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

Abstract

The present invention provides a negative electrode for a lithium secondary battery, comprising: a current collector; and a negative electrode active material layer including a negative electrode active material and formed on the current collector, in which the negative electrode active material includes a core body including artificial graphite and a case formed on a surface of the core body, the case including amorphous carbon, the core body including secondary particles formed of primary particles including artificial graphite, and the secondary particles including amorphous carbon. The primary particles are randomly oriented in the core body, a ratio (I (110) / I (002)) of a peak intensity of a 110 plane to a peak intensity of a 002 plane of the core body measured by XRD is in a range of 0.0075 to 0.0120, and a density of the negative electrode active material layer is 1.45 g / cm3 or more.

Description

[0001] This application is a divisional application of a patent application with application number 2018104577641, application date May 14, 2018, and invention name “Negative electrode for lithium secondary battery and lithium secondary battery comprising the same”.

[0002] Cross-reference to related applications and claim of priority

[0003] This application claims the benefit of Korean Patent Application No. 10-2017-0059830 filed on May 15, 2017 in the Korean Intellectual Property Office (KIPO), the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode. Background Art

[0005] According to the development of information and display technology, secondary batteries that can be repeatedly charged and discharged have been widely used as power sources for mobile electronic devices such as camcorders, mobile phones, laptop computers, etc. Recently, secondary batteries are being developed and applied as environmentally friendly power sources for electric vehicles, uninterruptible power supplies, artificial satellites, etc.

[0006] For example, a lithium secondary battery may include a negative electrode formed of a carbon-based material capable of absorbing and releasing lithium ions, a positive electrode formed of a lithium-containing oxide, and a nonaqueous electrolyte containing a mixed organic solvent and a lithium salt dissolved therein.

[0007] The negative electrode active material may include amorphous carbon or crystalline carbon. Crystalline carbon, which may include natural carbon or artificial carbon, may be advantageous due to high capacity.

[0008] Artificial carbon may have high charge / discharge efficiency, however its capacity may be relatively low.

[0009] For example, Korean Patent Publication No. 10-2005-0004930 discloses a negative electrode active material including artificial carbon which may not have sufficient discharge capacity and power output. Summary of the invention

[0010] According to one aspect of the present invention, there is provided a negative electrode for a lithium secondary battery having improved power output, lifespan, and high temperature storage characteristics.

[0011] According to one aspect of the present invention, there is provided a lithium secondary battery including a negative electrode for a lithium secondary battery.

[0012] According to an exemplary embodiment, a negative electrode for a lithium secondary battery includes: a current collector; and a negative electrode active material layer, which includes a negative electrode active material and is formed on the current collector, wherein the negative electrode active material includes a core containing artificial graphite and a shell formed on the surface of the core, the shell includes amorphous carbon, the core includes secondary particles formed of primary particles containing the artificial graphite, the primary particles are randomly oriented in the core, the ratio of the peak intensity of the 110 plane of the core to the peak intensity of the 002 plane (I(110) / I(002)) measured by XRD is in the range of 0.0075 to 0.0120, and the density of the negative electrode active material layer is 1.45 g / cm 3 or larger.

[0013] In some embodiments, the negative active material layer may further include a binder, and an amount of the binder may be 3 wt % or less based on the total weight of the negative active material and the binder.

[0014] In some embodiments, the average thickness of the shell can be in a range from about 5 nm to about 100 nm.

[0015] In some embodiments, the average value of the Raman R value of the negative electrode active material layer may be in the range of 0.5 to 0.65, and the standard deviation of the Raman R value may be less than 0.22, the Raman R value may be defined as the ratio (ID / IG) of the D band intensity (ID) relative to the G band intensity (IG), and the D band and the G band may be obtained from the Raman spectrum of the surface of the negative electrode active material layer. The average value and standard deviation of the Raman R value may be calculated based on a probability density function derived by normalizing the frequency distribution graph of the Raman R value.

[0016] In some embodiments, the G band intensity may be about 1,540 cm -1 To 1,620cm -1 The peak intensity of the wavenumber region, and the D band intensity can be about from 1,300 cm -1 To 1,420cm -1 The peak intensity in the wavenumber region.

[0017] In some embodiments, the average diameter (D 50 ) may be in the range of 5 μm to 15 μm, and the average diameter (D 50 ) can be in the range of 10μm to 25μm.

