbon from comparative example 1 and admixed at room temperature with NaOH solution (0.4424 g of NaOH in 50 ml of distilled water). The suspension was then stirred at room temperature for 1 h and subsequently filtered through a suction filter. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.5 g of a black solid.

[0135] Inventive example 5: Treatment of porous carbon particles with 1 M LiOH at room temperature. A 250 ml flask was charged with 20 g of carbon from comparative example 1 and admixed at room temperature with 160 ml of 1M LiOH (aqueous solution). The suspension was then heated to 100° C. and boiled under reflux for 3 hours. After cooling to ambient temperature, the suspension was filtered through a suction filter, and the solid product was washed with distilled water until the wash water had a pH of 7. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.6 g of a black solid.

[0136] Inventive example 6: Treatment of porous carbon particles with 1 M KOH at room temperature.

[0137] A 250 ml flask was charged with 20 g of carbon from comparative example 1 and admixed at room temperature with 160 ml of 1M KOH (aqueous solution). The suspension was then heated to 100° C. and boiled under reflux for 3 hours. After cooling to ambient temperature, the suspension was filtered through a suction filter, and the solid product was washed with distilled water until the wash water had a pH of 7. The resulting powder, lastly, was dried overnight in a vacuum drying cabinet at 80° C. and 10.sup.-2 bar. This gave 19.6 g of a black solid.

[0138] The physical properties of the porous carbon particles are summarized in Table 1 below.

TABLE-US-00001 BET surface area [m.sup.2/g] Gurvich pore volume [cm.sup.3/g] Metal content [%/ion] pH value Comparative example 1 * 2140 1.01 0.0025 / Na 0.0115 / K 5.4 Inventive example 1 2010 0.95 1.2 / Na 10.7 Inventive example 2 1980 0.98 0.57 / Na 9.0 Inventive example 3 1940 0.96 1.3 / Na 10.7 Inventive example 4 1900 0.94 1.2 / Na 9.8 Inventive example 5 2030 0.95 0.36 / Li 9.8 Inventive example 6 1990 0.93 2.03 / K 9.4 *not inventive

Production of Silicon-Carbon Composite Particles

[0139] Comparative example 1A: Silicon-carbon composite particles from porous carbon particles from comparative example 1.

[0140] A tubular reactor was charged with 3.0 g of the porous carbon particles from comparative example 1 (specific surface area = 2140 m.sup.2/g, Gurvich pore volume = 1.01 cm.sup.3/g, pH = 5.4) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 410° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 4.9 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0141] Comparative example 1B: Silicon-carbon composite particles from porous carbon particles from comparative example 1 at reduced temperature.

[0142] A tubular reactor was charged with 3.0 g of the porous carbon from comparative example 1 (specific surface area = 2140 m.sup.2/g, Gurvich pore volume = 1.01 cm.sup.3/g, pH = 5.4) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 10.2 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0143] Inventive example 1A: Silicon-carbon composite particles from porous carbon particles from inventive example 1.

[0144] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 1 (specific surface area = 2010 m.sup.2/g, Gurvich pore volume = 0.95 cm.sup.3/g, pH = 10.7) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature has been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 4.6 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0145] Inventive example 2A: Silicon-carbon composite particles from porous carbon particles from inventive example 2.

[0146] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 2 (specific surface area = 1980 m.sup.2/g, Gurvich pore volume = 0.98 cm.sup.3/g, pH = 9.0) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 8.5 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0147] Inventive example 3A: Silicon-carbon composite particles from porous carbon particles from inventive example 3.

[0148] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 3 (specific surface area = 1940 m.sup.2/g, Gurvich pore volume = 0.96 cm.sup.3/g, pH = 10.7) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 5.4 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0149] Inventive example 4A: Silicon-carbon composite particles from porous carbon particles from inventive example 4.

[0150] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 4 (specific surface area = 1900 m.sup.2/g, Gurvich pore volume = 0.94 cm.sup.3/g, pH = 9.8) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 5.7 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0151] Inventive example 5A: Silicon-carbon composite particles from porous carbon particles from inventive example 5.

[0152] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 5 (specific surface area = 2030 m.sup.2/g, Gurvich pore volume = 0.95 cm.sup.3/g, pH = 9.8) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 7.1 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0153] Inventive example 6A: Silicon-carbon composite particles from porous carbon particles from inventive example 6.

