Negative electrode for rechargeable lithium battery and rechargeable lithium battery comprising the same

Abstract

Disclosed herein are a negative electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. The negative electrode for a rechargeable lithium battery includes a current collector and a negative active material layer disposed on the current collector and including a carbon-based negative active material and a conductive agent, wherein the conductive agent includes a fibrous conductive agent having a length of about 1 µm to about 200 µm or a particulate conductive agent having a size (length diameter) of about 1 µm to about 20 µm, and a DD (dispersion degree) value of the negative electrode defined by Equation 1 is greater than or equal to about 24.[Equation 1] DD (Dispersion Degree) = (I a / I 总 )*100In Equation 1, I a is a sum of peak intensities at non-flat angles measured by XRD using Cu Kα rays, I 总 is a sum of peak intensities at all angles measured by XRD using Cu Kα rays.

Description

[0001] Divisional Statement

[0002] This application is a divisional application of patent application with the application date of April 25, 2019, application number 201910339767.X, and the title of "Anode for rechargeable lithium battery and rechargeable lithium battery comprising the same".

[0003] Cross Reference to Related Applications

[0004] This application claims priority to and the benefit of Korean Patent Application No. 10-2018-0049447, filed on April 27, 2018, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0005] An anode for a rechargeable lithium battery and a rechargeable lithium battery comprising the same are disclosed. BACKGROUND

[0006] Rechargeable lithium batteries have recently attracted attention as power sources for small portable electronic devices. Rechargeable lithium batteries use an organic electrolyte solution, and thus have a high energy density because the discharge voltage thereof is twice that of conventional batteries using an alkaline aqueous solution.

[0007] For a positive active material of a rechargeable lithium battery, lithium transition metal oxides having a structure capable of intercalating lithium ions, such as LiCoO2, LiMn2O4, LiNi 1-x Co x O2(0 < x < 1), etc., have been used.

[0008] For a negative active material, various carbon-based materials such as artificial graphite, natural graphite, hard carbon, etc., have been used. Recently, in order to obtain a high capacity, non-carbon-based negative active materials such as silicon or tin have been researched. SUMMARY

[0009] One embodiment of the present application provides an anode for a rechargeable lithium battery having improved electrochemical characteristics.

[0010] Another embodiment of the present application provides a rechargeable lithium battery comprising the anode.

[0011] One embodiment of the present application provides a negative electrode for a rechargeable lithium battery, the negative electrode including a current collector and a negative active material layer disposed on the current collector and including a carbon-based negative active material and a conductive agent, wherein the conductive agent includes at least one of a fibrous conductive agent having a length of about 1 μm to about 200 μm and a particulate conductive agent having a size (aspect ratio) of about 1 μm to about 20 μm, and the negative electrode has a DD (dispersion degree) value defined by Equation 1 of greater than or equal to about 24.

[0012] [Equation 1]

[0013] DD (Dispersion Degree) = (I a / I 总 )*100

[0014] In Equation 1,

[0015] I a is the sum of peak intensities at non-flat angles measured by XRD using Cu Kα rays, and I 总 is the sum of peak intensities at all angles measured by XRD using Cu Kα rays.

[0016] The conductive agent can include at least one of a fibrous conductive agent having a length of about 5 μm to about 50 μm and a particulate conductive agent having a size (aspect ratio) of about 5 μm to about 10 μm.

[0017] The specific surface area (based on surface area) of the conductive agent can be about 4 m 2 / g to about 1500 m 2 / g, for example, about 100 m 2 / g to about 1400 m 2 / g.

[0018] The aspect ratio of the conductive agent can be about 10 to about 3000, for example, about 10 to about 2500.

[0019] The conductive agent can have an area ratio (based on surface area) of the conductive agent to the carbon-based negative active material in a range of about 50% to about 300%, for example, about 80% to about 260%.

[0020] The conductive agent can have a volume ratio of the conductive agent to the carbon-based negative active material of less than or equal to about 1.5%, for example, about 0.005% to about 1.5%.

[0021] The single surface loading level (L / L) of the negative electrode can be about 6 mg / cm 2 to about 65 mg / cm 2 .

[0022] I aThe sum of the peak intensities at 2-theta = 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, and 77.5 ± 0.2°, as measured by XRD using CuKα rays, can be greater than or equal to about 0.04, for example, about 0.04 and about 0.07. 总 The sum of the peak intensities at 2-theta = 26.5 ± 0.2°, 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, 54.7 ± 0.2°, and 77.5 ± 0.2°, as measured by XRD using CuKα rays, can be greater than or equal to about 0.04, for example, about 0.04 and about 0.07.

[0023] The peak intensity can be a peak integral area value.

[0024] The negative electrode can have a ratio of the peak intensity at the (004) plane to the peak intensity at the (002) plane, as measured by XRD using CuKα rays, of greater than or equal to about 0.04, for example, about 0.04 and about 0.07. (004) / I (002) ) of greater than or equal to about 0.04, for example, about 0.04 and about 0.07.

[0025] The carbon-based negative electrode active material can be artificial graphite, or a mixture of artificial graphite and natural graphite.

[0026] The negative electrode active material layer can further include a Si-based negative electrode active material, a Sn-based negative electrode active material, a lithium vanadium oxide, or a combination thereof.

[0027] The negative electrode can have an active area facing the positive electrode and an inactive area not facing the positive electrode, and the DD value of the inactive area can be greater than or equal to about 24.

[0028] One embodiment of the present application provides a rechargeable lithium battery including a negative electrode; a positive electrode; and an electrolyte.

[0029] The rechargeable lithium battery can be a high-power rechargeable lithium battery.

[0030] The negative electrode for a rechargeable lithium battery according to one embodiment can provide a rechargeable lithium battery having improved battery characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram showing the orientation of the negative electrode active material.

[0032] Figure 2 is a view showing the active area and the inactive area of the negative electrode of the rechargeable lithium battery.

