SILICON PARTICLES HAVING A SPECIFIC CHLORINE CONTENT, AS ACTIVE ANODE MATERIAL FOR LITHIUM ION BATTERIES

Abstract

An anode active material for lithium ion batteries includes one or more unaggregated silicon particles having a mass-based chlorine content of from 5 to 200 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of from 0.5 μm to 10.0 μm.

Claims

1-14. (canceled)

15. An anode active material for lithium ion batteries, comprising one or more unaggregated silicon particles having a mass-based chlorine content of from 5 to 200 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of from 0.5 μm to 10.0 μm.

16. The anode active material for lithium ion batteries as claimed in claim 1, wherein ≥50% by weight of the silicon particles have, based on the total weight of the silicon particles, a mass-based chlorine content of from 5 to 200 ppm.

17. The anode active material for lithium ion batteries as claimed in claim 1, wherein the silicon particles are polycrystalline and have crystalline sizes of from 5 to 200 nm.

18. The anode active material for lithium ion batteries as claimed in claim 1, wherein the silicon particles are obtainable by 1) pyrolysis of a reaction gas comprising trichlorosilane and/or dichlorosilane in a fluidized-bed reactor at deposition temperatures of from 600° C. to 1000° C. to form granular silicon and subsequent 2) milling of the granular silicon from step 1) to form the silicon particles.

19. The anode active material for lithium ion batteries as claimed in claim 18, wherein step 1) is carried out in a fluidized-bed reactor.

20. The anode active material for lithium ion batteries as claimed in claim 18, wherein the reaction gas does not contain any monosilane (SiH.sub.4).

21. The anode active material for lithium ion batteries as claimed in claim 18, wherein the proportion of dichlorosilane and/or trichlorosilane in the reaction gas is from 50 to 100% by weight, based on the total weight of the silanes.

22. The anode active material for lithium ion batteries as claimed in claim 18, wherein the proportion of monochlorosilane in the reaction gas is from 0 to 50% by weight, based on the total weight of the silanes.

23. The anode active material for lithium ion batteries as claimed in claim 18, wherein the granular silicon is produced by deposition of a reaction gas on seed crystals composed of silicon in a fluidized bed.

24. The anode active material for lithium ion batteries as claimed in claim 18, wherein the pyrolysis is carried out at a temperature of the fluidized bed in the reaction region of from 700° C. to 1000° C.

25. An anode for lithium ion batteries which contains one or more anode active materials as claimed in claim 1.

26. A lithium ion battery comprising a cathode, an anode, a separator and an electrolyte, wherein the anode contains one or more anode active materials as claimed in claim 1.

27. The lithium ion battery as claimed in claim 26, wherein the anode is only partially lithiated in the fully charged lithium ion battery.

28. The lithium ion battery as claimed in claim 27, wherein the ratio of lithium atoms to silicon atoms in the anode material is ≤3.5 in the fully charged state of the lithium ion battery.

Description

EXAMPLE 1

(Ex.1): Production of Silicon Particles

[0089] A fluidized-bed reactor was operated using a trichlorosilane mass flow of 710 kg/h, a hydrogen flow of 445 standard m.sup.3/h, a fluidized bed temperature of 960° C. and a reactor pressure of 2.5 bar.

[0090] The granular silicon obtained in this way was subsequently comminuted by milling a fluidized-bed jet mill (Netzsch-Condux CGS16, using 90 m.sup.3/h of nitrogen at 7 bar as milling gas). The silicon particles obtained in this way had the following particle size distribution: d10=2.4 μm, d50=4.5 μm and d90=7.2 μm.

[0091] Further properties of the silicon particles are summarized in table 1.

[0092] The scanning electron micrograph of the dry silicon particles in FIG. 1 shows that silicon was present in the form of individual, unaggregated, splinter-shaped particles.

EXAMPLES 2-4

(Ex.2-4): Production of Silicon Particles

[0093] Analogous to example 1, with the difference that the deposition temperature was varied as indicated in table 2.

