Anode for a lithium secondary battery and lithium secondary battery with the same

Abstract

Anode for a lithium secondary battery, comprising: an anode current collector; and an anode active material layer formed on the anode current collector, wherein the anode active material layer comprises a first section and a second section, wherein Y / X of the anode active material layer is in a range of 0.57 to 0.87, and X is a maximum porosity obtained by an X-ray microscopy (XRM) measurement of the anode active material layer, and Y is a minimum porosity obtained by the XRM measurement of the anode active material layer, wherein the first section has a higher porosity than the second section, and the distance between a point of maximum porosity in the first section and a point of minimum porosity in the second section is in a range of 0.3 mm to 2 mm.

Description

BACKGROUND 1. Area The present invention relates to an anode for a lithium secondary battery and a lithium secondary battery comprising the same. In particular, the present invention relates to an anode with an anode current collector and an anode active material layer and a lithium secondary battery comprising the same. 2. Description of the related technology A secondary battery, which can be repeatedly charged and discharged, has been widely used as a power source for mobile electronic devices, such as camcorders, mobile phones, laptop computers, etc., in line with developments in information and display technologies. Recently, a battery pack incorporating a secondary battery has been developed and used as a power source for an environmentally friendly vehicle. The lithium secondary battery stands out due to its high operating voltage and energy density per unit of weight, high charging rate, compact dimensions, etc. During rapid charging of a lithium secondary battery at a high C-rate, lithium salts can be deposited on the anode surface due to anode resistance, thus reducing capacity with repeated charge / discharge cycles. Therefore, increasing the diffusivity of lithium ions is preferable to lower the anode resistance. To increase the lithium-ion diffusivity in an electrode, a lithium-ion channel can be formed within the electrode. For example, micro-holes or linear channels can be created in the electrode using laser etching, embossing, etc., allowing lithium ions to penetrate or diffuse into the electrode through these channels. However, with the method described above, ion channels with a fine pattern in the electrode may not be formed uniformly at a high rate, and production efficiency may also be reduced. Additionally, the formation of this fine pattern can cause a burr on the electrode surface and may increase the required electrode thickness. Furthermore, the micropatterning can negatively impact the pore properties and battery cell performance within the electrode. SUMMARY According to one aspect of the present invention, an anode for a lithium secondary battery with improved electrical, physical and chemical properties is provided. According to one aspect of the present invention, a lithium secondary battery containing the anode for a lithium secondary battery is provided. An anode for a lithium secondary battery according to embodiments of the present invention comprises an anode current collector and an anode active material layer formed on the anode current collector. The anode active material layer comprises a first section and a second section, which have different porosities and are arranged repeatedly and alternately. In some embodiments, the anode current collector may include an anode lug that projects from one side of the anode current collector. The first section and the second section may be arranged alternately and repeatedly along a projection direction of the anode lug or in a direction perpendicular to the projection direction of the anode lug. In some embodiments, the first section and the second section can extend in the direction perpendicular to the protrusion direction of the anode tab and are arranged alternately and repeatedly along the protrusion direction. In some embodiments, the first section and the second section can each have a uniform porosity along the protruding direction. In some embodiments, the first section and the second section can have the same thickness. In some embodiments, the Y / X ratio of the anode active material layer can range from 0.57 to 0.87. X is a maximum porosity obtained by X-ray microscopy (XRM) measurement of the anode active material layer, and Y is a minimum porosity obtained by XRM measurement of the anode active material layer. In some embodiments, the first section may have a higher porosity than the second section, and the distance between a point of maximum porosity in the first section and a point of minimum porosity in the second section is in a range of 0.3 mm to 2 mm. A lithium secondary battery contains a cathode and the anode for a lithium secondary battery according to embodiments as described above, which faces the cathode. An anode for a lithium secondary battery according to the embodiments of the present invention can have a high porosity, so that a channel can be formed through which lithium ions can easily penetrate. Accordingly, the resistance of the anode