Patent Description:
A secondary battery which can be charged and discharged repeatedly has been widely employed as a power source of a mobile electronic device such as a camcorder, a mobile phone, a laptop computer, etc., according to developments of information and display technologies. Recently, a battery pack including the secondary battery is being developed and applied as an eco-friendly power source of an electric automobile, a hybrid vehicle.

The secondary battery includes, e.g., a lithium secondary battery, a nickelcadmium battery, a nickel-hydrogen battery, etc. The lithium secondary battery is highlighted due to high operational voltage and energy density per unit weight, a high charging rate, a compact dimension, etc..

For example, the lithium secondary battery may include an electrode assembly including a cathode, an anode and a separation layer (separator), and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include an outer case having, e.g., a pouch shape for accommodating the electrode assembly and the electrolyte.

A graphite-based material may be used as an anode active material of the anode. However, as demands for lithium secondary batteries of high capacity/high power has been recently increased, a silicon-based material has been introduced as the anode active material.

However, the silicon-based material may cause side reactions with moisture, air, etc., and may cause contraction/expansion according to repeated charging/discharging.

Therefore, developments of an anode active material capable of providing high capacity while also providing sufficient life-span properties and operational stability are required.

For example, <CIT> discloses a metal-carbon composite anode active material for improving cycle properties.

According to an aspect of the present invention, there is provided an anode for a secondary battery having improved capacity property and stability.

According to an aspect of the present invention, there is provided a method of fabricating an anode for a secondary battery having improved capacity property and stability.

According to an aspect of the present invention, there is provided a lithium secondary battery including an anode for a secondary battery with improved capacity property and stability.

An anode for a lithium secondary battery includes an anode current collector, and an anode active material layer formed on the anode current collector, the anode active material layer including carbon-based active material particles and a silicon coating formed on surfaces of the carbon-based active material particles. A surface content of silicon of the anode active material layer measured by an X-ray photoelectric spectroscopy (XPS) is in a range from <NUM> atom% to <NUM> atom%. A peak intensity ratio defined as a ratio of a second peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV relative to a first peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV is in a range from <NUM> to <NUM>.

In some embodiments, a surface content of silicon of the anode active material layer measured by the XPS may be in a range from <NUM> atom% to <NUM> atom%.

In some embodiments, the carbon-based active material particles may form a porous carbon scaffold.

In some embodiments, the carbon-based active material particles may include a blend of artificial graphite and natural graphite.

In some embodiments, an amount of silicon at an outer surface of the anode active material layer may be greater than an amount of silicon at an inside of the anode active material layer.

In some embodiments, the carbon-based active material particles may be stacked in the anode active material layer so that surfaces of carbon-based active material particles may contact each other.

In some embodiments, the silicon coating may be discontinuously formed on the surfaces of the carbon-based active material particles.

In some embodiments, the first peak intensity may be a Si peak intensity, and the second peak intensity may be a Si—O peak intensity.

In some embodiments, a lithium secondary battery includes a cathode including lithium-transition metal composite oxide particles as a cathode active material, and the anode according to the above-described embodiments facing the cathode.

In a method of fabricating an anode for a secondary battery, a preliminary anode active material layer is formed by coating an anode slurry that includes carbon-based active material particles on an anode current collector. A deposition gas containing a silicon source is supplied on the preliminary anode active material layer to form a silicon coating on surfaces of the carbon-based active material particles.

In some embodiments, a ratio of the silicon source in the deposition gas may be in a range from <NUM> vol% to <NUM> vol%.

In some embodiments, the silicon coating may be formed by a chemical vapor deposition (CVD) process, and the silicon source may include SiH<NUM>.

In some embodiments, the anode slurry may further include a solvent, a binder and a carbon-based conductive material.

In some embodiments, in the formation of the preliminary anode active material layer, the coated anode slurry may be dried and pressed before forming the silicon coating.

In some embodiments, a surface content of silicon of the anode active material layer measured by an X-ray photoelectric spectroscopy (XPS) may be in a range from <NUM> atom% to <NUM> atom%. A peak intensity ratio defined as a ratio of a second peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV relative to a first peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV may be in a range from <NUM> to <NUM>.