[0154] A tubular reactor was charged with 3.0 g of the porous carbon particles from inventive example 6 (specific surface area = 1990 m.sup.2/g, Gurvich pore volume = 0.93 cm.sup.3/g, pH = 9.4) in a fused silica boat. After having been rendered inert with nitrogen, the reactor was heated to 380° C. When the reaction temperature had been reached, the reactive gas (10% SiH.sub.4 in N.sub.2, 10 L (STP)/h) was passed through the reactor for 8.0 h. The reactor was subsequently flushed with inert gas and cooled to room temperature, and the product was removed.

[0155] Inventive example 7A: Silicon-carbon composite particles from porous carbon particles from inventive example 1 by reaction in a pressure reactor.

[0156] The reaction was carried out using an electrically heated autoclave consisting of a cylindrical bottom part (beaker) and a lid with a number of connections (for gas supply, gas removal, temperature measurement and pressure measurement, for example) having a volume of 594 ml. The stirrer used was a very close-clearance helical stirrer. The height of this stirrer corresponded to about 50% of the clear height of the reactor interior. The helical stirrer was constructed such that it allowed temperature measurement directly in the bed. The autoclave was charged with 10.0 g of the porous carbon from inventive example 1 (specific surface area = 2010 m.sup.2/g, Gurvich pore volume = 0.95 cm.sup.3/g, pH = 10.7) and closed. The autoclave was first evacuated. Then SiH.sub.4 (15.6 g) was injected with a pressure of 15.1 bar. Thereafter the autoclave was heated over 90 minutes to a temperature of 425° C., the temperature being held for 240 minutes. In the course of the reaction, the pressure rose to 76 bar. Over the course of 12 hours, the autoclave cooled down to room temperature (21° C.). After cooling a pressure of 35 bar remained in the autoclave. The pressure in the autoclave was reduced to 1 bar and it was then flushed five times with nitrogen, five times with lean air having an oxygen fraction of 5%, five times with lean air having an oxygen fraction of 10%, and subsequently five times with air. An amount of 21.3 g of silicon-carbon composite particles was isolated in the form of a fine black solid.

[0157] The reaction conditions for producing the silicon-carbon composite particles, and the physical properties of said particles, are summarized in Table 2 below.

TABLE-US-00002 Temperature [°C] Reaction time [h] BET surface area [m.sup.2/g] Silicon content [wt%] Metal ion concentration [% / ion] pH Comp. example 1A* 410 4.9 10 57 < 0.0010 / Na 0.0053 / K 6.0 Comp. example 1B* 380 10.2 27 57 0.0037 / Na < 0.0025 / K 6.1 Inventive example 1A 380 4.6 35 49 0.53 / Na 9.7 Inventive example 2A 380 8.5 26 54 0.25 / Na 9.3 Inventive example 3A 380 5.4 74 52 0.55 / Na 10.1 Inventive example 4A 380 5.7 58 50 0.5 / Na 9.8 Inventive example 5A 380 7.1 32 51 0.16 / Li 9.8 Inventive example 6A 380 8.0 31 54 0.86 / K 9.6 Inventive example 7A n.a. n.a. 15 55 0.55 / Na 9.5 *not inventive

[0158] The data for the production of the silicon-carbon composite particles of the invention clearly indicate that the infiltration of silicon when employing the process of the invention for production from porous carbon particles having an alkali metal concentration > 0.05 wt% and a pH of greater than 7.5, advantageously, takes place much faster.

Evaluation of the Silicon-Carbon Composite Particles in Electrochemical Cells

[0159] Inventive example 8: Anode comprising silicon-carbon composite particles of the invention from inventive example 1A and electrochemical testing in a lithium-ion battery.

[0160] 29.71 g of polyacrylic acid (dried to constant weight at 85° C.; Sigma-Aldrich, Mw ~450 000 g/mol) and 756.60 g of deionized water were agitated by means of shaker (2901 /min) for 2.5 h until the polyacrylic acid was fully dissolved. Added in portions to the solution was lithium hydroxide monohydrate (Sigma-Aldrich) until the pH was 7.0 (measured using WTW pH 340i pH meter and SenTix RJD probe). The solution was subsequently mixed together by shaker for a further 4 h. 3.87 g of the neutralized polyacrylic acid solution and 0.96 g of graphite (Imerys, KS6L C) were introduced into a 50 ml vessel and combined in a planetary mixer (SpeedMixer, DAC 150 SP) at 2000 rpm. Then 3.40 g of the silicon-carbon composite particles of the invention from inventive example 1A were stirred in at 2000 rpm for 1 min. Next 1.21 g of an 8 percent conductive carbon black dispersion and 0.8 g of deionized water were added and were incorporated on the planetary mixer at 2000 rpm. This was followed by dispersion in a dissolver at 3000 rpm for 30 minutes at a constant 20° C. The ink was subsequently degassed again in the planetary mixer at 2500 rpm for 5 min under reduced pressure.

