NEGATIVE ELECTRODE ACTIVE MATERIAL FOR NON-AQUEOUS ELECTROLYTE SECONDARY BATTERY AND MANUFACTURING METHOD THEREOF

Abstract

The present disclosure relates to a negative electrode active material for non-aqueous electrolyte secondary battery and a manufacturing method thereof and, more specifically to, a negative electrode active material for non-aqueous electrolyte secondary battery, the negative electrode active material which not only improves conductivity by reacting, silicon, silicon dioxide and magnesium through a gas phase reaction to produce a reaction product and coating carbon on the surface of the reaction product so as to give conductivity to the reaction product, but also exhibits an effect of greatly improving lifetime characteristics and capacity characteristics by showing a structure that is stable in a volume change caused by intercalation or deintercalation of lithium, and a manufacturing method thereof.

Claims

1. A negative electrode active material for non-aqueous electrolyte secondary battery, the negative electrode active material comprising: a silicon oxide composite comprising silicon, a silicon oxide (SiO.sub.x, 0<x2); and a magnesium silicate, wherein the magnesium silicate includes MgSiO.sub.3, and the negative electrode active material has a ratio of a diffraction peak intensity I.sub.MgSiO(610) detected at 2=30 to 32 by MgSiO.sub.3 to a diffraction peak intensity I.sub.si(111) detected at 2=27.5 to 29.5 by Si(111) during X-ray diffraction analysis, i.e., 0.1<I.sub.MgSi03(610)/I.sub.si(111)<0.5.

2. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 1, wherein the silicon oxide composite comprises 2 to 30 wt % of magnesium based on the total weight of the silicon oxide composite.

3. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 1, wherein the silicon oxide composite allows a diffraction peak by Si(111) to be shown at 2=27.5 to 29.5 during X-ray diffraction analysis, and has a silicon crystallite size of 2 to 100 nm calculated from Full Width at Half Maximum (FWHM) of the diffraction peak.

4. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 1, wherein the magnesium silicate further comprises Mg.sub.2SiO.sub.4.

5. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 1, wherein the silicon oxide composite has a ratio (Si/O) of the number of silicon atoms to that of oxygen atoms of 0.5 to 2.

6. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 1, wherein the silicon oxide composite further comprises a carbon-containing coating layer on the surface thereof, and the silicon oxide composite comprises 2 to 20 parts by weight of the coating layer per 100 parts by weight of the total silicon oxide composite weight.

7. The negative electrode active material for non-aqueous electrolyte secondary battery of claim 6, wherein the carbon-containing coating layer comprises at least one selected from the group consisting of amorphous carbon, carbon nanofiber, carbon nanotube, graphite, graphene, graphene oxide, and reduced graphene oxide.

8. A negative electrode comprising a negative electrode active material for non-aqueous electrolyte secondary battery according to claim 1.

9. The negative electrode of claim 8, wherein the negative electrode comprises 30 to 95 wt % of at least one selected from the group consisting of graphite, conductive carbon black, soft carbon, hard carbon, carbon nanofiber, carbon nanotube, graphene, reduced graphene oxide, and graphene nanoflake with respect to the total weight of the negative electrode.

10. A non-aqueous electrolyte secondary battery comprising the negative electrode according to claim 9.

11. A method of manufacturing a negative electrode active material for non-aqueous electrolyte secondary battery according to claim 1, the method comprising: a first step of injecting a mixture of silicon particles and silicon dioxide particles, and magnesium into a reactor; a second step of adjusting pressure of the reactor to 0.000001 to 1 torr; a third step of heating the mixture and magnesium to 600 to 1600 C. to prepare a silicon oxide composite; a fourth step of cooling the silicon oxide composite, and depositing the cooled silicon oxide composite on a metal plate; and a fifth step of pulverizing and classifying the cooled silicon oxide composite deposited on the metal plate into a powder with an average particle diameter of 0.5 to 15 m.

12. The method of claim 11, wherein the silicon particle has an average particle size of 2 to 20 m, and the silicon dioxide particle has an average particle size of 10 to 300 nm.

13. The method of claim 11, further comprising a sixth step of injecting the silicon oxide composite of the fifth step and a carbon source, and heat-treating the silicon oxide composite and the carbon source at 600 to 1200 C., thereby forming a carbon-containing coating layer on the surface of the silicon oxide composite.

14. The method of claim 13, wherein the carbon source is at least one selected from the group consisting of methane, propane, butane, acetylene, benzene, and toluene.