can be reduced at a high C-rate and fast-charging characteristics can be improved. It is possible that a lithium-ion channel of the anode for a lithium secondary battery according to embodiments of the present invention is not a complete pore with 100% porosity, and a channel with a relatively high porosity can be provided. Accordingly, a high-density anode can be provided. According to embodiments of the present invention, a pattern serving as the lithium-ion channel can be formed while an anode slurry is being coated onto a current collector. Accordingly, the generation of burrs and impurities that can occur when forming a fine pattern, and production costs, can also be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a top view showing an anode for a lithium secondary battery according to exemplary embodiments. Figs. 2 and 3 are a schematic cross-sectional view and a top view, respectively, of a lithium secondary battery according to exemplary embodiments. Fig. 4 is a schematic view showing a slurry coating device containing a plurality of slots according to exemplary embodiments. Fig. 5 is a schematic cross-sectional view showing a preliminary anode active material layer and an anode active material layer according to exemplary embodiments. Fig. 6 is a graph showing electrode thicknesses before and after pressing according to Example 1 and Comparative Example 1, measured by a laser sensor. Fig. 7 is an image obtained by measuring electrodes before and after pressing according to Example 1 and Comparative Example 1 using a confocal 3D microscope.Figure 8 is a diagram showing fast charging characteristics of batteries according to Example 1 and Comparison Example 1. DETAILED DESCRIPTION OF THE EXECUTION FORMS According to exemplary embodiments of the present invention, an anode for a lithium secondary battery is provided which contains areas of different porosities. According to exemplary embodiments of the present invention, a lithium secondary battery with the anode is also provided. The present invention is described in detail below with reference to exemplary embodiments and the accompanying drawings. However, those skilled in the art will recognize that such embodiments, described with reference to the accompanying drawings, are provided to further illustrate the spirit of the present invention and do not limit the subject matter to be protected as disclosed in the detailed description and the attached claims. Fig. 1 is a top view showing an anode for a lithium secondary battery according to exemplary embodiments. Fig. 2 and Fig. 3 are a schematic cross-sectional view and a top view, respectively, of a lithium secondary battery according to exemplary embodiments. Referring to Fig. 1, an anode-active material layer 120 can comprise a first section 122 and a second section 124, which have different porosities and are arranged alternately and repeatedly. In some embodiments, the thickness of the anode-active material layer 120 can be essentially the same. The first section 122 and the second section 124 can be arranged repeatedly. In the present description, the same thickness can contain a thickness error range of ±2 µm and can be interpreted as being essentially the same within that range. Referring to Fig. 2, a lithium secondary battery can include an electrode arrangement comprising a cathode 100, an anode 130 and a separating layer 140 arranged between the cathode and the anode. The anode 130 can contain an anode electrode current collector 125 and the anode active material layer 120, which is formed by coating an anode active material onto the anode current collector 125. For example, an anode slurry can be prepared by mixing and stirring an anode active material with a binder, a conductive material, and / or a dispersing material in a solvent. The anode slurry can be coated onto at least one surface of an anode current collector 125 using a slurry coating device 200 (see Fig. 4), then dried and pressed to form the anode active material layer 120. A preliminary anode active material layer 220 with a corrugated top profile as described below can be formed by coating it with the anode slurry. The anode active material can contain a material capable of intercalating and deintercalating lithium ions. Examples include carbon-based materials such as crystalline carbon, amorphous carbon, carbon composites, and carbon fiber; lithium alloys; silicon (Si)-based compounds; or tin. Examples of amorphous carbon include hard carbon, coke, mesocarbon microspheres (MCMB), mesophase pitch-based carbon fiber (MPCF), etc. The silicon-based compound can contain, for example, silicon oxide, SiOx (0 < x < 2) or a silicon-carbon composite such as silicon carbide (SiC). The binder may contain a water-insoluble binder, a water-soluble binder, or a combination thereof. In some embodiments, the amount of the binder may be 3 percent by weight (wt%) or less, based on a total weight of the anode active material layer of 120. Examples of the water-insoluble binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide or a combination thereof. Examples of the water-soluble binder may include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, a copolymer of propylene and an olefin with 2 to 8 carbon atoms, a copolymer of (meth)acrylic acid and (meth)acrylic acid alkyl esters, or a combination thereof. When using a water-soluble binder, it may also contain a cellulose-based compound that can improve viscosity. This cellulose-based compound may contain carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or an alkali metal salt thereof. These may be used alone or in combination. The alkali metal may be sodium, potassium, or lithium. Conductive material can be added to the electrode to improve conductivity. Examples of conductive material include carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene carbon black, ketone carbon black, carbon fiber, carbon nanotubes, etc.; metallic materials such as metal powders or fibers made of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or a combination thereof. The anode current collector 125 can contain 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, etc. Preferably, copper foil can be used. Fig. 4 is a schematic view showing a slurry coating device containing a plurality of slots according to exemplary embodiments. Referring to Fig. 4, the slurry coating device 200 can include a slotted section 210 containing a plurality of slots arranged in a grid pattern at one end section thereof. The slots of the slotted section 210 can be defined as a discharge section 211. A closed section 212, corresponding to a non-discharge section, can be formed between the discharge sections 211. The anode slurry can be discharged and coated onto the anode current collector 125 using the slurry coating device 200. The anode slurry can be coated onto an area of ​​the current collector corresponding to the discharge section 211. The anode slurry cannot be discharged directly onto an area corresponding to the closed section 212 of the anode current collector 125, but the anode slurry in the coated area can flow and diffuse to the area corresponding to the closed section 212 of the anode current collector 125. While the anode slurry can be completely coated on the anode current collector 125, a local variation in the charge quantity can thus occur based on a structure of the discharge section 211. For example, a grid pattern formed in the slot section 210 can be implemented on the anode current collector 125. Fig. 5 is a schematic cross-sectional view showing a preliminary anode active material layer and an anode active material layer according to exemplary embodiments. Referring to Fig. 5, the height of the coated area through the discharge section 211 on the anode current collector 125 is given as H, and the coating height in the area corresponding to the closed section 212 is given as h. The heights H and h can be measured based on the surface of the anode current collector 125. The height H can be proportional to the amount of anode slurry discharged through the discharge section 211, and the height h can be proportional to the amount of anode slurry that has flowed and diffused. Accordingly, a coating height difference on the anode current collector 125 can be generated due to a variation in the amount of slurry charge. Thus, the preliminary anode active material layer 220, which, for example, has a corrugated top profile, can be formed. The preliminary anode active material layer 220, which has the wavy upper profile, can be converted into an active material layer with a uniform thickness after it has been pressed. The width W of the discharge section 211 can be in a range of 300 µm to 2000 µm. The width W' of the closed section 212 can also be in a range of 300 µm to 2000 µm. If the width is less than 300 µm, the preliminary anode active material layer 220 cannot be easily formed, and clogging of the discharge section 211 can be caused by particle agglomeration. If the width exceeds 2000 µm, the number of patterns per unit area of ​​the electrode can be reduced, and sufficient lithium-ion channel formation cannot be achieved. Preferably, the width of the discharge section 211 and / or the closed section 212 can be in the range of 1000 µm to 1500 µm. The slot or discharge section 210 can have a polygonal, circular, or elliptical shape. Preferably, the slot or discharge section 210 can have a rectangular shape, taking into account a desired pattern formation. If a maximum thickness of the preliminary anode active material layer 220 is designated as A and a minimum thickness as B, the B / A ratio can be in a range of 0.64 to 0.93. The thickness of the preliminary anode active material layer 220 can be suitably adjusted using the interval between the anode current collector 125 and the slurry coating device 200, the interval of the grid pattern of the slot section 210, the viscosity of the slurry, etc. If B / A exceeds 0.93, the effect of pattern formation cannot be sufficiently achieved. If B / A is less than 0.64, the porosity of the area with maximum thickness may be reduced during the pressing process, thus impairing capacity and service life characteristics. If the distance between a maximum thickness and a minimum thickness is denoted as L, L can be in a range from 0.3 mm to 2.0 mm. As shown in Fig. 6, in the electrode containing the preliminary anode active material layer 220, a thickness can be regularly repeated in one electrode longitudinal direction. If the spacing is greater