Negative electrode for secondary battery, method for manufacturing the same, and lithium secondary battery including the same

Abstract

A negative electrode for a secondary battery includes: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and containing carbon-based active material particles and a silicon coating layer formed on the surface of the carbon-based active material particles. The surface silicon content of the negative electrode active material layer, as measured by X-ray photoelectron spectroscopy (XPS), is 3-25 atomic %. In the XPS of the negative electrode active material layer, the peak intensity ratio defined as the ratio of a second peak intensity to a first peak intensity is 0.05 to 1, where the first peak intensity corresponds to the peak intensity at a binding energy in the range of 98-102 eV, and the second peak intensity is the peak intensity at a binding energy in the range of 102-106 eV.

Description

TECHNICAL FIELD

[0001] The present application relates to a negative electrode for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. In more detail, it relates to a negative electrode for a secondary battery including a composite active material, a method of manufacturing the same, and a lithium secondary battery including the same. BACKGROUND

[0002] Secondary batteries are batteries that can be repeatedly charged and discharged, and with the development of information communication and display industries, secondary batteries are widely used as power sources for portable electronic communication devices such as camcorders, mobile phones, notebook computers, etc. In addition, in recent years, battery packs including secondary batteries are being developed and used as power sources for environmentally friendly vehicles such as electric cars, hybrid cars, etc.

[0003] Among them, lithium secondary batteries have a high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and thus are actively being developed and applied.

[0004] For example, a lithium secondary battery can include an electrode assembly including a positive electrode, a negative electrode, and a separator film (separator), and an electrolyte impregnated in the electrode assembly. The lithium secondary battery can further include an outer material, such as a soft pack type outer material, which accommodates the electrode assembly and the electrolyte.

[0005] A graphite-based material can be used as an active material of the negative electrode. However, in recent years, as the demand for lithium secondary batteries with high capacity / high power increases, silicon-based materials are being introduced as negative electrode active materials.

[0006] However, the silicon-based material can cause side reactions with moisture, air, etc., and can cause shrinkage / expansion phenomena as charging / discharging is repeated.

[0007] Therefore, there is a need to develop a negative electrode active material that can ensure sufficient life characteristics and operating stability and provide high capacity characteristics.

[0008] For example, Korean Patent No. 10-1057162 discloses a metal-carbon composite negative electrode active material for improving cycle characteristics. SUMMARY

[0009] Technical problems to be solved

[0010] The present application relates to a negative electrode for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. In more detail, it relates to a negative electrode for a secondary battery including a composite active material, a method of manufacturing the same, and a lithium secondary battery including the same.

[0011] The present application relates to a negative electrode for a secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same. In more detail, it relates to a negative electrode for a secondary battery including a composite active material, a method of manufacturing the same, and a lithium secondary battery including the same.

[0012] An object of the present application is to provide a lithium secondary battery including a negative electrode for a secondary battery having improved capacity characteristics and stability.

[0013] Technical Solution

[0014] The negative electrode for a secondary battery according to an exemplary embodiment includes: a negative current collector; and a negative active material layer formed on the negative current collector and including carbon-based active material particles and a silicon coating layer formed on surfaces of the carbon-based active material particles. A surface silicon content of the negative active material layer measured by X-ray photoelectron spectroscopy (XPS) is 3-25 atom%. In the XPS of the negative active material layer, a peak intensity ratio defined as a ratio of a second peak intensity to a first peak intensity is 0.05 to 1, wherein the first peak intensity corresponds to a peak intensity at a binding energy in a range of 98-102 eV, and the second peak intensity is a peak intensity at a binding energy in a range of 102-106 eV.

[0015] In some embodiments, the surface silicon content of the negative active material layer measured by XPS can be 3-11 atom%.

[0016] In some embodiments, the carbon-based active material particles can form a porous carbon scaffold.

[0017] In some embodiments, the carbon-based active material particles can include a mixture of artificial graphite and natural graphite.

[0018] In some embodiments, a silicon amount of an outer surface of the negative active material layer can be greater than a silicon amount inside the negative active material layer.

[0019] In some embodiments, surfaces of the carbon-based active material particles can be laminated in the negative active material layer to contact each other.

[0020] In some embodiments, the silicon coating layer can be discontinuously formed on the surfaces of the carbon-based active material particles.

[0021] In some embodiments, the first peak intensity can be a Si peak intensity, and the second peak intensity can be a Si-O peak intensity.

[0022] The lithium secondary battery according to an exemplary embodiment includes: a positive electrode including lithium-transition metal composite oxide particles as a positive active material; and a negative electrode according to the above-described embodiment, the negative electrode being opposite to the positive electrode.