According to embodiments of the present invention, an anode for a secondary battery manufactured according to the above-described method is provided. Further, a lithium secondary battery including the anode is provided.

According to embodiments of the present invention, a preliminary anode active material layer including carbon-based active material particles is formed on an anode current collector, and then a silicon coating is formed on surfaces of the carbon-based active material particles by a dry deposition process. The silicon coating is formed after a coating process of an anode active material layer, so that generation of gas due to a side reaction with a solvent and oxidation of silicon that may be caused in an anode slurry may be suppressed. Additionally, capacity and energy density of an anode may be enhanced by the silicon coating while maintaining conductivity of the carbon-based active material.

According to embodiments of the present invention, the anode active material layer may have a Si content and a ratio between a Si peak and a Si—O peak measured from an X-ray photoelectric spectrum (XPS) adjusted within a predetermined range. Accordingly, sufficient capacity properties may be achieved while reducing gas generation and an anode resistance in an anode formation process.

According to embodiments of the present invention, an anode including an anode active material layer in which a carbon-based material and a silicon-based material are combined and a method for fabricating the anode are provided. Further, a lithium secondary battery including the anode is provided.

<FIG> is a schematic cross-sectional view illustrating an anode for a secondary battery according to exemplary embodiments.

For convenience of descriptions, an anode active material included in an anode active material layer <NUM> is only illustrated in <FIG>, and detailed illustrations of other components such as a binder and a conductive material included in the anode active material layer <NUM> are omitted.

Referring to <FIG>, an anode <NUM> includes an anode current collector <NUM>, and the anode active material layer <NUM> formed by coating the anode active material on the anode current collector <NUM>.

The anode current collector <NUM> may include gold, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, preferably may include copper or a copper alloy.

The anode active material layer <NUM> may be formed on at least one surface of the anode current collector <NUM>. As illustrate in <FIG>, the anode active material layer <NUM> may be formed on one surface of the anode current collector <NUM>. In some embodiments, the anode active material layer <NUM> may be formed on the one surface and the other surface opposite to the one surface of the anode current collector <NUM>. The anode active material layer <NUM> may directly contact the surface of the anode current collector <NUM>.

The anode active material layer <NUM> may include carbon-based active material particles <NUM> and a silicon coating <NUM> formed on the carbon-based active material particles <NUM>. Accordingly, the anode active material layer <NUM> may include carbon-silicon composite particles.

The carbon-based active material particles <NUM> may include crystalline carbon and may have a porous structure. In some embodiments, the carbon-based active material particles <NUM> may include porous graphite particles.

The carbon-based active material particles <NUM> may include natural graphite and/or artificial graphite. Preferably, the carbon-based active material particles <NUM> may include a blend of natural graphite particles and artificial graphite particles.

In an embodiment, a weight of the artificial graphite particles in the carbon-based active material particles <NUM> may be greater than or equal to a weight of the natural graphite particles. Preferably, the weight of the artificial graphite particles may be greater than the weight of the natural graphite particles. In this case, life-span properties and operational stability of the anode <NUM> may be improved by the artificial graphite particles having relatively improved chemical and mechanical stability.

For example, a weight ratio of the artificial graphite particles relative to the natural graphite particles may be in a range from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM>.

In some embodiments, the carbon-based active material particles <NUM> may include porous carbonaceous particles such as graphitized or carbonized resin particles, an activated carbon, etc..

The silicon coating <NUM> contains silicon (Si) and may be formed on at least a portion of the surface of the carbon-based active material particle <NUM>.

As illustrated in <FIG>, the carbon-based active material particles <NUM> may have a porous structure including pores therein, and the silicon coating <NUM> may also be formed on inner surfaces of the pores.

In some embodiments, the silicon coating <NUM> may be formed in the form of an island locally formed on an outer surface of the carbon-based active material particle <NUM>. For example, a plurality of silicon coating islands may be spaced apart and distributed on the outer surface of one carbon-based active material particle <NUM>.

Accordingly, the outer surfaces of the adjacent carbon-based active material particles <NUM> may be in contact with each other, and the silicon coating <NUM> may be discontinuously distributed on the outer surfaces of the carbon-based active material particles <NUM>.

