ANODE ACTIVE MATERIALS FOR LITHIUM-ION BATTERIES

Abstract

An anode active material for use within an anode of a lithium-ion battery along with a method or process for preparing the same. Where the anode active material includes one or more non-aggregated silicon particles having BET surface areas of 0.2 to 10.0 m.sup.2/g (determination according to DIN 66131 (with nitrogen), a chloride content of 220 to 5000 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 μm to 10.0 μm.

Claims

1-14.-(canceled)

15. An anode active material for lithium-ion batteries, comprising: wherein the anode active material contains one or more non-aggregated silicon particles having BET surface areas of 0.2 to 10.0 m.sup.2/g (determination according to DIN 66131 (with nitrogen), a chloride content of 220 to 5000 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 μm to 10.0 μm.

16. The anode active material of claim 15, wherein ≥50% by weight of the silicon particles based on the total weight of the silicon particles have a chloride content of 220 to 5000 ppm.

17. The anode active material of claim 15, wherein the silicon particles are polycrystalline and have crystallite sizes of <20 nm.

18. A process for producing anode active materials for lithium-ion batteries, comprising the steps of: (1) providing a reaction gas consisting to an extent of 11 to 19 mol % of silanes is subjected to a pyrolysis at 600° C. to 910° C. in a fluidized bed reactor to form granular silicon, wherein the silanes comprise dichlorosilane and/or monochlorosilane, and subsequently; and (2) obtaining the granular silicon from step (1) and milling it to form silicon particles.

19. The process of claim 18, wherein the proportion of dichlorosilane among the silanes in the reaction gas is 50% to 100% by weight based on the total weight of the silanes.

20. The process of claim 18, wherein the proportion of monosilane and/or trichlorosilane among the silanes in the reaction gas is ≤10% by weight based on the total weight of the silanes.

21. The process of claim 18, wherein the reaction gases contain exclusively dichlorosilane as the silanes.

22. The process of claim 18, wherein the reaction gas introduced in step (1) consists to an extent of 11 to 19 mol % of dichlorosilane.

23. The process of claim 18, wherein the reaction gas introduced in step (1) consists of dichlorosilane and hydrogen.

24. The process of claim 18, wherein an anode active materials is obtained.

25. An anode for lithium-ion batteries, comprising: wherein said lithium-ion batteries comprises one or more anode active materials; and wherein the anode active material contains one or more non-aggregated silicon particles having BET surface areas of 0.2 to 10.0 m.sup.2/g (determination according to DIN 66131 (with nitrogen), a chloride content of 220 to 5000 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 μm to 10.0 μm.

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; and wherein the one or more active materials contain one or more non-aggregated silicon particles having BET surface areas of 0.2 to 10.0 m.sup.2/g (determination according to DIN 66131 (with nitrogen), a chloride content of 220 to 5000 ppm and a volume-weighted particle size distribution having diameter percentiles d.sub.50 of 0.5 μm to 10.0 μm.

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

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

Description

Example 1 (Ex.1): Production of Silicon Particles

[0125] A fluidized bed reactor is operated with a dichlorosilane mass flow of 2261 kg/h per m.sup.2 of reactor cross-sectional area, a hydrogen flow of 2528 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area, a fluidized bed temperature of 775° C. and a reactor pressure of 3.0 barg.

[0126] The granular silicon obtained in this way was then comminuted by milling in a fluidized bed jet mill (Netzsch-Condux CGS16, with 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: d.sub.10=2.4 μm, d.sub.50=4.5 μm and d.sub.90=7.2 μm.

[0127] The BET surface area of the silicon particles was 2.9 [m2/g], the density 2.326 [g/cm3] and the compressive strength 235 [MPa]. The SEM micrograph of the dry silicon particles in FIG. 1 shows that the silicon was in the form of individual non-aggregated, shard-like particles.

[0128] Further properties of the silicon particles are summarized in table 1.