[0033] Figure 3 is a schematic diagram showing the structure of the rechargeable lithium battery.

[0034] Figure 4 is a graph showing the XRD peaks of the negative electrode according to Example 1-1, as measured using CuKα rays.

[0035] Figure 5 This is a graph showing the XRD peaks of the negative electrode according to Comparative Example 1-1, measured using CuKα rays.

[0036] Figure 6 This is a graph showing the DC internal resistance (DC-IR) of the rechargeable lithium battery cell according to Examples 1-1, 1-2, 1-3, Comparative Example 1-1, Comparative Example 1-2 and Reference Example 1.

[0037] Figure 7 This is a graph showing the high-rate cycle life retention rate of the rechargeable lithium battery cells manufactured according to Example 1-1, Comparative Example 1-1 and Reference Example 1.

[0038] <Symbol Explanation>

[0039] 1: Rechargeable lithium battery

[0040] 2: Positive electrode

[0041] 3: Partition

[0042] 4: Negative electrode

[0043] 5: Battery casing

[0044] 6: Sealing elements Detailed Implementation

[0045] The embodiments are described in detail below. However, these embodiments are exemplary, and the invention is not limited thereto; rather, the invention is defined by the scope of the claims.

[0046] The negative electrode for a rechargeable lithium battery according to an embodiment includes a current collector and a negative electrode active material layer disposed on the current collector and comprising a carbon-based negative electrode active material and a conductive agent, wherein the conductive agent comprises at least one of a fibrous conductive agent having a length of about 1 μm to about 200 μm and a particulate conductive agent having a size (major diameter) of about 1 μm to about 20 μm, and the DD (divergence) value of the negative electrode as defined by Equation 1 is greater than or equal to about 24.

[0047] [Equation 1]

[0048] DD (divergence) = (I a / I 总 )*100

[0049] In equation 1,

[0050] I a The sum of peak intensities at non-planar corners measured using XRD with CuKα rays, and

[0051] I总 the sum of the peak intensities at all angles measured by XRD using CuKα rays.

[0052] Herein, the non-plane angles, when measured by XRD using CuKα rays, represent 2θ = 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, and 77.5 ± 0.2°, i.e., the (100) plane, the (101)R plane, the (101)H plane, and the (110) plane. In general, the structure of graphite is classified into a hexagonal structure having an ABAB type stacking order of stacked graphene layers and an orthorhombic structure, and the R plane represents the orthorhombic structure, while the H plane represents the hexagonal structure.

[0053] In addition, the all angles, when measured by XRD using CuKα rays, represent 2θ = 26.5 ± 0.2°, 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, 54.7 ± 0.2°, and 77.5 ± 0.2°, i.e., the (002) plane, the (100) plane, the (101)R plane, the (101)H plane, the (004) plane, and the (110) plane. When one peak of the (101)R plane of the carbon-based negative electrode active material overlaps with another peak of the (111) plane of the current collector (e.g., Cu), a peak can occur at 2θ = 43.4 ± 0.2°.

[0054] In general, the peak intensity represents the height of the peak or the integrated area of the peak, and according to one embodiment, the peak intensity represents the integrated area of the peak.

[0055] In one embodiment, XRD is measured under measurement conditions of 2θ = 10° to 80°, a scan rate (° / S) of 0.044 to 0.089, and a step size (° / step) of 0.013 to 0.039, by using CuKα rays as target rays, but removing a monochromator to improve peak intensity resolution.

[0056] In one embodiment, the DD value of the negative electrode can be greater than or equal to about 24, for example, about 24 to about 70 or about 24 to about 60.

[0057] The DD value within the above range means that the negative electrode active material is not sufficiently horizontally placed with the current collector, but its orientation is sufficient to promote the movement of lithium ions in the negative electrode, i.e., control random orientation. When the DD value is less than 24, the DC internal resistance can increase and the rate capacity, in particular, the high-rate cycle life characteristics can be deteriorated.

[0058] In addition, within the above range of the DD value, an increase in the discharge terminal resistance can be suppressed to minimize the DC internal resistance (DC-IR) and exhibit improved cycle life characteristics. Furthermore, during charging and discharging, electrode swelling can be suppressed to improve the energy density.

[0059] In addition, within the above range of DD value, it means that the carbon-based negative active material is oriented at a certain angle with respect to the current collector, and the heat generated during the charging and discharging of the battery using the negative electrode including the carbon-based negative active material and the heat generated during the penetration or short circuit can be vertically diffused and can be easily released to the outside. This can inhibit ignition caused by thermal runaway, and can inhibit the internal temperature of the battery from rising, thus improving the battery characteristics. When the DD value is less than 24, it means that the carbon-based negative active material is substantially horizontally arranged in the current collector. In this case, the generated heat is horizontally diffused, thus not being easily released to the outside.

[0060] The DD value of the negative electrode within the range means that the negative active material contained in the negative active material layer is oriented at a predetermined angle, and maintains the DD value after charging and discharging. In general, in order to orient the negative active material contained in the negative active material layer at a predetermined angle, the negative active material composition can be coated on the current collector while applying a magnetic field.

[0061] In one embodiment, the negative electrode satisfying the DD value can be manufactured by adjusting the strength of the magnetic field, the time of exposure to the magnetic field, and the electrode plate density during compression of the negative electrode.

[0062] Hereinafter, a method of manufacturing a negative electrode is described. As shown in Figure 1 The negative electrode is manufactured by placing the current collector above and / or below the magnet, and then applying the negative active material composition including the negative active material on the current collector, exposing it to the magnetic field, and then drying and compressing.

[0063] Herein, the magnet can have a magnetic field strength ranging from about 1000 Gauss to about 10000 Gauss. In addition, the negative active material composition is coated on the current collector and maintained for about 2 seconds to about 9 seconds, that is, exposed to the magnetic field for about 2 seconds to about 9 seconds. After compression, the electrode plate density of the negative electrode can be about 1.4 g / cc to about 1.6 g / cc. As used herein, the electrode plate density refers to the density calculated by dividing the amount of load of the electrode plate measured during compression by the thickness of the electrode plate. As described above, the DD value can be adjusted within the range by controlling the strength of the magnetic field, the time of exposure to the magnetic field, or the electrode plate density during compression of the negative electrode.

