Negative electrode for lithium secondary battery and lithium secondary battery including the same

Abstract

To provide a negative electrode for a lithium secondary battery having improved capacity characteristics and stability, and a lithium secondary battery including the same.SOLUTION: A negative electrode for a lithium secondary battery and a lithium secondary battery including the same are provided. The negative electrode for the lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer formed on a surface of the negative electrode current collector. A Raman R1 value defined as ID / IG measured on a surface of the negative electrode active material layer is from 0.2 to 0.5. The Raman R1 value is measured from a Raman spectrum measured at a laser focus level of 100% using an inVia Raman microscope manufactured by Renishaw as a Raman spectroscope.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The disclosure of the present application relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, and more particularly to a negative electrode for a lithium secondary battery including a silicon-based and / or graphite-based active material and a lithium secondary battery including the same. [Background technology]

[0002] A secondary battery is a battery that can be repeatedly charged and discharged, and with the development of the information and communication and display industries, it is widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, notebook computers, etc. Recently, battery packs including secondary batteries have also been developed and applied as a power source for environmentally friendly automobiles such as hybrid automobiles and electric automobiles.

[0003] Examples of secondary batteries include lithium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. Among them, lithium secondary batteries have been actively developed and applied due to their high operating voltage and energy density per unit weight, as well as their advantages in terms of charging speed and weight reduction.

[0004] For example, a lithium secondary battery may include an electrode assembly including a positive electrode and a negative electrode that are repeatedly stacked, and an electrolyte that impregnates the electrode assembly. The lithium secondary battery may further include an exterior material, for example, in a pouch shape, that contains the electrode assembly and the electrolyte.

[0005] Recently, as lithium secondary batteries are applied to large-capacity batteries such as electric vehicle batteries, active materials that can provide higher capacity have been developed. For example, silicon-based active materials are used as negative electrode active materials. However, the silicon-based active materials are prone to contraction / expansion due to repeated charging / discharging, which may impair the stability of the battery.

[0006] Therefore, although graphite-based active materials can be used in combination with the silicon-based active materials, the manufacturing process for the anode / battery may not provide uniform electrochemical properties throughout the anode / battery. Summary of the Invention [Problem to be solved by the invention]

[0007] One object of the present disclosure is to provide a negative electrode for a lithium secondary battery having improved capacity characteristics and stability.

[0008] One object of the present disclosure is to provide a lithium secondary battery having improved capacity characteristics and stability. [Means for solving the problem]

[0009] The negative electrode for a lithium secondary battery includes a negative electrode current collector and a negative electrode active material layer formed on a surface of the negative electrode current collector, the Raman R1 value of which, as shown in Equation 1, is greater than 0.2 and is not greater than 0.5, measured on the surface of the negative electrode active material layer.

[0010] Raman R1=I D / I G (Formula 1)

[0011] (In formula 1, I D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 100%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak intensity for the absorption region of I G In the Raman spectrum, -1 ~1,600cm -1 is the peak intensity for the absorption region of

[0012] In some embodiments, the Raman R1 value may be between 0.23 and 0.50.

[0013] In some embodiments, the Raman R2 value of Equation 2 measured on the surface of the negative electrode active material layer may be 0.20 to 0.45.

[0014] Raman R2=A D / A G (Formula 2)

[0015] (In formula 2, A D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 100%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak area for the absorption region of A G In the Raman spectrum, -1 ~1,600cm -1 )

[0016] In some embodiments, the Raman R2 value may be between 0.22 and 0.40.

[0017] In some embodiments, the anode active material layer can include an anode active material including a silicon-based active material and a graphite-based active material.

[0018] In some embodiments, the silicon based active material can include a silicon-carbon composite.

[0019] In some embodiments, the silicon-carbon composite may include a carbon core and a silicon coating formed on the carbon core.

[0020] In some embodiments, the content of the graphite-based active material may be 60% by weight to 95% by weight, and the content of the silicon-based active material may be 5% by weight to 40% by weight, based on the total weight of the silicon-based active material and the graphite-based active material.

[0021] In some embodiments, the silicon based active material may have a Raman R3 value of Formula 3 between 0.8 and 2.0.

[0022] Raman R3=I D / I G (Formula 3)

[0023] (In formula 3, I D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 0%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak intensity for the absorption region of I G In the Raman spectrum, -1 ~1,600cm -1 is the peak intensity for the absorption region of

[0024] In some embodiments, the graphite-based active material may have a Raman R3 value of Formula 3 between 0.05 and 0.5.

[0025] In some embodiments, the silicon based active material may have a Raman R4 value of Formula 4 between 0.1 and 1.0.

[0026] Raman R4=A D / A G (Formula 4)

[0027] (In formula 4, A D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 0%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak area for the absorption region of A G In the Raman spectrum, -1 ~1,600cm -1 )

[0028] In some embodiments, the graphite-based active material may have a Raman R4 value of Formula 4 between 0.05 and 0.5.

[0029] In some embodiments, the content of the negative electrode active material may be 85% by weight to 98% by weight based on the total weight of the negative electrode active material layer.

[0030] In some embodiments, the electrode density of the negative electrode active material layer is 1.3 g / cm 3 ~1.8g / cm 3 may be also possible.

[0031] The lithium secondary battery includes the negative electrode for lithium secondary battery according to the above embodiment and a positive electrode facing the negative electrode.

[0032] In a method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode mix is ​​coated on a negative electrode current collector. A magnet is applied to the coated negative electrode mix to perform magnetic orientation. The self-oriented negative electrode mix is ​​dried. The dried negative electrode mix is ​​rolled to form a negative electrode active material layer. The Raman R1 value of Equation 1 measured on the surface of the negative electrode active material layer is greater than 0.2 and not greater than 0.5.

