Negative electrode for lithium secondary battery and negative electrode manufacturing apparatus therefor

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a negative electrode manufacturing apparatus therefor. The manufacturing apparatus for the negative electrode for a lithium secondary battery includes a drying unit using light energy at the widthwise edge of a magnet unit that aligns the crystal planes of a carbon-based negative electrode active material, so that the crystal plane orientation and pre-drying of the carbon-based negative electrode active material can be simultaneously performed at the edge of the negative electrode slurry. The negative electrode produced thereby exhibits a high crystal plane orientation of the carbon-based negative electrode active material contained in the sliding region of the negative electrode active layer, and thus shows excellent effects in terms of the overall orientation and orientation uniformity of the negative electrode active layer. In addition, a lithium secondary battery equipped with the same has the advantage of excellent charge and discharge performance.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0032299, filed on March 13, 2023, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a negative electrode for a lithium secondary battery and a manufacturing apparatus for manufacturing the same.

Background Art

[0003] In recent years, lithium secondary batteries have been widely applied not only to small devices such as portable electronic devices but also to medium and large-sized devices such as battery packs or power storage devices for hybrid vehicles and electric vehicles.

[0004] Such a lithium secondary battery is a power generation element capable of charge and discharge having a laminated structure of a positive electrode / separator / negative electrode. Generally, the positive electrode contains a lithium metal oxide as a positive electrode active material, and the negative electrode contains a carbon-based negative electrode active material such as graphite. In the above lithium secondary battery, lithium ions released from the positive electrode during charging are occluded inside the carbon-based negative electrode active material of the negative electrode, and lithium ions contained inside the carbon-based negative electrode active material during discharge are occluded in the lithium metal oxide of the positive electrode, and the charge and discharge are repeated.

[0005] At this time, examples of the negative electrode active material used for the negative electrode include graphite materials such as natural graphite. Graphite has a layered structure, in which carbon atoms form a network structure, and a large number of planar layers are stacked. Due to such a layered structure, in the above graphite, lithium ions penetrate from the edge plane (the plane where the layers overlap) of the layered structure and diffuse between the layers during charging, and lithium ions desorb and are released from the edge plane of the carbon layer during discharge. Further, since the electrical resistivity in the plane direction of the layer of the above graphite is lower than that in the stacking direction of the layers, an electron conduction path that detours along the plane direction of the layer is formed.

[0006] Regarding this, in a conventional lithium secondary battery using graphite, a technique has been proposed in which the graphite contained in the negative electrode is magnetically oriented to improve the charging performance of the negative electrode. Specifically, it has a configuration in which the (0, 0, 2) crystal plane of graphite is oriented to be substantially horizontal with respect to the negative electrode current collector during negative electrode formation and is fixed. In this case, since the edge surface of the graphite layer faces the positive electrode active layer, the insertion and extraction of lithium ions can be smoothly performed, and at the same time, the conduction path of electrons is shortened, the electron conductivity of the negative electrode can be improved, and thereby the charging performance of the battery can be improved.

[0007] On the other hand, the negative electrode slurry used during the production of the active layer of the negative electrode for a lithium secondary battery has a form in which graphite, which is a carbon-based negative electrode active material, is mixed with a dispersion medium. At this time, water is generally used as the dispersion medium. Water is a solvent with a high surface tension, and the negative electrode slurry containing it exhibits a phenomenon of reducing the surface area exposed to the air after being applied to the negative electrode current collector due to the high surface tension of water. As a result, the negative electrode slurry applied on the negative electrode current collector forms a curved surface at the edge portion with a predetermined angle with the surface of the negative electrode current collector inside the slurry. The curved surface causes the positional energy of the molecules near the liquid surface and the molecules inside the liquid to be different due to the high surface tension of water, and such an energy deviation can increase the kinetic energy of the components contained in the negative electrode slurry. The increase in the kinetic energy of each such component acts as a factor that inhibits the orientation of graphite using a magnetic field.

[0008] Specifically, the crystal plane orientation of graphite by magnetic force is realized by applying a magnetic force greater than the kinetic energy of graphite and rotating the crystal plane of graphite. However, at the edge portion of the negative electrode slurry, the energy of the molecules near the liquid surface and the molecules inside the liquid is different, and the kinetic energy of the graphite contained at the edge increases. As a result, when a magnetic field is applied to the entire surface of the negative electrode slurry, the central portion of the negative electrode slurry with a flat exposed surface has a high orientation of graphite, while the edge portion of the negative electrode slurry with a curved exposed surface has a low orientation of graphite.

