SILICON SUBHALIDE-CONTAINING COMPOSITE PARTICLES

Abstract

Silicon subhalide-containing composite particles along with processes for producing and uses for the same. Where the silicon subhalide-containing composite particles have a Si content >30% by weight. Wherein the silicon is placed in and on the pores of a porous matrix. The silicon subhalide-containing composite particles include a halogen concentration of 0.0003 to 16% by weight, a pH of 3 to 9, a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 to 20 m, and a specific BET surface area of at most 170 m.sup.2/g.

Claims

1-14. (canceled)

15. Silicon subhalide-containing composite particles, comprising: a Si content >30% by weight; wherein the silicon is placed in and on the pores of a porous matrix; a halogen concentration of 0.0003 to 16% by weight; a pH of 3 to 9; a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 to 20 m; and a specific BET surface area of at most 170 m.sup.2/g.

16. The composite particles of claim 15, wherein the halogen is chlorine and a Cl concentration of 0.0003 to 16% by weight.

17. The composite particles of claim 15, wherein the silicon is at least partially present in a form of silicon subchloride SiCl.sub.x, wherein x=0.00001-0.15.

18. The composite particles of claim 15, wherein the silicon subhalide-containing composite particles comprise at least 30% by weight of silicon obtained by silicon infiltration.

19. The composite particles of claim 15, wherein the composite particles are an anode material for a lithium-ion battery.

20. The composite particles of claim 19, wherein a current collector is coated with the anode material.

21. A process for producing the composite particles, comprising: silicon infiltration from silicon precursors selected from halogen-containing and halogen-free silicon precursors that are gaseous and/or liquid at 20 C. and 1013 mbar, wherein at least one halogen-containing silicon precursor is present, in the presence of porous particles having, (a) a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 to 20 m , (b) a total pore volume (Gurvich pore volume) of micropores and mesopores determined by N.sub.2 sorption in the range 0.4-2.2 cm.sup.3/g, and (c) a PD50 pore diameter determined by N.sub.2 sorption of not more than 30 nm.

22. The process of claim 21, wherein the composite particles are silicon subhalide-containing composite particles.

23. The process of claim 22, wherein silicon subhalide-containing composite particles have a Si content >30% by weight; wherein the silicon is placed in and on the pores of a porous matrix; a halogen concentration of 0.0003 to 16% by weight; a pH of 3 to 9; a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 to 20 m; and a specific BET surface area of at most 170 m.sup.2/g.

24. The process of claim 21, wherein the silicon infiltration is carried out in a reactor selected from fluidized bed reactors, rotary kilns arranged in a horizontal to vertical position, open or closed fixed-bed reactors and pressure reactors.

25. The process of claim 21, wherein silicon infiltration is performed at 280 C. to 900 C.

26. The process of claim 21, wherein the composite particles are produced by silicon infiltration from silanes selected from monosilane and chlorine-containing silanes, wherein at least one chlorine-containing silane is employed.

27. The process of claim 21, wherein reactive components free from silicon are also present in admixture or alternately with the silicon precursors.

28. A lithium-ion battery, comprising: at least one anode containing silicon subhalide-containing composite particles; and wherein the silicon subhalide-containing composite particles comprise a Si content >30% by weight, wherein the silicon is placed in and on the pores of a porous matrix, a halogen concentration of 0.0003 to 16% by weight, a pH of 3 to 9, a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 to 20 m , and a specific BET surface area of at most 170 m.sup.2/g.

29. The lithium-ion battery of claim 28, wherein the halogen is chlorine and a Cl concentration of 0.0003 to 16% by weight.

30. The lithium-ion battery of claim 28, wherein the silicon is at least partially present in a form of silicon subchloride SiCl.sub.x, wherein x=0.00001-0.15.

31. The lithium-ion battery of claim 28, wherein the silicon subhalide-containing composite particles comprise at least 30% by weight of silicon obtained by silicon infiltration.

Description

EXAMPLES

[0137] pH is determined according to ASTM Standard number D1512, Method A.