[0033] In some embodiments, the strength of the magnetic force applied in the magnetic orientation may be 3,000G to 10,000G.

[0034] In some embodiments, when the negative electrode mixture is dried, the moving speed of the negative electrode current collector can be adjusted to a range of 5 m / s to 15 m / s.

[0035] In some embodiments, the Raman R2 value of Equation 2 measured on the surface of the negative electrode active material layer may be 0.20 to 0.45.

[0036] In some embodiments, the negative electrode mixture may include a negative electrode active material including a silicon-based active material and a graphite-based active material, and a binder. The content of the negative electrode active material may be 85% by weight to 98% by weight, and the content of the binder may be 0.5% by weight to 5% by weight, based on the total weight of the negative electrode active material layer. Effect of the Invention

[0037] According to an embodiment of the present disclosure, the negative electrode active material layer included in the negative electrode of the lithium secondary battery has a Raman R1 value (I D / I G In this range, side reactions and contraction / expansion of the silicon-based active material can be suppressed, and sufficient high capacity characteristics can be uniformly achieved throughout the negative electrode active material layer.

[0038] In some embodiments, the negative electrode active material layer has a Raman R2 value (A D / A G ) range. This makes it possible to more effectively suppress local activity deviation in the negative electrode active material layer.

[0039] The negative electrode for a lithium secondary battery and the lithium secondary battery of the present disclosure can be widely applied in green technology fields such as electric vehicles, battery charging stations, solar power generation using other batteries, wind power generation, etc. In addition, the negative electrode for a lithium secondary battery and the lithium secondary battery of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, etc. that prevent climate change by suppressing air pollution and greenhouse gas emissions. [Brief description of the drawings]

[0040] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium secondary battery according to an exemplary embodiment. [Diagram 2]FIG. 2 is a schematic diagram for explaining measurement of the Raman R value at a laser focus level of 0%. [Diagram 3] FIG. 3 is a schematic diagram for explaining measurement of the Raman R value at a laser focus level of 100%. [Figure 4] FIG. 4 is a schematic plan view showing a lithium secondary battery according to an exemplary embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing a lithium secondary battery according to an exemplary embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] According to an embodiment of the present disclosure, there is provided a negative electrode for a lithium secondary battery having a predetermined range of Raman R value. Also, according to an embodiment of the present disclosure, there is provided a lithium secondary battery including the negative electrode.

[0042] Hereinafter, specific embodiments of the present disclosure will be described with reference to the drawings. However, the drawings attached to this specification are merely examples and do not limit the inventive idea of ​​the present disclosure. In addition, the drawings attached to this specification show exemplary structures and do not limit the configuration and structure of the present disclosure.

[0043] FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium secondary battery according to an exemplary embodiment.

[0044] Referring to FIG. 1, a negative electrode 130 for a lithium secondary battery (hereinafter, abbreviated as “negative electrode”) may include a negative electrode current collector 125 and a negative electrode active material layer 120 .

[0045] For example, the negative electrode current collector 125 can include copper, stainless steel, nickel, titanium, or alloys thereof. In one embodiment, the negative electrode current collector 125 can include copper or stainless steel that has been surface treated with carbon, nickel, titanium, or silver.

[0046] The negative electrode active material layer 120 can be formed by coating a negative electrode binder containing a negative electrode active material on the negative electrode current collector 125 and then drying and rolling. For example, the negative electrode active material can be mixed and stirred in a solvent with a negative electrode binder, a conductive material, and a thickening agent to produce the negative electrode binder.

[0047] The solvent can include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, t-butanol, and the like.

[0048] According to an exemplary embodiment, the negative electrode active material can include a silicon-based active material (e.g., a silicon-containing active material) and a carbon-based active material (e.g., a silicon-free and carbon-containing active material).

[0049] The silicon-based active material can include Si, SiO x (0 < x < 2), silicon-carbon composite (Si / C), silicon oxide (silicate)-carbon composite (SiO / C), silicon metal (Si-Metal), and the like. In some embodiments, the silicon-based active material can include a lithium-silicate compound, and can include a lithium-silicate compound containing a dopant such as magnesium or aluminum.

[0050] In some embodiments, the silicon-based active material can include the silicon-carbon composite. The silicon-carbon composite can include a carbon core and a silicon coating formed on the carbon core.

[0051] For example, the carbon core can have a porous structure, and the silicon coating can be formed on the porous carbon structure by a deposition process such as chemical vapor deposition (CVD).

[0052] This allows a larger silicon layer area to be secured, and the high capacity characteristics of silicon can be fully realized. In addition, the porous carbon structure can support and fix the silicon coating, thereby suppressing the contraction and expansion of the silicon-based active material that occurs during repeated charging and discharging.

[0053] Therefore, the high capacity characteristics of the silicon-based active material can be sufficiently ensured while the mechanical / chemical instability of the silicon-based active material can be mitigated or suppressed.

[0054] In some embodiments, the silicon-carbon composite may further include an amorphous carbon coating, in which case the silicon-carbon composite may have the following structure: carbon core-silicon coating-amorphous carbon coating.

[0055] The amorphous carbon coating reduces the exposed surface area of ​​the silicon coating and reduces or suppresses side reactions with the electrolyte, thereby preventing gas generation due to the side reactions during repeated charging and discharging, and improving the operational stability of the battery.

[0056] The carbon-based active material may include crystalline carbon or amorphous carbon. For example, the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. For example, the crystalline carbon may include natural graphite, artificial graphite, graphitized coke, graphitized MCMB, graphitized MPCF, etc.