[0009] Therefore, there is a need for a technology that can improve the low orientation of graphite due to the curved surface structure induced at the edge of the negative electrode slurry, and manufacture a negative electrode active layer in which the crystal planes of graphite are uniformly aligned at a high angle with respect to the surface of the current collector overall.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] An object of the present invention is to provide a negative electrode manufacturing technology in which a carbon-based negative electrode active material such as graphite contained in a negative electrode active layer not only has high orientation but also such orientation is uniformly realized.

MEANS FOR SOLVING THE PROBLEMS

[0011] In order to solve the above problems, in one embodiment of the present invention, an orientation unit that applies a magnetic field to the upper and lower portions of an electrode sheet coated with a negative electrode slurry containing a carbon-based negative electrode active material on its surface, and a drying unit that dries the negative electrode slurry of the electrode sheet to which the magnetic field is applied by the orientation unit are included. The drying unit includes a first drying unit and a second drying unit, and the first drying unit pre-dries the edge portion of the negative electrode slurry when a magnetic field is applied to the electrode sheet by the orientation unit, and the second drying unit dries the entire surface of the negative electrode slurry after the magnetic field application by the orientation unit is completed, and provides a manufacturing apparatus for a negative electrode of a lithium secondary battery.

[0012] Here, the orientation unit may include a first magnet unit disposed on the upper portion of the electrode sheet and a second magnet unit disposed on the lower portion of the electrode sheet.

[0013] The first magnet unit and the second magnet unit may include a plurality of unit magnets arranged along the transfer direction (x-axis direction) and the width direction (y-axis direction) of the electrode sheet.

[0014] Further, the first magnet portion and the second magnet portion may have a length of 0.5 m to 10 m along the transfer direction of the electrode sheet, and the length in the width direction may each have a ratio of 105% to 150% based on the length in the width direction of the negative electrode slurry.

[0015] Further, the first drying portion may be arranged alone at the widthwise edge portion of the magnet portion along the transfer direction of the electrode sheet, or may be arranged so as to form a row alternately with the unit magnets at the widthwise edge portion of the magnet portion.

[0016] Further, the first magnet portion and the second magnet portion are divided into a first section in which the length ratio of the magnet portion corresponds to 0% to 10% based on the point where the electrode sheet is introduced along the transfer direction of the electrode sheet, a second section in which the length ratio of the magnet portion corresponds to 10% to 90%, and a third section in which the length ratio of the magnet portion corresponds to 90% to 100%. The first drying portion may be arranged in the second section of any one of the first magnet portion and the second magnet portion.

[0017] Further, the first drying portion may include one or more of an ultraviolet dryer, a near-infrared dryer, and a far-infrared dryer.

[0018] Further, the second drying portion may be arranged adjacent to the end of the alignment portion where the electrode sheet with a magnetic field applied is carried out.

[0019] Further, the second drying portion may include one or more of a hot air dryer, a vacuum oven, and a heater.

[0020] Further, in one embodiment of the present invention, a negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material are included. A negative electrode for a lithium secondary battery manufactured by the manufacturing apparatus according to the present invention is provided.

[0021] At this time, the negative electrode active layer is divided into a flat region that includes the center in the width direction of the negative electrode active layer and has a uniform thickness, and a sliding region that is located at the edge of the negative electrode active layer and has a thickness gradient. The flat region and the sliding region may satisfy the following formula (1):

[0022] [Formula (1)] 0.9 ≦ [O.I sliding / [O.I center ≦ 1.3

[0023] In Formula (1), O.I sliding represents the degree of alignment (O.I) in the sliding region, and O.I center represents the degree of alignment (O.I) in the flat region. The degree of alignment (O.I) is the ratio (I 004 ) of the area of the peak indicating the (0, 0, 4) crystal plane to the area of the peak indicating the (1, 1, 0) crystal plane (I 110 ) during XRD measurement with respect to the negative electrode active layer (I 004 / I 110 ).

[0024] Here, the flat region of the negative electrode active layer may have a degree of alignment (O.I center ) of 0.1 to 1.5.

[0025] In addition, the flat region of the negative electrode active layer may have a ratio of 95% or more of the total length in the width direction of the negative electrode active layer, and the sliding region of the negative electrode active layer may have a ratio of 5% or less of the total length in the width direction of the negative electrode active layer.

[0026] Furthermore, the carbon-based negative electrode active material contained in the negative electrode active layer may include one or more of natural graphite and artificial graphite.