Example 2 (Ex.2): Production of Silicon Particles

[0129] Analogous to example 1 with the exceptions of altering the dichlorosilane amount to 1704 kg/h per m.sup.2 of reactor cross-sectional area, the hydrogen flow to 2675 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area and the deposition temperature to 900° C. as reported in Table 1.

[0130] The granular silicon obtained in this way was subsequently comminuted by milling as in example 1.

[0131] The silicon particles obtained in this way had the following particle size distribution: d10=2.5 μm, d50=4.7 μm and d90=7.7 μm. The BET surface area of the silicon particles was 3.0 [m2/g], the density 2.322 [g/cm3] and the compressive strength 280 [MPa]. Further properties of the silicon particles obtained in this way are summarized in table 1.

Comparative Example 3 (Comp. Ex. 3)

[0132] Production of Silicon Particles:

[0133] A fluidized bed reactor is operated with a trichlorosilane mass flow of 2269 kg/h per m.sup.2 of reactor cross-sectional area, a hydrogen flow of 1433 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area, a fluidized bed temperature of 960° C. and a reactor pressure of 2.5 bar.

[0134] The granular silicon obtained in this way was then comminuted by milling in a fluidized bed jet mill (Netzsch-Condux CGS16, with 90 m.sup.3/h of nitrogen at 7 bar as milling gas). Further properties of the silicon particles are summarized in table 1.

Comparative Example 4 (Comp. Ex. 4)

[0135] Production of Silicon Particles:

[0136] Analogous to Comparative example 3, with the exception that the deposition temperature was reduced to 785° C., as indicated in table 1.

[0137] The properties of the silicon particles obtained in this way are summarized in table 1. Reaction gas conversion, reactor yield and deposition rate were reduced by 50% compared to example 1 and therefore not economic.

Comparative Example 5 (Comp. Ex. 5)

[0138] Production of Silicon Particles:

[0139] Analogous to example 1 with the exceptions of altering the dichlorosilane amount to 1230 kg/h per m.sup.2 of reactor cross-sectional area, the hydrogen flow to 2770 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area and the deposition temperature to 960° C. as reported in Table 1.

[0140] The properties of the silicon particles obtained in this way are summarized in table 1.

Comparative Example 6 (Comp. Ex. 6)

[0141] Production of Silicon Particles:

[0142] Analogous to example 1 with the exceptions of altering the dichlorosilane amount to 2890 kg/h per m.sup.2 of reactor cross-sectional area, the hydrogen flow to 2400 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area and the deposition temperature to 960° C. as reported in Table 1.

[0143] The properties of the silicon particles obtained in this way are summarized in table 1.

(Comparative) Examples 7 to 12 ((Comp.) Ex. 7-12)

[0144] Electrodes comprising silicon particles from examples 1 or 2 or comparative examples 3 to 6:

[0145] 29.709 g of polyacrylic acid (Sigma-Aldrich, Mw ˜450,000 g/mol) dried to a constant weight at 85° C. and 751.60 g of deionized water were agitated for 2.5 h until complete dissolution of the polyacrylic acid using a shaker (290 rpm). Lithium hydroxide monohydrate (Sigma-Aldrich) was added portionwise to the solution until the pH was 7.0 (measured with WTW pH 340i pH meter and SenTix RJD probe). The solution was then mixed for a further 4 hours using the shaker.

[0146] 7.00 g of the silicon particles of the respective (comparative) example 1 to 6 were dispersed in 12.50 g of the neutralized polyacrylic acid solution (concentration 4% by weight) and 5.10 g of deionized water using a dissolver at a circulation speed of 4.5 m/s for 5 min and of 12 m/s for 30 min with cooling at 20° C. After addition of 2.50 g of graphite (Imerys, KS6L C) the mixture was then stirred for a further 30 min at a circulation speed of 12 m/s. After degassing, the dispersion was applied to a copper foil having a thickness of 0.030 mm (Schlenk metal foils, SE-Cu58) using a film-drawing frame with a gap height of 0.10 mm (Erichsen, model 360).