In some embodiments, an amount of the silicon coating <NUM> formed on the carbon-based active material particles <NUM> (e.g., first carbon-based active material particles 122a) exposed on an outer surface of the anode active material layer <NUM> may be greater than an amount of the silicon coating <NUM> formed on the carbon-based active material particles <NUM> (the second carbon-based active material particles 122b) included at an inside of the anode active material layer <NUM>.

As described above, carbon-silicon composite particles in which the carbon-based active material particles <NUM> and the silicon coating <NUM> are combined or integrated may be used as the anode active material. A silicon-based active material may be included as the partial silicon coating <NUM>, so that excessive contraction/expansion and chemical instability caused by the silicon-based active material may be suppressed while achieving high capacity/energy density properties of the silicon-based active material.

For example, the carbon-based active material particles <NUM> may contact each other to provide a backbone structure of the anode active material layer <NUM>, so that expansion/contraction of the anode caused by the silicon coating <NUM> may be prevented or reduced. For example, the carbon-based active material particles <NUM> may form a porous scaffold.

As described above, a relatively large number of the silicon coating <NUM> may be formed on the first carbon-based active material particles 122a provided as outer surface particles. Therefore, a sufficient capacity improvement effect through the silicon-based active material may be implemented on the outer surface of the anode active material layer <NUM>, and chemical and mechanical stability may be enhanced at the inside of the anode active material layer <NUM>.

Additionally, the contact of the carbon-based active material particles <NUM> may be maintained at the inside of the anode active material layer <NUM>. Accordingly, a resistance increase of the anode active material layer <NUM> due to the silicon coating <NUM> may be suppressed, and power properties from the anode <NUM> may also be improved.

In exemplary embodiments, a content of silicon (Si) on the surface of the anode active material layer <NUM> measured by an X-ray photoelectric spectrum (XPS) may be in a range from <NUM> atom% to <NUM> atom%.

For example, the surface silicon content may be measured using an intensity of Si-containing peaks in the XPS.

For example, if the silicon content on the surface of the anode active material layer <NUM> is less than <NUM> atom%, a sufficient capacity enhancement through the silicon-based active material may not be obtained. If the silicon content on the surface of the anode active material layer <NUM> exceeds <NUM> atom%, stability of the anode active material layer <NUM> may be excessively degraded, thereby deteriorating life-span properties of the secondary battery.

In an embodiment, the silicon content on the surface of the anode active material layer <NUM> may be in a range from <NUM> atom% to <NUM> atom%, preferably from <NUM> atom% to <NUM> atom%, more preferably from <NUM> atom% to <NUM> atom%, or from <NUM> atom% to <NUM> atom%.

In exemplary embodiments, a ratio of a second peak intensity corresponding to a peak intensity (a maximum peak intensity) at a binding energy ranging from <NUM> eV to <NUM> eV relative to a first peak intensity corresponding to a peak intensity at a binding energy ranging from <NUM> eV to <NUM> eV in the XPS of the anode active material layer <NUM> (hereinafter, which may be abbreviated as a peak intensity ratio) may be in a range from <NUM> to <NUM>.

The first peak intensity may be a peak corresponding to a silicon element (Si). The second peak intensity may be an intensity of a peak corresponding to a Si—O.

Thus, an intensity of the Si-O may be is suppressed in the range of the peak intensity ratio, so that a decrease of a conductivity and an initial efficiency of the anode <NUM> due to an oxidation of the silicon-based active material may be suppressed. For example, if the peak intensity ratio exceeds <NUM>, a resistance of the anode <NUM> may be excessively increased, and capacity enhancement by employing the silicon-based active material may not be sufficiently implemented.

For example, if the peak intensity ratio is less than <NUM>, a sufficient amount of the silicon coating may not be achieved.

In an embodiment, the peak intensity ratio may be in a range from <NUM> to <NUM>, preferably from <NUM> to <NUM>, or from <NUM> to <NUM>.

As described above, the silicon content on the surface of the anode active material layer <NUM> and the ratio of the Si—O component may be controlled in the silicon coating <NUM>, so that a substantial increase of capacity/efficiency from the introduction of the silicon-based active material may be realized. Further, the resistance increase due to the introduction of the silicon-based active material may be prevented to achieve sufficient conductivity and power.