Scanning Electron Microscopy (SEM/EDX):

[0138] The microscope analyses were carried out using a Zeiss Ultra 55 scanning electron microscope and an energy-dispersive Oxford X-Max 80N x-ray spectrometer. Before analysis, the samples underwent vapor deposition of carbon, using a Safematic Compact Coating Unit 010/HV, to prevent charging phenomena. Cross sections of the silicon-containing materials were produced with a Leica TIC 3X ion cutter at 6 kV.

Inorganic/Elemental Analysis:

[0139] The C contents were determined using a Leco CS 230 analyzer and a Leco TCH-600 analyzer was used to determine oxygen and nitrogen contents. The qualitative and quantitative determination of other elements, especially the determination of the alkali or alkaline earth metals, was carried out by ICP (inductively coupled plasma) emission spectrometry (Optima 7300 DV, Perkin Elmer). To this end the samples were subjected to acid digestion (HF/HNO.sub.3) in a microwave (Microwave 3000, Anton Paar). The ICP-OES determination is guided by 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 used for analysis of acidic aqueous solutions (for example acidified drinking water, wastewater and other water samples, aqua regia extracts of soils and sediments).

X-ray Fluorescence Analysis:

[0140] The chlorine content was determined by X-ray fluorescence analysis on a Bruker AXS SB Tiger 1 with a rhodium anode.

[0141] To this end, 5.00 g of the sample were mixed with 1.00 g of Boreox and 2 droplets of ethanol and pressed into tablets in an HP 40 tablet press from Herzog for 15 seconds at a pressure of 150 kN.

Particle Size Determination:

[0142] The particle size distribution was determined in accordance with ISO 13320 by static laser scattering using a Horiba LA 950. In the preparation of the samples particular care must be taken when dispersing the particles in the measurement solution to ensure it is not the size of agglomerates that is measured, but of the individual particles. For the materials examined here, these were dispersed in ethanol. To this end, the dispersion was treated with 250 W ultrasound in a Hielscher UIS250v ultrasound laboratory instrument with LS24d5 sonotrode for 4 minutes prior to measurement if required.

BET Surface Area Measurement:

[0143] The specific surface area of the materials was measured by gas sorption with nitrogen using a Sorptomatic 199090 instrument (Porotec) or BELSorp MAX II instrument (Microtrac) or SA-9603MP instrument (Horiba) by the BET method (determination according to DIN ISO 9277:2003-05 using nitrogen).

Skeletal Density:

[0144] The skeletal density, i.e, the density of the porous solid based on the volume of only the pore spaces accessible to gas from the outside, was determined by helium pycnometry in accordance with DIN 66137-2.

Gas-Accessible Pore Volume (Gurvich Pore Volume):

[0145] Gurvich gas-accessible pore volume was determined by gas sorption measurements with nitrogen according to DIN 66134.

PD50 Pore Diameter:

[0146] The PD50 pore diameter was calculated as a volumetric average pore diameter, based on the total volume of the micropores defined by the Horvath-Kawazoe method according to DIN 66135 and mesopores defined by the BJH method according to DIN 66134.

[0147] The following examples 1-6 and comparative example 1 describe the production and properties of the porous carbon particles used for the production of the silicon-carbon according to the invention.

Production of Silicon Composite Particles

Comparative Example 1A (Noninventive): Silicon-Carbon Composite Particles From Porous Carbon Particles

[0148] An electrically heated autoclave consisting of a cylindrical lower part (cup) and a lid with a plurality of connections (for example for the gas inflow, gas outflow, temperature and pressure measurement) having a volume of 5.3 L was used for the reaction. The stirrer employed was a virtually close-clearance helical stirrer. This had a height corresponding to about 50% of the clearance height of the reactor interior. The helical stirrer had a design such that it allowed temperature measurement directly in the bed. The autoclave was charged with 342.5 g of the porous carbon (spec. surface area=1617 m.sup.2/g, Gurvich pore volume=0.80 cm.sup.3/g) and sealed. The autoclave was initially evacuated. It was subsequently pressurized to a pressure of 16.0 bar with SiH.sub.4 (70 g) at 350 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (59 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (57 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (55 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (54 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (52 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 16.0 bar with SiH.sub.4 (51 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The pressure was then reduced to 1.5 bar and the autoclave was pressurized to a pressure of 10.0 bar with SiH.sub.4 (29 g) at a temperature of 370 C. The autoclave was then heated to a temperature of 420 C. within 20 minutes and the temperature was maintained for 60 minutes. The autoclave was then cooled to a temperature of 100 C. before purging five times with nitrogen, five times with lean air having an oxygen content of 5%, five times with lean air having an oxygen content of 10% and then five times with air.