[0064] In particular, when the coating process is performed while moving the current collector, the magnetic field (magnetic flux) generated by the magnet can be formed perpendicular to the current collector, but since the magnetic field according to the coating speed (the speed of moving the current collector) is formed as a vector function at a predetermined angle, the negative active material contained in the negative active material composition can be fixed, that is, oriented at a predetermined angle on the surface of the current collector.

[0065] When XRD is measured by using Cu Kα rays, the peak intensity ratio of the negative electrode at the (004) plane relative to the (002) plane, i.e., I (004) / I (002) , can be greater than or equal to about 0.04, and specifically, about 0.04 to about 0.07. When the I (004) / I (002) of the negative electrode is greater than or equal to about 0.04, the DC internal resistance can not increase, but the rate capacity and especially the high-rate capacity can be improved, and the cycle life characteristics can also be improved.

[0066] In addition, when XRD is measured by using Cu Kα rays, the peak intensity ratio of the negative electrode at the (110) plane relative to the (004) plane, i.e., I (110) / I (004) , can be greater than or equal to about 0.3, and specifically, greater than or equal to about 0.1, greater than or equal to about 0.2, greater than or equal to about 0.3, and less than or equal to about 0.8 or less than or equal to about 0.7. When the I (110) / I (004) of the negative electrode is greater than or equal to about 0.1, the DC internal resistance can not increase and the rate capacity, especially the high-rate cycle life characteristics can be improved. In one embodiment, since the DD value is the peak value at the non-plane angle relative to the peak value at all angles, and thus is not closely related to the I (110) / I (004) , the I (110) / I (004) greater than or equal to about 0.1 does not mean that the DD value is greater than or equal to about 24.

[0067] When XRD is measured by using Cu Kα rays, the peak intensity ratio of the negative electrode at the (101)H plane relative to the (004) plane, i.e., I (101)H / I (004) , can be greater than or equal to about 0.4, for example, about 0.4 to about 3.0. When the I (101)H / I (004) of the negative electrode is greater than or equal to about 0.4, the DC internal resistance can not increase and the rate capacity, especially the high-rate cycle life characteristics can be improved.

[0068] In one embodiment, the DD value is a value obtained by charging / discharging a rechargeable lithium battery including the negative electrode, disassembling the battery at a fully discharged state, and then measuring XRD of the negative electrode. Herein, the charging and discharging are performed once to twice at 0.1 C to 0.2 C.

[0069] The BET specific surface area of the carbon-based negative electrode active material can be less than about 5.0 m 2 / g, or about 0.6 m 2 / g to about 2.0 m 2 / g. When the BET specific surface area of the carbon-based negative active material is less than about 5.0 m 2 / g, electrochemical cycle life characteristics of the battery can be improved. In one embodiment, the BET is measured as follows: a rechargeable lithium battery including the carbon-based negative active material is charged and discharged, the battery is fully discharged to less than or equal to about 3 V, the battery is disassembled to obtain a negative electrode, the negative electrode is cut into a predetermined size, and the cut negative electrode is placed in a BET sample holder in a nitrogen adsorption method.

[0070] The negative electrode can have a single surface loading level (L / L) of about 6 mg / cm 2 to about 65 mg / cm 2 .

[0071] The carbon-based negative active material can be artificial graphite or a mixture of artificial graphite and natural graphite. When the carbon-based negative active material is a crystalline carbon-based material obtained by mixing natural graphite with artificial graphite or by artificial graphite, the crystalline carbon-based material has more developed crystalline characteristics than an amorphous carbon-based negative active material, and thus can further improve the orientation characteristics of the carbon-based negative active material around an external magnetic field in the electrode plate. The artificial graphite or the natural graphite can be shapeless, plate-shaped, sheet-shaped, spherical, fibrous, or a combination thereof, without specific limitation. In addition, the ratio of the artificial graphite mixed with the natural graphite is about 5 wt%:95 wt% to about 95 wt%:5 wt%, for example, about 30 wt%:70 wt% to about 70 wt%:30 wt%.

[0072] In addition, the negative active material layer can further include at least one of a Si-based negative active material, a Sn-based negative active material, or a lithium vanadium oxide negative active material. When the negative active material layer further includes these materials, i.e., the carbon-based negative active material as a first negative active material and the above-described negative active material as a second negative active material, the first and second negative active materials can be mixed in a weight ratio of about 50:50 to about 99:1.

[0073] The Si-based negative active material can be Si, a Si-C composite material, SiO x(0 < x < 2) and Si-Q alloy (where Q is an element selected from alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Si), and the Sn-based negative electrode active material is selected from Sn, Sn02, Sn-R alloy (where R is an element selected from alkali metal, alkaline earth metal, Group 13 element, Group 14 element, Group 15 element, Group 16 element, transition metal, rare earth element, and combinations thereof, but not Sn), and the like, and also can be at least one of mixtures thereof with Si02. The elements Q and R can be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0074] The conductive agent includes at least one of a fibrous conductive agent having a length of about 1 μm to about 200 μm and a particulate conductive agent having a size (aspect ratio) of about 1 μm to about 20 μm, for example, at least one of a fibrous conductive agent having a length of about 5 μm to about 50 μm and a particulate conductive agent having a size (aspect ratio) of about 5 μm to about 10 μm.

[0075] Examples of the fibrous conductive agent can include carbon nanotube, vapor-grown carbon fiber, single-walled carbon nanotube (SWCNT), and multi-walled carbon nanotube (MWCNT).

[0076] The particulate conductive agent can have a shape such as a spherical shape, an elliptical shape, a flaky shape, and the like. Specific examples thereof can include flaky graphite such as SFG series (for example, SFG6, SFG10, SFG15, and the like manufactured by TIMCAL TIMREX).