than 2.0 mm, the number of patterns across the entire electrode may be reduced, and the effect of pattern formation may not be sufficiently achieved. If the L is less than 0.3 mm, the gap between the discharge sections 211 of the slot section 210 may become small, the slurry may not discharge uniformly, and blockage of the discharge section 211 due to particle agglomeration may occur. The minimum thickness of the preliminary anode active material layer 220 can be greater than the thickness of the anode active material layer 120. As described above, the anode active material layer 120 with a uniform thickness can be formed by pressing the preliminary anode active material layer 220. For example, the wavy upper profile of the preliminary anode active material layer 220 can be removed before and after pressing to form the anode active material layer 120 with uniform thickness. The preliminary anode active material layer 220 may have a uniform porosity, but may exhibit a local variation in the charge quantity of the active material. Although the anode active material layer 120 is formed to have a uniform thickness after pressing, a difference in the pressing ratio (thickness after rolling - thickness before rolling) and a local difference in porosity in the anode active material layer 120 may thus be induced. Accordingly, the anode active material layer 120 formed on the anode current collector 125 can contain the first section 122 and the second section 124 with the same thickness but different porosities. As shown in Fig. 7, in Example 1, which will be described later, the anode active material layer containing areas with different porosities was formed. Referring again to Fig. 1, the anode current collector 125 can include an anode tab 126 as an electrode tab projecting from one side of the anode current collector 125. As described above, the anode active material layer 120, in which the first section 122 and the second section 124, which have different porosities, are repeatedly arranged, can be formed on the anode current collector 125. A direction parallel to the protruding direction of the anode lug 126 can be defined as a longitudinal direction of an electrode. Furthermore, a direction perpendicular to the protruding direction of the anode lug 126 can be defined as a transverse direction of an electrode. The first section 122 and the second section 124 can be arranged alternately and repeatedly in a protruding direction of the anode lug 126 or in a direction perpendicular to the protruding direction. For example, the first section 122 and the second section 124 can be arranged alternately and repeatedly along the longitudinal or transverse direction of the electrode. The thicknesses of the first section 122 and the second section 124 can be substantially the same. In exemplary embodiments, the first section 122 can have a porosity greater than that of the second section 124, and lithium ions can readily penetrate the electrode through the first section 122, which is a highly porous section. The penetrating lithium ions can readily diffuse to a circumferential section of the electrode, thereby reducing anode resistance at a high C-rate. Preferably, the first section 122 and the second section 124 can extend in a direction perpendicular to the protruding direction of the anode lug 126 and can be arranged alternately and repeatedly along the protruding direction. For example, the first part 122 and the second part 124 can be arranged alternately and repeatedly along the longitudinal direction of the electrode. In this case, both the first section 122 and the second section 124 can exhibit uniform porosity along the longitudinal direction of the electrode. The term "uniform porosity" may include an error range of, for example, ±1%, and the porosity within this range can be interpreted as being essentially the same. The first section 122 and the second section 124 can be arranged alternately and repeatedly along the longitudinal direction of the electrode, thus allowing the porosities to be repeated alternately. In exemplary embodiments, the region with a higher porosity can serve as a lithium-ion channel. The lithium-ion channel may not be a perfect pore with 100% porosity, but rather an area that can serve as a passage with relatively high porosity. The porosity may be relatively reduced in the second section 124, thus improving electrode cell performance while maintaining high energy density. This allows for the implementation of fast-charging capabilities for the battery. In some embodiments, the porosity of the anode active material layer 120 can form a pattern period. If a maximum porosity value obtained by X-ray microscopy (XRM) measurement is denoted as X (%) and a minimum value as Y (%), Y / X can range from 0.57 to 0.87. If Y / X is less than 0.57, the diffusion of lithium ions may be inhibited due to an excessive reduction in porosity in a specific area. If Y / X exceeds 0.87, an insufficient lithium-ion channel may be provided due to a small local difference in porosity. The XRM measurement conditions, which are widely used in the state of the art, can be used for the measurement above. In some embodiments, the first section 122 may have a porosity greater than that of the second section 