[0094] The properties of the silicon particles obtained in this way are summarized in table 1.

EXAMPLES 5-8

Ex.5-8

[0095] Electrodes comprising silicon particles from examples 1-4:

[0096] 29.709 g of polyacrylic acid (Sigma-Aldrich, Mw 450.000 g/mol) dried to constant weight at 85° C. and 751.60 g of deionized water were agitated by means of a shaker (290 l/min) for 2.5 hours until the polyacrylic acid had completely dissolved. Lithium hydroxide monohydrate (Sigma-Aldrich) was added a little at a time to the solution until the pH was 7.0 (measured using pH meter WTW pH 340i and SenTix RJD electrode). The solution was subsequently mixed for a further 4 hours by means of the shaker.

[0097] 7.00 g of the silicon particles of the respective example 1-4 were then dispersed in 12.50 g of the neutralized polyacrylic acid solution (concentration 4% by weight) and 5.10 g of deionized water by means of a high-speed mixer at a circumferential velocity of 4.5 m/s for 5 minutes and at 12 m/s for 30 minutes while cooling at 20° C. After addition of 2.50 g of graphite (Imerys, KS6L C), stirring was continued at a circumferential velocity of 12 m/s for a further 30 minutes. After degassing, the dispersion was applied by means of a film drawing frame having a gap height of 0.10 mm (Erichsen, model 360) to a copper foil having a thickness of 0.030 mm (Schlenk Metallfolien, SE-Cu58).

[0098] The anode coating produced in this way was subsequently dried for 60 minutes at 80° C. and 1 bar atmospheric pressure.

[0099] The anode coating which had been dried in this way had an average weight per unit area of 2.90 mg/cm.sup.2 and a layer thickness of 32 μm.

[0100] FIG. 2: Scanning electron micrograph of the FIB section of the electrode coating with the silicon particles from example 1 (silicon particles identifiable by the light-grey color).

EXAMPLES 9-12

Ex.9-12

[0101] Testing of the electrodes from examples 5-8:

[0102] The electrochemical studies were carried out on a button cell (type CR2032, Hohsen Corp.) in a two-electrode arrangement. The electrodes from examples 5-8 were used as counterelectrode or negative electrode (Dm=15 mm), and a coating based on lithium-nickel-manganese-cobalt oxide 1:1:1 having a content of 94.0% and an average weight per unit area of 14.5 mg/cm.sup.2 was used as working electrode or positive electrode (Dm=15 mm). A glass fiber filter paper (Whatman, GD Type D) impregnated with 120 μl of electrolyte served as separator (Dm=16 mm). The electrolyte used consisted of a one molar solution of lithium hexafluorophosphate in a 3:7 (v/v) mixture of fluoroethylene carbonate and ethyl methyl carbonate which had been admixed with 2% by weight of vinylene carbonate. The construction of the cell was carried out in a Glove box (<1 ppm H.sub.2O, O.sub.2), and the water content in the dry mass of all components used was below 20 ppm.

[0103] The electrochemical testing was carried out at 20° C. The charging of the cell was carried out by the cc/cv method (constant current/constant voltage) with a constant current of 5 mA/g (corresponds to C/25) in the first cycle and of 60 mA/g (corresponds to C/2) in the subsequent cycles and after reaching the voltage limit of 4.2 V at a constant voltage until the current had gone below C/100 or C/8. Discharging of the cell was carried out by the cc method (constant current) using a constant current of 5 mA/g (corresponds to C/25) in the first cycle and of 60 mA/g (corresponds to C/2) in the subsequent cycles until the voltage limit of 3.0 V had been attained. The specific current selected was based on the weight of the coating of the positive electrode.

[0104] The results of electrochemical testing are summarized in table 2.