[0161] The completed dispersion was then applied using a film-drawing frame with a 0.1 mm gap height (Erichsen, model 360) to a copper foil with a thickness of 0.03 mm (Schlenk Metallfolien, SE-Cu58). The anode coating produced in this way was subsequently dried for 60 min at 60° C. and air pressure 1 bar. The mean weight per unit area of the dry anode coating was 2.2 mg/cm.sup.2 and the coating density was 0.8 g/cm.sup.3.

[0162] The electrochemical studies were carried out on a button cell (CR2032 type, Hohsen Corp.) in a two-electrode arrangement. The electrode coating was used as counterelectrode or negative electrode (Dm = 15 mm), a coating based on lithium nickel manganese cobalt oxide 6:2:2 with a content of 94.0% and a mean weight per unit area of 15.9 mg/cm.sup.2 (sourced from the company SEI) was used as working electrode or positive electrode (Dm = 15 mm). A glass fiber filter paper (Whatman, GD Type D) soaked with 60 .Math.l of electrolyte served as the separator (Dm = 16 mm). The electrolyte used consisted of a 1.0-molar solution of lithium hexafluorophosphate in a 1:4 (v/v) mixture of fluoroethylene carbonate and diethyl carbonate. The cell was constructed in a glovebox (< 1 ppm H.sub.2O, O.sub.2); the water content in the dry mass of all the components used was below 20 ppm.

[0163] The electrochemical testing was carried out at 22° C. The cell was charged by the cc/cv (constant current / constant voltage) method with a constant current of 15 mA/g (corresponding to C/10) in the first cycle and of 75 mA/g (corresponding to C/2) in the subsequent cycles, and, on attainment of the voltage limit of 4.2 V, at constant voltage until the current went below 1.5 mA/g (corresponding to C/100) or 3 mA/g (corresponding to C/50). The cell was discharged by the cc (constant current) method with a constant current of 15 mA/g (corresponding to C/10) in the first cycle and of 75 mA/g (corresponding to C/2) in the subsequent cycles, until the voltage limit of 2.5 V was attained. The specific current chosen was based on the weight of the coating of the positive electrode. The electrodes were selected such as to establish a cathode:anode capacity ratio of 1:1.2.

[0164] Inventive example 9: Anode comprising silicon-carbon composite particles of the invention from inventive example 5A, and electrochemical testing in a lithium-ion battery.

[0165] The silicon-containing material of the invention from inventive example 5A was used to produce an anode as described in inventive example 8. As described in inventive example 8, the anode was built up to a lithium-ion battery and subjected to the same testing procedure.

[0166] Inventive example 10: Anode comprising silicon-carbon composite particles of the invention from inventive example 6A, and electrochemical testing in a lithium-ion battery.

[0167] The silicon-containing material of the invention from inventive example 6A was used to produce an anode as described in inventive example 8. As described in inventive example 8, the anode was built up to a lithium-ion battery and subjected to the same testing procedure.

[0168] Comparative example 11: Anode comprising silicon-carbon composite particles of the invention from inventive example 6A, and electrochemical testing in a lithium-ion battery. The noninventive silicon-containing material from comparative example 1A was used to produce an anode as described in inventive example 8. As described in inventive example 8, the anode was built up to a lithium-ion battery and subjected to the same testing procedure.

[0169] The results from the electrochemical evaluations are summarized in Table 3 below.

TABLE-US-00003 Rev. capacity in the second cycles [mAh/g] Cycle with 80% capacity retention Inventive example 8 1000 759 Inventive example 9 1200 546 Inventive example 10 1200 775 Comparative example 11* 1250 224 *not inventive

[0170] It is clearly apparent that significantly higher cycling stabilities can be achieved by means of the silicon-carbon composite particles of the invention than with conventional silicon-carbon composite particles.