[0077] In a negative electrode in which the DD value is greater than or equal to about 24, when the graphite is oriented, the high-rate cycle life characteristics can be improved (effect of improving the resistance characteristics of ion migration according to orientation), but the cycle life can decrease at a low rate. This seems to be because of large electronic resistance due to the influence of the conductive network between the particles at a low rate. The conductive agent satisfying the length and / or size can be added to the negative electrode active material layer in which the negative electrode active material is oriented, thereby effectively improving the conductive network problem and improving the electrical conductivity of the electrode plate, and thus the cycle life retention rate at a low rate as well as the high-rate cycle life characteristics can be improved.

[0078] The specific surface area (based on the surface area) of the conductive agent can be about 4 m 2 / g to about 1500 m 2 / g, about 50 m2 / g to about 1400 m 2 / g, or about 100 m 2 / g to about 1400 m 2 / g.

[0079] The specific surface area refers to a specific surface area of the conductive agent based on a surface area, and is different from a conventional BET specific surface area, which refers to a specific surface area of a surface excluding a surface area of internal pores. The specific surface area based on a surface area is a value calculated based on only an actual contact surface area.

[0080] The specific surface area (based on a surface area) can be calculated according to Equation 2.

[0081] [Equation 2]

[0082] Specific surface area (based on a surface area) = surface area of each conductive agent / mass of each conductive agent

[0083] In Equation 2, the mass of one conductive agent can be calculated according to Equation 3.

[0084] [Equation 3]

[0085] Mass of each conductive agent = volume of one conductive agent x true density

[0086] In Equation 2, each surface area of each conductive agent can be calculated assuming that the fibrous conductive agent is a cylinder and the particulate conductive agent is a sphere.

[0087] When the negative active material layer includes a conductive agent having a specific surface area (based on a surface area) of about 4 m 2 / g to about 1500 m 2 / g, the contact area between the conductive agent and the negative active material increases and the conductive network can be effectively improved, and thus the electrical conductivity of the electrode plate and the cycle life characteristics of the rechargeable battery are improved.

[0088] The conductive agent can have an aspect ratio of about 10 to about 3000, for example, greater than or equal to about 10, greater than or equal to about 20, or greater than or equal to about 30 and less than or equal to about 2600, less than or equal to about 2500, less than or equal to about 2400, or less than or equal to about 2300. The aspect ratio, in the case of the fibrous conductive agent, can be calculated as length / diameter, and in the case of the particulate conductive agent, can be calculated as major axis length / minor axis length. When the particulate conductive agent has a flaky shape, in the case of the flaky conductive agent, the aspect ratio can be calculated as length / thickness.

[0089] When the negative active material layer includes a conductive agent satisfying the aspect ratio, the area in contact with the negative active material can be sufficiently secured, the conductive network can be effectively improved, and thus the electrical conductivity of the electrode plate and the cycle life characteristics of the rechargeable battery are improved.

[0090] The conductive agent can have an area ratio (based on surface area) of the conductive agent to the carbon-based negative active material of about 50% to about 300%, for example, greater than or equal to about 55%, greater than or equal to about 60%, greater than or equal to about 70%, or greater than or equal to about 80%, and less than or equal to about 280%, less than or equal to about 270%, less than or equal to about 260%, less than or equal to about 250%, or less than or equal to about 240%. When this area ratio is satisfied, the area of contact with the negative active material can be increased, the conductive network can be effectively improved, and thus the electrical conductivity of the electrode plate and the cycle life characteristics of the rechargeable battery can be improved.

[0091] The conductive agent can have a volume ratio of the conductive agent to the carbon-based negative active material of less than or equal to about 1.5%, for example, greater than or equal to about 0.005%, greater than or equal to about 0.01%, or greater than or equal to about 0.02%, and less than or equal to about 1.4%, less than or equal to about 1.3%, or less than or equal to about 1.2%. When this volume ratio is satisfied, the channel clogging in the electrode plate due to the conductive agent can be inhibited and the decrease in ionic conductivity can be prevented.

[0092] In one embodiment, the negative active material layer can further include a binder in addition to the carbon-based negative active material and the conductive agent. In this case, the negative active material layer can include about 90 wt% to about 98 wt% of the carbon-based negative active material, about 1 wt% to about 5 wt% of the binder, and about 1 wt% to about 5 wt% of the conductive agent.

[0093] The binder improves the adhesion of the negative active material particles to each other and the adhesion of the negative active material particles to the current collector. The binder can be a non-aqueous binder, an aqueous binder, or a combination thereof.

[0094] The non-aqueous binder can be polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or a combination thereof.

[0095] The aqueous binder can be styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, ethylene propylene copolymer, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, acrylate-based resin, or a combination thereof.

[0096] When the aqueous binder is used as the negative electrode binder, a cellulose-based compound can be further used as a thickening agent for providing viscosity. The cellulose-based compound includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal can be Na, K, or Li. The amount of the thickening agent that can be included is about 0.1 parts by weight to about 3 parts by weight, based on 100 parts by weight of the negative electrode active material.

[0097] The current collector can include one selected from the group consisting of a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, a polymer substrate coated with a conductive metal, and combinations thereof, but is not limited thereto.

[0098] According to another embodiment, the negative electrode can have an active area facing the positive electrode and an inactive area not facing the positive electrode. In other words, as shown in FIG. 1A, the area (A) of the negative electrode facing the positive electrode is the active area, and the other area (B) of the negative electrode not facing the positive electrode is the inactive area. Figure 2 The reason is that the inactive area in which the negative electrode does not face the positive electrode is formed because the negative electrode is manufactured to be larger than the positive electrode to improve battery safety. However, with the generation of the inactive area, safety regarding short circuit between the positive electrode and the negative electrode that can occur due to lithium deposition on the surface of the negative electrode during charging can be improved, the inactive area has a relatively greater resistance to lithium ions than the active area facing the positive electrode because the migration path of lithium ions transmitted from the positive electrode is long, and exists as a non-buffer region. However, the DD value of the inactive area is increased to 24, lithium can easily diffuse due to the decrease in the non-buffer region and capacity can be increased.