[0023] In a method of manufacturing a negative electrode for a secondary battery according to an exemplary embodiment, a negative electrode slurry including carbon-based active material particles is coated on a negative electrode current collector to form a primary negative electrode active material layer. A deposition gas containing a silicon source is supplied to the primary negative electrode active material layer to form a negative electrode active material layer having a silicon coating layer formed on surfaces of the carbon-based active material particles.

[0024] In some embodiments, the proportion of the silicon source in the deposition gas can be 3-22 vol. %.

[0025] In some embodiments, the silicon coating layer can be formed by a chemical vapor deposition (CVD) process, and the silicon source can include SiH4.

[0026] In some embodiments, the negative electrode slurry, which is coated before the silicon coating layer is formed, can further include a solvent, a binder, and a carbon-based conductive material.

[0027] In some embodiments, the negative electrode slurry, which is coated before the silicon coating layer is formed, can be dried and pressed.

[0028] In some embodiments, the surface silicon content of the negative electrode active material layer, as measured by X-ray photoelectron spectroscopy (XPS), can be 3-25 at. %. In the XPS of the negative electrode active material layer, a peak intensity ratio defined as the ratio of a second peak intensity to a first peak intensity can be 0.05 to 1, where the first peak intensity corresponds to the peak intensity at a binding energy in the range of 98-102 eV, and the second peak intensity is the peak intensity at a binding energy in the range of 102-106 eV.

[0029] Advantageous effects

[0030] According to exemplary embodiments, a silicon coating layer can be formed on surfaces of carbon-based active material particles after a primary negative electrode active material layer including the carbon-based active material particles is formed on a negative electrode current collector by a dry deposition process. The silicon coating layer is formed after a negative electrode active material layer coating process, and thus can inhibit oxidation of silicon, generation of gas due to side reactions with a solvent, which can be caused in a negative electrode slurry. In addition, the electrical conductivity of carbon-based active material can be maintained and the negative electrode capacity and energy density can be effectively improved by the silicon coating layer.

[0031] According to exemplary embodiments, the negative electrode active material layer can have a Si content, as measured by X-ray photoelectron spectroscopy (XPS), adjusted to a prescribed range, and a ratio between a Si peak and a Si-O peak. Thus, the amount of gas generation and the negative electrode resistance in a negative electrode formation process can be reduced and sufficient capacity characteristics can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1is a cross-sectional schematic view showing a negative electrode for a secondary battery according to an exemplary embodiment.

[0033] Figure 2 and Figure 3 is a cross-sectional schematic view for explaining a method of manufacturing a negative electrode for a secondary battery according to an exemplary embodiment.

[0034] Figure 4 and Figure 5 are a plan view and a cross-sectional schematic view, respectively, showing a lithium secondary battery according to an exemplary embodiment.

[0035] Figure 6 is an X-ray photoelectron spectroscopy (XPS) analysis chart of the negative electrode active material layer of the example and the comparative example. DETAILED DESCRIPTION

[0036] According to an embodiment of the present application, a negative electrode including a negative electrode active material layer in which a carbon-based material and a silicon-based material are combined, and a method of manufacturing the same are provided. Further, a lithium secondary battery including the negative electrode is provided.

[0037] Hereinafter, embodiments of the present application will be described more specifically with reference to the accompanying drawings. However, the drawings in the present specification are only for illustrating preferred embodiments of the present application, and serve together with the above-summarized summary of the application to further understand the technical idea of the present application, and thus should not be construed as limiting the present application only to the contents recited in these drawings.

[0038] Figure 1 is a cross-sectional schematic view showing a negative electrode for a secondary battery according to an exemplary embodiment.

[0039] For convenience of explanation, Figure 1 In FIG. 1, only the negative electrode active material included in the negative electrode active material layer 120 is shown, and detailed illustrations of other components such as the binder, the conductive material, etc. included in the negative electrode active material layer 120 are omitted.

[0040] Referring to FIG. 1, Figure 1 The negative electrode 130 can include a negative electrode current collector 125 and a negative electrode active material layer 120 formed by coating the negative electrode active material on the negative electrode current collector 125.

[0041] The negative electrode current collector 125 can include gold, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably can include copper or a copper alloy.

[0042] The negative electrode active material layer 120 can be formed on at least one face of the negative electrode current collector 125. As Figure 1As shown, the negative electrode active material layer 120 can be formed on one side of the negative electrode current collector 125. In some embodiments, the negative electrode active material layer 120 can be formed on both one side and the other side of the negative electrode current collector 125. The negative electrode active material layer 120 can be in direct contact with the surface of the negative electrode current collector 125.