[0018] In some embodiments, the average diameter (D 50 ) may be in the range of 7 μm to 10 μm, and the average diameter (D50 ) can be in the range of 13μm to 20μm.

[0019] According to an exemplary embodiment, a lithium secondary battery includes the negative electrode for a lithium secondary battery as described above, a positive electrode; and a separator interposed between the negative electrode and the positive electrode.

[0020] According to an exemplary embodiment, the negative electrode for a lithium secondary battery may have improved charge / discharge power output and fast charge power. In addition, the lithium secondary battery including the negative electrode for a lithium secondary battery may have improved lifespan and high temperature storage characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a graph showing capacity retention rates according to the number of cycles of lithium secondary batteries according to Examples and Comparative Examples. DETAILED DESCRIPTION

[0022] According to an exemplary embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery, the negative electrode being formed of a negative electrode active material and comprising a core body containing artificial carbon and a shell body comprising amorphous carbon on a surface of the core body. D / I G ) may be in the range of about 0.5 to about 0.65, and the standard deviation of the Raman R value may be less than about 0.22. A lithium secondary battery including the negative electrode may have improved charge / discharge power output and fast charge power output without reducing lifespan and high temperature storage characteristics.

[0023] Hereinafter, the present invention will be described in detail with reference to exemplary embodiments. However, those skilled in the art will appreciate that these embodiments are provided to further understand the essence of the present invention, and these embodiments do not limit the subject matter to be protected as disclosed in the specific implementation manner and the appended claims.

[0024] Negative electrode for lithium secondary battery

[0025] If natural graphite is used as the negative electrode active material, clogging of the filter membrane may occur during the mixing process, and the dispersion characteristics of the suspension may be reduced. However, relatively speaking, artificial graphite may not have the above problems and may have improved lifespan and high temperature storage characteristics compared to natural graphite.

[0026] Artificial graphite used as a negative electrode active material of a lithium secondary battery may include a multilayer structure having a plurality of layers, and lithium ions may be intercalated and separated between the plurality of layers, so that charging and discharging operations may be performed. In this case, the intercalation and separation of lithium ions may occur along the layer direction of the artificial graphite, and thus the power output may be limited.

[0027] Therefore, the lithium secondary battery according to the exemplary embodiment may include a negative electrode active material including a core and a shell formed on the surface of the core. The core may include artificial graphite, and the shell may include amorphous carbon. The Raman R value (I D / I G ) can be in the range of about 0.5 to about 0.65, and the standard deviation of the Raman R value is less than about 0.22. Therefore, the thickness uniformity of the shell coated on the core can be improved, and the power output of the lithium secondary battery can be increased without reducing the life span and high temperature storage characteristics.

[0028] If the standard deviation is 0.22 or more, the thickness uniformity of the shell may be deteriorated and the power output may not be sufficiently increased. D / I G ) may not be within the above range, but the power output may be reduced. For example, if the average value of the Raman R value is less than about 0.5, the power output may not be sufficiently improved, and the long-term stability of the battery may be deteriorated due to irregular coating of the shell. If the average value of the Raman R value exceeds about 0.65, irregular coating may result due to coating aggregation.

[0029] If a shell containing amorphous carbon is uniformly coated on the surface of the core, insertion and separation of lithium ions on the negative electrode can occur in all directions of the negative electrode active material, so that power output characteristics of the battery such as charge / discharge power and fast charging can be enhanced.

[0030] If the surface shape of the core is not uniform, coating uniformity may be more critical to the power output characteristics. The coating uniformity of the shell can be defined by the standard deviation of the Raman R-values.

[0031] In an exemplary embodiment, the mean and standard deviation of the Raman R-values ​​may be measured as follows.

[0032] A negative electrode active material layer including a negative electrode active material may be formed, and Raman spectroscopy analysis may be performed at 100 points or more (e.g., 100 to 5000 points, with confidence becoming higher as the number of points increases) of the negative electrode active material layer. D / I G ), i.e., the ratio of the D band intensity to the G band intensity, to obtain a frequency distribution diagram. The frequency distribution diagram can be normalized by Gaussian fitting according to the following equation 1 to obtain the Raman R value (I D / I G ) is a probability density function. The Raman R value (I D / I G )’s mean and standard deviation.