[0057] According to an exemplary embodiment, the carbon-based active material may be crystalline carbon, and a graphite-based active material (natural graphite and / or artificial graphite) may be used.

[0058] Natural graphite can provide a relatively higher capacity than synthetic graphite. Synthetic graphite can have a relatively higher chemical and physical stability than natural graphite.

[0059] In some embodiments, the graphite-based active material may be natural graphite or artificial graphite. In some embodiments, the graphite-based active material may be a mixture of natural graphite and artificial graphite. In this case, the mixture may have a weight ratio of natural graphite to artificial graphite of 1:9 to 9:1, 3:7 to 7:3, or 4:6 to 6:4.

[0060] In an exemplary embodiment, the content of the graphite-based active material may be 60% to 95% by weight, and the content of the silicon-based active material (e.g., silicon-carbon composite) may be 5% to 40% by weight, based on the total weight of the negative electrode active material. In some embodiments, the content of the graphite-based active material may be 75% to 95% by weight, 77% to 92% by weight, or 80% to 90% by weight, and the content of the silicon-based active material may be 5% to 25% by weight, 8% to 23% by weight, or 10% to 20% by weight.

[0061] The negative electrode binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (Poly(vinylidene fluoride-co-hexafluoropropylene)), polyacrylonitrile, polymethylmethacrylate, acrylonitrile butadiene rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), polyacrylic acid-based binder, poly(3,4-ethylenedioxythiophene, PEDOT)-based binder, and the like.

[0062] In some embodiments, the negative electrode binder can include a styrene-butadiene rubber (SBR) based binder and can be used with a thickening agent such as carboxymethyl cellulose (CMC).

[0063] The conductive material may be added to improve the electrical conductivity and / or mobility of lithium ions or electrons. Non-limiting examples of the conductive material include carbon-based conductive materials such as graphite, carbon black, acetylene black, ketjen black, graphene, carbon nanotubes, vapor-grown carbon fiber (VGCF), and carbon fibers, and / or tin, tin oxide, titanium oxide, LaSrCoO 3 , LaSrMnO 3 The conductive material may include metal-based conductive materials, including perovskite materials such as

[0064] With respect to the total weight of the negative electrode active material layer 120, the content of the negative electrode active material may be 85% by weight to 98% by weight, the content of the binder may be 0.5% by weight to 5% by weight, the content of the conductive material may be 0.5% by weight to 10% by weight, and the content of the thickener may be 0.5% by weight to 5% by weight.

[0065] The electrode density of the negative electrode active material layer 120 is 1.3 g / cm 3 ~1.8g / cm 3 In some embodiments, the electrode density of the negative electrode active material layer 120 may be 1.35 g / cm 3 ~1.75g / cm 3 , or 1.4 g / cm 3 ~1.7g / cm 3 The electrode density of the negative electrode active material layer 120 may be calculated by measuring the width, length, and height of the negative electrode active material layer 120, calculating the volume, and dividing the volume by the weight obtained by subtracting the weight of the negative electrode current collector from the weight of the negative electrode.

[0066] Within this range, the range of the Raman R value of the negative electrode active material layer 120 described below can be easily ensured.

[0067] In an embodiment of the present disclosure, the Raman R1 value measured on the surface of the negative electrode active material layer 120 and defined by Equation 1 may be greater than 0.2 and less than or equal to 0.5. According to an embodiment of the present disclosure, the Raman R1 value can be measured on the upper surface of the negative electrode active material layer 120 that faces the contact surface of the negative electrode active material layer 120 with the negative electrode current collector 125.

[0068] Raman R1=I D / I G (Formula 1)

[0069] In formula 1, I D In the Raman spectrum, -1 ~1,380cm -1 is the peak intensity in the absorption region (D band) of I G In the Raman spectrum, -1 ~1,600cm -1 is the peak intensity in the absorption region (G band).

[0070] The Raman spectrum is measured using a Renishaw inVia Raman microscope as a Raman spectrometer under the condition of a laser focus level of 100%.

[0071] The analysis by the Raman spectrometer can be performed under the conditions of a laser wavelength of 532 nm, a magnification of x20, a laser output of 100%, 12 mV, and a laser exposure time of 10 seconds. The Raman measurement can be performed three times, and the average value can be used as the Raman R1 value of the negative electrode active material layer.

[0072] In the above-mentioned range of Raman R1 value, it is possible to effectively suppress particle damage caused by contraction / expansion that occurs during repeated charging / discharging of silicon-based particles and side reactions with the electrolyte, thereby ensuring improved capacity retention and life characteristics. In addition, it is possible to prevent an increase in resistance due to an excessive increase in the amorphous characteristics of the negative electrode active material, while achieving sufficient capacity characteristics by introducing a silicon-based active material.

[0073] In some embodiments, the Raman R1 value of the negative electrode active material layer 120 may be 0.21 to 0.50, 0.22 to 0.50, or 0.23 to 0.50. In one embodiment, the Raman R1 value of the negative electrode active material layer 120 may be 0.25 to 0.50, 0.26 to 0.50, or 0.30 to 0.49. In this range, the capacity characteristics and the mechanical stability of the negative electrode can be further improved while maintaining the appropriate amorphous characteristics of the negative electrode active material.

[0074] In some embodiments, the Raman R2 value defined by Equation 2 measured on the surface of the negative electrode active material layer 120 under the above-mentioned Raman spectroscopic analysis conditions may be 0.20 to 0.45.