Advantages of the Invention

[0027] The manufacturing apparatus for a negative electrode of a lithium secondary battery according to the present invention includes a drying unit using light energy at the widthwise edge of a magnet unit that aligns the crystal planes of a carbon-based negative electrode active material, thereby enabling simultaneous crystal plane orientation and preliminary drying of the carbon-based negative electrode active material at the edge of the negative electrode slurry.

[0028] The negative electrode thus manufactured exhibits a high crystal plane orientation of the carbon-based negative electrode active material contained in the sliding region of the negative electrode active layer, and thus shows excellent effects in the overall orientation and orientation uniformity of the negative electrode active layer. In addition, the lithium secondary battery equipped with the same has the advantage of excellent charge and discharge performance.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0030] The present invention can be subjected to various modifications and can have various embodiments, so specific embodiments will be described in detail.

[0031] However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all modifications, equivalents, or alternatives included in the spirit and technical scope of the present invention.

[0032] In the present invention, terms such as "comprising" and "having" are intended to specify the presence of the features, numbers, steps, operations, components, parts or combinations thereof described in the specification, and are to be understood as not precluding the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

[0033] In the present invention, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only the case where it is directly "on" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, plate, etc. is described as being "under" another part, it includes not only the case where it is directly "under" the other part, but also the case where there is another part in between. Also, in the present application, being "disposed on" may include not only the upper part but also the case of being disposed on the lower part.

[0034] In this specification, "comprising as a main component" may mean containing 50% by weight or more (or 50% by volume or more), 60% by weight or more (or 60% by volume or more), 70% by weight or more (or 70% by volume or more), 80% by weight or more (or 80% by volume or more), 90% by weight or more (or 90% by volume or more), or 95% by weight or more (or 95% by volume or more) of the component defined with respect to the total weight (or total volume). For example, "comprising graphite as a main component as the negative electrode active material" may mean containing 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more of graphite with respect to the total weight of the negative electrode active material, and in some cases, it may also mean that the entire negative electrode active material consists of graphite and contains graphite at 100% by weight.

[0035] In this specification, "electrode sheet" may mean an article in a state where a negative electrode slurry is applied on a negative electrode current collector, or in a state where the negative electrode slurry applied on the negative electrode current collector is dried to form a negative electrode active layer.

[0036] In addition, in this specification, "the carbon-based negative electrode active material is oriented" or "the carbon-based negative electrode active material is aligned" means that the crystal planes of the carbon-based negative electrode active material constituting the particles of the negative electrode active material are distributed so as to have a predetermined directionality with respect to the surface of the negative electrode current collector. At this time, the crystal plane is a crystal plane showing the planar structure of the carbon-based negative electrode active material, and may mean a (1,0,0) crystal plane or a (1,1,0) crystal plane. Also, "the carbon-based negative electrode active material is oriented" may be different from the case where the particles of the carbon-based negative electrode active material are arranged so as to have a specific direction inside the negative electrode active layer.

[0037] Also, "the orientation (or degree of orientation) of the carbon-based negative electrode active material is high" may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high frequency with respect to the surface of the negative electrode current collector. In some cases, it may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle (for example, more than 45°, specifically 60° or more) with respect to the surface of the negative electrode current collector.

[0038] Also, "the degree of alignment of the carbon-based negative electrode active material is high" means that the "degree of alignment (O.I)" mentioned in this specification has a large value, and may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a low angle (for example, less than 45°) with respect to the surface of the negative electrode current collector. Conversely, "the degree of alignment of the carbon-based negative electrode active material is low" means that the "degree of alignment (O.I)" has a small value, and may mean that the carbon-based negative electrode active material contained in the negative electrode active layer is aligned at a high angle (for example, more than 45°, specifically 60° or more) with respect to the surface of the negative electrode current collector.

[0039] Furthermore, in this specification, the "crystal plane of the carbon-based negative electrode active material" means a plane on which the atoms of the carbon-based negative electrode active material form the outer shape of the crystal, and in the present invention, it may mean a crystal plane including the plane of the carbon-based negative electrode active material, or a crystal plane including the a-axis / a-b axis of the carbon-based negative electrode active material crystal.

[0040] Hereinafter, the present invention will be described in more detail.