<FIG> are schematic cross-sectional views for explaining a method of fabricating an anode for a secondary battery according to exemplary embodiments.

Referring to <FIG>, a preliminary anode active material layer <NUM> may be formed on an anode current collector <NUM>.

In exemplary embodiments, an anode slurry including the carbon-based active material particles <NUM> as described above may be formed, and the anode slurry may be coated on a surface of the anode current collector <NUM> to form a preliminary coating layer. Thereafter, the preliminary coating layer may be dried and pressed to form the preliminary anode active material layer <NUM>.

The anode slurry may be formed by dissolving the carbon-based active material particles <NUM> together with an anode binder in a solvent (e.g., water). In some embodiments, a conductive material may be further included in the anode slurry, and an additional component such as a dispersive agent may be further included.

In some embodiments, the binder may include, e.g., a styrene-butadiene rubber (SBR)-based material, and may be used together with a thickener such as carboxymethyl cellulose (CMC). In some embodiments, the conductive material may include a carbon-based conductive material such as carbon nanotube, carbon black, Super P, etc..

Referring to <FIG>, a silicon coating <NUM> may be formed on the preliminary anode active material layer <NUM> by a dry process. Accordingly, the anode active material layer <NUM> including a carbon-silicon composite active material may be formed.

In exemplary embodiments, a silicon source may be supplied on the surface of the preliminary anode active material layer <NUM> by a chemical vapor deposition (CVD) process to from the silicon coating <NUM>. For example, the silicon source may include a silane-based gas (e.g., SiH<NUM>).

In some embodiments, the silicon source may be mixed with a carrier gas to form a deposition gas. The carrier gas may include an inert gas such as nitrogen (N<NUM>), helium, argon, etc..

A molar ratio of the silicon source in the deposition gas may be adjusted to control an amount of the silicon coating <NUM>.

In some embodiments, a concentration (or volume ratio) of the silicon source (e.g., silane (SiH<NUM>)) may be in a range from <NUM> volume percents (vol%) to <NUM> vol%, preferably from <NUM> vol% to <NUM> vol%, more preferably from <NUM> vol% to <NUM> vol%.

Within the above range, the surface content of silicon and the peak intensity ratio on the anode active material layer <NUM> may be effectively implemented.

As described above, the preliminary anode active material layer <NUM> having the form of the porous carbon scaffold may be fixed on the anode current collector <NUM> in advance, and then the silicon coating <NUM> may be formed by the deposition process.

Accordingly, mechanical instability such as a poor adhesion of the anode active material layer <NUM>, and a peel-off from the anode current collector <NUM> due to contraction/expansion of the silicon-based active material may be reduced.

In a comparative example, the silicon source may be included in the anode slurry to form a silicon coating on the carbon-based active material particles <NUM>. In the comparative example, hydrogen (H<NUM>) gas may be generated by being reacted with the solvent and silicon, and thus a battery explosion due to a pressure increase may be caused.

Further, silicon may be oxidized to increase a formation of a silicon oxide layer. Accordingly, a resistance of the anode active material layer <NUM> may be increased, and sufficient capacity increase by the introduction of the silicon-based active material may not be implemented.

However, according to embodiments of the present invention, a network of carbon-based active material particles <NUM> may be formed from the preliminary anode active material layer <NUM>, and then the silicon coating <NUM> may be formed. Accordingly, an ion conductive path in the anode active material layer <NUM> may be substantially maintained, and the resistance increase in the anode <NUM> due to the introduction of the silicon-based active material may be prevented.

Additionally, a relatively large amount of the silicon coating <NUM> may be distributed on the surface of the anode active material layer <NUM>. Thus, the ion conductive path in the anode active material layer <NUM> may be more effectively achieved, and expansion of the anode <NUM> may be suppressed.

According to exemplary embodiments, the silicon coating <NUM> may be formed by a dry deposition process, so that a side reaction with the solvent and a degradation of dispersibility of the anode slurry due to the silicon source may be avoided. Thus, the uniform anode active material layer <NUM> having stable chemical and electrical properties may be formed.

