NEGATIVE ELECTRODE ACTIVE MATERIAL, NEGATIVE ELECTRODE INCLUDING THE NEGATIVE ELECTRODE ACTIVE MATERIAL, SECONDARY BATTERY INCLUDING THE NEGATIVE ELECTRODE, AND METHOD OF PREPARING THE NEGATIVE ELECTRODE ACTIVE MATERIAL

Abstract

According to an exemplary embodiment of the present disclosure, a negative electrode active material includes metal-silicon-carbon based particles including a M.sub.aSi.sub.bC matrix, wherein M in the M.sub.aSi.sub.bC matrix is one or more selected from the group consisting of Li, Mg, Na, Ca, and Al, 0.3≤a≤1, and 1≤b≤2. Since at the time of charging and discharging a battery, formation of an irreversible phase may be minimized by the M.sub.aSi.sub.bC matrix, initial efficiency of the battery may be improved, and electrical conductivity, physical strength, and chemical stability may be improved, such that capacity and lifecycle characteristics of the battery may be improved.

Claims

1. A negative electrode active material comprising metal-silicon-carbon based particles including a M.sub.aSi.sub.bC matrix, wherein M in the M.sub.aSi.sub.bC matrix is one or more selected from the group consisting of Li, Mg, Na, Ca, and Al, 0.3≤a≤1, and 1≤b≤2.

2. The negative electrode active material according to claim 1, wherein an average particle size (D.sub.50) of the metal-silicon-carbon based particles is 1 μm to 10 μm.

3. The negative electrode active material according to claim 1, wherein the M.sub.aSi.sub.bC matrix includes Si, SiC, and M.sub.xSi.sub.yC, M in M.sub.xSi.sub.yC being one or more selected from the group consisting of Li, Mg, Na, Ca, and Al, 1<x≤3, and 0.5<y≤2.

4. The negative electrode active material according to claim 1, wherein the M.sub.aSi.sub.bC matrix includes 10 wt % to 35 wt % of M, 45 wt % to 75 wt % of Si, and 15 wt % to 25 wt % of C based on a total weight of M.sub.aSi.sub.bC matrix.

5. The negative electrode active material according to claim 1, wherein in the M.sub.aSi.sub.bC matrix, a weight ratio of Si to M is 1.5 to 7.

6. A method of preparing the negative electrode active material according to claim 1, the method comprising forming a matrix fluid through thermal treatment by introducing a vaporized silicon source, a carbon source, a metal source, and a carrier gas into a reaction furnace, wherein in the forming of the matrix fluid, a ratio of a flow rate of the vaporized silicon source, a flow rate of the carbon source, and a flow rate of the metal source is 1:0.2:0.2 to 1:0.8:0.8.

7. The method according to claim 6, wherein the thermal treatment is performed at 1,000° C. to 2,500° C.

8. The method according to claim 6, wherein the carrier gas is one or more selected from the group consisting of Ar, He, and Ne.

9. A negative electrode comprising the negative electrode active material of claim 1.

10. The negative electrode according to claim 9, further comprising a graphite based active material.

11. A secondary battery comprising: the negative electrode of claim 9; a positive electrode; a separator interposed between the positive electrode and the negative electrode; and and an electrolyte.

Description

EXAMPLE

Example 1

[0066] (1) Preparation of Silicon-Carbon Based Particles

[0067] 1) Formation of Matrix Fluid

[0068] Pure silicon was used as a silicon source, methane gas was used as a carbon source, a Mg metal was used as a metal source, and Ar was used as a carrier gas. While silicon was vaporized and introduced into a tube type furnace, a temperature of the furnace was maintained at 2,000° C. to perform thermal treatment in a section of 80 cm. Here, a flow rate of the vaporized silicon was 200 sccm, a flow rate of the methane gas was 100 sccm, a flow rate of Mg gas was 100 sccm, and a flow rate of the Ar gas was 1,500 sccm. In this way, Mg.sub.0.52Si.sub.1.51C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

