CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2018-0110336 filed on Sep. 14, 2018 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The present disclosure relates to an anode including a multilayer anode mixture layer, and more particularly, to a multilayer anode with multiple layers having different contents of natural graphite contained as an anode active material in an anode mixture layer, and a lithium secondary battery including the same.

As technological development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, exhibiting high energy density and operating potential and which have a long cycle life and a low self-discharge rate, have been commercialized and widely used.

As interest in environmental issues has increased in recent years, research into electric vehicles (EVs) and hybrid electric vehicles (HEVs), which may replace fossil-fueled vehicles such as gasoline vehicles, diesel vehicles and the like, significant causes of air pollution, has been conducted. Lithium secondary batteries having high energy density, high discharge voltage and output stability have mainly been researched and used as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs).

Such a lithium secondary battery is under development as a model capable of implementing a high voltage and a high capacity in line with consumer demand. To implement a high capacity thereof, a lithium secondary battery is required to have an optimization process of a cathode material, an anode material, a separator, and an electrolyte, four elements of the lithium secondary battery, within a limited space.

On the other hand, the use of artificial graphite in the place of natural graphite as an anode active material has been increasing in recent years in order to improve cell lifespan and the like in the production of an anode used in a secondary battery. However, as the artificial graphite content increases, the adhesive force between a current collector and an electrode is lowered, and a phenomenon in which the electrode is separated from a substrate in the electrolyte may be serious.

Further, in the process of calendering an electrode using artificial graphite, an active material on the surface of an electrode mixture layer is deposited on a calendering calender, and thus, calender contamination becomes serious, which causes a problem in which productivity in a calendering process is significantly lowered.

SUMMARY

An aspect of the present disclosure is to provide a multilayer anode in which calendering-calender contamination occurring in a calendering process and an electrode stripping phenomenon may be prevented, and a lithium secondary battery including the same.

According to an embodiment of the present disclosure, a multilayer anode includes an anode collector, and a plurality of anode mixture layers sequentially stacked on at least one surface of the anode collector and including natural graphite as an anode active material. A weight ratio of the natural graphite in innermost and outermost anode mixture layers is greater than a weight ratio of the natural graphite in an anode mixture layer located between the innermost and outermost anode mixture layers in a stacking direction, from among the plurality of anode mixture layers.

The anode mixture layer may be comprised of three or more layers.

A weight ratio of the natural graphite in portions of the plurality of anode mixture layers, corresponding to 0 to 20% and 80 to 100% of a total height of the plurality of anode mixture layers, from the anode collector, in a thickness direction of the plurality of anode mixture layers, may be greater than a weight ratio in a portion of the plurality of anode mixture layers, except for the portions thereof.

The natural graphite of the innermost anode mixture layer may be contained in an amount of 50 to 100 wt % based on a total active material weight of the innermost anode mixture layer.

The natural graphite of the outermost anode mixture layer may be contained in an amount of 50 to 100 wt % based on a total active material weight of the outermost anode mixture layer.

The anode mixture layer may further include one or more anode active materials selected from artificial graphite, natural graphite, soft carbon, hard carbon, acetylene carbon black, Ketjen black, carbon nanotubes, carbon nanofiber and silicon oxide.

The plurality of anode mixture layers may further include a binder and a conductive material.

According to an embodiment of the present disclosure, a lithium secondary battery including the multilayer anode as described above is provided.