[0043] The negative electrode active material layer 120 may include carbon-based active material particles 122 and a silicon coating 124 formed on the carbon-based active material particles 122. Therefore, the negative electrode active material layer 120 may include carbon-silicon composite particles.

[0044] The carbon-based active material particles 122 may contain crystalline carbon and may have a porous structure. In some embodiments, the carbon-based active material particles 122 may contain porous graphite particles.

[0045] The carbon-based active material particles 122 may comprise natural graphite and / or artificial graphite. Preferably, the carbon-based active material particles 122 may comprise a mixture of natural graphite particles and artificial graphite particles.

[0046] In one embodiment, the weight of the artificial graphite particles in the carbon-based active material particles 122 can be greater than the weight of the natural graphite particles; preferably, the weight of the artificial graphite particles can be greater than the weight of the natural graphite particles. In this case, the lifespan characteristics and operational stability of the negative electrode 130 can be increased by using chemically and mechanically relatively stable artificial graphite particles.

[0047] For example, the weight ratio of artificial graphite particles to natural graphite particles can be 1 to 10, preferably 1.5 to 10, and more preferably 2.5 to 10.

[0048] In some embodiments, the carbon-based active material particles 122 may also include porous carbon particles such as graphitized or carbonized resin particles and activated carbon.

[0049] The silicon coating 124 may contain silicon (Si) and be formed on at least a portion of the surface of the carbon-based active material particles 122.

[0050] like Figure 1 As shown, the carbon-based active material particles 122 may have a porous structure containing pores inside, and the silicon coating 124 may also be formed on the inner surface of the pores.

[0051] In some embodiments, the silicon coating 124 may be formed in the form of islands locally formed on the outer surface of the carbon-based active material particles 122. For example, multiple silicon coating islands may be distributed and spaced apart on the outer surface of a carbon-based active material particle 122.

[0052] Accordingly, the outer surfaces of the adjacent carbon-based active material particles 122 can contact each other, and the silicon coating 124 can be discontinuously distributed on the outer surfaces of the carbon-based active material particles 122.

[0053] In some embodiments, the amount of the silicon coating 124 formed on the carbon-based active material particles 122 (e.g., the first carbon-based active material particles 122a) exposed to the outer surface of the negative active material layer 120 can be greater than the amount of the silicon coating 124 formed on the carbon-based active material particles 122 (the second carbon-based active material particles 122b) included in the inside of the negative active material layer 120.

[0054] As described above, as the negative active material, carbon-silicon composite particles that combine or integrate the carbon-based active material particles 122 and the silicon coating 124 can be used. The silicon-based active material is included in the form of the partial silicon coating 124, and thus the high capacity / energy density characteristics of the silicon-based active material can be secured and the excessive shrinkage / expansion phenomenon and chemical instability caused by the silicon-based active material can be inhibited.

[0055] For example, the carbon-based active material particles 122 contact each other and provide a skeleton of the negative active material layer 120, and thus the negative expansion / shrinkage phenomenon caused by the silicon coating 124 can be prevented or reduced. For example, the carbon-based active material particles 122 can form a porous scaffold.

[0056] As described above, the first carbon-based active material particles 122a provided with the outer surface particles can have the relatively large amount of the silicon coating 124 formed thereon. Accordingly, the sufficient capacity improvement effect by the silicon-based active material can be secured on the outer surface of the negative active material layer 120, and the chemical stability and the mechanical stability can be increased in the inside of the negative active material layer 120.

[0057] Further, the contact of the carbon-based active material particles 122 can be maintained in the inside of the negative active material layer 120. Accordingly, the increase in the electrical resistance of the negative active material layer 120 caused by the silicon coating 124 can be inhibited, and the power characteristics through the negative electrode 130 can also be improved.

[0058] According to an exemplary embodiment, the silicon (Si) content of the surface of the negative active material layer 120 can be 3-25 atomic % as measured by X-ray photoelectron spectroscopy (XPS).

[0059] For example, the surface silicon content can be measured by the intensity of the Si-containing peak in the XPS.

[0060] For example, when the silicon content of the surface of the negative electrode active material layer 120 is less than 3 atomic%, it can be impossible to achieve a sufficient capacity increase effect by the silicon-based active material. When the silicon content of the surface of the negative electrode active material layer 120 exceeds 25 atomic%, the stability of the negative electrode active material layer 120 is excessively hindered, and thus the life characteristics of the secondary battery can be deteriorated.