124, and the first section 122 may correspond to the thickness h of Fig. 5. The second section 124 may correspond to the thickness H in Fig. 5. The distance between a point of maximum porosity in the first section 122 and a point of minimum porosity in the second section 124 can range from 0.3 mm to 2 mm. If the distance exceeds 2 mm, sufficient lithium-ion channels cannot be formed because the number of patterns formed in the electrode decreases. If the distance is less than 0.3 mm, the distance between the discharge sections 211 may be reduced, leading to uneven discharge of the slurry and clogging of the discharge section 211 due to particle agglomeration. Referring again to Figs. 2 and 3, the lithium secondary battery can include an electrode assembly 150 comprising the cathode 100, an anode 130, and the separating layer 140 located between the cathode and the anode. The electrode assembly 150 can be housed in a casing 160 and impregnated with an electrolyte. The cathode 100 can contain a cathode active material layer 110, which is formed by coating a cathode active material onto the cathode current collector 105. The cathode active material can contain a compound that can reversibly intercalate and deintercalate lithium ions. In exemplary embodiments, the cathode active material can contain a lithium transition metal composite oxide particle. For example, the lithium transition metal composite oxide particle can contain nickel (Ni) and can further contain at least one of cobalt (Co) and manganese (Mn). For example, the lithium transition metal composite oxide particle can be represented by the following chemical formula 1: LixNi1-yMyO2+z [Chemical Formula 1] In chemical formula 1, 0.9 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7 and -0.1 ≤ z ≤ 0.1. M can contain at least one element chosen from the group consisting of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn and Zr. In some embodiments, a molar ratio or concentration (1-y) of Ni in chemical formula 1 may be 0.8 or more and may preferably exceed 0.8. Ni can act as a transition metal, which is related to the performance and capacity of the lithium secondary battery. Therefore, as described above, a high-Ni composition can be used in the lithium transition metal composite oxide particle, enabling the implementation of a high-capacity cathode and a high-capacity lithium secondary battery. However, if the nickel content increases, the long-term storage stability and lifetime stability of the cathode or secondary battery can be relatively impaired. In exemplary embodiments, lifetime stability and capacity retention can be improved by introducing manganese, while electrical conductivity is maintained by including cobalt. In some embodiments, the cathode active material or the lithium transition metal composite oxide particle may further contain a coating element or a doping element. For example, the coating element or doping element may contain Al, Ti, Ba, Zr, Si, B, Mg, P, W, V, an alloy thereof, or an oxide thereof. These may be used alone or in combination. The cathode active material particle may be passivated by the coating or doping element, further improving stability and lifetime, even in the event of intrusion by an external object. A slurry can be prepared by mixing and stirring the cathode active material with a binder, a conductive material, and / or a dispersant in a solvent. The slurry can be coated onto the cathode current collector 105, dried, and pressed to form the cathode 100. The cathode current collector 105 can contain, for example, stainless steel, nickel, aluminum, titanium, copper or an alloy thereof, and may preferably contain aluminum or an aluminum alloy. The binder and the conductive material can contain materials that are essentially the same as or similar to those used in the anode. For example, a PVDF-based binder can be used as a cathode binder. The separating layer 140 can be arranged between the cathode 100 and the anode 130. The separating layer 140 can contain a porous polymer film, which is made, for example, from a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, an ethylene / methacrylate copolymer, or the like. The separating layer 140 can also contain a nonwoven fabric formed from a high-melting-point glass fiber, a polyethylene terephthalate fiber, or the like. In some embodiments, the area and / or volume of the anode 130 (e.g., a contact area with the separating layer 140) can be larger than that of the cathode 100. Thus, lithium ions generated by the cathode 100 can be easily transferred to the anode 130 without loss, e.g., by precipitation or sedimentation. In exemplary embodiments, an electrode cell can be defined by the cathode 100, the anode 130, and the separating layer 140, and a plurality of electrode cells can be stacked to form an electrode arrangement 150, which may, for example, have a jelly-roll shape. For example, the electrode arrangement 150 can be formed by winding, laminating, or folding the separating layer 140. The electrode arrangement 150 can be housed together with an electrolyte in the casing 160 to define the lithium secondary battery. In exemplary embodiments, a non-aqueous electrolyte can be used as the electrolyte. For example, the non-aqueous electrolyte can