<FIG> are a schematic plan view and a cross-sectional view, respectively, illustrating a lithium secondary battery according to exemplary embodiments. For example, <FIG> is a cross-sectional view taken along a line I-I' of <FIG> in a thickness direction. Detailed descriptions of elements and structures of the cathode <NUM> described with reference to <FIG> are omitted herein.

Referring to <FIG>, a lithium secondary battery includes a cathode <NUM> and the anode <NUM> according to the above-described exemplary embodiments, and may further include a separation layer <NUM> interposed between the cathode <NUM> and the anode <NUM>.

The cathode <NUM> may include a cathode active material layer <NUM> formed by coating a cathode active material on a cathode current collector <NUM>. The cathode active material may include a compound capable of reversibly intercalating and de-intercalating lithium ions.

In exemplary embodiments, the cathode active material may include lithium-transition metal composite oxide particles. For example, the lithium-transition metal composite oxide particles may include nickel (Ni), and may further include at least one of cobalt (Co) and manganese (Mn).

For example, the lithium-transition metal composite oxide particles may be represented by Chemical Formula <NUM> below.

[Chemical Formula <NUM>]     LixNi<NUM>-yMyO<NUM>+z.

In Chemical Formula <NUM>, <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM> and -<NUM>≤z≤<NUM>. M may represent at least one element selected from Na, Mg, Ca, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn and Zr.

In some embodiments, a molar ratio or a concentration (<NUM>-y) of Ni in Chemical Formula <NUM> may be <NUM> or more, and may exceed <NUM> in a preferable embodiment. In an embodiment, the molar ratio of Ni may be, e.g., <NUM> or more, <NUM> or more, <NUM> or more, or <NUM> or more.

Ni may serve as a transition metal related to power and capacity of the lithium secondary battery. Thus, as described above, the high-Ni composition in the lithium-transition metal composite oxide particles may be employed, so that the cathode and the lithium secondary battery of high power may be implemented.

However, as the content of Ni increases, long-term storage and life-span stability of the cathode or secondary battery may be relatively degraded. However, according to exemplary embodiments, the life-span stability and capacity retention properties may be improved using Mn while maintaining an electrical conductivity by including Co.

In some embodiments, the cathode active material or the lithium-transition metal composite oxide particles may further include a coating element or a doping element. For example, the coating element or the doping element may include Al, Ti, Ba, Zr, Si, B, Mg, P, W, V, an alloy thereof, or an oxide thereof. These may be used alone or in combination thereof. The cathode active material particles may be protected by the coating or doping element, so that the stability against penetration of an external object and the life-span properties may be further improved.

A slurry may be prepared by mixing and stirring the cathode active material with a binder, a conductive material and/or a dispersive agent in a solvent. The slurry may be coated on the cathode current collector <NUM>, and then dried and pressed to form the cathode <NUM>.

The cathode current collector <NUM> may include, e.g., stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, preferably may include aluminum or an aluminum alloy.

The binder may include an organic based binder such as a polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc., or an aqueous based binder such as styrene-butadiene rubber (SBR) that may be used with a thickener such as carboxymethyl cellulose (CMC).

For example, a PVDF-based binder may be used as a cathode binder. In this case, an amount of the binder for forming the cathode active material layer <NUM> may be reduced, and an amount of the cathode active material or lithium metal oxide particles may be relatively increased. Thus, capacity and power of the lithium secondary battery may be further improved.

The conductive material may be added to facilitate electron mobility between active material particles. For example, the conductive material may include a carbon-based material such as graphite, carbon black, graphene, carbon nanotube, etc., and/or a metal-based material such as tin, tin oxide, titanium oxide, a perovskite material such as LaSrCoO<NUM> or LaSrMnO<NUM>, etc..

The separation layer <NUM> may be interposed between the cathode <NUM> and the anode <NUM>. The separation layer <NUM> may include a porous polymer film prepared from, e.g., a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, an ethylene/methacrylate copolymer, or the like. The separation layer <NUM> may also include a non-woven fabric formed from a glass fiber with a high melting point, a polyethylene terephthalate fiber, or the like.