[0061] In one embodiment, the silicon content of the surface of the negative electrode active material layer 120 can be 3 to 11 atomic%, preferably can be 3 to 8 atomic%, and more preferably can be 3 to 6 atomic% or 3.5 to 6 atomic%.

[0062] According to an exemplary embodiment, in the XPS of the negative electrode active material layer 120, the ratio of the second peak intensity to the first peak intensity (hereinafter, can be simply referred to as the peak intensity ratio) can be 0.05 to 1, wherein the first peak intensity is the peak intensity (maximum peak intensity) at a binding energy corresponding to the range of 98 to 102 eV, and the second peak intensity is the peak intensity at a binding energy corresponding to the range of 102 to 106 eV.

[0063] The first peak intensity can be the intensity of a peak corresponding to a silicon element (Si). The second peak intensity can be the intensity of a peak corresponding to Si-O.

[0064] Accordingly, by suppressing the intensity of Si-O within the above-described peak intensity ratio range, it is possible to prevent a decrease in the electrical conductivity of the negative electrode 130 and a decrease in the initial efficiency caused by oxidation of the silicon-based active material. For example, when the peak intensity ratio exceeds 1, the resistance of the negative electrode 130 is excessively increased, and it can be impossible to sufficiently ensure the capacity increase effect by using the silicon-based active material.

[0065] For example, when the peak intensity ratio is less than 0.05, it can be impossible to achieve a sufficient amount of silicon coating.

[0066] In one embodiment, the peak intensity ratio can be 0.05 to 0.9, and preferably can be 0.05 to 0.85 or 0.1 to 0.8.

[0067] As described above, by suppressing the silicon content of the surface of the negative electrode active material layer 120 and the proportion of the Si-O component in the silicon coating 124, it is possible to achieve a substantial capacity / efficiency increase by introducing the silicon-based active material. In addition, it is possible to suppress an increase in the resistance caused by using the silicon-based active material, and it is possible to achieve sufficient electrical conductivity and power.

[0068] Figure 2 and Figure 3 is a cross-sectional schematic view for explaining a method of manufacturing a negative electrode for a secondary battery according to an exemplary embodiment.

[0069] Referring to Figure 2The primary negative active material layer 50 can be formed on the negative current collector 125.

[0070] According to an exemplary embodiment, a negative slurry including the carbon-based active material particles 122 described above can be formed, and the negative slurry can be coated on the surface of the negative current collector 125 to form a primary coating layer. Thereafter, the primary coating layer can be dried and pressed to form the primary negative active material layer 50.

[0071] The negative slurry can be formed by dissolving the carbon-based active material particles 122 together with a negative binder in a solvent (e.g., water). In some embodiments, a conductive material can also be included in the negative slurry, and additional ingredients such as a dispersant can also be further included.

[0072] In some embodiments, the binder can include, for example, a styrene butadiene rubber (SBR)-based material, and can be used together with a thickening agent such as carboxymethyl cellulose (CMC). In some embodiments, the conductive material can include a carbon-based conductive material such as a carbon nanotube, carbon black, Super P, etc.

[0073] Referring to Figure 3 The silicon coating layer 124 can be formed on the primary negative active material layer 50 by a dry process. Accordingly, the negative active material layer 120 including a carbon-silicon composite active material can be formed.

[0074] According to an exemplary embodiment, the silicon coating layer 124 can be formed by supplying a silicon source to the surface of the primary negative active material layer 50 through a chemical vapor deposition (CVD) process. For example, the silicon source can include a silane (e.g., SiH4)-based gas.

[0075] In some embodiments, the silicon source can be mixed with a carrier gas to form a deposition gas. The carrier gas can include an inert gas such as nitrogen (N2), helium, argon, etc.

[0076] By adjusting the molar ratio of the silicon source in the deposition gas, the amount of the silicon coating layer 124 can be adjusted.

[0077] In some embodiments, the concentration (or volume ratio) of the silicon source (e.g., silane (SiH4)) can be 3-22 vol%, preferably can be 4-20 vol%, and more preferably can be 4-15 vol%.

[0078] Within the above-described range, the ratio of the silicon surface content and the peak intensity on the negative active material layer 120 described above can be effectively achieved.

[0079] As described above, the primary negative electrode active material layer 50 in the form of a porous carbon support can be first fixed to the negative electrode current collector 125, and then the silicon coating 124 can be formed through a deposition process.

[0080] Accordingly, mechanical instability such as poor adhesion and peeling from the negative electrode current collector 125 of the negative electrode active material layer 120 caused by the contraction / expansion of the silicon-based active material can be reduced.