15. The method of claim 13, wherein the sixth step comprises additionally injecting at least one selected from the group consisting of nitrogen, helium, argon, carbon dioxide, hydrogen, and water vapor besides the carbon source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 to FIG. 4 show results of measuring X-ray diffraction (XRD) analysis values of carbon-coated silicon oxide composites prepared in Examples and Comparative Examples of the present disclosure.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0046] Hereinafter, the present disclosure will be described in more detail by Examples. However, the present disclosure is not limited to the following Examples.

EXAMPLE 1

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0047] After heat-treating 15 kg of a mixed powder obtained by uniformly mixing a silicon powder with a silicon dioxide (SiO.sub.2) powder to a molar ratio of 1:1 and 1.5 kg of magnesium to 1,400 C. under a reduced-pressure atmosphere of 0.0001 to 1 torr, thereby simultaneously generating a silicon oxide vapor caused by the mixed powder of the silicon powder and the silicon dioxide (SiO.sub.2) powder, and a magnesium vapor such that the silicon oxide vapor and the magnesium vapor are reacted in a vapor phase to obtain a reaction product, cooling and precipitating the reaction product at 700 C. to obtain a precipitated reaction product, and pulverizing and classifying the precipitated reaction product by a jet mill, a magnesium-containing silicon oxide composite powder having an average particle diameter (D.sub.50) of 6.3 m was recovered.

[0048] A silicon oxide composite comprising 6.2 wt % of magnesium, the silicon oxide composite having a carbon coating layer containing 5 wt % of carbon formed thereon (sample 1) was prepared by performing a chemical vapor deposition (CVD) treatment process on the recovered magnesium-containing silicon oxide composite powder under a mixed gas of argon (Ar) and methane (CH.sub.4) at conditions of 1,000 C. and 2 hours by using a tube-type electric furnace in order to form a carbon-containing coating layer.

[0049] It was confirmed that the magnesium-containing silicon oxide composite (sample 1) had a BET specific surface area of 6.2 m.sup.2/g, a specific gravity of 2.3 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.3 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 8 nm.

EXAMPLE 2

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0050] A silicon oxide composite comprising 9 wt % of magnesium (sample 2) was prepared, and the silicon oxide composite powder having a carbon coating layer containing 5 wt % of carbon formed thereon was prepared by the same method as in Example 1 except that the reaction product was cooled and precipitated at 800 C. to obtain a precipitated reaction product.

[0051] It was confirmed that the magnesium-containing silicon oxide composite (sample 2) had a BET specific surface area of 6.3 m.sup.2/g, a specific gravity of 2.3 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.2 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 8 nm.

EXAMPLE 3

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0052] A silicon oxide composite comprising 11.7 wt % of magnesium (sample 3) was prepared, and the silicon oxide composite powder having a carbon coating layer containing 10 wt % of carbon formed thereon was prepared by the same method as in Example 1 except that the reaction product was cooled and precipitated at 900 C. to obtain a precipitated reaction product.

[0053] It was confirmed that the magnesium-containing silicon oxide composite (sample 3) had a BET specific surface area of 5.8 m.sup.2/g, a specific gravity of 2.4 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.7 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 11 nm.

EXAMPLE 4

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0054] A silicon oxide composite comprising 4.6 wt % of magnesium (sample 4) was prepared, and the silicon oxide composite powder having a carbon coating layer containing 7 wt % of carbon formed thereon was prepared by the same method as in Example 1 except that the reaction product was cooled and precipitated at 1000 C. to obtain a precipitated reaction product.

[0055] It was confirmed that the magnesium-containing silicon oxide composite (sample 4) had a BET specific surface area of 7.3 m.sup.2/g, a specific gravity of 2.3 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.2 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 7 nm.

EXAMPLE 5

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0056] A silicon oxide composite comprising 16.6 wt % of magnesium (sample 5) was prepared, and the silicon oxide composite powder having a carbon coating layer containing 4 wt % of carbon formed thereon was prepared by the same method as in Example 1 except that the reaction product was cooled and precipitated at 1100 C. to obtain a precipitated reaction product.

[0057] It was confirmed that the magnesium-containing silicon oxide composite (sample 5) had a BET specific surface area of 6.8 m.sup.2/g, a specific gravity of 2.4 g/cm.sup.3, an average particle diameter (D.sub.50) of 7.1 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 14 nm.

EXAMPLE 6

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0058] A silicon oxide composite comprising 3 wt % of magnesium (sample 6) was prepared, and the silicon oxide composite powder having a carbon coating layer containing 5 wt % of carbon formed thereon was prepared by the same method as in Example 1 except that the reaction product was cooled and precipitated at 800 C. to obtain a precipitated reaction product.