[0041] <Manufacturing Apparatus for Negative Electrode of Lithium Secondary Battery>

[0042] In one embodiment, the present invention an orientation unit that applies a magnetic field to the upper and lower portions of an electrode sheet having a negative electrode slurry containing a carbon-based negative electrode active material applied to its surface, and a drying unit that dries the negative electrode slurry of the electrode sheet to which the magnetic field is applied by the orientation unit, the drying unit includes a first drying unit and a second drying unit, and the first drying unit preliminarily dries the edge portion of the negative electrode slurry when a magnetic field is applied to the electrode sheet by the orientation unit, The second drying unit provides a manufacturing apparatus for a negative electrode of a lithium secondary battery that dries the entire surface of the negative electrode slurry after the magnetic field application by the orientation unit is completed.

[0043] The manufacturing apparatus for the negative electrode according to the present invention is an apparatus applied when manufacturing a negative electrode used in a lithium secondary battery. By applying a magnetic field to the surface of the negative electrode current collector, specifically, to the negative electrode slurry containing a carbon-based negative electrode active material and applied on the negative electrode current collector, the crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry can be aligned at a large angle close to perpendicular to the negative electrode current collector. At this time, the negative electrode manufacturing apparatus not only aligns the carbon-based negative electrode active material contained in the negative electrode slurry with a high degree of orientation, but also has the advantage that the carbon-based negative electrode active material can be easily oriented at the edge portion of the negative electrode slurry where it is difficult to align the carbon-based negative electrode active material (i.e., the sliding region of the negative electrode active layer). Therefore, the negative electrode manufacturing apparatus can realize a uniform alignment of the carbon-based negative electrode active material contained in the negative electrode slurry.

[0044] For this purpose, the negative electrode manufacturing apparatus includes an orientation unit for aligning the crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry and a drying unit for drying the negative electrode slurry.

[0045] FIG. 1 is a structural diagram schematically showing the structure of a negative electrode manufacturing apparatus according to the present invention. Referring to FIG. 1, the negative electrode manufacturing apparatus 10 includes an orientation unit 110: 110a and 110b that apply magnetic fields to the upper and lower portions of the electrode sheet along the transfer direction (x-axis direction) of the electrode sheet, and a drying unit 120 that dries the negative electrode slurry of the electrode sheet to which the magnetic field is applied by the orientation unit.

[0046] The orientation units 110: 110a and 110b are respectively disposed on the upper and lower portions of the electrode sheet during transfer, and serve to apply magnetic fields to the exposed surface of the negative electrode slurry S and the exposed surface of the negative electrode current collector C of the electrode sheet. At this time, when the orientation units 110: 110a and 110b apply a magnetic field to the negative electrode slurry S coated and transferred on the negative electrode current collector C, the electrode sheet surface (i.e., the upper surface) where the negative electrode slurry S is exposed and the electrode sheet surface (i.e., the lower surface) where the current collector C is exposed are respectively provided with a first magnet portion 110a and a second magnet portion 110b disposed on the upper and lower portions of the electrode sheet so that the magnetic field is uniformly applied.

[0047] In this case, compared with the case where the magnet portion is disposed only on the upper surface of the electrode sheet (the inclination of the carbon-based negative electrode active material: about 40 to 50°), the crystal plane inclination of the carbon-based negative electrode active material with respect to the negative electrode current collector C can be increased, whereby the crystal plane inclination of the carbon-based negative electrode active material with respect to the surface of the negative electrode current collector C can have an angle close to perpendicular.

[0048] Further, the first magnet portion 110a and the second magnet portion 110b may each include unit magnets 111a and 111b, and support portions 112a and 112b that fix the unit magnets.

[0049] The unit magnets of the first magnet portion 110a and the second magnet portion 110b each include one large-area unit magnet, or, as shown in FIGS. 3 and 4, when the direction in which the electrode sheet coated with the negative electrode slurry S is transferred is defined as the x-axis direction and the width direction of the transferred electrode sheet is defined as the y-axis direction, the first magnet portion 110a and the second magnet portion 110b may each include a plurality of small-area unit magnets in the x-axis direction and the y-axis direction. At this time, the unit magnets may include m (where m is an integer of 2 or more) and n (where n is an integer of 2 or more) unit magnets in the x-axis direction and the y-axis direction, respectively, to form a magnet row, and thus one magnet portion may include m×n unit magnets.

[0050] Further, the unit magnet may include an electromagnet and / or a permanent magnet. The electromagnet may include both a direct current electromagnet and an alternating current electromagnet. Further, examples of the permanent magnet include magnets having ferromagnetic properties such as NdFeB-based magnets, SmCo-based magnets, ferrite magnets, alnico magnets, FeCrCo-based magnets, and bond magnets (Nd-Fe-B-based, Sm-Fe-N-based, Sm-Co-based, ferrite-based), and magnets having soft magnetic properties.