[0081] In the comparative example, a silicon source is included together in the negative electrode slurry, and thus a silicon coating can be formed on the carbon-based active material particles 122. In the case of the comparative example, a reaction of the solvent and the silicon can form hydrogen (H2) gas, and thus a battery explosion caused by an increase in pressure can occur.

[0082] In addition, the silicon can be oxidized, and thus the generation of a silicon oxide layer can increase. Accordingly, the resistance of the negative electrode active material layer 120 can increase, and thus the capacity increase effect of the introduction of the silicon-based active material can not be achieved.

[0083] However, according to the exemplary embodiment, the silicon coating 124 can be formed after the primary negative electrode active material layer 50 forms a mesh of the carbon-based active material particles 122. Accordingly, the ion conduction path in the negative electrode active material layer 120 can be substantially maintained, and an increase in the resistance of the negative electrode 130 caused by the introduction of the silicon-based active material can be prevented.

[0084] In addition, the silicon coating 124 can be distributed relatively more on the surface of the negative electrode active material layer 120. Accordingly, the ion conduction path inside the negative electrode active material layer 120 can be more effectively secured, and the expansion of the negative electrode 130 can also be inhibited.

[0085] According to the exemplary embodiment, the silicon coating 124 is introduced through a dry deposition process, and thus a side reaction with a solvent and a decrease in the dispersibility of the negative electrode slurry caused by a silicon source can also be avoided. Accordingly, the negative electrode active material layer 120 having uniform and stable chemical and electrical properties can be substantially formed.

[0086] Figure 4 and Figure 5 are a plan view and a cross-sectional view, respectively, illustrating a lithium secondary battery according to an exemplary embodiment. For example, Figure 5 is a cross-sectional view taken along the line I-I' of Figure 4 in the thickness direction. Detailed descriptions of the structure and composition of the negative electrode 130 described with reference to Figures 1 to 3 are omitted.

[0087] Reference is made to Figure 4 and Figure 5The lithium secondary battery can include a cathode 100 and a negative electrode 130 according to the above exemplary embodiment, and can further include a separator 140 interposed between the cathode 100 and the negative electrode 130.

[0088] The cathode 100 can include a cathode active material layer 110 formed by coating a cathode active material on a cathode current collector 105. The cathode active material can include a compound that can reversibly intercalate and deintercalate lithium ions.

[0089] In an exemplary embodiment, the cathode active material can include lithium-transition metal composite oxide particles. For example, the lithium-transition metal composite oxide particles include nickel (Ni), and can further include at least one of cobalt (Co) or manganese (Mn).

[0090] For example, the lithium-transition metal composite oxide particles can be represented by the following Chemical Formula 1.

[0091] [Chemical Formula 1]

[0092] Li x Ni 1-y M y O 2+z

[0093] In Chemical Formula 1, 0.9≤x≤1.1, 0≤y≤0.7, -0.1≤z≤0.1 can be satisfied. M can represent one or more elements selected from Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, or Zr.

[0094] In some embodiments, in Chemical Formula 1, the molar ratio or concentration of Ni (1-y) can be 0.8 or more, and in a preferred embodiment, the molar ratio or concentration of Ni (1-y) can exceed 0.8. In one embodiment, the molar ratio of Ni can be, for example, 0.83 or more, 0.85 or more, 0.88 or more, or 0.9 or more.

[0095] Ni can be provided as a transition metal related to the power and capacity of a lithium secondary battery. Accordingly, a high content (High-Ni) composition is applied to the lithium-transition metal composite oxide particles as described above, and thus a high-power cathode and a high-power lithium secondary battery can be provided.

[0096] However, as the content of Ni increases, the long-term storage stability and life stability of the cathode or secondary battery can be relatively reduced. However, according to the exemplary embodiment, the electrical conductivity can be maintained by including Co and the life stability and capacity retention characteristics can be improved by Mn.

[0097] In some embodiments, the positive electrode active material or the lithium-transition metal composite oxide particles can further include a coating element or a doping element. For example, the coating element or the doping element can include Al, Ti, Ba, Zr, Si, B, Mg, P, W, V, or alloys thereof or oxides thereof. These can be used alone or in combination with two or more. The positive electrode active material particles are passivated by the coating element or the doping element, thereby further improving the stability against penetration of external objects and the lifespan.

[0098] A slurry can be prepared by mixing the positive electrode active material with a binder, a conductive material, and / or a dispersing material, etc. in a solvent and stirring. The slurry can be coated on the positive electrode current collector 105 followed by pressing and drying to manufacture the positive electrode 100.