[0069] (2) Manufacture of Negative Electrode

[0070] The prepared metal-silicon-carbon based active material particles, graphite, carbon black corresponding to a conductive material, carboxylmethyl cellulose (CMC) corresponding to a binder, and styrene butadiene rubber (SBR) were mixed at a weight ratio of 4.8:91:1:1.7:1.5 to prepare 5 g of a mixture. Negative electrode slurry was prepared by adding 28.9 g of distilled water to the mixture. The negative electrode slurry was applied and dried on a copper (Cu) metal thin film having a thickness of 20 μm, corresponding to a negative electrode current collector. Here, a temperature of circulated air was 60° C. Subsequently, the resultant was roll-pressed, dried in a vacuum oven at 130° C. for 12 hours, and then, punched in a circular form of 1.4875 cm.sup.2 to manufacture a negative electrode.

[0071] (3) Manufacture of Secondary Battery

[0072] The prepared negative electrode was used, and a lithium (Li) metal thin film cut in a circular form of 1.7671 cm.sup.2 was used as a positive electrode. A porous polyethylene separator was interposed between the positive electrode and the negative electrode, an electrolyte obtained by dissolving 0.5 wt % of vinylene carbonate in a mixed solution in which methyl ethyl carbonate (MEC) and ethylene carbonate (EC) was mixed at a mixing ratio of 7:3 and dissolving 1M LiPF.sub.6 was injected, thereby manufacturing a lithium coin half-cell.

Example 2

[0073] Metal-silicon-carbon based active material particles in Example 2 were prepared by the same method as in Example 1 except that the flow rate of the vaporized silicon was adjusted to 200 sccm, the flow rate of the methane gas was adjusted to 100 sccm, a flow rate of the Mg gas was adjusted to 70 sccm, and the flow rate of the Ar gas was adjusted to 1,500 sccm. In this way, Mg.sub.0.35Si.sub.1.53C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

Example 3

[0074] Metal-silicon-carbon based active material particles in Example 3 were prepared by the same method as in Example 1 except that the flow rate of the vaporized silicon was adjusted to 145 sccm, the flow rate of the methane gas was adjusted to 100 sccm, a flow rate of the Mg gas was adjusted to 100 sccm, and the flow rate of the Ar gas was adjusted to 1,500 sccm. In this way, Mg.sub.0.54Si.sub.1.08C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

Comparative Example 1

[0075] Silicon-carbon based particles, a negative electrode, and a secondary battery were manufactured by the same methods as in Example 1 except that a metal source gas was not introduced.

Comparative Example 2

[0076] (1) Preparation of Silicon-Oxygen Based Particles

[0077] Metal-silicon-oxygen based particles in Comparative Example 2 were prepared by the same method as in Example 1 except that SiO.sub.2 was used instead of the methane gas in Example 1.

[0078] Here, a content ratio of the metal, silicon, and oxygen confirmed by ICP was 15:9:36 based on a total weight of the particle. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

[0079] (2) Manufacture of Negative electrode and Secondary Battery

[0080] A negative electrode and a secondary battery were manufacture by the same method as in Example 1 except that the prepared silicon-oxygen based particles were used.

Comparative Example 3

[0081] Metal-silicon-carbon based active material particles in Comparative Example 3 were prepared by the same method as in Example 1 except that the flow rate of the vaporized silicon was adjusted to 40 sccm, the flow rate of the methane gas was adjusted to 200 sccm, a flow rate of the Mg gas was adjusted to 100 sccm, and the flow rate of the Ar gas was adjusted to 1,500 sccm. In this way, Mg.sub.0.22Si.sub.1.56C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

Comparative Example 4

[0082] Here, a flow rate of the vaporized silicon was 200 sccm, a flow rate of the methane gas was 200 sccm, a flow rate of Mg gas was 200 sccm, and a flow rate of the Ar gas was 1,500 sccm. In this way, Mg.sub.0.52Si.sub.0.02C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

Comparative Example 5

[0083] Here, a flow rate of the vaporized silicon was 300 sccm, a flow rate of the methane gas was 100 sccm, a flow rate of Mg gas was 100 sccm, and a flow rate of the Ar gas was 1,500 sccm. In this way, Mg.sub.0.53Si.sub.2.12C was formed. Here, an atomic ratio of Mg and Si was measured by ICP. Further, an average particle size (D.sub.50) of silicon-carbon based particles confirmed by a laser diffraction method was 5 μm.