[0051] Also, the unit magnets of the first magnet portion 110a and the second magnet portion 110b may be arranged so as to have opposite poles. For example, the N pole of the unit magnet of the first magnet portion 110a and the S pole of the unit magnet of the second magnet portion 110b may face each other, or the S pole of the unit magnet of the first magnet portion 110a and the N pole of the unit magnet of the second magnet portion 110b may be arranged to face each other. Thus, when the electrode sheet passes between the spaces where the unit magnets have opposite poles, an attractive force acts between the first magnet portion 110a and the second magnet portion 110b. Since the crystal planes of the carbon-based negative electrode active material contained in the negative electrode slurry S are aligned along the direction in which the attractive force acts, the crystal planes of the carbon-based negative electrode active material are aligned at a higher angle with respect to the current collector C (or the electrode sheet).

[0052] Also, the separation distance between the first magnet portion 110a and the second magnet portion 110b can be 10 mm to 50 mm, specifically 10 mm to 40 mm, 20 mm to 50 mm, or 15 mm to 45 mm. In the present invention, by adjusting the separation distance between the first magnet portion 110a and the second magnet portion 110b within the above range, the crystal plane alignment of the carbon-based negative electrode active material contained in the negative electrode slurry S can be more efficiently performed with less energy.

[0053] Also, the first magnet portion 110a and the second magnet portion 110b may have a predetermined length along the transfer direction of the electrode sheet in order to sufficiently apply a magnetic field necessary for the crystal plane of the carbon-based negative electrode active material contained in the negative electrode slurry S to be aligned at a high angle with respect to the negative electrode current collector C. Specifically, the first magnet portion 110a and the second magnet portion 110b may have a length of 0.5 m to 10 m along the transfer direction of the electrode sheet, and more specifically 0.5 m to 7.5 m, 0.5 m to 5 m, 0.5 m to 2.5 m, 1 m to 5 m, 3 m to 8 m, 6 m to 10 m, or 4 m to 9 m.

[0054] Also, the size of the first magnet portion 110a and the second magnet portion 110b in the width direction (y-axis direction) can be adjusted to be larger than the size of the negative electrode slurry S in the width direction (y-axis direction). For example, the magnet portions 110a and 110b may have a length ratio of 105% to 150% based on the width direction length of the negative electrode slurry S, specifically 110% to 150%, 110% to 130%, 110% to 120%, 105% to 120%, 130% to 150%, 105% to 120%, or 105 to 110% based on the width direction length of the negative electrode slurry S. Referring to FIG. 2, a magnetic field is uniformly applied in a direction perpendicular to the surface of the electrode sheet between the first magnet portion 110a and the second magnet portion 110b.

[0055] At this time, when the lengths of the first magnet portion 110a and the second magnet portion 110b have the same length ratio as the negative electrode slurry applied to the electrode sheet and / or the electrode sheet, it is difficult to sufficiently overcome the intermolecular energy deviation due to the surface tension of the solvent of the negative electrode slurry at the edge portion of the negative electrode slurry. Therefore, the crystal plane of the carbon-based negative electrode active material is difficult to be aligned at a high angle with respect to the negative electrode current collector. However, in the present invention, by satisfying the above-described range for the widthwise lengths of the first magnet portion 110a and the second magnet portion 110b, as shown in FIG. 2, a magnetic field M in the same direction as the central portion S1 of the negative electrode slurry S is strongly applied to the edge portion S2 of the negative electrode slurry S having a curved surface shape. Therefore, the degree of orientation of the carbon-based negative electrode active material G distributed at the edge portion S2 can be highly realized.

[0056] Furthermore, the drying unit 120 dries the negative electrode slurry S, thereby serving to fix the carbon-based negative electrode active material aligned by the alignment units 110: 110a and 110b.

[0057] At this time, the drying unit 120 includes a first drying unit 121 that pre-dries the edge portion S2 of the negative electrode slurry when a magnetic field is applied to the electrode sheet by the alignment units 110: 110a and 110b, and a second drying unit 122 that dries the entire surface of the negative electrode slurry S after the magnetic field application of the alignment units 110: 110a and 110b is completed.

[0058] The first drying unit 121 functions to fix the crystal plane orientation of the carbon-based negative electrode active material contained in the negative electrode slurry simultaneously with or immediately after the orientation by selectively applying light energy only to the edge portion S2 of the negative electrode slurry when the alignment units 110: 110a and 110b apply a magnetic field to the negative electrode slurry for pre-drying.