[0075] Raman R2=A D / A G (Formula 2)

[0076] In formula 2, A D In the Raman spectrum, -1 ~1,380cm -1 is the peak area for the absorption region (D band) of A G In the Raman spectrum, -1 ~1,600cm -1 The area of ​​the peak in the absorption region (G band) of

[0077] When both of the Raman R2 value ranges are satisfied, the improvement in the negative electrode capacity characteristics / stability due to the adjustment of the Raman R1 value can be reliably ensured. For example, by checking both of the Raman R2 value ranges, the uniformity of the Raman spectroscopic characteristics of the negative electrode active material layer 120 as a whole can be further ensured.

[0078] In some embodiments, the Raman R2 value of the negative electrode active material layer 120 may be 0.20 to 0.40, 0.21 to 0.40, or 0.22 to 0.40. In one embodiment, the Raman R2 value of the negative electrode active material layer 120 may be 0.23 to 0.40, or 0.25 to 0.39.

[0079] Within this range, the effect achieved within the range of the Raman R1 value can be maintained, while the uniformity of the Raman characteristics over the entire region of the negative electrode active material layer 120 can be improved.

[0080] As described above, the Raman R1 and R2 values ​​can be measured under the condition of a laser focus level of 100% of the Raman spectrometer. A laser focus level of 100% refers to a level where the measurement area of ​​a single shot or a single scan of the Raman spectrometer is set to a maximum value. For example, a laser focus level of 0% refers to a level where the measurement area of ​​a single shot or a single scan of the Raman spectrometer is set to a minimum value.

[0081] 2 and 3 are schematic diagrams for explaining the measurement of the Raman R value at a laser focus level of 0% and a laser focus level of 100%, respectively.

[0082] 2, when the laser focus level of the Raman spectrometer 50 is 0%, a minimum area (MA1) that can be measured is set on the surface of the negative electrode active material layer 120. In this case, the signal intensity obtained in the minimum area (MA1) increases, and the characteristics in the local area can be measured more accurately and reliably.

[0083] However, if the distribution of the negative electrode active material in the negative electrode active material layer 120 is non-uniform, the measured values ​​may vary depending on the selected region. Also, the characteristics of only the selected region may be reflected, and the characteristics of the entire region of the negative electrode active material layer 120 may not be reflected.

[0084] For example, if the minimum region (MA1) contains a large amount of conductive material and binder locally, the components of the conductive material and binder may fluctuate or interfere with the signal from the active material.

[0085] 3, when the laser focus level of the Raman spectrometer 50 is 100% according to the embodiment of the present disclosure, a maximum area (MA2) that can be measured is set on the surface of the negative electrode active material layer 120. Therefore, the components and amounts of the negative electrode active material layer 120 included in the measurable area increase, and a Raman value that reflects the composition characteristics of the entire area of ​​the negative electrode active material layer 120 can be obtained.

[0086] Thus, the Raman R1 and R2 values ​​described above can reflect the amorphous / crystalline characteristics, the distribution of the silicon-based active material, and the uniformity of the expansion stability over the entire region of the negative electrode active material layer 120.

[0087] Therefore, by adjusting the values ​​of Raman R1 and R2 within the aforementioned ranges, the improvement in capacity due to the introduction of the silicon-based active material and the improvement in mechanical and chemical stability due to the suppression of expansion can be ensured / confirmed over the entire region of the negative electrode active material layer 120.

[0088] The Raman R1 and R2 values ​​described above may vary depending on the components / contents of the negative electrode active material, the components / contents of the conductive material / binder, etc., and may also vary depending on the conditions under which the negative electrode active material layer 120 is formed.

[0089] According to the exemplary embodiment, even if the same negative electrode mixture is used, different Raman R1 / R2 values ​​can be calculated depending on the stirring speed of the negative electrode mixture, the type / amount of solvent, the viscosity of the negative electrode mixture, the coating speed of the negative electrode mixture, the drying speed after coating, the drying temperature, the drying conditions such as humidity, and the like.

[0090] For example, the viscosity and drying speed of the negative electrode mixture can be adjusted to adjust the Raman R1 and R2 values ​​to the above-mentioned ranges. As a non-limiting example, the viscosity of the negative electrode mixture at room temperature (25°C) can be adjusted to a range of 1,000cp to 5,000cp, 2,000cp to 5,000cp, or 3,000cp to 4,000cp. As a non-limiting example, the drying speed (moving speed of the negative electrode current collector coated with the negative electrode mixture in the drying device) can be adjusted to a range of 5m / s to 15m / s, 5m / s to 10m / s, 6m / s to 10m / s, or 7m / s to 10m / s.

[0091] In one embodiment, magnetic orientation can be performed before drying the negative electrode mixture. The above-mentioned Raman R1 and R2 values ​​can be finely adjusted by the magnetic orientation. As a non-limiting example, the strength of the magnetic force applied in the magnetic orientation can be adjusted to a range of 3,000G to 10,000G, 4,000G to 10,000G, or 5,000G to 9,000G.

[0092] In some embodiments, the silicon-based active material or silicon-carbon composite contained in the negative electrode active material may have a Raman R3 value, as defined by Equation 3, of 0.8 to 2.0. The Raman R3 value is the intrinsic Raman I D / I G The value of can be reflected.

[0093] Raman R3=I D / I G (Formula 3)

[0094] In formula 3, I D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 0%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak intensity for the absorption region of I G In the Raman spectrum, -1 ~1,600cm -1 is the peak intensity for the absorption region of

[0095] For example, the Raman R3 value of the silicon-carbon composite may be 0.8 to 1.5, 0.8 to 1.4, 0.8 to 1.3, 0.8 to 1.2, 0.8 to 1.1, or 0.8 to 1.0.