[0099] Herein, the DD value of the active area and the inactive area can be greater than or equal to about 24, for example, about 24 to about 70, according to an embodiment, only the DD value of the inactive area can be greater than or equal to about 24, for example, about 24 to about 60. When only the DD value of the inactive area is greater than or equal to about 24, the DD value of the active area is not limited.

[0100] The rechargeable lithium battery according to another embodiment includes a negative electrode, a positive electrode, and an electrolyte.

[0101] The rechargeable lithium battery can be a high-power battery. In other words, the rechargeable lithium battery can be usefully used for electronic devices requiring high power, such as power tools, electric vehicles, vacuum cleaners, etc. The reason is that the rechargeable lithium battery including the negative electrode according to an embodiment can easily release heat generated during charging and discharging, and in particular, when applied to a high-capacity battery and used for electronic devices for high power, and thus can suppress deterioration due to heat and be effectively used as a high-power battery. In addition, the rechargeable lithium battery can easily release heat according to charging and discharging, and effectively suppress an increase in battery temperature, and thus effectively improve cycle life characteristics, in particular, at a high rate.

[0102] The high-power battery can be a cylindrical battery, a prismatic battery, or a pouch battery.

[0103] The positive electrode can include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material can include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. Specifically, one or more complex oxides of metals selected from cobalt, manganese, nickel, and combinations thereof and lithium can be used. More specifically, a compound represented by one of the following chemical formulas can be used. Li a A 1-b X b D2(0.90≤a≤1.8,0≤b≤0.5);Li a A 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a E 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a E 2- b X b O 4-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05);Li a Ni 1-b-c Co b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2);Li a Ni 1-b-c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mn b X c D α(0.90 < a < 1.8, 0 < b < 0.5, 0 < c < 0.05, 0 < a < 2); Li a Ni 1-b-c Mn b X c O 2-α T α (0.90 < a < 1.8, 0 < b < 0.5, 0 < c < 0.05, 0 < a < 2); Li a Ni 1-b-c Mn b X c O 2-α T2(0.90 < a < 1.8, 0 < b < 0.5, 0 < c < 0.05, 0 < a < 2); Li a Ni b E c G d O2(0.90 < a < 1.8, 0 < b < 0.9, 0 < c < 0.5, 0.001 < d < 0.1); Li a Ni b Co c Mn d G e O2(0.90 < a < 1.8, 0 < b < 0.9, 0 < c < 0.5, 0 < d < 0.5, 0.001 < e < 0.1); Li a NiG b O2(0.90 < a < 1.8, 0.001 < b < 0.1); Li a CoG b O2(0.90 < a < 1.8, 0.001 < b < 0.1); Li a Mn 1-b G b O2(0.90 < a < 1.8, 0.001 < b < 0.1); Li a Mn2G b O4(0.90 < a < 1.8, 0.001 < b < 0.1); Li a Mn 1-g G g PO4(0.90 < a < 1.8, 0 < g < 0.5); QO2; QS2; LiQS2; V2O5; LiV2O5; LiZO2; LiNiVO4; Li (3-f) J2(PO4)3(0 < f < 2); Li (3-f) Fe2(PO4)3(0 < f < 2); or Li a FePO4(0.90 < a < 1.8).

[0104] In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; and J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

[0105] The compound can have a coating layer on the surface, or can be mixed with another compound having a coating layer. The coating layer can include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, a hydroxy oxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compound for the coating layer can be amorphous or crystalline. The coating element included in the coating layer can include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer can be provided by using these elements in the compound by a method that does not adversely affect the performance of the positive electrode active material. For example, the method can include any coating method known in the art related to the present application, and can be appropriately selected as long as they do not deviate from the scope of the present application.

[0106] In the positive electrode, the content of the positive electrode active material can be about 90 wt% to about 98 wt% based on the total weight of the positive electrode active material layer.

[0107] In one embodiment, the positive electrode active material layer can further include a binder and a conductive agent. Herein, the amount of the binder and the conductive agent that can be included can be about 1 wt% to about 5 wt% each based on the total weight of the positive electrode active material layer.

[0108] The binder improves the adhesion of the positive electrode active material particles to each other and the adhesion of the positive electrode active material particles to the current collector. Examples thereof can be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, etc., but are not limited thereto.

[0109] The electrically conductive agent is included to provide electrical conductivity of the electrode. Any electrically conductive agent can be used as the conductive material, except for those that cause chemical changes. Examples of the electrically conductive agent include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyparaphenylene derivatives; or mixtures thereof.

[0110] The current collector can use Al, but is not limited thereto.

[0111] The electrolyte includes a non-aqueous organic solvent and a lithium salt.

[0112] The non-aqueous organic solvent is used as a medium for transporting ions involved in the electrochemical reactions of the battery.

[0113] The non-aqueous organic solvent can include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or an aprotic solvent.

[0114] The carbonate-based solvent can include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. The ester-based solvent can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, methyl hydroxy valerate, hexalactone, etc. The ether-based solvent can include dibutyl ether, tetraglyme, diglyme, glyme, 2-methyl tetrahydrofuran, tetrahydrofuran, etc. The ketone-based solvent includes cyclohexanone, etc. The alcohol-based solvent includes ethanol, isopropyl alcohol, etc., and examples of the aprotic solvent include nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon, a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolane, etc.

[0115] The organic solvent can be used alone or in a combination of two or more. When a plurality of organic solvents are used, the mixing ratio can be appropriately adjusted according to the desired performance of the battery, which is well known in the technical field of the present application.