[0033] The G band intensity is the intensity of the Raman band around 1,540 cm -1 About 1,620cm -1 The D band intensity is the peak intensity in the wavenumber region of the Raman spectrum around 1,300 cm -1 About 1,420cm -1 The peak intensity in the wavenumber region.

[0034] [Equation 1]

[0035]

[0036] In the above equation 1, x represents the Raman R value (I D / I G ), a0 represents the amplitude coefficient, and a1 represents the maximum Raman R value (I D / I G ), and a2 represents the half-width at half-maximum (FWHM) of the graph.

[0037] In an embodiment of the present invention, the Raman R value (I D / I G ) may be in the range of about 0.55 to about 0.60. D / I G ) can represent the relative thickness of the shell. D / I G ), the battery life and power output can be further enhanced.

[0038] In an embodiment of the present invention, the Raman R value (I D / I G ) can be less than about 0.20, and can represent a parameter related to the thickness uniformity of the shell. Within this range, the life and power output of the battery or electrode can be further enhanced.

[0039] In an exemplary embodiment, Raman spectroscopy analysis may be performed as follows: an active material including a core and a shell on a surface of the core may be prepared (S1); an active material layer including the active material may be formed on at least one surface of a current collector (S2); a Raman spectrum of the active material layer may be obtained, and a Raman R value may be calculated therefrom (I D / I G )(S3); a frequency distribution diagram of the Raman R value can be obtained (S4); the frequency distribution diagram can be normalized to obtain a probability density function (S5); the Raman R value can be calculated from the curve diagram of the probability density function (I D / I G) to evaluate the shell (S6).

[0040] For example, Raman spectroscopy analysis can be performed using a Raman spectrometer known in the art.

[0041] For example, in a Raman spectrometer, a specific region may be selected on the surface of the negative electrode active material layer, and Raman imaging may be performed on the selected region using the Raman spectrometer.

[0042] As described above, 100 to 5000 regions may be randomly selected on the surface of the negative active material layer to perform Raman spectroscopy analysis, and the area of ​​each region may be about (30 μm to 50 μm)×(30 μm to 75 μm).

[0043] For example, the imaging interval of the Raman imaging may be set to be about 1 μm to about 10 μm in the x-axis direction, and about 1 μm to about 5 μm in the y-axis direction.

[0044] For example, the laser wavelength of the Raman spectrometer may be in the range of about 532 nm to about 785 nm, the laser power may be in the range of about 5 mW to about 90 mW, the laser exposure time may be in the range of about 3 seconds to about 20 seconds, and the number of scans may be 1 to 5.

[0045] The carbon atoms forming the core and shell included in the active material may be present in at least one bond structure. The bond structure may include a hexagonal system formed by sp2 bonds, in which one carbon atom is bonded to three adjacent carbon atoms in the same plane at a bond angle of about 120°. The bond structure may also include a tetragonal system formed by sp3 bonds, in which one carbon atom is bonded to four adjacent carbon atoms at a bond angle of about 109.5°.

[0046] The G band is a peak generally observed in graphite-based materials and is observed when carbon atoms are present in a hexagonal crystal system. The D band is generated by a symmetric vibration mode and is not observed in an ideal lattice structure. For example, the D band is observed when the hexagonal crystal system is not expanded or there are defects therein.

[0047] As described above, the core included in the active material may include crystalline carbon, and the shell may include amorphous carbon. In terms of the ratio of the structure formed by the sp2 bond and other bonds, the bond structure of the carbon atoms in the core is different from the bond structure of the carbon atoms in the shell. Therefore, the G band intensity and the D band intensity measured in the core and the shell may be different from each other.

[0048] Therefore, if the thickness or uniformity of the shell changes, the Raman R value (I D / I G ) may also change.

[0049] In the evaluation method described above, a frequency distribution graph may be obtained. For example, the frequency distribution graph may be a histogram.

[0050] For example, the data of Raman R values ​​may be classified into classification intervals of about 0.01 to about 0.02, and the frequency of each classification may be counted to obtain a frequency distribution table. A frequency distribution graph may be obtained from the frequency distribution table.

[0051] In the evaluation method, the frequency distribution graph may be normalized to obtain a probability density function. When the probability density function is obtained, a kernel density estimation (KDE) method may be used to perform normalization to obtain the probability density function.

