CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0102618, filed on Aug. 8, 2014, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Field

One or more exemplary embodiments relate to a negative active material, a lithium battery including the negative active material, and a method of preparing the negative active material.

2. Description of the Related Art

Lithium secondary batteries produce electrical energy by oxidation and reduction reactions when lithium ions undergo intercalation/deintercalation in positive and negative electrodes, in which the lithium ions move through an organic electrolytic solution and/or a polymer electrolytic solution filled between the positive and negative electrodes, and the electrodes include active materials capable of intercalation and deintercalation of lithium ions.

Studies have been made on negative active materials for lithium secondary batteries including various forms of carbonaceous materials (such as artificial graphite, natural graphite, or hard carbon capable of intercalation/deintercalation of lithium), and non-carbonaceous materials (such as Si or Sn).

Although the non-carbonaceous materials such as Si or Sn may have very high capacities (because the capacity densities thereof are 10 times or more higher than that of graphite), the capacities may rapidly decrease due to volume expansion during charging and discharging processes. Therefore, various alloys and complexes are currently being studied to address this problem.

SUMMARY

An aspect according to one or more exemplary embodiments is directed toward a negative active material including a silicon based alloy that is capable of improving lifetime characteristics of lithium batteries.

An aspect according to one or more exemplary embodiments is directed toward a negative electrode including the negative active material.

An aspect according to one or more exemplary embodiments is directed toward a lithium battery including the negative electrode.

An aspect according to one or more exemplary embodiments is directed toward a method of preparing the negative active material.

Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.

According to one or more exemplary embodiments, a negative active material includes: a core particle including a silicon based alloy; carbon nanoparticles on a surface of the core particle; and an amorphous carbonaceous coating layer on at least a portion of the surface of the core particle.

The carbon nanoparticles may have an average particle diameter of about 1/10 or less of that of the core particle. For example, the carbon nanoparticles may have an average particle diameter ranging from about 1/1000 to about 1/10 of that of the core particle. For example, the carbon nanoparticles may have an average particle diameter ranging from about 1/100 to about 1/50 of that of the core particle.

The core particle may have an average particle diameter ranging from about 1 μm to about 10 μm.

The carbon nanoparticles may be amorphous carbon particles with an average particle diameter of about 10 nm to about 100 nm.

The silicon based alloy may be represented by the following Formula 1:
SiaMbFormula 1

wherein, M includes at least one selected from the group consisting of group 2 to 14 metal elements other than silicon, and wherein 0.5≤a≤0.9, 0.1≤b≤0.5, and a+b=1.

M may include at least one selected from the group consisting of iron (Fe), copper (Cu), magnesium (Mg), chromium (Cr), nickel (Ni), zinc (Zn), manganese (Mn), cobalt (Co), titanium (Ti), germanium (Ge), calcium (Ca), and aluminum (Al).

The silicon based alloy may be represented by SiaFeb, wherein 0.5≤a≤0.9, 0.1≤b≤0.5, and a+b=1.

The silicon based alloy may include: an inactive matrix including silicon and at least one selected from the group consisting of group 2 to 14 metal elements other than silicon; and active silicon nanoparticles dispersed in the inactive matrix.

The amorphous carbonaceous coating layer may include a carbide of a carbon precursor selected from the group consisting of hydrocarbons, soft carbons, hard carbons, coal, coal based pitch, petroleum based pitch, mesophase pitch, coal based oil, petroleum based heavy oil, organic synthetic pitch, and combinations thereof.

The amorphous carbonaceous coating layer may surround the surface of the core particle and may cover the carbon nanoparticles.

The amorphous carbonaceous coating layer may have a thickness of about 0.1 μm to about 10 μm.

An amount of the amorphous carbonaceous coating layer may be 1 part to about 30 parts based on 100 parts by weight of the core particle.

According to one or more exemplary embodiments, a negative electrode includes the negative active material.

According to one or more exemplary embodiments, a lithium battery includes the negative electrode.

According to one or more exemplary embodiments, a method of preparing a negative active material includes: mixing carbon nanoparticles with a core particle including a silicon based alloy to obtain a first particle in which the carbon nanoparticles are adhered onto a surface of the core particle; mixing the first particle with an amorphous carbon precursor to obtain a second particle in which the amorphous carbon precursor is coated on a surface of the first particle; and heat-treating the second particle at a temperature of about 500° C. to about 700° C. in an inert atmosphere.

The silicon based alloy may be represented by the following Formula 1:
SiaMbFormula 1

wherein, M includes at least one selected from the group consisting of group 2 to 14 metal elements other than silicon, and wherein 0.5≤a≤0.9, 0.1≤b≤0.5, and a+b=1.

M may include at least one selected from the group consisting of iron (Fe), copper (Cu), magnesium (Mg), chromium (Cr), nickel (Ni), zinc (Zn), manganese (Mn), cobalt (Co), titanium (Ti), germanium (Ge), calcium (Ca), and aluminum (Al).

The silicon based alloy may be represented by SiaFeb, wherein 0.5≤a≤0.9, 0.1≤b≤0.5, and a+b=1.

For example, the carbon nanoparticles may be amorphous carbon particles having a nanoparticle size of about 100 nm or less, or about 10 nm to about 100 nm.

The amorphous carbon precursor may include a carbon precursor selected from the group consisting of hydrocarbons, soft carbons, hard carbons, coal, coal based pitch, petroleum based pitch, mesophase pitch, coal based oil, petroleum based heavy oil, organic synthetic pitch, and combinations thereof.

The heat-treating of the second particle may be performed at a temperature of about 500° C. to about 600° C. in a nitrogen atmosphere.