[0116] The carbonate-based solvent can include a mixture of a cyclic carbonate and a chain carbonate. The cyclic carbonate and the chain carbonate are mixed together in a volume ratio of about 1:1 to about 1:9. When the mixture is used as the electrolyte, it can have enhanced performance.

[0117] The organic solvent can further include an aromatic hydrocarbon-based solvent as well as the carbonate-based solvent. The carbonate-based solvent and the aromatic hydrocarbon-based solvent can be mixed together in a volume ratio of about 1:1 to about 30:1.

[0118] The aromatic hydrocarbon-based organic solvent can be an aromatic hydrocarbon-based compound represented by Chemical Formula 1.

[0119] [Chemical Formula 1]

[0120]

[0121] In Chemical Formula 1, R1 to R6 are the same or different, and are selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof.

[0122] Examples of the aromatic hydrocarbon-based organic solvent can be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, fluorotoluene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylenes, and combinations thereof.

[0123] The electrolyte can further include an additive of vinylene carbonate, a vinylene carbonate-based compound represented by Chemical Formula 2, or propene sultone to improve the cycle life.

[0124] [Chemical Formula 2]

[0125]

[0126] In Chemical Formula 2, R7 and R8 are the same or different, and can each independently be hydrogen, halogen, cyano (CN), nitro (NO2), or C1 to C5 fluoroalkyl, provided that at least one of R7 and R8 is halogen, cyano (CN), nitro (NO2), or C1 to C5 fluoroalkyl, and R7 and R8 are not hydrogen at the same time.

[0127] Examples of the vinylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive to improve the cycle life can be used flexibly within an appropriate range.

[0128] Lithium salts dissolved in organic solvents provide lithium ions for the battery, enabling the basic operation of rechargeable lithium batteries, and improving the transport of lithium ions between the positive and negative electrodes. Examples of lithium salts include at least one supporting salt selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2)(wherein x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2(lithium bis(oxalato)borate; LiBOB). The concentration of the lithium salt can range from about 0.1 M to about 2.0 M. When the electrolyte includes a lithium salt in the above concentration range, the electrolyte can have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

[0129] Depending on the type of rechargeable lithium battery, a separator can be included between the positive and negative electrodes. Examples of suitable separator materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof, such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene tri-layer separators, and polypropylene / polyethylene / polypropylene tri-layer separators.

[0130] Figure 3 is an exploded perspective view of a rechargeable lithium battery according to an embodiment. Figure 3 The rechargeable lithium battery shown in FIG. 1 is a cylindrical battery, but the rechargeable lithium battery can be a prismatic battery or a pouch-type battery.

[0131] Reference Figure 3 The rechargeable lithium battery 1 according to an embodiment includes an electrode assembly including a positive electrode 2, a negative electrode 4, and a separator 3 disposed between the positive electrode 2 and the negative electrode 4; an electrolyte solution (not shown) impregnated in the electrode assembly; a battery case 5 housing the electrode assembly; and a sealing element 6 sealing the battery case 5.

[0132] Hereinafter, embodiments and comparative examples of the present application are described. However, these embodiments are not to be construed in any sense as limiting the scope of the present application.

[0133] The conductive agents used in the examples, comparative examples, and reference examples are shown in Table 1.

[0134] (Table 1)

[0135]

[0136] (Example 1-1)

[0137] A negative active material slurry was prepared by mixing 97.45 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 0.05 wt% of the SWCNT conductive agent of Table 1, and 1 wt% of carboxymethyl cellulose in an aqueous solvent.

[0138] After placing a Cu foil on a magnet having a magnetic field strength of 3000 Gauss, the negative active material slurry was coated on the Cu foil, exposed to a magnetic field for 9 seconds while moving the Cu foil, and then dried and compressed to manufacture a negative electrode having an electrode plate density of 1.45 g / cc and a single surface load level (L / L) of 6.2 mg / cm 2

[0139] A positive active material slurry was prepared by mixing 96 wt% of LiCoO2positive active material, 2 wt% of carbon black conductive agent, and 2 wt% of polyvinylidene fluoride binder in an N-methylpyrrolidone solvent. The slurry was coated on an Al substrate, and then dried and compressed to manufacture a positive electrode.

[0140] A pouch-type rechargeable lithium battery cell having a unit capacity of 550 mAh and a current density of 2.63 mAh / cm 2 was manufactured using the negative electrode, the positive electrode, and an electrolyte. Herein, the electrolyte was prepared by using a mixed solvent in which 1 M of LiPF6was dissolved in ethylene carbonate and diethyl carbonate (volume ratio of 50:50).

[0141] (Example 1-2)

[0142] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as in Example 1-1, except that 97.3 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 0.2 wt% of the MWCNT conductive agent shown in Table 1, and 1 wt% of carboxymethyl cellulose were mixed in an aqueous solvent.

[0143] (Example 1-3)

[0144] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as in Example 1-1, except that 92.9 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 4.6 wt% of the SFG6 conductive agent (TIMCAL TIMREx) shown in Table 1, and 1 wt% of carboxymethyl cellulose were mixed in an aqueous solvent.

[0145] (Example 2-1)

[0146] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as in Example 1-1, except that the electrode plate density was 1.4 g / cc. ​

[0147] (Example 2-2)

[0148] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-2, except that the electrode plate density was 1.4 g / cc.

[0149] (Example 2-3)

[0150] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-3, except that the electrode plate density was 1.4 g / cc.

[0151] (Example 3-1)

[0152] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-1, except that the electrode plate density was 1.6 g / cc.

[0153] (Example 3-2)

[0154] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-2, except that the electrode plate density was 1.6 g / cc.

[0155] (Example 3-3)

[0156] A negative electrode and a rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-3, except that the electrode plate density was 1.6 g / cc.

[0157] (Example 4-1)

[0158] A pouch-type rechargeable lithium battery cell was manufactured according to the same method as Example 1-1, except that the time of exposure to the magnetic field was changed from 9 seconds to 5 seconds.