[0052] Kernel density estimation is one of the nonparametric density estimation methods that performs normalization using a predetermined kernel function. The kernel function may include a non-negative function whose integral value is 1 and is centrally symmetric. For example, a Gaussian function may be used as the kernel function.

[0053] As described above, normalization may be performed by Gaussian fitting according to the following Equation 1.

[0054] [Equation 1]

[0055]

[0056] In the above equation 1, x represents the Raman R value (I D / I G ), a0 represents the amplitude coefficient, and a1 represents the maximum Raman R value (I D / I G ), and a2 represents the half-width at half-maximum (FWHM) of the graph.

[0057] In the above Equation 1, a1 may represent a maximum value of a probability density function, and a Raman R value representing the maximum value may be a Raman R value corresponding to a median value of the probability density function.

[0058] Raman R value (I D / I G ) can be used as an indicator of the relative thickness of the shell included in the negative electrode active material, and / or the Raman R value (I D / I G ) can be used as an indicator of the relative uniformity of the shell thickness included in the negative electrode active material. However, it may not be possible to obtain the Raman R value (I D / I G ) to obtain the absolute shell thickness or the absolute uniformity of the shell thickness (e.g., roughness).

[0059] The thickness may indicate the width between two opposing surfaces, and the uniformity of the thickness may indicate, for example, the roughness of the housing surface.

[0060] For example, when evaluating active materials with different shell thicknesses, the Raman R value (I D / I G ) are compared with each other to evaluate the relative thickness included in each active material. D / I G ) becomes smaller, the shell thickness can be determined to be smaller. D / I G ) becomes larger, the shell thickness can be determined to be larger.

[0061] In the evaluation of active materials having different uniformity or roughness of shell thickness, the standard deviations derived as described above can be compared with each other to evaluate the relative uniformity or roughness of each shell thickness included in each active material. As the standard deviation becomes narrower, the uniformity of shell thickness can be determined to be improved or the roughness can be determined to be reduced. As the width of the peak becomes wider, the uniformity of shell thickness can be determined to be worse, and the roughness of shell thickness can be determined to be greater.

[0062] In an embodiment, when the active material includes at least two core-shell particles having different shell thicknesses and / or different uniformity of shell thicknesses, a probability density function including at least two peaks may be obtained. In this case, the Raman R value (I D / I G ) and the standard deviation of each peak.

[0063] Therefore, even if the active material includes at least two core-shell particles having different thickness characteristics as described above, an active material layer including at least two core-shell particles and thickness characteristics can be easily evaluated by a single evaluation method without the need for each core-shell particle to form a separate active material layer and evaluating each active material layer separately.

[0064] For example, if the active material includes two core-shell particles with different shell thicknesses and the same uniformity, a probability density function with two peaks can be obtained. The two peaks can have different average values ​​of Raman R values ​​and can have the same width at the same y-axis value or the same height.

[0065] For example, if the active material includes two core-shell particles with different uniformity and the same shell thickness, a probability density function with two peaks can be obtained. The two peaks can have different widths at the same y-axis value or the same height, and can have the same average Raman R value.

[0066] For example, if the active material includes two core-shell particles with different uniformity and shell thickness, a probability density function with two peaks can be obtained. The two peaks can have different widths at the same y-axis value or the same height, and can have different average values ​​of Raman R values.

[0067] A negative active material according to an exemplary embodiment may include a core including artificial graphite and a case formed on a surface of the core and including amorphous carbon.

[0068] The shell may be a coating layer formed on the core. The shell may include amorphous carbon, and the amorphous carbon may include soft carbon and / or hard carbon.

[0069] The soft carbon may include, for example, coal-based pitch, oil-based pitch, polyvinyl chloride, mesophase pitch, tar, low molecular weight intermediate crude oil, etc. These may be used alone or in combination.

[0070] Hard carbon may include, for example, citric acid, stearic acid, sucrose, polyvinylidene fluoride, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), polyacrylic acid, polyacrylonitrile, glucose, gelatin, phenolic resin, naphthalene resin, polyamide resin, furan resin, polyvinyl alcohol resin, polyimide resin, cellulose resin, styrene resin, epoxy resin, etc. These may be used alone or in combination.

[0071] For example, the average thickness of the shell may be in the range of about 5 nm to about 100 nm.