[0149] The pressure in the autoclave was reduced to 1 bar before purging three times with nitrogen. An amount of 651 g of silicon-carbon composite particles in the form of a black, fine solid were isolated under an Ar atmosphere.

Comparative example 1B (Noninventive): Silicon-Subchloride-Containing Composite Particles From Porous Carbon Particles

[0150] A tubular reactor was charged with 3.0 g of the porous carbon particles (spec. surface area=2140 m.sup.2/g, Gurvich pore volume=1.01 cm.sup.3/g, pH=5.4) in a quartz glass boat. After inertization with nitrogen, the reactor was heated to 450 C. Upon reaching the reaction temperature the reactive gas (mixture of 20 g/h of trichlorosilane (liquid) and 10 NL/h of Ar) was passed through the reactor for 24 h. The reactor was then purged with inert gas and cooled to room temperature and the product was withdrawn.

Example 1: Silicon-Subchloride-Containing Composite Particles from Porous Carbon Particles

[0151] A tubular reactor was charged with 3.0 g of the porous carbon particles (spec. surface area=2140 m.sup.2/g, Gurvich pore volume=1.01 cm.sup.3/g, pH=5.4) in a quartz glass boat. After inertization with nitrogen, the reactor was heated to 450 C. Upon reaching the reaction temperature the reactive gas (mixture of 20 g/h of trichlorosilane (liquid) and 10 NL/h of Ar) was passed through the reactor for 24 h. The reactor was then purged with inert gas and cooled to room temperature and the product was withdrawn. The product was then suspended in the water at 20 C. (30 ml water/1 g product), stirred for 10 minutes and filtered off in a Buchner funnel while measuring the pH. The whole procedure was repeated until the pH of the washing water was >3 (generally 3-5 times).

Example 2: Silicon-Carbon Composite Particles From Porous Carbon Particles

[0152] A tubular reactor was charged with 3.0 g of the porous carbon particles (spec. surface area=2140 m.sup.2/g, Gurvich pore volume=1.01 cm.sup.3/g, pH=5.4) in a quartz glass boat. After inertization with nitrogen, the reactor was heated to 415 C. Upon attaining the reaction temperature the reactive gas (mixture of 5 NL/h of dichlorosilane and 10 NL/h of Ar) was passed through the reactor for 15 h. The reactor was then purged with inert gas and cooled to room temperature and the product was withdrawn. The product was then suspended in water at 20 C. (30 ml water/1 g product), treated for 1 h in an ultrasonic bath at 80 C. and filtered off in a Buchner funnel while measuring the pH. The whole procedure was repeated until the pH of the washing water was >3.

Example 3: Silicon-Carbon Composite Particles From Porous Carbon Particles

[0153] A tubular reactor was charged with 3.0 g of the porous carbon particles (spec. surface area=2140 m.sup.2/g, Gurvich pore volume=1.01 cm.sup.3/g, pH=5.4) in a quartz glass boat. After inertization with nitrogen, the reactor was heated to 380 C. Upon attaining the reaction temperature the reactive gas 1 (mixture of 33 g/h of trichlorosilane (liquid) and 10 NL/h of Ar) was passed through the reactor for 8 h. Subsequently, the reactive gas 2 (10% SiH.sub.4 in N.sub.2, 10 NL/h) was passed through the reactor for 9 h. The reactor was then purged with inert gas and cooled to 20 C. and the product was withdrawn.

Example 4: Silicon-Carbon Composite Particles From Porous Carbon Particles

[0154] A tubular reactor was charged with 3.0 g of the porous carbon particles (spec. surface area=2140 m.sup.2/g, Gurvich pore volume=1.01 cm.sup.3/g, pH=5.4) in a quartz glass boat. After inertization with nitrogen, the reactor was heated to 380 C. Upon attaining the reaction temperature the reactive gas 1 (mixture of 5 NL/h of dichlorosilane and 10 NL/h of Ar) was passed through the reactor for 15 h. The reactor was then heated to 400 C. Upon attaining the reaction temperature the reactive gas 2 (10% SiH.sub.4 in N.sub.2, 10 NL/h) was passed through the reactor for 7.6 h. The reactor was then purged with inert gas and cooled to room temperature and the product was withdrawn.