[0059] For this purpose, the first drying unit 121 can be disposed on one or more side surfaces of the first magnet portion 110a and the second magnet portion 110b, and can include means for irradiating light or applying a wavelength to the surface of the negative electrode slurry.

[0060] Generally, when drying the negative electrode slurry, it is performed by applying hot air at a high temperature. In this case, the drying time of the negative electrode slurry is long, and the alignment of the carbon-based negative electrode active material in the negative electrode slurry may be disrupted. Also, in order to solve such problems, when reducing the speed of the hot air and increasing the temperature, the solvent of the negative electrode slurry tends to be dried relatively quickly on the surface of the negative electrode slurry. Such a phenomenon induces the solvent existing inside the negative electrode slurry to move to the surface in order to volatilize. Such movement of the solvent causes a phenomenon (migration) in which the binder inside the negative electrode slurry concentrates on the surface of the negative electrode slurry, and there is a problem of reducing the adhesion strength between the negative electrode active layer and the negative electrode current collector. However, the present invention can rapidly fix the carbon-based negative electrode active material with the crystal planes oriented without loss of the degree of orientation by selectively applying light energy, rather than thermal energy, only to the edge portion of the negative electrode slurry.

[0061] Thereby, the first drying unit 121 may include means capable of applying energy to the negative electrode slurry S in the form of light or wavelength. For example, the first drying unit 121 may include an ultraviolet dryer, a near-infrared dryer, a far-infrared dryer, an ultrasonic dryer, or the like.

[0062] As an example, the first drying unit 121 may include a far-infrared dryer that emits energy with a wavelength of 1 μm or more, more specifically 5 μm or more, 10 μm or more, or 20 μm or more, in order to achieve a uniform drying rate of the negative electrode slurry S. Unlike the near-infrared dryers and infrared rays commonly applied in the industry, the far-infrared dryer has a long light or wavelength, good energy efficiency, and can uniformly apply energy not only to the surface but also to the inside of the negative electrode slurry S. Therefore, there is an advantage that the adhesive force between the negative electrode slurry S and the negative electrode current collector C can be increased in a short time.

[0063] At this time, the first drying unit 121 may emit energy at an output density of 50 kW / m 2 ~1,000 kW / m 2 and specifically 50 kW / m 2 ~500 kW / m 2, 50 kW / m 2 ~250 kW / m 2 , or 50 kW / m 2 and 200 kW / m 2 and can release energy at an output density of. By controlling the output density of the first drying unit 121 within the above range, the present invention can prevent non-uniform drying of the negative electrode slurry from being induced by an excessive output density.

[0064] Further, the present invention can arrange the first drying unit 121 and the second drying unit 122 at specific positions in order to uniformly and highly embody the crystal plane orientation of the carbon-based negative electrode active material contained in the negative electrode active layer.

[0065] Specifically, the first drying unit 121 can be located on the edge side surface in the width direction of a magnet part (for example, the first magnet part) located above the negative electrode slurry in order to preliminarily dry the edge part S2 of the negative electrode slurry while a magnetic field is being applied.

[0066] As an example, as shown in FIG. 3, the first drying unit 121 can be arranged alone on the edge side surface in the width direction (y-axis direction) of a magnet part located above the negative electrode slurry being transferred along the transfer direction of the electrode sheet. In this case, not only is it easy to add the equipment of the first drying unit 121 to the equipment used during conventional negative electrode manufacturing, but maintenance during use is also easy, so there is an advantage of high economic efficiency.

[0067] As another example, as shown in FIG. 4, the first drying unit 121 is arranged on the edge side surface in the width direction (y-axis direction) of a magnet part located above the negative electrode slurry being transferred along the transfer direction of the electrode sheet, and can be arranged to form a column by being mixed with the unit magnets 111a' and 111b' constituting the magnet part.