[0072] The amount of the shell may be in the range of about 0.5 wt % to about 10 wt % based on the total weight of the core and the shell.

[0073] The core may include artificial graphite. For example, the average diameter (D 50 ) may be in the range of about 7 μm to about 30 μm.

[0074] In some embodiments, the core may include secondary particles having an average diameter of about 10 μm to 25 μm, which may be formed from primary particles having an average diameter of about 5 μm to about 15 μm. The primary particles may include artificial graphite, and I(110) / I(002) of the secondary particles may be in the range of 0.0075 to 0.0120.

[0075] The core can be used together with the case as described above, which can achieve long life and high temperature storage characteristics of the battery while also improving power output characteristics. Artificial graphite with improved pressing characteristics can be used to increase the energy density of the battery.

[0076] Within the average diameter range of the primary particles, the product yield and the life of the battery can be improved, and the control of the size of the secondary particles can be easily performed.

[0077] A plurality of primary particles may be aggregated to form secondary particles. The number of primary particles used to form secondary particles may not be particularly limited. For example, 3 to 9 primary particles may be aggregated to form secondary particles.

[0078] The average diameter of the secondary particles may be within the above range, so that the size of pores generated during the manufacture of the electrode can be appropriately adjusted. Therefore, the impregnation of the electrode can be facilitated, and the thickness of the electrode can be easily controlled.

[0079] Preferably, the average diameter of the primary particles may be in the range of about 7 μm to about 10 μm, thereby increasing power output while minimizing the reduction in lifespan and high temperature storage characteristics. The average diameter of the secondary particles may be in the range of about 13 μm to about 20 μm for effective use in electrodes.

[0080] The orientation of each primary particle of the artificial graphite may be randomly distributed, so that lithium ions may easily pass through the artificial graphite. According to an exemplary embodiment, the orientation of the particles may be adjusted, so that the power output of the battery may be further improved.

[0081] The orientation of the particles can be determined by X-ray diffraction (XRD) analysis. For example, incident X-rays of a specific wavelength λ can produce diffraction peaks of different intensities at a specific incident angle θ or diffraction angle 2θ, and the ratio of the peaks can be calculated to determine the orientation of the particles.

[0082] I(002) represents the intensity (height) of the peak near the position of 2θ=26.5 in XRD analysis, I(110) represents the intensity (height) of the peak near the position of 2θ=77.5 in XRD analysis, and I(110) / I(002) represents the ratio of the intensities.

[0083] XRD analysis can be performed using XRD measurement conditions commonly used in the related art. For example, the following conditions can be used.

[0084] X-ray: Cu K alpha, K-Alpha1 Wavelength:

[0085] Generator voltage: 40kV, tube current: 30mA

[0086] Scan range: 10~80, scan step: 0.026

[0087] Nickel filter, Soller slit (0.04rad, 2ea), diffraction anti-scatter slit 7.5mm

[0088] Divergence slit: 1 / 4°, Anti-scatter slit: 1 / 2°

[0089] Each step time: 100s

[0090] In some embodiments, the I(110) / I(002) of the secondary particles may be in the range of about 0.0075 to about 0.0120 to further improve the power output of the battery. Preferably, from the perspective of further improving the charge / discharge power, the I(110) / I(002) of the secondary particles may be in the range of about 0.0075 to 0.0100.

[0091] If I(110) / I(002) is less than about 0.0075, a negative electrode active material may not be easily formed, and electrochemical characteristics such as capacity of artificial graphite may also be deteriorated due to excessive control of particle shape and size.

[0092] The shape of the primary particles may not be particularly limited. For example, the primary particles may have a spherical shape or a plate shape to facilitate absorption and release of lithium ions.

[0093] The negative electrode active material may be mixed with a solvent and optionally with a binder, a conductive agent, a dispersant, etc. to form a mixture. The mixture may be coated on a metal current collector by, for example, spraying or dipping, and pressed and dried to form a negative electrode for a lithium secondary battery.

[0094] The solvent may include a non-aqueous solvent, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0095] The binder may include an organic binder such as a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or an aqueous binder such as styrene butadiene rubber (SBR) which may be used with a thickener such as carboxymethyl cellulose (CMC).