[0099] The positive electrode current collector 105 can include, for example, stainless steel, nickel, aluminum, titanium, copper, or alloys thereof, and preferably can include aluminum or an aluminum alloy.

[0100] The binder can include, for example, an organic binder such as a vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc., or a water-based binder such as styrene butadiene rubber (SBR), and can be used with a thickening agent such as carboxymethyl cellulose (CMC).

[0101] For example, a PVDF-based binder can be used as the positive electrode binder. In this case, the amount of the binder used to form the positive electrode active material layer can be reduced and the amount of the positive electrode active material can be relatively increased, and thus the power and capacity of the secondary battery can be improved.

[0102] The conductive material can be included to facilitate electron migration between the active material particles. For example, the conductive material can include a carbon-based conductive material such as graphite, carbon black, graphene, carbon nanotubes, etc., and / or a metal-based conductive material including tin, tin oxide, titanium oxide, LaSrCoO3, LaSrMnO3, etc., perovskite substances, etc.

[0103] A separator 140 can be interposed between the positive electrode 100 and the negative electrode 130. The separator 140 can include a porous polymer film prepared from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, etc. The separator 140 can further include a non-woven fabric formed of a high-melting point glass fiber, a polyethylene terephthalate fiber, etc.

[0104] In some embodiments, the area (e.g., the contact area with the separator 140) and / or the volume of the negative electrode 130 can be larger than that of the positive electrode 100. Thus, for example, lithium ions formed from the positive electrode 100 can smoothly migrate to the negative electrode 130 without being deposited in the middle.

[0105] According to an exemplary embodiment, an electrode unit is defined by the positive electrode 100, the negative electrode 130, and the separator 140, and a plurality of electrode units can be stacked to form an electrode assembly 150 in the form of, for example, a jelly roll. The electrode assembly 150 can be formed, for example, by winding, lamination, folding, etc. of the separator 140.

[0106] The electrode assembly 150 is accommodated in a case 160 together with an electrolyte, thereby defining a lithium secondary battery. According to an exemplary embodiment, the electrolyte can use a non-aqueous electrolyte.

[0107] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent, for example, LiPF6 + X - represents an anion (X - ) of the lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN- and (CF3CF2SO2)2N - wait.

[0108] The organic solvents may include, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, γ-butyrolactone, propylene sulfite, and tetrahydrofuran. These may be used alone or in combination of two or more.

[0109] like Figure 4 As shown, the tabs (positive tab and negative tab) protrude from the positive current collector 105 and negative current collector 125 belonging to each electrode unit and extend to one end of the housing 160. The tabs are fused to said one end of the housing 160 and connected to electrode leads (positive lead 107 and negative lead 127) extending to or exposed outside the housing 160.

[0110] Figure 4 The diagram shows the positive electrode lead 107 and the negative electrode lead 127 protruding from the upper side of the housing 160 in the planar direction, but the position of the electrode leads is not limited to this. For example, the electrode leads may also protrude from at least one of the two sides of the housing 160, or from the lower side of the housing 160. Alternatively, the positive electrode lead 107 and the negative electrode lead 127 may be formed to protrude from different sides of the housing 160, respectively.

[0111] The lithium secondary battery can be manufactured in various shapes, such as cylindrical, triangular, pouch, and coin, for use in containers.

[0112] The following preferred experimental examples are presented to help understand the present invention. However, these embodiments are only used to illustrate the present invention and are not intended to limit the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept. This is obvious to those skilled in the art, and it is natural that such modifications and variations fall within the scope of the claims.

[0113] Examples and Comparative Examples

[0114] Example 1

[0115] 1) Manufacturing of the negative electrode

[0116] A negative electrode slurry was prepared by mixing 24 wt% of natural graphite, 70 wt% of artificial graphite, 1 wt% of carboxymethyl cellulose (CMC), 4 wt% of butadiene styrene rubber, and 1 wt% of carbon nanotube (CNT), an electrically conductive material, in distilled water. The negative electrode slurry was coated on a Cu foil current collector and dried and pressed, thereby forming a primary negative electrode active material layer containing carbon-based active material particles.

[0117] A negative electrode formed with the primary negative electrode active material layer was loaded in a chamber and treated in 5 vol% SiH4deposition gas mixed with nitrogen at 500°C for 90 minutes. Thus, a negative electrode active material layer formed with a silicon coating layer was formed.