[0096] In some embodiments, the silicon-based active material or silicon-carbon composite contained in the negative electrode active material may have a Raman R4 value, as defined by formula 4, of 0.1 to 1.0. The Raman R4 value is the intrinsic Raman A D / A G The value of can be reflected.

[0097] Raman R4=A D / A G (Formula 4)

[0098] In formula 4, A D The Raman spectrum was measured using a Renishaw inVia Raman microscope at a laser focus level of 0%, and the peak at 1,330 cm -1 ~1,380cm -1 is the peak area for the absorption region of A G In the Raman spectrum, -1 ~1,600cm -1 is the peak area for the absorption region of

[0099] For example, the Raman R4 value of the silicon-carbon composite may be 0.2 to 0.9, 0.3 to 0.9, 0.3 to 0.8, 0.3 to 0.7, or 0.3 to 0.6.

[0100] In some embodiments, the Raman R3 value and the Raman R4 value of the graphite-based active material included in the negative electrode active material may be 0.05 to 0.5, for example, the Raman R3 value and the Raman R4 value of the graphite-based active material may be 0.05 to 0.4, 0.05 to 0.3, 0.05 to 0.2, or 0.05 to 0.15, respectively.

[0101] The intrinsic Raman value of the active material may be a value measured at a laser focus level of 0% of the Raman spectrometer.

[0102] By using active materials whose intrinsic Raman values ​​are in the ranges mentioned above, the ranges of Raman R1 and R2 values ​​at a laser focus level of 100% mentioned above can be more easily obtained.

[0103] 4 and 5 are schematic plan and cross-sectional views, respectively, showing a lithium secondary battery according to an exemplary embodiment, for example, FIG 5 is a cross-sectional view cut in the thickness direction along "II'" in FIG 4.

[0104] 4 and 5, the lithium secondary battery includes a negative electrode 130 including the above-described negative electrode active material layer 120 and negative electrode current collector 125, and a positive electrode 100. The lithium secondary battery may further include a separator 140 interposed between the positive electrode 100 and the negative electrode 130.

[0105] The positive electrode 100 may include a positive electrode active material layer 110 formed by applying a positive electrode active material to a positive electrode current collector 105. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0106] The positive current collector 105 can include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector 105 can also include aluminum or stainless steel that is surface treated with carbon, nickel, titanium, or silver.

[0107] According to an exemplary embodiment, the positive electrode active material can include a lithium-nickel metal oxide, which can further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0108] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered or crystalline structure represented by Formula 1:

[0109] [Chemical formula 1] Li x Ni a M b O 2+z

[0110] In Chemical Formula 1, 0.9≦x≦1.2, 0.6≦a≦0.99, 0.01≦b≦0.4, and −0.5≦z≦0.1. As mentioned above, M can include Co, Mn, and / or Al.

[0111] The chemical structure represented by Chemical Formula 1 shows the bonding relationship contained in the layered structure or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M may include Co and / or Mn, and Co and / or Mn may be provided as main active elements of the positive electrode active material together with Ni. Chemical Formula 1 is provided to show the bonding relationship of the main active elements, and should be understood as a formula including the introduction and substitution of additional elements.

[0112] In one embodiment, in addition to the main active element, an auxiliary element may be further included to improve the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary element may be incorporated together with the layered structure / crystal structure to form a bond. It should be understood that this case is also included within the scope of the chemical structure represented by Chemical Formula 1.

[0113] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, and Zr. The auxiliary element may also act as an auxiliary active element, such as Al, that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn.

[0114] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or a crystal structure represented by the following Formula 1-1.

[0115] [Chemical formula 1-1] Li x Ni a M1 b1 M2 b2 O 2+z

[0116] In the formula 1-1, M1 can include Co, Mn and / or Al, and M2 can include the above-mentioned auxiliary elements. In the formula 1-1, 0.9≦x≦1.2, 0.6≦a≦0.99, 0.01≦b1+b2≦0.4, and −0.5≦z≦0.1 may be satisfied.

[0117] The positive electrode active material may further include a coating element or a doping element. For example, an element substantially the same as or similar to the auxiliary element may be used as the coating element or the doping element. For example, the above elements may be used alone or in combination of two or more as the coating element or the doping element.

[0118] The coating element or doping element may be present on the surface of the lithium-nickel metal oxide particles, or may penetrate from the surface of the lithium-nickel metal composite oxide particles and be included in the bonding structure represented by Chemical Formula 1 or Chemical Formula 1-1.

[0119] The positive electrode active material may include a nickel-cobalt-manganese (NCM)-based lithium oxide, in which case an NCM-based lithium oxide having an increased nickel content may be used.

[0120] Ni can be provided as a transition metal related to the output and capacity of a lithium secondary battery. Therefore, by adopting a high-Ni content (High-Ni) composition as the positive electrode active material as described above, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0121] However, as the Ni content increases, the long-term storage stability and life stability of the positive electrode or secondary battery may relatively decrease, and side reactions with the electrolyte may increase. In contrast, according to the exemplary embodiment, the electrical conductivity is maintained by including Co, while the life stability and capacity retention characteristics are improved by including Mn.

[0122] The Ni content in the NCM-based lithium oxide (e.g., the mole fraction of nickel in the total moles of nickel, cobalt, and manganese) may be 0.6 or more, 0.7 or more, or 0.8 or more, in some embodiments, the Ni content may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0123] In some embodiments, the positive electrode active material is a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate-based (LFP) active material (e.g., LiFePO 4 ).

[0124] In some embodiments, the positive electrode active material may include a Mn-rich active material, a Li-rich layered oxide (LLO) / Over Lithiated Oxide (OLO) active material, or a Co-less active material, for example having a chemical structure or crystal structure represented by Chemical Formula 2.