[0068] In this case, the unit magnets 111a' and 111b' that form a column with the first drying part 121 on the edge side surface in the width direction (y-axis direction) of the magnet part may include magnets in which the magnetic flux density Br is relatively less affected by temperature as compared with the unit magnets arranged at the central part in the width direction (y-axis direction) of the magnet part. The above-mentioned "magnetic flux density Br" indicates the density of magnetic field lines per unit area. Generally, as the temperature rises, the magnetic flux density Br decreases and ultimately the magnetic force is lost, but the degree of decrease in the magnetic flux density Br is affected by the temperature coefficient of the magnetic flux density Br. Since heat generation can be induced during the drying of the edge part of the negative electrode slurry in the first drying part 121 of the present invention, the unit magnets 111a' and 111b' that form a column with the first drying part 121 may be composed of unit magnets in which the temperature coefficient of the magnetic flux density Br satisfies a predetermined range so that the magnetic flux density Br can be less affected by temperature. For example, the unit magnets 111a' and 111b' may include strontium and ferrite alloy magnets (temperature coefficient: about -0.18%), samarium and cobalt alloy magnets (temperature coefficient: about -0.03%), neodymium, iron and boron alloy magnets (temperature coefficient: about -0.12 to -0.09%), samarium, iron and nitrogen alloy magnets (temperature coefficient: about -0.07%), aluminum, nickel and cobalt alloy magnets (i.e., alnico magnets, temperature coefficient: about -0.02%), etc. as unit magnets. By adjusting the position of the first drying part 121 as described above, the present invention has the advantage that the crystal plane orientation and fixation of the carbon-based negative electrode active material contained in the edge part S2 of the negative electrode slurry are carried out step by step, and thus the orientation performance of the carbon-based negative electrode active material is excellent.

[0069] Further, the first drying part 121 may be arranged on the edge side surface of a magnet part (for example, the first magnet part) located above the negative electrode slurry during transfer, and may be arranged at a position separated by a predetermined distance from the inlet where the electrode sheet is introduced into the magnet part and the outlet where the electrode sheet is carried out.

[0070] For example, as shown in FIGS. 3 and 4, the first magnet portion 110a and the second magnet portion 110b are each divided into a first section 111a-1 and 111b-1 where the length ratio of the magnet portion corresponds to more than 0% and 10% or less, a second section 111a-2 and 111b-2 where the length ratio of the magnet portion corresponds to more than 10% and 90% or less, and a third section 111a-3 and 111b-3 where the length ratio of the magnet portion corresponds to more than 90% and 100% or less, based on the point where the electrode sheet is introduced along the transfer direction of the electrode sheet. At this time, the first drying portion 121 can be selectively arranged in the second section of the first magnet portion 111a and the second magnet portion 111b according to the position of the negative electrode slurry. That is, when the negative electrode slurry is applied only on the upper surface of the electrode sheet, the first drying portion 121 can be arranged in the second section 111a-2 of the first magnet portion 111a, and when the negative electrode slurry is applied on both surfaces of the electrode sheet, the first drying portion 121 can be arranged in the second sections 111a-2 and 111b-2 of the first magnet portion 111a and the second magnet portion 111b.

[0071] When the first drying portion 121 is arranged in the first sections 111a-1 and 111b-1 of the magnet portion, since the negative electrode slurry is pre-dried before the crystal planes of the carbon-based negative electrode active material contained in the edge portion S2 of the negative electrode slurry are aligned, the degree of crystal plane orientation of the carbon-based negative electrode active material may be low. Further, when the first drying portion 121 is arranged in the third sections 111a-3 and 111b-3 of the magnet portion, since the time for pre-drying by the first drying portion is extremely short and it is difficult to fix the oriented carbon-based negative electrode active material, a loss of the degree of orientation may occur due to the volatilization of the solvent in the negative electrode slurry in the second drying portion using thermal energy.

[0072] Therefore, the present invention can perform sufficient crystal plane orientation and fixation of the carbon-based negative electrode active material contained in the edge portion S2 of the negative electrode slurry by arranging the position of the first drying portion 121 in the second section of the magnet portion.

[0073] Furthermore, the second drying portion 122 functions to completely dry the entire negative electrode slurry to form a negative electrode active layer.

[0074] At this time, in order to prevent the orientation degree from being lost after the crystal planes of the carbon-based negative electrode active material contained in the central portion of the negative electrode slurry are carried out from the orientation portions 110:110a and 110b, the second drying portion 122 may be disposed adjacent to the ends of the orientation portions 110:110a and 110b from which the electrode sheet is carried out, that is, the ends of the respective magnet portions 110a and 110b. Here, "the second drying portion is disposed adjacent to the ends of the orientation portion / magnet portion" may mean that the outlet of the orientation portions 110:110a and 110b from which the electrode sheet with a magnetic field applied to the negative electrode slurry is carried out and the inlet of the second drying portion 122 into which the electrode sheet is introduced are arranged to be in contact with each other, or are arranged to have a predetermined separation distance.