[0084] Experimental Example 1 Evaluation of Discharge Capacity, Initial Efficiency, Capacity Retention Rate, and Electrode Thickness Change Rate

[0085] Charging and discharging were performed on the batteries in Examples 1 to 3 and Comparative Examples 1 to to evaluate discharge capacity, initial efficiency, a capacity retention rate, and an electrode (negative electrode) thickness change rate. The results were described in the following Table 1.

[0086] Meanwhile, the charging and discharging were performed at 0.1 C in first and second cycles, and performed at 0.5 C from third up to 49th cycles. The 50th cycle was terminated in a charging state (in a state in which lithium was in the negative electrode), and after decomposing the battery to measure a thickness, an electrode thickness change rate was calculated.

[0087] Charge condition: CC (constant current)/CV (constant voltage (5 mV/0.005 C current cut-off)

[0088] Discharge condition: CC (constant current) condition, 1.5 V

[0089] Charge capacity (mAh/g) and initial efficiency (%) were derived through results at the time of one-time charge and discharge. Specifically, the initial efficiency (%) was derived by the following calculation.

Initial efficiency (%)=(discharge capacity after one-time discharge/one-time charge capacity)×100

[0090] A capacity retention rate and an electrode thickness change rate were derived by the following Calculations, respectively.

Capacity retention rate (%)=(discharge capacity at 49.sup.th cycle/discharge capacity at first cycle)×100

Electrode thickness change rate (%)=(final negative electrode thickness change amount/initial negative electrode thickness)×100

TABLE-US-00001 TABLE 1 Electrode Capacity thickness a value of b value of Discharge Initial retention change M.sub.aSi.sub.bC or M.sub.aSi.sub.bC or capacity efficiency rate rate Battery M.sub.aSi.sub.bO.sub.2 M.sub.aSi.sub.bO.sub.2 (mAh/g) (%) (%) (%) Example 1 0.52 1.51 410 91.8 88.1 36.5 Example 2 0.35 1.53 412 90.9 86.2 38.2 Example 3 0.54 1.08 401 91.2 86.5 37.9 Comparative 0   1.56 405 90.8 79.0 44.6 Example 1 Comparative 0.55 1.52 395 87.9 70.5 52.8 Example 2 Comparative 0.22 1.56 400 90.2 80.4 37.2 Example 3 Comparative 0.52 0.82 382 90.9 83.2 45.9 Example 4 Comparative 0.53 2.12 420 90.0 71.2 65.1 Example 5

[0091] Referring to Table 1, it may be appreciated that in Examples 1 to 3, discharge capacity, initial efficiency, and the capacity retention rate were simultaneously improved to significantly excellent levels, and the electrode thickness change rate was low.

[0092] However, it may be appreciated that in Comparative Example 1 in which a metal was not introduced into a matrix, since electrical conductivity was decreased, initial efficiency and the capacity retention rate were decreased, and the electrode thickness change rate was high.

[0093] Further, it may be appreciated that in Comparative Example 2, due to a SiO.sub.2 phase forming an irreversible phase, initial efficiency and the capacity retention rate were decreased, and the electrode thickness change rate was significantly high.

[0094] Further, it may be confirmed that in Comparative Examples 3 to 5 in which contents of a metal, silicon, and carbon contained in the metal-silicon-carbon based particles were not suitable, initial efficiency and the capacity retention rate were low, and the electrode thickness change rate was significantly high. Specifically, in Comparative Example 3, a doping content of the metal was low, such that initial efficiency was low, and the capacity retention rate was low due to side reactions with an electrolyte, and in Comparative Example 4, the content of Si was low, such that the capacity of the battery was excessively decreased, and since a ratio of M in the matrix was excessive, which caused instability of the active material, in view of the capacity retention rate and the electrode thickness change rate, undesirable effects were obtained. Further, it may be appreciated that in Comparative Example 5, the content of Si in the matrix was excessively high, initial efficiency was low, and side reactions of the electrolyte by Si were intensified, such that the capacity retention rate was low, and the electrode thickness change rate was high.