COMPARATIVE EXAMPLE 13

CEx.13

[0105] Production of silicon particles by the Siemens process:

[0106] A reaction gas consisting of 33 mol % of trichlorosilane in hydrogen was fed into a bell-shaped reactor (“Siemens” reactor) into which thin rods had been introduced as target substrate. At a temperature of 1070° C., silicon was deposited from a trichlorosilane stream of 108 kg/h/m.sup.2 of thin rod surface area and 36 standard m.sup.3 of H.sub.2/h/m.sup.2 of thin rod surface area.

[0107] The silicon obtained in this way was firstly broken up manually and subsequently precomminuted by means of roller crushers, before subsequently being comminuted in a manner analogous to examples 1-4 by dry milling to a size of d50=4.6 μm.

[0108] The properties of the silicon particles obtained in this way are recorded in table 1.

COMPARATIVE EXAMPLE 14

CEx.14

[0109] Production of silicon particles by the FBR from monosilane:

[0110] In a fluidized-bed reactor, a monosilane mass flow of 22.7 kg/h, a hydrogen flow of 110 standard m.sup.3/h, a fluidized bed temperature of 640° C. and a reactor pressure of 2.5 bar were set. The granular silicon obtained in this way was subsequently comminuted by milling in a fluidized-bed jet mill (Netzsch-Condux CGS16, using 90 m.sup.3/h of nitrogen at 7 bar as milling gas).

[0111] The silicon particles obtained in this way had the following particle size distribution: d10=2.6 μm, d50=4.8 μm and d90=7.9 μm and a breadth (d90-d10) of 5.3 μm.

[0112] The properties of the silicon particles obtained in this way are summarized in table 1.

[0113] As can be seen from table 1, the silicon particles according to the invention of examples 1-4 have, at 18-85 ppm, a significantly higher proportion of chlorine than the comparative materials of comparative examples 13 and 14, the chlorine content of which is below the detection limit.

TABLE-US-00001 TABLE 1 Properties of the silicon particles: Deposition Chlorine BET surface Particle size temperature content area d.sub.10/d.sub.50/d.sub.90 [° C.] [ppm] [m.sup.2/g] [μm] Ex. 1 960 33 2.8 2.4/4.5/7.2 Ex. 2 980 18 2.7 2.5/4.7/7.7 Ex. 3 965 42 2.5 2.8/4.8/7.6 Ex. 4 950 85 2.9 2.3/4.4/7.4 CEx. 13 1070 <5 2.5 2.4/4.6/7.6 CEx. 14 640 <5 2.4 2.6/4.8/7.9

COMPARATIVE EXAMPLE 15

[0114] Electrodes were produced in a manner analogous to example 5 with the difference that the silicon particles of comparative example 13 were used instead of the silicon particles of example 1.

COMPARATIVE EXAMPLE 16

[0115] Electrodes were produced in a manner analogous to example 5 with the difference that the silicon particles of comparative example 14 were used instead of the silicon particles of example 1.

COMPARATIVE EXAMPLE 17

[0116] The cell construction and the electrochemical testing were carried out in a manner analogous to example 9 with the difference that electrodes from comparative example 15 were used.

[0117] The electrochemical data are summarized in table 2.

COMPARATIVE EXAMPLE 18

[0118] The cell construction and the electrochemical testing were carried out in a manner analogous to example 9 with the difference that electrodes from comparative example 16 were used.

[0119] The electrochemical data are summarized in table 2.

TABLE-US-00002 TABLE 2 Electrochemical testing of (comparative) examples 9-12 and 17-18: Coulombic Initial discharging efficiency in capacity during Cycle with 80% formation [%] cycling [mAh/cm.sup.2] residual capacity Example 9 81.5 2.09 320 Example 10 81.3 2.16 291 Example 11 81.3 2.17 346 Example 12 81.2 2.18 302 Comparative 81.7 2.10 246 example 17 Comparative 82.1 2.09 279 example 18

[0120] The testing results in table 2 show that the chlorine-containing silicon particles of examples 1-4 give lithium ion batteries having significantly improved cycling stabilities compared to the chlorine-free silicon particles of comparative examples 13-14.