[0096] The amount of the binder may be appropriately adjusted to form an electrode and improve resistance characteristics. For example, the amount of the binder may be about 3 wt % or less based on the total weight of the negative electrode active material and the binder. The lower limit of the binder may not be particularly limited, for example, it may be about 0.5 wt % or about 1 wt % based on the total weight of the negative electrode active material and the binder.

[0097] For example, a conductive carbon-based material may be used as the conductive agent.

[0098] The metal current collector may include a metal having high electrical conductivity, which may not react within the voltage range of the battery and may be easily coated with a mixture of a negative electrode active material or a positive electrode active material. For example, copper or a copper alloy; stainless steel, nickel, aluminum, titanium or an alloy thereof; or copper or stainless steel that may be surface-treated with carbon, nickel, titanium, silver, etc. may be used as the negative electrode current collector.

[0099] In an embodiment, the electrode density of the negative active material layer formed of the negative active material may be about 1.43 g / cm 3 or more, and the upper limit of the electrode density may not be particularly limited. Within the above range, the power output, lifespan, and high temperature storage characteristics of the electrode or battery may be improved.

[0100] Lithium secondary battery

[0101] A lithium secondary battery according to an exemplary embodiment may include a negative electrode formed of the negative electrode active material as described above, a positive electrode, and a separator interposed between the positive electrode and the negative electrode.

[0102] For example, an electrode assembly including a negative electrode, a positive electrode, and a separator may be packaged in a battery case, and an electrolyte may be injected to obtain a lithium secondary battery.

[0103] positive electrode

[0104] Positive electrode active materials known in the art can be used to form the positive electrode.

[0105] A positive electrode active material may be coated on a positive electrode collector to form a positive electrode.

[0106] The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof; or aluminum or stainless steel that may be surface-treated with carbon, nickel, titanium, silver, or the like.

[0107] A positive electrode active material commonly used in the prior art can be used. For example, a composite oxide of lithium and at least one of cobalt, manganese, and nickel, such as the compounds listed below, can be used.

[0108] Li x Mn 1-y M y A2

[0109] Li x Mn 1-y M y O 2-z X z

[0110] Li x Mn2O 4-z X z

[0111] Lix Mr 2-y M y m' z A4

[0112] Li x Co 1-y M y A2

[0113] Li x Co 1-y M y O 2-z X z

[0114] Li x Ni 1-y M y A2

[0115] Li x Ni 1-y M y O 2-z X z

[0116] Li x Ni 1-y Co y O 2-z X z

[0117] Li x Ni 1-y-z Co y M z A α

[0118] Li x Ni 1-y-z Co y M z O 2-α X α

[0119] Li x Ni 1-y-z Mr y M z A α

[0120] Li x Ni 1-y-z Mr y M z O 2-α X

[0121] In the above chemical formula, 0.9≤x≤1.1, 0≤y≤0.5, 0≤z≤0.5, 0≤α≤2, M and M' are the same as or different from each other and can be selected from Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V or rare earth metals, A can be selected from O, F, S or P, and X can be selected from F, S or P.

[0122] The positive electrode active material may be mixed with a solvent, and optionally with a binder, a conductive agent, a dispersant, etc. to form a mixture. The mixture may be coated on a positive electrode current collector coating, and pressed and dried to form a positive electrode.

[0123] The solvent may include a non-aqueous solvent, for example, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like.

[0124] The binder may include an organic binder such as a copolymer of vinylidene fluoride and hexafluoropropylene (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, or an aqueous binder such as styrene butadiene rubber (SBR) which may be used with a thickener such as carboxymethyl cellulose (CMC).

[0125] Conductive carbon-based materials may be used as the conductive agent.

[0126] Diaphragm

[0127] The separator may include a porous polymer film. For example, a polyolefin-based polymer including at least one of the following may be used: an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer. Conventional porous nonwoven fabrics, high melting point glass, polyethylene terephthalate fibers may also be used in the separator. The separator may be applied to the battery by winding, laminating, stacking, folding, etc. with the electrode.

[0128] Non-aqueous electrolyte

[0129] The non-aqueous electrolyte may include a lithium salt and an organic solvent.

[0130] A lithium salt commonly used in an electrolyte for a lithium secondary battery may be used and may be represented by Li + X - .

[0131] Non-limiting examples of anions of lithium salts may include 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 - ,

[0132] (CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - 、CH3CO2 - 、SCN - 、(CF3CF2SO2)2N - wait.

