CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0106955 filed in the Korean Intellectual Property Office on Sep. 7, 2018, the entire content of which is incorporated herein by reference.

BACKGROUND

1. Field

One or more aspects of example embodiments of the present disclosure are related to a negative active material for a rechargeable lithium battery, a method for preparing the same, and a negative electrode and a rechargeable lithium battery including the same.

2. Description of the Related Art

Ongoing efforts to develop rechargeable lithium batteries with high capacity are being driven by an increasing demand for mobile devices with portable batteries.

Lithium-transition metal oxides having a structure capable of intercalating lithium ions (such as LiCoO2, LiMn2O4, LiNi1-xCoxO2(0≤x<1), and/or the like) have been used as positive active materials for rechargeable lithium batteries.

Various types of carbon-based materials capable of intercalating and deintercalating lithium, including artificial graphite, natural graphite, and hard carbon, and Si-based active materials including Si and Sn, have been used as negative active materials for rechargeable lithium batteries.

SUMMARY

One or more aspects of embodiments of the present disclosure are directed toward a negative active material for a rechargeable lithium battery with improved cycle-life characteristics, which exhibits decreased thickness expansion during use, due to a reduction in side reactions with an electrolyte solution.

One or more aspects of embodiments of the present disclosure are directed toward a method for preparing the negative active material.

One or more aspects of embodiments of the present disclosure are directed toward a negative electrode including the negative active material.

One or more aspects of embodiments of the present disclosure are directed toward a rechargeable lithium battery including the negative electrode.

One or more example embodiments of the present disclosure provide a negative active material for a rechargeable lithium battery including: natural graphite including a plurality of primary particles assembled into a spheroidal secondary particle; amorphous carbon, a first portion of the amorphous carbon being on the surface of the plurality of primary particles, internal to the secondary particle; and a second portion of the amorphous carbon included within a coating layer surrounding the secondary particle, the plurality of primary particles having an average particle diameter of about 5 μm to about 15 μm, the secondary particle having an average particle diameter of about 8 μm to about 24 μm, and a peak intensity ratio I(002)/I(110) of the negative active material being less than or equal to about 120, as measured by X-ray diffraction.

The natural graphite may be flake-shaped natural graphite.

The negative active material may have a pore volume fraction of less than or equal to about 2%.

The negative active material may have a pore volume fraction of about 1.0% to about 1.5%.

The coating layer may have a thickness of about 5 nm to about 50 nm.

The negative active material may have a specific surface area (BET surface area) of less than or equal to about 10 m2/g.

The negative active material may have tap density of about 0.7 g/cc to about 1.3 g/cc.

The negative active material may include the natural graphite and the amorphous carbon in a weight ratio of about 90:10 to about 75:25.

The amorphous carbon may be selected from soft carbons, hard carbons, mesophase pitch carbonized products, fired cokes, and mixtures thereof.

One or more example embodiments of the present disclosure provide a method of preparing the negative active material for a rechargeable lithium battery including: pulverizing a natural graphite raw material into a plurality of primary particles having a small particle size; assembling the plurality of primary particles into the spheroidal secondary particle; adding an amorphous carbon precursor to the secondary particle to prepare a mixture; and heat-treating the mixture.

The natural graphite raw material may have an average particle diameter of about 80 μm to about 140 μm, the primary particles may have an average particle diameter of about 5 μm to about 15 μm, and the secondary particles may have an average particle diameter of about 8 μm to about 24 μm.

The negative active material may include the natural graphite and the amorphous carbon in a weight ratio of about 90:10 to about 75:25.

The amorphous carbon precursor may be selected from phenolic resins, furan resins, epoxy resins, polyacrylonitriles, polyamide resins, polyimide resins, polyamideimide resins, synthetic pitches, petroleum-based pitches, coal-based pitches, tars, and combinations thereof.

The heat-treating may be performed by maintaining the mixture in a furnace at about 1,000° C. to about 2,000° C. for about 1 hour to about 5 hours.

One or more example embodiments of the present disclosure provide a negative electrode including the negative active material.

One or more example embodiments of the present disclosure provide a rechargeable lithium battery including the negative electrode, a positive electrode including a positive active material, and an electrolyte.

By reducing the internal pore volume and reducing side reactions with electrolyte, expansion of the negative active material may be suppressed or reduced, and cycle-life characteristics may be improved.