[0125] [Chemical formula 2] p[Li 2 MnO 3 ]·(1-p)[Li q J.O. 2 ]

[0126] In Chemical Formula 2, 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J can contain at least one element among Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0127] For example, the positive electrode active material can be mixed in a solvent to produce a positive electrode slurry. After coating the positive electrode slurry on the positive electrode current collector 105, it can be dried and rolled to produce the positive electrode active material layer 110.

[0128] The positive electrode active material layer 110 can further contain a binder, and can optionally further contain a conductive material, a thickener, and the like.

[0129] As the positive electrode binder and the conductive material, substances substantially the same as or similar to the aforementioned binder / conductive material can be used. In some embodiments, a PVDF-based binder can be used as the positive electrode binder.

[0130] The separator 140 can include a porous polymer film or a porous nonwoven fabric. The porous polymer film can include polyolefin-based polymers such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. The porous nonwoven fabric can include high-melting-point glass fibers, polyethylene terephthalate fibers, and the like.

[0131] The separator 140 can also include a ceramic-based material. For example, inorganic particles can be coated on the polymer film or dispersed in the polymer film to improve heat resistance.

[0132] According to an exemplary embodiment, an electrode cell is defined by the positive electrode 100, the negative electrode 130, and the separator 140, and a plurality of the electrode cells may be stacked to form, for example, an electrode assembly 150. The electrode assembly 150 may be of a winding type, a stacking type, a Z-folding type, or a stack-folding type.

[0133] A lithium secondary battery can be defined by housing the electrode assembly 150 together with an electrolyte in a case 160. According to an exemplary embodiment, a non-aqueous electrolyte can be used as the electrolyte.

[0134] The non-aqueous electrolyte contains a lithium salt as an electrolyte and an organic solvent. The lithium salt is, for example, Li + X - and the anion (X - ) is F - , Cl - , Br - , I - , NO 3 - , N(CN) 2 - , B.F. 4 - , ClO 4 - , P.F. 6 - , (CF 3 ) 2 PF 4 - , (CF 3 ) 3 PF 3 - , (CF 3 ) 4 PF 2 - , (CF 3 ) 5 PF - , (CF 3 ) 6 P - , C.F. 3 SO 3 - , C.F. 3 CF2 SO 3 - 、(CF 3 SO 2 ) 2 N - 、(FSO 2 ) 2 N - 、CF 3 CF 2 (CF 3 ) 2 CO - 、(CF 3 SO 2 ) 2 CH - 、(SF 5 ) 3 C - 、(CF 3 SO 2 ) 3 C - 、CF 3 (CF 2 ) 7 SO 3 - 、CF 3 CO 2 - 、CH 3 CO 2 - 、SCN - 、(CF 3 CF 2 SO 2 ) 2 N - such as etc.

[0135] Examples of the organic solvent that can be used include 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, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These can be used alone or in combination of two or more.

[0136] In some embodiments, a solid electrolyte may be used instead of the non-aqueous electrolyte. In this case, the lithium secondary battery may be manufactured in the form of an all-solid-state battery. Also, a solid electrolyte layer may be disposed between the positive electrode and the negative electrode instead of the separator.

[0137] The solid electrolyte can include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte can include a sulfide-based electrolyte. As a non-limiting example, the sulfide-based electrolyte can include Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -LiCl-LiBr, Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 S-SiS 2 , Li 2 S-SiS2 - LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 - LiI, Li 2 S-SiS 2 -P 2 S 5 - LiI, Li 2 S.B. 2 S 3 , Li 2 SP 2 S 5 -Z m S n (m and n are positive numbers, and Z is Ge, Zn, or Ga.) Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li p MO q (p and q are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In.), Li 7 - x P.S. 6 - x Cl x (0≦x≦2), Li 7 - x P.S. 6 - x Br x (0≦x≦2), Li 7 - x P.S. 6-x I x (0≦x≦2) and the like. These can be used alone or in combination of two or more.

[0138] In one embodiment, the solid electrolyte is, for example, Li 2 Alumni 2 O 3 -P 2 O 5 , Li 2O-SiO 2 , Li 2 Alumni 2 O 3 , Li 2 Alumni 2 O 3 It may also contain an oxide-based amorphous solid electrolyte such as ZnO.

[0139] 4, electrode tabs (positive electrode tab and negative electrode tab) may protrude from each of the positive electrode current collectors 105 and the negative electrode current collectors 125 belonging to each electrode cell and extend to one end of the case 160. The electrode tabs may be fused together with the one end of the case 160 and connected to electrode leads (positive electrode lead 107 and negative electrode lead 127) extended or exposed to the outside of the case 160.

[0140] 4 shows that the positive electrode lead 107 and the negative electrode lead 127 protrude from the upper side of the case 160 in the planar direction, but the positions of the electrode leads are not limited to this. For example, the electrode leads may protrude from at least one of both sides of the case 160, or may protrude from the lower side of the case 160. Alternatively, the positive electrode lead 107 and the negative electrode lead 127 may be formed so as to protrude from different sides of the case 160.

[0141] The lithium secondary battery may be manufactured in, for example, a cylindrical type using a can, a square type, a pouch type, or a coin type.

[0142] In the following, specific examples are presented to aid in understanding the present invention, but these examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It is clear to those skilled in the art that various changes and modifications can be made to these examples within the scope of the scope and technical ideas of the present invention, and it is natural that these changes and modifications fall within the scope of the appended claims.

