Preformed silicon-based negative electrode and method for its manufacture

Abstract

The present invention relates to a method for manufacturing a silicon-based negative electrode, a method for manufacturing a lithium-ion battery from a preformed silicon-based negative electrode, and a lithium-ion battery thus obtained.

Claims

1. A method for manufacturing at least one silicon-based negative electrode, wherein the method comprises the following method steps: a) providing at least one silicon-based negative electrode precursor, an electrolyte, and at least one lithium-based counter electrode, b) applying at least three successive constant voltages of 1.2 V-1.8 V, 400 mV-800 mV, and 200 mV-390 mV, respectively, between the at least one silicon-based negative electrode precursor and the at least one lithium-based counter electrode for a period of at least 35 minutes in each case, and c) obtaining the silicon-based negative electrode.

2. The method according to claim 1, wherein the three successive, constant voltages are 1.5 V, 600 mV, and 300 mV, respectively.

3. The method according to claim 1, wherein the lithium-based counter electrode is made of metallic lithium.

4. The method according to claim 1, wherein the respective successive, constant voltages in method step b) are applied for a period of 35 minutes to 14 hours in each case.

5. The method according to claim 1, wherein the three successive, constant voltages in method step b) are each applied for the same or different periods of time.

6. The method according to claim 5, wherein the successive, constant voltages in method step b) are each applied for exactly two hours.

7. The method according to claim 1, wherein the applied current corresponds to a C-rate of C/5 to C/20.

8. The method according to claim 7, wherein the applied current corresponds to a C-rate of C/10.

9. The method according to claim 1, wherein the silicon-based negative electrode precursor is a precursor of a silicon-based negative composite electrode.

10. The method according to claim 1, wherein the electrode material of the silicon-based negative electrode precursor contains active material and at least one binder.

11. The method according to claim 1, wherein the active material of the silicon-based negative electrode precursor contains or is made of silicon and graphite.

12. The method according to claim 1, wherein in method step c) the silicon-based negative electrode is obtained after washing with an organic wash solution and drying.

13. A silicon-based negative electrode that is manufacturable according to the method of claim 1.

14. A lithium-ion battery comprising at least one silicon-based negative electrode that is manufacturable according to the method of claim 1.

15. A device comprising at least one lithium-ion battery according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in greater detail with reference to the following examples and associated figures.

(2) The figures show the following:

(3) FIG. 1 shows the half cell voltage in volts in relation to the relative capacity (in percent (%)) during the first formation cycle. A silicon-based negative electrode according to the invention (A-SEI, dashed line) obtained in method step c) is compared to a silicon-based negative electrode (baseline, solid line) not according to the invention, namely, not preformed. The half cell voltage in relation to the relative capacity during lithiation (the left line in each case) and delithiation (the right line in each case) is illustrated;

(4) FIG. 2 shows the initial, irreversible capacity loss (Q.sub.IR) of the electrodes in percent, according to FIG. 1;

(5) FIG. 3 shows the half cell voltage in volts in relation to the relative capacity (in percent (%)) during the first formation cycle. A preformed silicon-based negative electrode according to the invention (A-SEI, dashed line) obtained in method step c) is compared to an insufficiently preformed silicon-based negative electrode (A-SEI, dotted line). The half cell voltage in relation to the relative capacity during lithiation ((the left line in each case) and delithiation (the right line in each case) is illustrated; and

(6) FIG. 4 shows the initial, irreversible capacity loss (Q.sub.IR) of the electrodes in percent, according to FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Examples

Example 1

(7) 1.1 The following formulation was used for manufacturing the electrodes:

(8) 20 wt % silicon (Nanostructured and Armorphous Material Inc.Si, 98+%, 30-50 nm);

(9) 60 wt % graphite (ImerysC-NERGY SFG6)

(10) 12 wt % carbon black (ImerysC-NERGY SUPER C65)

(11) 8 wt % binder (carboxymethyl cellulose (700,000 g/mol):poly(acrylic acid) (450,000 g/mol):poly(acrylic acid-co-maleic acid) (350 g/mol), 1:1:1).

(12) 1.2 These solids, with the exception of the binder, were initially combined with tungsten carbide spheres (electrode support) in dissolver, and subsequently diluted by adding the binder in two steps, and the viscosity was adjusted, wherein the pH of the paste obtained was 3.

(13) 1.3 The electrode precursors manufactured in this way were preformed as follows.

(14) A button cell was opened, the electrode precursor was inserted, and voltages of 1.5 V, then 600 mV, and lastly 300 mV, were applied for two hours in each case and held constant. Metallic lithium was used as a counter electrode or sacrificial anode. The applied current corresponded to a C-rate of C/10.

(15) 1.4 The silicon-based negative electrode preformed in this way was removed from the button cell, washed with dimethyl carbonate, and installed in another button cell for testing.

(16) 1.5 As a comparative electrode, an electrode with the same formulation and manufacturing method according to paragraphs 1.1, 1.2, and 1.4 was manufactured (referred to as baseline), but without carrying out preforming according to paragraph 1.3.

(17) 1.6 The electrode that was preformed according to the invention as well as the electrode that was not preformed according to the invention were examined with regard to their half cell voltage and their capacity loss in the first formation cycle.

(18) With reference to FIG. 1, the improvement in the relative capacity of the electrode according to the invention in the first formation cycle is clearly apparent. In addition, the initial, irreversible capacity loss may be reduced from just below 20% to 9% by use of the method according to the invention (FIG. 2).

Example 2

(19) 2.1 In another exemplary embodiment, a silicon-based negative electrode precursor was manufactured from the same materials as in Example 1, and subsequently preformed, as a comparative electrode.

(20) The electrode precursor obtained according to paragraph 1.2 in Example 1 was inserted into a button cell, using metallic lithium as a counter anode. Constant voltages of 1.5 V, 600 mV, and 300 mV were applied in succession to the silicon-based negative electrode precursor for 30 minutes in each case.

(21) The silicon-based negative electrode precursor preformed in this way was removed from the button cell, washed with dimethyl carbonate, and installed in another button cell.

(22) 2.2 In addition, a silicon-based negative electrode according to the invention with the same formulation, manufacturing method, and preforming as described in Example 1, paragraphs 1.1 through 1.4 was manufactured.

(23) 2.3 The electrode that was preformed according to the invention (paragraph 2.2) as well as the electrode that was not preformed according to the invention (paragraph 2.1) were examined with regard to their half cell voltage and their capacity loss in the first formation cycle.

(24) 2.4 As is apparent from FIG. 3, an electrode that is preformed according to the invention has a great improvement in its relative capacity in the first formation cycle, while an insufficiently preformed electrode (constant voltages for only 30 minutes in each case) has a much poorer relative capacity. In addition, according to FIG. 4 the initial, irreversible capacity loss of the electrode that is preformed according to the invention is much less than the irreversible capacity loss of the electrode that is not preformed according to the invention.