contain a lithium salt and an organic solvent. The lithium salt can be represented by Li+X. An anion of the lithium salt, X, can be represented by, for example, Li+X. B. F-, Cl-, Br-, I-, NO3-, N(CN)2-, BF4-, ClO4-, PF6-, (CF3)2PF4-, (CF3)3PF3-, (CF3)4PF2-, (CF3)5PF-, (CF3)6P-, CF3SO3-, CF3CF2SO3-, (CF3SO2)2N-, (FSO2)2N-,CF3CF2(CF3)2CO-, (CF3SO2)2CH-, (SF5)3C-, (CF3SO2)3C-, CF3(CF2)7SO3-, CF3CO2-, CH3CO2-, SCN-, (CF3CF2SO2)2N- etc. contain. The organic solvent may contain, for example, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite, tetrahydrofuran, etc. These may be used alone or in combination. As shown in Fig. 3, an electrode tab (a cathode tab and an anode tab) can be formed by either the cathode current collector 105 or the anode current collector 125 to extend to one end of the housing 160. The electrode tabs can be welded together with one end of the housing 160 to form an electrode conductor (a cathode conductor 107 and an anode conductor 127) that is exposed on an outer surface of the housing 160. Fig. 3 shows that the cathode lead 107 and the anode lead 127 project from both lateral sides of the housing 160 in a planar view, but the positions of the electrode leads are not restricted, as shown in Fig. 3. For example, the electrode leads can project from a top side or a bottom side of the housing 160. The lithium secondary battery can be manufactured into a cylindrical shape using a can, a prismatic shape, a pouch shape, a coin shape, etc. Preferred embodiments are proposed below to describe the present invention more precisely. However, the following examples are given only to illustrate the present invention, and it will be obvious to the person skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. Such changes and modifications are duly included in the appended claims. MANUFACTURING A SECONDARY BATTERY ANODE Graphite and SiOx (0 < x < 2) as anode active material, styrene-butadiene rubber (SBR) as aqueous binder, carboxymethylcellulose (CMC), carbon nanotubes as conductive material were mixed in a weight ratio of 93.0:3.0:1.8:1.2:1.0 and then dispersed in water to form an anode slurry. The anode slurry was coated with an 8 µm thick copper foil using the slurry coating apparatus of the structure shown in Fig. 4 (rectangular slot), resulting in an anode slurry charge value of 12.0 mg / cm² or 14.0 mg / cm². The slots were arranged so that charge values ​​were repeated alternately along a longitudinal direction. The coated slurry was dried in an oven at 120 °C for 2 minutes and then pressed to form an anode with an anode active material layer having a density of 1.7 g / cm³. <kathode> LiNi0,8Co0,1Mn0,1O2 as the cathode active material, Denka Black as the conductive material, and PVDF as the binder were mixed in a mass ratio of 97.3:1.2:1.5 to prepare a cathode slurry. The cathode slurry was coated onto an aluminum substrate with a thickness of 12 µm and then dried and pressed to form a cathode. <Sekundärbatterie> The cathode and anode, prepared as described above, were each notched to a predetermined size and stacked with a separator (polyethylene, 13 µm thick) positioned between them to form a battery cell. Each tab section of the cathode and anode was welded. The welded cathode / separator / anode assembly was placed in a bag, and three sides of the bag, except for one electrolyte injection side, were sealed. The tab sections were also enclosed in sealed sections. An electrolyte was injected through the electrolyte injection side, which was then also sealed. Subsequently, the above structure was impregnated for more than 24 hours to obtain a lithium secondary battery. The electrolyte was prepared by forming a 1M LiPF6 solution in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethylene carbonate (DEC) (25 / 45 / 30; volume ratio) and then adding 7 wt% fluoroethylene carbonate (FEC), 0.5 wt% 1,3-propensultone (PRS), 0.5 wt% lithium bis(oxalato)borate (LiBOB) and 0.5 wt% ethylene sulfate (ESA). Examples and comparative examples The conditions of the slurry coating were modified as shown in Table 1 to obtain the secondary batteries of the examples and comparison examples as described above. [Table 1] [Table 1] Example 13003001270.93 Example 21000100012100.89 Example 31000150012240.76 Example 42000200012400.64 Example 51000100014140.88 Comparison example 1--12-- Comparison example 220020012 not measurable (irregular coating) Comparison example 31000300012540.54 Comparison example 410003001240.96 Comparison example 53000200012340.68 Experimental example (1) Measurement of XRM porosity A measurement area was configured to completely encompass a pattern cycle based on an electrode longitudinal direction. Solid sections and pores in the electrode were segmented using XRM imaging. The entire area was divided into 100 µm segments along the longitudinal direction, and the porosity in each segment was calculated using pore analysis software to measure maximum and minimum porosity within the pattern. (2) Measurement of charging / discharging efficiency during high-rate charging A constant current was applied at a rate of 1.5C at 25°C until the battery voltage reached 4.2V, and the charge capacity was measured. The battery was then discharged at a rate of 0.3C until the voltage reached 2.5V, and