[0059] It was confirmed that the magnesium-containing silicon oxide composite (sample 6) had a BET specific surface area of 6.3 m.sup.2/g, a specific gravity of 2.3 g/cm.sup.3, an average particle diameter (D.sub.50) of 5.9 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 6 nm.

[0060] COMPARATIVE EXAMPLE 1

Preparation of a Magnesium-Noncontaining Silicon Oxide Composite

[0061] A silicon oxide composite having a carbon coating layer containing 5 wt % of carbon formed thereon (sample 7) was prepared by the same method as in Example 1 except that the mixed powder was heat-treated without adding magnesium to the mixed powder.

[0062] It was confirmed that the silicon oxide composite (sample 7) had a BET specific surface area of 6.5 m.sup.2/g, a specific gravity of 2.0 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.0 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 5 nm.

COMPARATIVE EXAMPLE 2

Preparation of a Magnesium-Containing Silicon Oxide Composite

[0063] A silicon oxide composite comprising 1 wt % of magnesium, the silicon oxide composite having a carbon coating layer containing 5 wt % of carbon formed thereon (sample 8) was prepared by the same method as in Example 1 except that the reaction product was naturally cooled and precipitated to obtain a precipitated reaction product.

[0064] It was confirmed that the magnesium-containing silicon oxide composite (sample 8) had a BET specific surface area of 5 m.sup.2/g, a specific gravity of 2.2 g/cm.sup.3, an average particle diameter (D.sub.50) of 6.5 m, and a size of silicon crystal measured by X-ray diffraction analysis (CuK) of 8 nm.

EXPERIMENTAL EXAMPLE 1

[0065] After analyzing average particle diameters, specific surface areas and magnesium contents of the silicon oxide composites (samples 1 to 8) prepared in Examples 1 to 6 and Comparative Examples 1 and 2, analysis results are shown in the following Table 1.

TABLE-US-00001 TABLE 1 Comparison of the silicon oxide composites prepared by Examples 1 to 6, and Comparative Examples 1 and 2 Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 1 Example 2 D.sub.50 (m) 6.3 6.2 6.7 6.2 7.1 5.9 6.0 6.5 BET (m.sup.2/g) 6.2 6.3 5.8 7.3 6.8 6.3 6.5 5.0 Mg content (wt %) 6.2 9.0 11.7 4.6 16.6 3.0 0 1 Si C, S (nm) 8 8 11 7 14 6 5 8

EXPERIMENTAL EXAMPLE

XRD Analysis

[0066] After measuring XRD values of the magnesium-containing silicon oxide composites (samples 1 to 8) prepared in Examples 1, 2 and 6, measurement results are shown in the following Table 2 and FIG. 1 to FIG. 3.

[0067] The XRD values were measured by an X-ray diffraction equipment (equipment name: X'Pert3) manufactured by Malvern Panalytical, and the measurement process was performed from 10 to 60 at 45 kV and 40 mV for 30 minutes.

[0068] A height from a center value to a maximum peak point was determined as Intensity Si(111) by connecting an Si(111) peak starting point and an Si(111) peak ending point with a line through X-ray diffraction analysis (CuK), and Intensity MgSiO.sub.3(610) was set in an MgSiO.sub.3(610) peak also by the same method as in the Si(111) peak. Further, size of an Si crystal was calculated by the following Scherrer's equation.

D=0.9*/(*cos ) <Scherrer's equation>

D: Particle diameter size

: FWHM (full width at half maximum)

: Wave length of X-ray (0.1541 nm)

[0069] When examining a ratio I.sub.MgSi03(610)/I.sub.Si(111) of a diffraction peak intensity I.sub.MgSiO3(610) by MgSiO.sub.3 detected at 2=30 to 32 to a diffraction peak intensity I.sub.Si(111) detected at 2=27.5 to 29.5 during X-ray diffraction analysis, it can be confirmed from the following Table 2 that the silicon oxide composites in Examples 1 to 6 according to the present disclosure have more than 0.1 of the ratio I.sub.MgSi03(610)/I.sub.Si(111) while the MgSiO.sub.3(610) peak is not detected in the silicon oxide composites in Comparative Examples according to the present disclosure, or the silicon oxide composites in Comparative Examples according to the present disclosure has less than 0.1 of the ratio I.sub.MgSi03(610)/I.sub.Si(111).

TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 1 Example 2 Si(111)2() 28.5056 28.5056 28.5476 28.4796 28.5836 28.5606 28.5216 28.4762 Si(111)FWHM() 1.02 1.03 0.75 1.16 0.59 137 1.65 1.03 FWHM (radians) 0.0178 0.0180 0.0131 0.0202 0.0103 0.0239 0.0287 0.0179 Intensity 147.22 154.11 181.97 150.03 140.87 147.51 21.5 MgSiO.sub.3(610) Intensity Si(111) 715.94 712.22 828.42 755.37 840.81 618.33 317.85 551.50 MgSiO.sub.3(610)/Si(111) 0.21 0.22 0.22 0.20 0.17 0.24 0.04

MANUFACTURING EXAMPLE

Manufacturing of Batteries

[0070] Negative electrodes for lithium secondary batteries comprising the above-mentioned silicon oxide composite powders prepared according to Examples and Comparative Examples as electrode active materials, and batteries (coil cells) were manufactured.

[0071] Negative electrode slurry compositions were prepared by mixing water with mixtures having the active materials, SUPER-P as a conductive material, and polyacrylic acid mixed therein at a weight ratio of 80:10:10.

[0072] Electrodes with a thickness of 70 m were manufactured by applying the compositions to a copper foil with a thickness of 18 m and drying the compositions applied to the copper foil, coil cell negative electrodes were manufactured by punching the electrode-applied copper foils into a circular shape with a diameter of 14 mm, and a metal lithium foil with a thickness of 0.3 mm was used as an opposite electrode.

[0073] A porous polyethylene sheet with a thickness of 0.1 mm was used as a separator, an electrolyte prepared by dissolving LiPF6 with a concentration of 1M in a solution having ethylene carbonate (EC) and diethylene carbonate (DEC) mixed therein at a volume ratio of 1:1 was used as an electrolytic solution, and coin cells (batteries) having a thickness of 2 mm and a diameter of 32 mm were manufactured by applying the above-mentioned elements.

EXPERIMENTAL EXAMPLE

[0074] After obtaining charge capacities (mAh/g), discharge capacities (mAh/g), and initial charging/discharging efficiency (%) by charging the coin cells manufactured in Manufacturing Example until it was a voltage of 0.005 V at a constant current of 0.1 C, and discharging the coin cells manufactured in Manufacturing Example until it was a voltage of 2.0 V at the constant current of 0.1 C, obtained results are shown in the following Table 3.

[0075] Further, after obtaining cycle characteristics (50 cycle capacity retention rates) by performing one cycle of a charging and discharging process on the coin cells manufactured for each of the samples in Manufacturing Example, and charging the coin cells until it was a voltage of 0.005 V at the constant current of 0.5 C and discharging the coin cells until it was a voltage of 2.0 V at the constant current of 0.5 C from a second cycle of the charging and discharging process, obtained results are shown in the following Table 3.

[0076] It can be confirmed that the silicon oxide composites according to Examples of the present disclosure have greatly improved initial efficiencies and 50 cycle capacity retention rates (%) when a ratio I.sub.MgSi03(610)/I.sub.Si(111) of a diffraction peak intensity I.sub.MgSiO3(610) by MgSiO.sub.3 detected at 2=30 to 32 to a diffraction peak intensity I.sub.Si(111) by Si(111) detected at 2=27.5 to 29.5 is in a range of 0.1<I.sub.MgSi03(610)/I.sub.Si(111)<0.5.

TABLE-US-00003 TABLE 3 Evaluation results of battery characteristics Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 1 Example 2 Initial discharge 1410 1346 1343 1433 1307 1478 1577 1465 capacity (mAh/g) Initial efficiency (%) 81.4 80.7 82.4 80.4 85.8 77.6 74 76 50 cycle capacity 85 87 84 83 80 84 81 80 retention rate (%)

[0077] A negative electrode active material for non-aqueous electrolyte secondary battery according to the present disclosure can improve lifetime characteristics, charging and discharging capacities, initial charging and discharging efficiencies, and capacity retention rate by reacting silicon, silicon dioxide and magnesium through a gas phase reaction and coating carbon on the surface of the silicon oxide composite so as to give conductivity to a silicon oxide composite, thereby exhibiting a structure which is stable to a volume change according to intercalation or deintercalation of lithium as well as conductivity of a non-aqueous electrolyte secondary battery comprising a negative electrode active material for non-aqueous electrolyte secondary battery according to the present disclosure. Therefore, a non-aqueous electrolyte secondary battery which is stable and has high performance by comprising a negative electrode active material according to the present disclosure can be provided.