[0159] (Example 4-2)

[0160] A pouch-type rechargeable lithium battery cell was manufactured according to the same method as Example 1-2, except that the time of exposure to the magnetic field was changed from 9 seconds to 5 seconds.

[0161] (Example 4-3)

[0162] A pouch-type rechargeable lithium battery cell was manufactured according to the same method as Example 1-3, except that the time of exposure to the magnetic field was changed from 9 seconds to 5 seconds.

[0163] (Comparative Example 1-1)

[0164] A negative active material slurry was prepared by mixing 96.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 1 wt% of DB conductive agent (Denka Black, manufactured by Denka, Korea) shown in Table 1, and 1 wt% of carboxymethyl cellulose in a water solvent.

[0165] The negative active material slurry was coated on a Cu foil, and then, dried and compressed to manufacture a negative electrode having an electrode plate density of 1.45 g / cc and a single surface load level (L / L) of 6.2 mg / cm 2

[0166] The negative electrode was used together with the positive electrode used in Example 1-1 and the electrolyte to manufacture a pouch-type rechargeable lithium battery cell.

[0167] (Comparative Example 1-2)

[0168] A negative electrode and a pouch-type rechargeable lithium battery cell using the same were manufactured according to the same method as Comparative Example 1-1, except that 97.45 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 0.05 wt% of SWCNT conductive agent shown in Table 1, and 1 wt% of carboxymethyl cellulose were mixed in a water solvent.

[0169] (Comparative Example 2)

[0170] A negative electrode and a pouch-type rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-1, except that a negative active material slurry was prepared by mixing 97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1 wt% of carboxymethyl cellulose in a water solvent, and the time of exposure to a magnetic field was changed from 9 seconds to 2 seconds.

[0171] (Comparative Example 3)

[0172] A negative electrode and a pouch-type rechargeable lithium battery cell using the same were manufactured according to the same method as Comparative Example 2, except that the time of exposure to a magnetic field was changed from 2 seconds to 4 seconds, and the electrode plate density was 1.79 g / cc.

[0173] (Reference Example 1)

[0174] A negative electrode and a pouch-type rechargeable lithium battery cell using the same were manufactured according to the same method as Example 1-1, except that 96.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, 1 wt% of DB conductive agent shown in Table 1, and 1 wt% of carboxymethyl cellulose were mixed in a water solvent.

[0175] Measurement of X-ray Diffraction Characteristics

[0176] ​The rechargeable lithium battery cells according to Examples 1-1, 2-1, 3-1, and 4-1 and Comparative Examples 1-1, 2, and 3 were charged and discharged twice at 0.1C, and then fully discharged down to 2.75V at 0.1C. The fully discharged battery cells were disassembled to obtain the negative electrodes. For these negative electrodes, an X'Pert (PANalytical B.V.) XRD device using CuKa rays as target rays, and a monochromator was removed in order to improve the peak intensity resolution. Herein, the measurement was performed under the following conditions: 2theta = 10° to 80°, scan rate (° / S) = 0.06436, and step size of 0.026° / step.

[0177] The measured XRD results are shown in Figure 4 (Example 1-1), and Figure 5 (Comparative Example 1-1). As shown in Figure 4 and 5 , the negative electrode of Comparative Example 1-1 showed a higher peak at 2theta = 26.5±0.2° than the negative electrode of Example 1-1. In addition, as shown in Figure 4 and 5 , the negative electrodes of Example 1-1 and Comparative Example 1-1 showed peaks at 2theta = 26.5±0.2° ((002) plane), 42.4±0.2° ((100) plane), 43.4±0.2° ((101) R plane), 44.6±0.2° ((101) H plane), 54.7±0.2° ((004) plane), and 77.5±0.2° ((110) plane).

[0178] As shown in Figure 4 and Figure 5 , the areas of the peaks shown at 2theta = 26.5±0.2° ((002) plane), 42.4±0.2° ((100) plane), 43.4±0.2° ((101) R plane), 44.6±0.2° ((101) H plane), 54.7±0.2° ((004) plane), and 77.5±0.2° ((110) plane) were measured, and the results are shown in Table 2. In addition, in Table 2, the areas of the peaks shown at 2theta = 42.4±0.2° ((100) plane), 43.4±0.2° ((101) R plane), 44.6±0.2° ((101) H plane), 77.5±0.2° ((110) plane) and as I a , the areas of the peaks shown at 2theta = 26.5±0.2° ((002) plane), 42.4±0.2° ((100) plane), 43.4±0.2° ((101) R plane), 44.6±0.2° ((101) H plane), 54.7±0.2° ((004) plane), and 77.5±0.2° ((110) plane) and as I 总and DD values thereof were calculated ((I a / I 总 )*100) and are shown in Table 2. In addition, I (004) / I (002) , I (110) / I (004) , and I (101)H / I (004) were calculated and are shown in Table 2. In particular, a peak corresponding to the (101) R-plane of graphite and a peak of the (111) plane of the Cu current collector overlapped at 43.4 ± 0.2°.

[0179] (Table 2)

[0180]

[0181] XRD of the rechargeable lithium battery cells according to Examples 2-1, 3-1, and 4-1 and Comparative Examples 2 and 3 were measured according to the same method as those of Example 1-1 and Comparative Example 1-1, and were used to calculate DD values, I (004) / I (002) , I (110) / I (004) , and I (101)H / I (004) , and the results are shown in Table 3. DD values, I (004) / I (002) , I (110) / I (004) , and I (101)H / I (004) of the rechargeable lithium battery cells of Example 1-1 and Comparative Example 1-1 are also shown in Table 3 for comparison with the above results.