[0147] The anode coating produced in this way was then dried at 80° C. and 1 bar of air pressure for 60 min.

[0148] The anode coating dried in this way had an average basis weight of 2.90 mg/cm.sup.2 and a film thickness of 32 μm.

[0149] FIG. 2: SEM micrograph of FIB section of the electrode coating with the silicon particles from example 1 (silicon particles discernible by their light gray color).

(Comparative) Examples 13 to 18 ((Comp.) Ex. 13-18)

[0150] Testing the electrodes from (comparative) examples 7-12: The electrochemical investigations were carried out on a button cell (type CR2032, Hohsen Corp.) in a 2-electrode arrangement. The electrode from the respective (comparative) example 7 to 12 was used as the counter electrode or negative electrode (Dm=15 mm) and a coating based on lithium-nickel-manganese-cobalt oxide 1:1:1 with a content of 94.0% and an average basis weight of 14.5 mg/cm.sup.2 was used as the working electrode/positive electrode (Dm=15 mm). A glass fiber filter paper (Whatman, GD Type D) saturated with 120 μl of electrolyte was used as the separator (Dm=16 mm). The employed electrolyte consisted of a 1 molar solution of lithium hexafluorophosphate in a 3:7 (v/v) mixture of fluoroethylene carbonate and ethyl methyl carbonate admixed with 2% by weight of vinylene carbonate. The cell was constructed in a glove box (<1 ppm H.sub.2O, O.sub.2) and the water content in the dry matter of all components used was below 20 ppm.

[0151] The electrochemical testing was carried out at 20° C. The cell was charged by the cc/cv method (constant current/constant voltage) at 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 constant voltage until the current falls below a current of C/100 or C/8. The cell was discharged by the cc method (constant current) at 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 achieving the voltage limit of 3.0 V. The specific current chosen was based on the weight of the positive electrode coating.

[0152] As a result of the ratio of anode to cathode capacity resulting from the formulation the lithium-ion battery was operated with partial utilization of the anode at a Li/Si ratio of 1.1.

[0153] The results of the electrochemical testing are summarized in table 2.

Comparative Example 19 (Comp. Ex. 19)

[0154] Production of silicon particles via the Siemens process:

[0155] A reaction gas consisting of 33 mol % of trichlorosilane in hydrogen was introduced into a bell-shaped reactor (“Siemens” reactor) into which slim rods had been introduced as the target substrate. At a temperature of 1070° C. silicon was deposited from a trichlorosilane stream of 108 kg/h/m.sup.2 of slim rod surface and 36 Nm.sup.3 of H.sub.2/h/m.sup.2 of slim rod surface.

[0156] The silicon obtained in this way was initially subjected to manual pre-crushing and then pre-comminuted with roller crushers before it was subsequently comminuted to a size of d.sub.50=4.6 μm by dry milling analogously to example 1.

[0157] The properties of the silicon particles obtained in this way are summarized in table 1.

Comparative Example 20 (Comp. Ex. 20)

[0158] Production of silicon particles from monosilane using the FBR process:

[0159] In a fluidized bed reactor a monosilane mass flow of 81 kg/h per m.sup.2 of reactor cross-sectional area, a hydrogen flow of 876 Nm.sup.3/h per m.sup.2 of reactor cross-sectional area, a fluidized bed temperature of 640° C. and a reactor pressure of 2.5 bar were established.

[0160] The granular silicon obtained in this way was then comminuted by milling in a fluidized bed jet mill (Netzsch-Condux CGS16, with 90 m.sup.3/h of nitrogen at 7 bar as milling gas). The properties of the silicon particles obtained in this way are summarized in table 1.