the discharge capacity was measured. The charge / discharge efficiency was calculated by dividing the measured discharge capacity by the charge capacity. (3) Measurement of lifetime property (capacity conservation) The secondary batteries in the examples and comparison examples were manufactured to cells with a capacity of approximately 70 Ah, and then a lifetime assessment was performed in a chamber maintained at a predetermined constant temperature (25 °C) within a range of SOC 8 to 80 at a charge / discharge C-rate of 2 C / 0.3 C. Specifically, capacity retention after 300 cycles relative to an initial capacity was measured. The results are shown in Table 2 below. [Table 2] [Table 2] Example 10,870,399,589 Example 20,76199,794 Example 30,631,2599,693 Example 40,57299,591 Example 50.69199.286 Comparison example 1 - 98,360 Comparative example 30,52298,558 Comparison example 40,910,6598,662 Comparative example: 50,692,598,463 Referring to Table 2, in Examples 1 to 4 the ratio (B / A) of the maximum and minimum thickness of the preliminary anode active material layer was adjusted between 0.64 and 0.93 in a range of 300 µm to 2000 µm of slot and closed section widths, and the porosity of the anode active material layer was controlled. Accordingly, the charge / discharge efficiency and the lifetime characteristic at high charging rates were improved. In Example 5, the thickness of the preliminary anode active material layer was adjusted by controlling the amount of charge on the active material. As described above, if patterns with different porosities are repeatedly arranged, a section with high porosity can act as a lithium-ion channel to improve fast charge and discharge characteristics. Furthermore, even in the high-density electrode of 1.7 g / cm3 or more, the fast charging / discharging properties were improved. Fig. 8 is a diagram showing fast charging characteristics of batteries according to Example 1 and Comparative Example 1. As shown in Fig. 8, in comparative example 1 the pore pattern arrangement in the anode active material layer was not formed, and the lifetime characteristic was obviously worsened compared to those from example 1. In comparative example 2, the slot width decreased during the slurry coating process, resulting in poor slurry discharge and uneven coating thickness. In comparative examples 3 and 5, a gap between the slots or between the closed sections in the slurry coating device was not formed within the range of 300 µm to 2000 µm, and the charge / discharge efficiency and lifetime characteristic were degraded. In comparative example 4, the ratio (B / A) of the maximum and minimum thickness of the preliminary anode active material layer was not within 0.64 to 0.93, and the charge / discharge efficiency and lifetime characteristics were also degraded.< / kathode>

Claims

An anode for a lithium secondary battery, comprising: an anode current collector; and an anode active material layer formed on the anode current collector, wherein the anode active material layer comprises a first section and a second section, wherein Y / X of the anode active material layer is in a range of 0.57 to 0.87, and X is a maximum porosity obtained by an X-ray microscopy (XRM) measurement of the anode active material layer, and Y is a minimum porosity obtained by the XRM measurement of the anode active material layer, wherein the first section has a higher porosity than the second section, and the distance between a point of maximum porosity in the first section and a point of minimum porosity in the second section is in a range of 0.3 mm to 2 mm. Anode for a lithium secondary battery according to claim 1, wherein the anode active material layer comprises a plurality of the first section and a plurality of the second section. Anode for a lithium secondary battery according to claim 1, wherein the first section and the second section are arranged alternately along a longitudinal direction of the anode active material layer. Anode for a lithium secondary battery according to claim 1, wherein the anode current collector comprises an anode tab projecting from one side of the anode current collector, and the first section and the second section are arranged alternately and repeatedly along a projection direction of the anode tab or a direction perpendicular to the projection direction of the anode tab. Anode for a lithium secondary battery according to claim 4, wherein the first section and the second section extend in the direction perpendicular to the protrusion direction of the anode tab and are arranged alternately and repeatedly along the protrusion direction. Anode for a lithium secondary battery according to claim 1, wherein the first section and the second section each have a uniform porosity along the forward direction. Anode for a lithium secondary battery according to claim 1, wherein the first section and the second section have the same thickness. Anode for a lithium secondary battery according to claim 1, wherein the first section and the second section are formed from the same anode slurry. Lithium secondary battery comprising: a cathode; and the anode for a lithium secondary battery according to claim 1, which is facing the cathode.

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