In some embodiments, an area and/or a volume of the anode <NUM> (e.g., a contact area with the separation layer <NUM>) may be greater than that of the cathode <NUM>. Thus, lithium ions generated from the cathode <NUM> may be easily transferred to the anode <NUM> without a loss by, e.g., precipitation or sedimentation to further improve power and capacity of the secondary battery.

In exemplary embodiments, an electrode cell may be defined by the cathode <NUM>, the anode <NUM> and the separation layer <NUM>, and a plurality of the electrode cells may be stacked to form an electrode assembly <NUM> that may have e.g., a jelly roll shape. For example, the electrode assembly <NUM> may be formed by winding, laminating or folding the separation layer <NUM>.

The electrode assembly <NUM> may be accommodated together with an electrolyte in a case <NUM> to define the lithium secondary battery. In exemplary embodiments, a non-aqueous electrolyte may be used as the electrolyte.

The non-aqueous electrolyte solution may include a lithium salt and an organic solvent. The lithium salt may be represented by Li+X- , and an anion of the lithium salt X- may include, e.g., F-, Cl-, Br-, I-, NO<NUM>-, N(CN)<NUM>-, BF<NUM>-, ClO<NUM>-, PF<NUM>-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF<NUM>-, (CF<NUM>)<NUM>PF-, (CF<NUM>)<NUM>P-, CF<NUM>SO<NUM>-, CF<NUM>CF<NUM>SO<NUM>-, (CF<NUM>SO<NUM>)<NUM>N-, (FSO<NUM>)<NUM>N-, CF<NUM>CF<NUM>(CF<NUM>)<NUM>CO-, (CF<NUM>SO<NUM>)<NUM>CH-, (SF<NUM>)<NUM>C-, (CF<NUM>SO<NUM>)<NUM>C-, CF<NUM>(CF<NUM>)<NUM>SO<NUM>-, CF<NUM>CO<NUM>-, CH<NUM>CO<NUM>-, SCN-, (CF<NUM>CF<NUM>SO<NUM>)<NUM>N-, etc..

The organic solvent may include, e.g., propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxy ethane, diethoxy ethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in a combination of two or more therefrom.

As illustrated in <FIG>, electrode tabs (a cathode tab and an anode tab) may protrude from the cathode current collector <NUM> and the anode current collector <NUM> included in each electrode cell to one side of the case <NUM>. The electrode tabs may be welded together with the one side of the case <NUM> to be connected to an electrode lead (a cathode lead <NUM> and an anode lead <NUM>) that may be extended or exposed to an outside of the case <NUM>.

<FIG> illustrates that the cathode lead <NUM> and the anode lead <NUM> are positioned at the same side of the lithium secondary battery or the case <NUM>, but the positions of the electrode leads are not limited thereto. For example, the cathode lead <NUM> and the anode lead <NUM> may protrude from at least one of both lateral sides of the case <NUM>, or may protrude from a lower side of the case <NUM>. For example, the cathode lead <NUM> and the anode lead <NUM> may be formed to protrude from different sides of the case <NUM>.

The lithium secondary battery may be manufactured in, e.g., a cylindrical shape using a can, a square shape, a pouch shape or a coin shape.

<NUM> wt% of natural graphite, <NUM> wt% of artificial graphite, <NUM> wt% of carboxymethyl cellulose (CMC), <NUM> wt% of styrene butadiene rubber, and <NUM> wt% of a conductive material (CNT) were mixed in distilled water to prepare an anode slurry. The anode slurry was coated on a Cu foil current collector, dried and pressed to form a preliminary anode active material layer including carbon-based active material particles.

The anode including the preliminary anode active material layer was loaded into a chamber and treated at <NUM> for <NUM> minutes in <NUM> vol% SiH<NUM> deposition gas mixed with nitrogen gas. Accordingly, an anode active material layer having a silicon coating was formed.

The anode fabricated as described in the above <NUM>) and a lithium foil as a counter electrode were used. A PE separator was interposed between the anode and the counter electrode, and then an electrolyte was injected to prepare a coin cell. The assembled coin cell was maintained at room temperature for <NUM> to <NUM> hours. The electrolyte was prepared by mixing <NUM> vol% of FEC as an electrolyte additive in a lithium salt <NUM> LiPF<NUM> solution (solvent: EC and EMC mixed solvent, mixing ratio <NUM> vol%:<NUM> vol%).