Example 5: Silicon-Carbon Composite Particles From Porous Carbon Particles by Reaction in a Pressure Reactor

[0155] An electrically heated autoclave consisting of a cylindrical lower part (cup) and a lid with a plurality of connections (for example for the gas inflow, gas outflow, temperature and pressure measurement) having a volume of 594 ml was used for the reaction. The stirrer employed was a virtually close-clearance helical stirrer. This had a height corresponding to about 50% of the clearance height of the reactor interior. The helical stirrer had a design such that it allowed temperature measurement directly in the bed. The autoclave was charged with 10.0 g of the porous carbon (spec. surface area=2010 m.sup.2/g, Gurvich pore volume=0.95 cm.sup.3/g) and sealed. The autoclave was initially evacuated. It was subsequently pressurized to a pressure of 15.1 bar with DCS (1 g) and SiH.sub.4 (15 g). The autoclave was then heated to a temperature of 420 C. within 90 minutes and the temperature was maintained for 210 minutes. The pressure increased to 74 bar over the course of the reaction. The autoclave cooled to room temperature (20 C.) within 12 hours. An autoclave pressure of 33.5 bar remained after cooling. The pressure in the autoclave was reduced to 1 bar before purging three times with nitrogen. An amount of 20.8 g of silicon-carbon composite particles in the form of a black, fine solid were isolated under an Ar atmosphere. After exchanging the Ar atmosphere for air the product was suspended in water (30 ml/1 g product), treated for 1 h in an ultrasonic bath at 80 C. and filtered off in a Bchner funnel while measuring pH. The whole procedure was repeated until the pH of the washing water was >3.

[0156] The reaction conditions for production and the material properties of the silicon-carbon composite particles are summarized in the following table 2.

TABLE-US-00001 TABLE 1 BET temper- surface ature area Si content CI content O content. H content. N content CVI precursor [ C.] [m.sup.2/g] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] pH Comparative Monosilane 430 39 52 0 2.6 0.80 0.64 5.9 Example 1A* Comparative Trichlorsilane 450 122 42.0 8.0 13.5 0.47 0.83 1.6 Example 1B* Example 1 Trichlorsilane 450 156 42.4 7.7 12.1 0.92 0.43 3.1 Example 2 Dichlorsilane 415 29 45.2 3.9 1.6 0.75 0.97 3.9 Example 3 Trichlorsilane + 380.380 27 50.0 0.68 15.6 1.22 0.95 4.5 Monosilane Example 4 Dichlorsilane + 380.400 14.5 48 1.1 17.0 1.08 0.64 3.5 Monosilan Example 5 Dichlorsilane + 420 45 57 0.2 3.4 0.85 1.21 4.5 Monosilane mixed (parallel) *noninventive

[0157] Identical material characteristics are obtainable irrespective of the employed silicon precursors.

Evaluation of the Silicon-Carbon Composite Particles in Electrochemical Cells

[0158] Comparative example 7: Anode containing noninventive silicon-carbon composite particles from comparative example 1A and electrochemical testing in a lithium-ion battery.

[0159] 29.71 g of polyacrylic acid (dried to constant weight at 85 C.; Sigma-Aldrich, Mw450 000 g/mol) and 756.60 g of deionized water were agitated using a shaker (290 rpm) for 2.5 h until complete dissolution of the polyacrylic acid. Lithium hydroxide monohydrate (Sigma-Aldrich) was added to the solution a little at a time until the pH was 7.0 (measured using WTW pH 340i PH meter and SenTix RJD probe). The solution was then mixed 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 initially charged in a 50 ml vessel and blended at 2000 rpm in a planetary mixer (SpeedMixer, DAC 150 SP). Subsequently 3.40 g of the silicon-carbon composite particles according to the invention from example 1A were stirred at 2000 rpm for 1 min. 1.21 g of an 8 percent conductive carbon black dispersion and 0.8 g of deionized water were then added and incorporated at 2000 rpm using the planetary mixer. This was followed by dispersion using the dissolver for 30 min at 3000 rpm at a constant 20 C. Degassing of the ink was again carried out using the planetary mixer at 2500 rpm for 5 minutes under vacuum.