[0118] 2) Manufacture of coin-type half cell

[0119] A coin-type battery was manufactured using the negative electrode prepared in 1) and a lithium foil as a counter electrode, and after inserting a PE separator between the negative electrode and the counter electrode, an electrolyte was injected. The assembled coin-type battery was rested at normal temperature for 3-24 hours. The electrolyte was prepared by mixing 2 vol% FEC as an electrolyte additive in a lithium salt 1.0 M LiPF6solution (solvent: a mixed solvent of EC and EMC (mixed ratio of 3:7 vol%).

[0120] Examples 2 to 4 and Comparative Examples 1 to 2

[0121] A coin-type battery was manufactured by the same method as in Example 1 except that the concentration of SiH4was changed, as described in Table 1.

[0122] Comparative Example 3

[0123] A coin-type battery was manufactured by the same method as in Example 1 except that the silicon coating (SiH4deposition) was omitted.

[0124] Comparative Example 4

[0125] 1) Manufacture of negative electrode

[0126] Twenty-four wt% of natural graphite and 70 wt% of artificial graphite were uniformly mixed, and then heat-treated at 500°C in a 5 vol% SiH4gas atmosphere mixed with nitrogen for 90 minutes. The heat-treated powder was recovered and pulverized, thereby preparing a carbon-silicon composite as a negative electrode active material.

[0127] A negative electrode slurry was prepared by mixing 94 wt% of the carbon-silicon composite as a negative electrode active material, 1 wt% of carboxymethyl cellulose, 4 wt% of butadiene styrene rubber, and 1 wt% of carbon nanotube (CNT), an electrically conductive material, in distilled water. The negative electrode slurry was coated on a Cu foil current collector and dried and pressed to manufacture a negative electrode.

[0128] 2) Manufacture of coin-type half-batteries

[0129] A coin-type battery was manufactured using the negative electrode prepared in 1) and a lithium foil as a counter electrode, and after inserting a PE separator between the negative electrode and the counter electrode, injecting an electrolyte. The assembled coin-type battery was rested at normal temperature for 3-24 hours. The electrolyte was prepared by mixing 2% by volume of FEC as an electrolyte additive in a 1.0M LiPF6 solution of a lithium salt (organic solvent: a mixed solvent of EC and EMC (mixing ratio: 3:7 by volume)).

[0130] Comparative Example 5

[0131] A coin-type battery was manufactured by the same method as Comparative Example 4, except that the concentration of SiH4 was changed, as described in Table 1.

[0132] Experimental Examples

[0133] 1) XPS analysis

[0134] The negative electrode prepared in the examples and comparative examples was attached to a carbon tape to prepare a sample, and XPS analysis was performed according to the following conditions, thereby measuring the silicon surface content and the peak intensity ratio (Si-O / Si).

[0135] i) X-ray: Al kα, 1486.68 eV, 900 μm beam size

[0136] ii) Analyzer: CAE mode

[0137] iii) Number of scans: 2 (survey scan), 20 (narrow scan)

[0138] iv) Pass energy: 150 eV (survey scan), 20 eV (narrow scan)

[0139] v) Ion gun: Ar ion

[0140] vi) Ion energy: 4000 eV

[0141] Figure 6 FIG. 1 is an X-ray photoelectron spectroscopy (XPS) analysis graph of the negative electrode active material layer of Example 1, Comparative Example 4, and Comparative Example 5.

[0142] Reference Figure 6The surface Si content of the comparative example in which the silicon coating layer was formed before forming the slurry decreased while the ratio of Si-O increased.

[0143] 2) Measurement of slurry gas generation

[0144] 4 mL of the negative electrode slurry used in the examples and comparative examples was injected into a gas-tight syringe and left at room temperature for 7 days in a state in which the injection port was sealed. Thereafter, the slurry gas generation rate was calculated by the following mathematical formula 1.

[0145] [mathematical formula 1]

[0146] Slurry gas generation rate = (slurry volume after 7 days - initial slurry volume) / initial slurry volume

[0147] 3) Evaluation of charge-discharge characteristics

[0148] The coin-type batteries of the examples and comparative examples were charged at room temperature (25°C) at a constant current of 0.1C rate until the voltage reached 0.01 V, and then held at 0.01 V in a constant voltage mode and cut off at a current of 0.01C rate, and constant voltage charging was performed.

[0149] Thereafter, discharging was performed at a constant current of 0.1C rate until the voltage reached 1.5 V. The above charging and discharging were taken as one cycle, and further, charging and discharging were performed for one cycle in the same manner, and then the current applied during charging and discharging was changed to 0.5C to perform 50 cycles, and a rest period of 10 minutes was provided between cycles.

[0150] In the 50 cycles, the charge-discharge efficiency (%) of the initial cycle (initial discharge capacity / initial charge capacity) and the discharge capacity were designated as the initial efficiency and the initial discharge capacity, respectively, and the capacity retention rate for 50 cycles with respect to the initial discharge capacity was calculated.