A coin cell was fabricated by the same method as that in Example <NUM>, except that the concentration of SiH<NUM> was changed as shown in Table <NUM>.

A coin cell was fabricated by the same method as that in Example <NUM>, except that silicon coating (SiH<NUM> deposition) was omitted.

<NUM> wt% of natural graphite and <NUM> wt% of artificial graphite were evenly mixed, and then heat-treated at <NUM> for <NUM> minutes in an atmosphere of <NUM> vol% SiH<NUM> gas mixed with nitrogen gas. A carbon-silicon composite was prepared as an anode active material by collecting and pulverizing the heat-treated powder.

<NUM> wt% of the carbon-silicon composite as an anode active material, <NUM> wt% of carboxymethyl cellulose, <NUM> wt% of styrene butadiene rubber, and <NUM> wt% of a conductive material (CNT) were mixed in distilled water to prepare an anode slurry. The anode slurry was coated on a Cu foil current collector, dried and pressed to prepare aa anode.

A coin cell was fabricated by the same method as that in Comparative Example <NUM>, except that the concentration of SiH<NUM> was changed as shown in Table <NUM>.

The anode prepared in Examples and Comparative Examples was attached to a carbon tape to prepare a sample, and an XPS analysis was performed under the following conditions to measure a surface content of silicon surface and a peak intensity ratio (Si-O/Si).

<FIG> is an X-ray photoelectric spectrum (XPS) analysis graph in anode active material layers of Example <NUM> and Comparative Examples <NUM> and <NUM>.

Referring to <FIG>, in Comparative Examples where the silicon coating was formed before the formation of the slurry, the Si—O ratio was increased while the surface Si content was reduced.

<NUM> of the anode slurry used in Examples and Comparative Examples was injected into a gas tight syringe, and an inlet was sealed and left at room temperature for <NUM> days. Thereafter, a slurry gas generation rate was calculated by Equation <NUM> below.

The coin cell of Examples and Comparative Examples was charged with a constant current at room temperature (<NUM>) at a current of <NUM>. 1C rate until the voltage reached <NUM>. 01V, and then charged with a constant voltage while maintaining <NUM>. 01V in a constant voltage mode and cut-off at a current of <NUM>.

Thereafter, the battery was discharged at a constant current of <NUM>. 1C rate until the voltage reached <NUM>. The charging and discharging were performed as one cycle. The one cycle was further by the same method, and <NUM> cycles were performed by changing an applied current to <NUM>. 5C during the charging and discharging with a <NUM> minute rest period between the cycles.

The charge/discharge efficiency (%) (an initial discharge capacity/an initial charge capacity) and a discharge capacity of the first cycle among the <NUM> cycles were designated as an initial efficiency and an initial discharge capacity, respectively, and the capacity retention at the 50th cycle compared to the initial discharge capacity was calculated.

An interfacial resistance of the anodes prepared in Examples and Comparative Examples was measured under conditions of a current 10mA and a voltage range <NUM>. 5V using HIOKI XF057 PROBE UNIT equipment.

The evaluation results are shown in Table <NUM> below.

Referring to Table <NUM>, improved initial capacity/efficiency and capacity retention were obtained in Examples satisfying the surface Si content and peak intensity ratio (Si-O/Si) measured by the XPS, while the gas generation and electrode resistance were reduced.

Claim 1:
An anode for a lithium secondary battery, comprising:
an anode current collector; and
an anode active material layer formed on the anode current collector, the anode active material layer comprising carbon-based active material particles and a silicon coating formed on surfaces of the carbon-based active material particles,
wherein a surface content of silicon of the anode active material layer measured by an X-ray photoelectric spectroscopy (XPS) is in a range from <NUM> atom% to <NUM> atom%, and
a peak intensity ratio defined as a ratio of a second peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV relative to a first peak intensity corresponding to a peak intensity at a binding energy in a range from <NUM> eV to <NUM> eV is in a range from <NUM> to <NUM>,
wherein the first peak intensity is a Si peak intensity, and the second peak intensity is a Si-O peak measured according to the description.