[0182] (Table 3)

[0183] DD value I (004) / I (002) ]]> I (110) / I (004) ]]> I (101)H / I (004) ]]> Example 1-1 46.20 0.04 0.389 1.855 Example 2-1 52 0.041 0.6 2.76 Example 3-1 40 0.058 0.387 1.99 Example 4-1 24.6 0.0459 0.144 0.425 Comparative Example 1-1 15.60 0.03 0.047 0.169 Comparative Example 2 20.8 0.051 0.08 0.21 Comparative Example 3 23.0 0.025 0.122 0.085

[0184] Referring to Table 3, the negative electrodes according to Examples 1-1, 2-1, 3-1, and 4-1 satisfy a DD value of greater than or equal to 24 (24.6 to 52), an I (004) / I (002) of greater than or equal to 0.04, an I (110) / I (004) of greater than or equal to 0.1, and an I (101)H / I (004) of greater than or equal to 0.4. In addition, the negative electrode of Comparative Example 3 shows a DD value of 23, which is less than 24, but an I (110) / I (004) of 0.122, which is greater than or equal to 0.1, and thus, the DD value and I (110) / I (004) are not closely related to each other.

[0185] Measurement of DC internal resistance (DC-IR)

[0186] Under 0.1C charging and discharging conditions, rechargeable lithium battery cells according to Examples 1-1, 1-2 and 1-3, Comparative Examples 1-1 and 1-2 and Reference Example 1 were evaluated, and their discharge capacity was first measured and regarded as 1C reference.

[0187] After measuring the discharge capacity, the battery cell was charged under constant current / constant voltage conditions at 0.7C and 4.25V with a cutoff of 0.025C, and then discharged under constant current conditions at 0.1C and 2.8V with a cutoff. In this paper, the DC internal resistance (DC-IR) is calculated by measuring the voltage drop (V) generated when the current flows at 1C for 1 second under SOC conditions, such as SOC70 (based on 100% of the battery cell's total charge capacity, the battery cell is charged to a state with 70% charge capacity and, in terms of discharge state, the battery cell is discharged to 30%), SOC20 (based on 100% of the battery cell's total charge capacity, the battery cell is charged to a state with 20% charge capacity and, in terms of discharge state, the battery cell is discharged to 80%), and SOC10 (based on 100% of the battery cell's total charge capacity, the battery cell is charged to a state with 10% charge capacity and, in terms of discharge state, the battery cell is discharged to 90%). The results of Examples 1-1, 1-2 and 1-3, Comparative Examples 1-1 and 1-2, and Reference Example 1 are shown respectively. Figure 6 In the middle. For example Figure 6 As shown, the rechargeable lithium battery cells of Examples 1-1, 1-2, and 1-3 with a DD value greater than or equal to 24 and using a conductive agent with a length greater than or equal to 1 μm maintain a DC internal resistance of 1.2 (mΩ·m). 2 ) to 1.3 (mΩ·m 2 In contrast, the rechargeable lithium battery cell of Reference Example 1, with a DD value greater than or equal to 24 and using a conductive agent with a length less than 1 μm, showed a DC internal resistance of 1.3 (mΩ·m). 2 ) to 1.35 (mΩ·m 2 Within the range of ), the DD values ​​of Comparative Examples 1-2 are less than 24, and the rechargeable lithium battery cells using conductive agents with a length greater than or equal to 1 μm show a DC internal resistance greater than or equal to 1.4 (mΩ·m). 2 Furthermore, the rechargeable lithium-ion battery cell of Comparative Example 1-1, with a DD value less than 24 and using a conductive agent with a length less than 1 μm, exhibited a DC internal resistance greater than or equal to 1.6 (mΩ·m). 2 ).

[0188] Evaluation of cycle life characteristics

[0189] The rechargeable lithium battery cells according to the examples, comparative examples and reference example were constant current / constant voltage charged at 1.8C, 4.25V and 0.025C cut-off condition, paused for 10 minutes, constant current discharged at 1.0C and 3.0V cut-off condition, and again paused for 10 minutes, which was regarded as one charge and discharge cycle, and in this context, a total of 200 charge and discharge cycles were conducted. Subsequently, the capacity retention ratio according to these charge and discharge cycles was obtained by calculating the ratio of the discharge capacity at each cycle with respect to the discharge capacity at the 1st cycle, and the results of Example 1-1, Comparative Example 1-1 and Reference Example 1 are shown in Table 1. Figure 7 Figure 7 As shown in Table 1, the rechargeable lithium battery cell of Example 1-1 having a DD value of 24 to 60 maintained a capacity retention ratio of greater than or equal to 84% even at the 200th cycle, but the rechargeable lithium battery cell of Reference Example 1 having a DD value of 24 to 60 (the same as that of Example 1-1) and using a conductive agent having a length of less than 1 µm maintained a capacity retention ratio of less than or equal to 82% at the 200th cycle, and the rechargeable lithium battery cell of Comparative Example 1-1 having a DD value of less than 24 and using a conductive agent having a length of less than 1 µm showed a significantly decreased capacity retention ratio of less than 65% at the 200th cycle.

[0190] While the disclosure has been described in connection with what is presently considered to be the exemplary embodiments, it is to be understood that the application is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.​

Claims

1. A negative electrode for a rechargeable lithium battery, comprising: a current collector; and a negative electrode active material layer disposed on the current collector and including a carbon-based negative electrode active material and a conductive agent, wherein the conductive agent includes at least one of a fibrous conductive agent having a length of 1 μm to 200 μm and a particulate conductive agent having a size of 1 μm to 20 μm, the size being a major axis, wherein the negative electrode has a divergence DD value defined by Equation 1 of greater than or equal to 24, and The negative electrode has a single surface load level of 6 mg / cm 2 to 65 mg / cm 2 2. [Equation 1] DD = (I a / I 总 )*100 wherein, in Equation 1, I a the sum of the peak intensities at 2Θ = 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2° and 77.5 ± 0.2° measured by XRD using CuKα rays, and I 总 the sum of the peak intensities at 2-theta = 26.5 ± 0.2°, 42.4 ± 0.2°, 43.4 ± 0.2°, 44.6 ± 0.2°, 54.7 ± 0.2° and 77.5 ± 0.2° measured by XRD using CuKa radiation.

Images