[0143] Example 1 Anode production A silicon-carbon composite (hereinafter abbreviated as "Si / C") was prepared in which the Raman R3 value of Equation 3 was 0.99 and the Raman R4 value of Equation 4 was 0.5, both measured at a laser focus level of 0%, and graphite was prepared in which the Raman R3 value of Equation 3 was 0.11 and the Raman R4 value of Equation 4 was 0.11, both measured at a laser focus level of 0%.

[0144] The graphite and Si / C were mixed in a weight ratio of 85:15 to form the negative electrode active material, and the conductive material (SWCNT), CMC as a thickener, and SBR as a binder were mixed in a weight ratio of 97.2:0.1:1.2:1.5, and the mixture was dispersed in water to prepare a slurry-like negative electrode mixture. The viscosity of the negative electrode mixture was 4,000cp (25℃).

[0145] The negative electrode mixture prepared above was applied to the top and bottom surfaces of a negative electrode current collector (Cu foil) in a thickness of 180 μm, and then the negative electrode current collector was passed through a drying device at 80° C. at a speed of 8 m / s and dried.

[0146] A neodymium magnet was placed in the drying device so as to apply a magnetic force to the top and bottom surfaces of the negative electrode current collector, respectively. Before the drying process, a magnetic field having a magnetic field line oriented perpendicular to the negative electrode current collector was applied by the magnet with a maximum magnetic force of 8,000 G for 2 seconds.

[0147] Thereafter, the negative electrode mixture was rolled to an electrode density of 1.5 g / cm 3 A negative electrode including the negative electrode active material layer was produced.

[0148] Secondary battery manufacturing A positive electrode was prepared by applying a slurry containing an NCM-based active material, which is a Li-transition metal oxide, onto an aluminum foil and drying it. A polyolefin separator was interposed between the positive electrode and the negative electrode prepared as described above to prepare a secondary battery cell. The secondary battery cell was then placed in a pouch, and 1M LiPF using a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was added. 6 The solution was injected as an electrolyte and sealed to produce a pouch-type lithium secondary battery.

[0149] Then, pre-charging was performed for 20% of the total capacity at a current equivalent to 0.25 C. After that, degassing was performed and the cells were aged for more than 24 hours, after which formation charge and discharge were performed (charge conditions: CC-CV 0.65 C 4.2 V 0.05 C CUT-OFF, discharge conditions: CC 0.65 C 2.5 V CUT-OFF).

[0150] Example 2 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that the weight ratio of the graphite to Si / C was changed to 80:20.

[0151] Example 3 The electrode density of the negative electrode active material layer is 1.6 g / cm 3 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except for the above change.

[0152] Example 4 A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that graphite having a Raman R3 value of 0.28 and a Raman R4 value of 0.29, as measured at a focus level of 0%, as determined by Equation 3, was used.

[0153] Example 5 A negative electrode and a secondary battery were manufactured in the same manner as in Example 1, except that Si / C having a Raman R3 value of 1.02 and a Raman R4 value of 0.7, as measured at a focus level of 0%, as shown in Equation 3, was used.

[0154] Comparative Example 1 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that the maximum magnetic force of the magnetic field applied in the drying device was changed to 2,000 G.

[0155] Comparative Example 2 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that the speed of the negative electrode current collector in the drying device was changed to 12 m / s.

[0156] Comparative Example 3 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that the drying temperature was changed to 100°C.

[0157] Comparative Example 4 A negative electrode and a secondary battery were produced in the same manner as in Example 1, except that the viscosity of the negative electrode mixture was adjusted to 6,000 cp.

[0158] Experimental Example 1 (1) Measurement of Raman R value The Raman R1 and R2 values ​​defined by Equations 1 and 2 were measured from the surface of the negative electrode active material layer under the following conditions. Specifically, three areas were selected from the surface of the negative electrode active material layer, and the Raman R1 and R2 values ​​were obtained as the average of these values. i) Raman spectrometer: inVia Raman Microscope, Renishaw (UK) ii) Laser focus level: 100% ii) Argon ion laser light wavelength: 532 nm iii) Exposure time: 10 seconds, number of mappings: 10 iv) Magnification:x20 v) Laser power: 100%, 12mV

[0159] (2) Measurement of general life capacity retention rate Charging (CCCV, SOC98, 0.05C CUT-OFF) and discharging (CC, SOC4 CUT-OFF) at 25°C constitute one cycle, and the battery was repeatedly charged and discharged 1,000 times. The capacity efficiency was measured by expressing the discharge capacity after 1000 cycles relative to the discharge capacity after 1 cycle as a percentage.

[0160] (3) Evaluation of quick charging life characteristics The secondary battery sample was charged 150 times at 25° C. for 25 minutes in the range of SOC 10 to 82% and discharged at 0.3 C. The discharge capacity retention rate at 150 cycles relative to the initial discharge capacity at 1 cycle was measured in %. The evaluation results are summarized in Table 1 below.

[0161] [Table 1]

[0162] As shown in Table 1, in the examples in which the Raman R1 and R2 values ​​were within the above-mentioned ranges, improved general capacity retention rate and rapid charging capacity retention rate were ensured.

[0163] Experimental Example 1 Comparison of Raman R values ​​at 0% laser focus level For the negative electrode active material layers of Example 1 and Example 2, the Raman R3 and Raman R4 values ​​were measured at a laser focus level of 0% of the Raman spectrometer. i) Raman spectrometer: inVia Raman Microscope, Renishaw (UK) ii) Laser focus level: 0% ii) Argon ion laser light wavelength: 532 nm iii) Exposure time: 10 seconds, number of mappings: 30 iv) Magnification:x50 v) Laser power: 10%, 0.69mV

[0164] Comparative Example 5 A negative electrode was produced in the same manner as in Example 1, except that the weight ratio of graphite to Si / C was changed to 50:50.