[0160] The finished dispersion was then applied to a copper foil having a thickness of 0.03 mm (Schlenk Metallfolien, SE-Cu58) using a film-drawing frame with a gap clearance of 0.1 mm (Erichsen, model 360). The anode coating thus produced was then dried at 60 C. and 1 bar of air pressure for 60 min. The average basis weight of the dry anode coating was 2.2 mg/cm.sup.2 and the coating density 0.9 g/cm.sup.3.

[0161] The electrochemical studies were carried out using a button cell (CR2032 type, Hohsen Corp.) in a 2-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 having a content of 94.0% and average basis weight of 15.9 mg/cm.sup.2 (obtained from SEI) was used as the working electrode or positive electrode (Dm=15 mm). A glass fiber filter paper (Pall, GF type A/E) soaked with 60 l of electrolyte was used as the separator (Dm=16 mm). The employed electrolyte was composed of a 1.0 molar solution of lithium hexafluorophosphate in a 1:4 (v/v) mixture of fluoroethylene carbonate and diethyl carbonate. The construction of the cell was carried out in a glovebox (<1 ppm H.sub.2O, O.sub.2) and the water content in the dry matter of all employed components was below 20 ppm.

[0162] Electrochemical testing was carried out at 22 C. The cell was charged by the cc/cv method (constant current/constant voltage) 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 a current fell below 1.5 mA/g (corresponding to C/100) or 3 mA/g (corresponding to C/50). The cell was discharged by the cc method (constant current) 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 attainment of the voltage limit of 2.5 V. The specific current chosen was based on the weight of the coating of the positive electrode. The electrodes were selected in such a way that a capacitance ratio of cathode: anode=1:1.2 was established.

[0163] Comparative example 8: Anode containing noninventive silicon-carbon composite particles from comparative example 1B and electrochemical testing in a lithium-ion battery.

[0164] The noninventive silicon-containing material from comparative example 1B was used to produce an anode as described in comparative example 7. The anode was installed in a lithium-ion battery as described in comparative example 7 and subjected to testing by the same procedure.

[0165] Comparative example 9: Anode containing noninventive silicon-carbon composite particles from comparative example 1C and electrochemical testing in a lithium-ion battery.

[0166] Noninventive silicon-carbon composite particles from comparative example 1C were used to produce an anode as described in comparative example 7. The anode was installed in a lithium-ion battery as described in comparative example 7 and subjected to testing by the same procedure.

[0167] Example 10: Anode Containing Silicon-Carbon Composite Particles From Example 3 and Electrochemical Testing in a Lithium-Ion Battery

[0168] The silicon-containing material according to the invention from example 3 was used to produce an anode as described in comparative example 7. The anode was installed in a lithium-ion battery as described in comparative example 7 and subjected to testing by the same procedure.

[0169] The results from the electrochemical evaluations are summarized in table 3 which follows.

[0170] Example 11: Anode Containing Silicon-Carbon Composite Particles From Example 1 and Electrochemical Testing in a Lithium-Ion Battery

[0171] The silicon-containing material according to the invention from example 1 was used to produce an anode as described in comparative example 7. The anode was installed in a lithium-ion battery as described in comparative example 7 and subjected to testing by the same procedure.

[0172] The results from the electrochemical evaluations are summarized in table 3 which follows.

TABLE-US-00002 TABLE 2 Rev. capacity in second Cycle with 80% cycle [mAh/g] capacity retention Comparative 916 346 example 7* Comparative 365 125 example 8* Example 10 892 419 Example 11 648 217 (from Ex. 1) *noninventive

[0173] The comparison between comparative example 7 and example 10 according to the invention reveals that the presence of a chlorine content in the material does not show any adverse effects on the electrochemical performance. The comparison between comparative example 8 and example 11 according to the invention reveals that an excessively low pH has an adverse effect on the electrochemical performance in the battery, whereas adapting the pH stabilizes the performance.