[0151] 4) Electrode resistance

[0152] The interface resistance value of the negative electrode produced in the examples and comparative examples was measured using a HIOKI XF057 probe unit under conditions of a current of 10 mA and a voltage range of 0.5 V.

[0153] The evaluation results are described in Table 1 below.

[0154] [Table 1]

[0155]

[0156]

[0157] Referring to Table 1, in the examples satisfying the surface Si content and the peak intensity ratio (Si-O / Si) measured by the above XPS, the generation of gas and the electrode resistance were reduced while securing excellent initial capacity / efficiency and capacity retention rate.

[0158] In Comparative Example 4 and Comparative Example 5 including a silicon coating in the negative electrode slurry, the generation of gas was increased due to a side reaction with water, and the electrode resistance was also increased as the Si-O ratio increased.

Claims

1. A negative electrode for a secondary battery, comprising: Negative electrode current collector; as well as A negative electrode active material layer is formed on the negative electrode current collector and includes carbon-based active material particles and a silicon coating formed on the surface of the carbon-based active material particles. The surface silicon content of the negative electrode active material layer, as measured by X-ray photoelectron spectroscopy (XPS), is 3-25 atomic%. In the XPS of the negative electrode active material layer, the peak intensity ratio, defined as the ratio of the second peak intensity to the first peak intensity, is between 0.05 and 1, wherein the first peak intensity corresponds to the peak intensity at a binding energy in the range of 98-102 eV, and the second peak intensity corresponds to the peak intensity at a binding energy in the range of 102-106 eV. The first peak intensity is the Si peak intensity, and the second peak intensity is the Si-O peak intensity.

2. The negative electrode for a secondary battery according to claim 1, wherein, The surface silicon content of the negative electrode active material layer, as measured by XPS, is 3-11 atoms.

3. The negative electrode for a secondary battery according to claim 1, wherein, The carbon-based active material particles form a porous carbon scaffold.

4. The negative electrode for a secondary battery according to claim 1, wherein, The carbon-based active material particles comprise a mixture of artificial graphite and natural graphite.

5. The negative electrode for a secondary battery according to claim 1, wherein, The amount of silicon on the outer surface of the negative electrode active material layer is greater than the amount of silicon inside the negative electrode active material layer.

6. The negative electrode for a secondary battery according to claim 1, wherein, The surfaces of the carbon-based active material particles are stacked in the negative electrode active material layer to allow them to contact each other.

7. The negative electrode for a secondary battery according to claim 6, wherein, The silicon coating is formed discontinuously on the surface of the carbon-based active material particles.

8. A lithium secondary battery, comprising: The positive electrode comprises lithium-transition metal composite oxide particles as the positive electrode active material; as well as The negative electrode of claim 1, wherein the negative electrode is relative to the positive electrode.

9. A method for manufacturing a negative electrode for a secondary battery, comprising the following steps: A negative electrode slurry containing carbon-based active material particles is coated onto the negative electrode current collector to form a primary negative electrode active material layer. as well as A deposition gas containing a silicon source is supplied to the primary negative electrode active material layer to form a negative electrode active material layer with a silicon coating on the surface of the carbon-based active material particles. The surface silicon content of the negative electrode active material layer, as measured by X-ray photoelectron spectroscopy (XPS), is 3-25 atomic%. In the XPS of the negative electrode active material layer, the peak intensity ratio, defined as the ratio of the second peak intensity to the first peak intensity, is between 0.05 and 1, wherein the first peak intensity corresponds to the peak intensity at a binding energy in the range of 98-102 eV, and the second peak intensity corresponds to the peak intensity at a binding energy in the range of 102-106 eV. The first peak intensity is the Si peak intensity, and the second peak intensity is the Si-O peak intensity.

10. The method for manufacturing a negative electrode for a secondary battery according to claim 9, wherein, The proportion of the silicon source in the deposition gas is 3-22% by volume.

11. The method for manufacturing a negative electrode for a secondary battery according to claim 9, wherein, The silicon coating is formed by a chemical vapor deposition (CVD) process, and the silicon source contains SiH4.

12. The method for manufacturing a negative electrode for a secondary battery according to claim 9, wherein, The negative electrode slurry also includes a solvent, a binder, and a carbon-based conductive material.

13. The method for manufacturing a negative electrode for a secondary battery according to claim 9, wherein, The step of forming the primary negative electrode active material layer includes drying and pressing the negative electrode slurry coated prior to forming the silicon coating.

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