[0161] As is apparent from table 1 the inventive silicon particles in examples 1 and 2 have a significantly higher chloride content, at 290 ppm and 1480 ppm respectively, than the products of comparative examples 3 to 5 and in particular comparative examples 19 and 20 whose chloride content is even below the detection limit located. By contrast, the silicon particles of comparative example 6 have a higher chloride content than the silicon particles of examples 1 and 2.

[0162] When employed as anode active material the silicon particles of the comparative examples result in lithium-ion batteries having a significantly lower cycling stability than the silicon particles of inventive examples 1 and 2, as shown in table 2.

TABLE-US-00001 TABLE 1 Reaction conditions during deposition of silicon and properties of the silicon particles: Deposition Properties of Si particles Silane Cl Particle size (Comp.) Temperature content G.sup.e) content d.sub.10/d.sub.50/d.sub.90 Ex. [° C.] [mol %] [μm/ min] [ppm] [μm] 1.sup.a) 775 17 0.30 1480 2.4/4.5/7.2 2.sup.a) 900 12 0.28 290 2.5/4.7/7.7 3.sup.b) 960 21 0.16 23 2.4/4.5/7.2 4.sup.b) 785 21 0.08 102 2.5/4.7/7.7 5.sup.a) 960 9 0.16 39 2.5/4.6/7.5 6.sup.a) 960 21 0.57 6000 2.4/4.4/7.1 19.sup.c)  1070 33 30 <3 2.4/4.6/7.6 20.sup.d)  640 6 0.15 <3 2.6/4.8/7.9 Silane and reactor for deposition of silicon: .sup.a)Dichlorosilane, fluidized bed reactor; .sup.b)Trichlorosilane, fluidized bed reactor; .sup.c)Trichlorosilane, Siemens reactor; .sup.d)Monosilane, fluidized bed reactor. .sup.e)G: Deposition rate of silicon.

Comparative Example 21 (Comp. Ex. 21)

[0163] Electrodes were produced analogously to example 7 with the exception that the silicon particles from comparative example 19 were employed instead of the silicon particles from example 1.

Comparative Example 22 (Comp. Ex. 22)

[0164] Electrodes were produced analogously to example 7 with the exception that the silicon particles from comparative example 20 were employed instead of the silicon particles from example 1.

Comparative Example 23 (Comp. Ex. 23)

[0165] The cell construction and the electrochemical testing were performed analogously to example 13 with the exception that electrodes from comparative example 21 were employed.

[0166] The electrochemical characteristics are summarized in table 2.

Comparative Example 24 (Comp. Ex. 24)

[0167] The cell construction and the electrochemical testing were performed analogously to example 13 with the exception that electrodes from comparative example 22 were employed.

[0168] The electrochemical characteristics are summarized in table 2.

TABLE-US-00002 TABLE 2 Electrochemical testing of (comparative) examples 13 to 18 and 23 to 24: Coulombic Initial discharging Cycle with Silicon efficiency capacity cycling 80% particles formation [%] [mAh/cm.sup.2] residual capacity Ex. 13 Ex. 1 81.4 2.12 386 Ex. 14 Ex. 2 81.6 2.15 374 Comp. Comp. 81.5 2.09 312 Ex. 15 Ex. 3 Comp. Comp. 81.2 2.18 320 Ex. 16 Ex. 4 Comp. Comp. 81.6 2.07 291 Ex. 17 Ex. 5 Comp. Comp. 81.4 2.09 308 Ex. 18 Ex. 6 Comp. Comp. 81.7 2.10 246 Ex. 23 Ex. 19 Comp. Comp. 82.1 2.09 279 Ex. 24 Ex. 20

[0169] The test results of table 2 show that the silicon particles of examples 1 and 2 result in lithium-ion batteries having markedly improved cycle stabilities compared to the low-chloride silicon particles of comparative examples 3 to 5, the high-chloride silicon particles of example 6 and the chloride-free silicon particles of comparative examples 19 and 20.