[0165] Comparative Example 6 A negative electrode was produced in the same manner as in Example 1, except that the weight ratio of graphite to Si / C was changed to 97:3. For the negative electrode active material layers of Comparative Example 5 and Comparative Example 6, the Raman R1 and Raman R2 values ​​at a laser focus level of 100% and the Raman R3 and Raman R4 values ​​at a laser focus level of 0% of the Raman spectrometer were measured. The measurement results are shown in Table 2 below.

[0166] [Table 2]

[0167] As shown in Table 2, in Examples 1 and 2, it can be confirmed that the Raman value at a focus level of 0% has a deviation from the Raman R value at a focus level of 100%.

[0168] With reference to Comparative Examples 5 and 6, it can be seen that even if the Raman values ​​at a focus level of 0% are locally within the range of the embodiments of the present disclosure, the Raman values ​​at a focus level of 100% may be outside the range of the embodiments of the present disclosure.

Claims

1. A negative electrode current collector; a negative electrode active material layer formed on a surface of the negative electrode current collector, a Raman R1 value of Formula 1 measured on the surface of the negative electrode active material layer is greater than 0.2 and is not greater than 0.5; Raman R1 = I Ｄ / I Ｇ (Formula 1) (In formula 1, I Ｄ In the Raman spectrum measured at a laser focus level of 100% using a Renishaw inVia Raman microscope as a Raman spectrometer, －１ ~1,380cm －１ is the peak intensity for the absorption region of I Ｇ In the Raman spectrum, －１ ~1,600cm －１ is the peak intensity for the absorption region of

2. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the Raman R1 value is 0.23 to 0.

50.

3. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the Raman R2 value of Equation 2 measured on the surface of the negative electrode active material layer is 0.20 to 0.

45. Raman R2=A Ｄ / A Ｇ (Formula 2) (In formula 2, A Ｄ is a Raman spectrum measured at a laser focus level of 100% using a Renishaw inVia Raman microscope as a Raman spectrometer, and is expressed as 1,330 cm －１ ~1,380cm －１ is the peak area for the absorption region of A Ｇ In the Raman spectrum, －１ ~1,600cm －１ )

4. 4. The negative electrode for a lithium secondary battery according to claim 3, wherein the Raman R2 value is 0.22 to 0.

40.

5. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer contains a negative electrode active material including a silicon-based active material and a graphite-based active material.

6. 6. The negative electrode for a lithium secondary battery according to claim 5, wherein the silicon-based active material comprises a silicon-carbon composite.

7. 7. The negative electrode for a lithium secondary battery according to claim 6, wherein the silicon-carbon composite comprises a carbon core and a silicon coating formed on the carbon core.

8. 6. The negative electrode for lithium secondary batteries according to claim 5, wherein the content of the graphite-based active material is 60% by weight to 95% by weight, and the content of the silicon-based active material is 5% by weight to 40% by weight, based on the total weight of the silicon-based active material and the graphite-based active material.

9. The negative electrode for lithium secondary batteries according to claim 5, wherein the Raman R3 value of the formula 3 of the silicon-based active material is 0.8 to 2.

0. Raman R3=I Ｄ / I Ｇ (Formula 3) (In formula 3, I Ｄ In the Raman spectrum measured at a laser focus level of 0% using a Renishaw inVia Raman microscope as a Raman spectrometer, －１ ~1,380cm －１ is the peak intensity for the absorption region of I Ｇ In the Raman spectrum, －１ ~1,600cm －１ is the peak intensity for the absorption region of

10. 6. The negative electrode for a lithium secondary battery according to claim 5, wherein the Raman R3 value of the graphite-based active material in formula 3 is 0.05 to 0.

5. Raman R3=I Ｄ / I Ｇ (Formula 3) (In formula 3, I Ｄ In the Raman spectrum measured at a laser focus level of 0% using a Renishaw inVia Raman microscope as a Raman spectrometer, －１ ~1,380cm －１ is the peak intensity for the absorption region of I Ｇ In the Raman spectrum, －１ ~1,600cm －１ is the peak intensity for the absorption region of

11. The negative electrode for lithium secondary batteries according to claim 5, wherein the Raman R4 value of the formula 4 of the silicon-based active material is 0.1 to 1.

0. Raman R4=A Ｄ / A Ｇ (Formula 4) (In formula 4, A Ｄ In the Raman spectrum measured at a laser focus level of 0% using a Renishaw inVia Raman microscope as a Raman spectrometer, －１ ~1,380cm －１ is the peak area for the absorption region of A Ｇ In the Raman spectrum, －１ ~1,600cm －１ )

12. 6. The negative electrode for a lithium secondary battery according to claim 5, wherein the Raman R4 value of the graphite-based active material in formula 4 is 0.05 to 0.

5. Raman R4=A Ｄ / A Ｇ (Formula 4) (In formula 4, A Ｄ In the Raman spectrum measured at a laser focus level of 0% using a Renishaw inVia Raman microscope as a Raman spectrometer, －１ ~1,380cm －１ is the peak area for the absorption region of A Ｇ In the Raman spectrum, －１ ~1,600cm －１ )

13. 6. The negative electrode for a lithium secondary battery according to claim 5, wherein the content of the negative electrode active material is 85% by weight to 98% by weight based on the total weight of the negative electrode active material layer.

14. The electrode density of the negative electrode active material layer is 1.3 g / cm ３ ~1.8g / cm ３ 2. The negative electrode for a lithium secondary battery according to claim 1 ,

15. The negative electrode for a lithium secondary battery according to any one of claims 1 to 14, and a positive electrode facing the negative electrode.

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