[0133] Organic solvents commonly used in the electrolyte of lithium secondary batteries can be used. Non-limiting examples of organic solvents may include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, fluoroethylene carbonate (FEC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, cyclopentane, γ-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These can be used alone or in combination.

[0134] A nonaqueous electrolyte may be injected into an electrode assembly including a positive electrode, a negative electrode, and a separator interposed therebetween to form a lithium secondary battery.

[0135] The lithium secondary battery may be manufactured in a cylindrical shape, a pouch shape, or a coin shape, for example, using a can.

[0136] Hereinafter, preferred embodiments are proposed to more specifically describe the present invention. However, the following examples are only used to illustrate the present invention, and it will be apparent to those skilled in the relevant art that various changes and modifications can be made within the scope and essence of the present invention. These changes and modifications are appropriately included in the appended claims.

[0137] Examples and Comparative Examples

[0138] Example 1:

[0139] <Negative electrode>

[0140] The artificial graphite is crushed by coke and collision crusher to form an average diameter D 50 The primary particles are 7.2 μm.

[0141] The primary particles are aggregated using pitch to form secondary particles, and heat treated at 3,000°C to form a core body, wherein D 50 =15.3μm, La(100)=23, Lc(002)=21, I(110) / I(002)=0.0084.

[0142] The core prepared above and a solid binder pitch having a softening point of 250° C. or higher were mixed in a ratio of 100:10, and then mechanically mixed in a high-speed stirrer at 2,200 rpm for 10 minutes to form a mixture. The mixture was fired in an electric furnace by increasing the temperature from 25° C. to 1,100° C. within 2 hours, and maintained at 1,100° C. for 1 hour to form a shell on the surface of the core, and a negative electrode active material as a core-shell particle was obtained.

[0143] The negative electrode active material prepared above, styrene butadiene rubber (SBR) as a thickener and carboxymethyl cellulose (CMC) were mixed in a weight ratio of 97.8:1.2:1.0 and then dispersed in distilled water to form a mixture. The mixture was coated on the surface of the Cu foil current collector and then dried and pressed to form a 10 cm × 10 cm × 50 μm electrode with an electrode density of 1.50 ± 0.05 g / cm 3 negative electrode active material layer.

[0144] <Positive electrode>

[0145] Li as the positive electrode active material 1.0 Ni 0.6 Co 0.2 Mn 0.2 O2, superconductive acetylene black (Denka Black) as a conductive additive, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent were mixed in a weight ratio of 46:2.5:1.5:50 to form a positive electrode mixture. The positive electrode mixture was coated on an aluminum substrate and then dried and pressed to form a positive electrode.

[0146] <Lithium Secondary Battery>

[0147] The positive electrode and negative electrode prepared above were cut into appropriate sizes, and a separator (polyethylene, thickness: 25 μm) was placed between the positive electrode and the negative electrode to form an electrode unit. The electrode units were stacked, and electrode joints of the positive electrode and the negative electrode were welded to form an electrode assembly.

[0148] The electrode assembly was placed in a bag, and then three sides of the bag, including the electrode tab protruding side, were sealed except for the electrolyte injection side. The electrolyte was injected through the electrolyte injection side, and immersed for more than 12 hours after the electrolyte injection side was sealed. 1M LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC), and then 1wt% of vinylene carbonate, 1,3-propylene sultone (PRS) and 0.5wt% of lithium bis(oxalato)borate (LiBOB) were added to prepare the electrolyte.

[0149] Pre-charge was performed for 36 minutes using a current of 2.5 A corresponding to 0.25 C. After 1 hour, degassing was performed, aging was performed for more than 24 hours, and then forming charge / discharge was performed (charge conditions: CC-CV 0.2C 4.2V 0.05C CUT-OFF, discharge conditions: CC 0.2C 2.5V CUT-OFF).

[0150] Subsequently, standard charge / discharge was performed (charge condition: CC-CV 0.5C 4.2V 0.05C CUT-OFF, discharge condition: CC 0.5C 2.5V CUT-OFF).

[0151] Examples 2 to 8, Comparative Examples 1 to 6

[0152] Change Raman R value (I D / I G ) and at least one of the weight ratio of the core to the shell to prepare the batteries of Examples 2 to 8 and Comparative Examples 1 to 6. Specifically, the stirring speed, firing temperature, thickness, etc. during the formation of the shell were adjusted to change the Raman R value (I D / I G )’s mean and standard deviation.

[0153] The Raman R values ​​(I D / I G ) and the weight ratio of the core to the shell.

[0154] [Table 1]

[0155]

[0156] Examples 9 to 14, Comparative Example 7

[0157] As listed in Table 2 below, by changing the type of core (components: secondary particles formed of primary particles, ordinary artificial graphite, and natural graphite), the average diameter (D 50 ) and I(110) / I(002) of the negative electrode active material to prepare the batteries of Examples 9 to 14 and Comparative Example 7. The Raman R values ​​(I D / I G ) and the weight ratio of the core to the shell.

[0158] [Table 2]

[0159]

[0160] [Table 3]

[0161]

[0162] Experimental example

[0163] The rapid charging characteristics of the lithium secondary batteries according to the examples and comparative examples were evaluated.

[0164] <Evaluation of fast charging characteristics>

[0165] A battery with a large capacity of 10Ah or more was manufactured using the negative electrodes of the examples and comparative examples and the same positive electrodes. The fast charging characteristics of the battery were evaluated in a constant temperature (25°C) room at a charge rate (c-rate) of 1.4C charge / 1C discharge within the DOD90 range. After repeating 300 cycles, the fast charging capacity retention rate was measured. The results are shown in Table 4 below.

[0166] [Table 4]

[0167]

[0168] Figure 1 is a graph showing capacity retention rates according to the number of cycles of lithium secondary batteries according to Examples and Comparative Examples.

[0169] Reference Figure 1 , Example( Figure 1 The decrease in the capacity retention rate (%) over time in the lithium secondary batteries of the examples (denoted as "Ex.") 1 to 3 is less than that in the comparative example ( Figure 1 The capacity retention rate (%) in (denoted as “Com.”)3 decreases over time, and improved charging, life, and power output are achieved.

Claims

1. A negative electrode for a lithium secondary battery, comprising: current collector; as well as a negative electrode active material layer, which includes a negative electrode active material and is formed on the current collector, wherein the negative electrode active material comprises a core body containing artificial graphite and a shell formed on a surface of the core body, the shell comprising amorphous carbon, The core includes secondary particles formed of primary particles containing the artificial graphite, The primary particles are randomly oriented in the core, The ratio of the peak intensity of the 110 plane to the peak intensity of the 002 plane of the core (I(110) / I(002)) measured by XRD is in the range of 0.0075 to 0.0120, and The density of the negative electrode active material layer is 1.45 g / cm 3 or larger.

2. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode active material layer further comprises a binder, The amount of the binder is 3 wt % or less based on the total weight of the negative electrode active material and the binder. 3 . The negative electrode for a lithium secondary battery according to claim 1 , wherein an average thickness of the shell is in the range of 5 nm to 100 nm.

4. The negative electrode for a lithium secondary battery according to claim 1, wherein the average value of the Raman R value of the negative electrode active material layer is in the range of 0.5 to 0.65, and the standard deviation of the Raman R value is less than 0.22, The Raman R value is defined as a ratio (ID / IG) of D band intensity (ID) to G band intensity (IG), and the D band and the G band are obtained from a Raman spectrum of the surface of the negative electrode active material layer. The mean value and the standard deviation of the Raman R value are calculated according to a probability density function derived by normalizing the frequency distribution graph of the Raman R value.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the G band intensity is about -1 To 1,620cm -1 The peak intensity of the wavenumber region is about 1,300 cm -1 To 1,420cm -1 The peak intensity in the wavenumber region.

6. The negative electrode for a lithium secondary battery according to claim 1, wherein the average diameter (D 50 ) is in the range of 5 μm to 15 μm, and the average diameter (D 50 ) is in the range of 10μm to 25μm.

7. The negative electrode for a lithium secondary battery according to claim 6, wherein the average diameter (D 50 ) is in the range of 7 μm to 10 μm, and the average diameter (D 50 ) is in the range of 13μm to 20μm.

8. A lithium secondary battery comprising: The negative electrode for a lithium secondary battery according to any one of claims 1 to 7, A positive electrode; and A separator is disposed between the negative electrode and the positive electrode.

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