[0075] Kinetic energy is applied to the negative electrode slurry S in the direction (x-axis direction) in which the electrode sheet is transferred. However, when the crystal planes of the oriented carbon-based negative electrode active material are carried out from the orientation portions 110:110a and 110b and the magnetic field is removed, the aligned crystal planes will tilt toward the negative electrode current collector C side and be aligned at a low angle due to the kinetic energy associated with the transfer of the electrode sheet. However, in the present invention, by arranging the ends (i.e., the outlets) of the orientation portions 110:110a and 110b adjacent to the inlet of the second drying portion 122, the negative electrode slurry S can be introduced into and dried inside the drying portion 120 immediately after passing through the ends of the orientation portion, thereby minimizing the reduction of the orientation of the carbon-based negative electrode active material.

[0076] Here, the ends of the orientation portion and the inlet of the second drying portion 122 may be arranged to be in contact with each other as shown in FIG. 1, and the separation distance may be close to 0 mm, and in some cases, may be arranged to have a separation distance of 10 mm or less, 8 mm or less, 5 mm or less, 3 mm or less, 0.5 mm to 5 mm, 5 mm to 10 mm, or 1 mm to 3 mm.

[0077] By adjusting the separation distance between the ends of the first magnet part 110a and the second magnet part 110b and the drying part as described above, it is possible not only to prevent the loss of the crystal plane alignment degree of the carbon-based negative electrode active material contained in the negative electrode slurry due to an excessive separation distance, but also to prevent the magnet parts 110a and 110b from being introduced into the second drying part 122 and the performance of the magnet parts from being deteriorated due to high temperature.

[0078] On the other hand, the second drying part 122 may include a drying means for applying thermal energy to uniformly and completely dry the entire surface of the negative electrode slurry. Such a second drying part 122 may be included without particular limitation as long as it is commonly applied in the art, and specifically, it may be included by using a hot air dryer, a vacuum oven, a heater, etc. alone or in combination.

[0079] Further, the second drying part 122 may have a structure including a wall body that blocks the periphery except for the inlet and outlet for introducing and discharging the electrode sheet, and a drying means (not shown) for drying the electrode sheet having the electrode slurry S applied to the inner wall surface of the wall body.

[0080] When the electrode sheet is introduced through the inlet of the second drying part 122, the electrode sheet will receive thermal energy from the drying means on the inner wall surface of the wall body. Therefore, it is preferable that the wall body is made of a heat insulating material so as to prevent the internal thermal energy from being transmitted to the outside and causing loss.

[0081] Due to having the above-described configuration, the negative electrode manufacturing apparatus according to the present invention is excellent in the crystal plane orientation of the carbon-based negative electrode active material contained in the edge part of the negative electrode slurry, and thus has an advantage that a negative electrode excellent in the overall orientation and orientation uniformity of the negative electrode active layer can be manufactured.

[0082] <Negative electrode for lithium secondary battery>

[0083] In one embodiment, the present invention includes a negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material. Provided is a negative electrode for a lithium secondary battery manufactured by the manufacturing apparatus according to the above-described present invention.

[0084] The negative electrode for a lithium secondary battery according to the present invention includes a negative electrode active layer containing a carbon-based negative electrode active material on at least one surface of a negative electrode current collector. The above negative electrode active layer is a layer that embodies the electrical activity of the negative electrode, and after applying a negative electrode slurry containing a negative electrode active material that embodies an electrochemical oxidation-reduction reaction during charging and discharging of the battery to at least one surface of the negative electrode current collector, it is manufactured by drying and rolling it.

[0085] Here, when the negative electrode is manufactured using the negative electrode manufacturing apparatus of the present invention described above, by orienting and drying the crystal planes of the carbon-based negative electrode active material contained in the negative electrode slurry, the negative electrode is characterized by including a negative electrode active layer with high and uniform crystal plane orientation of the carbon-based negative electrode active material.

[0086] Generally, the negative electrode slurry used in manufacturing the active layer of the negative electrode has a form in which a carbon-based negative electrode active material is mixed with a dispersion medium, and generally water is used as the above dispersion medium. Water is a solvent with a large surface tension, and the negative electrode slurry containing it exhibits a phenomenon of trying to reduce the surface area exposed to the air after being applied to the negative electrode current collector due to the large surface tension of water. As a result, the negative electrode slurry applied on the negative electrode current collector forms a curved surface at the edge portion with a predetermined angle with the surface of the negative electrode current collector inside the slurry. The above curved surface causes the positional energy of the molecules near the liquid surface and the molecules inside the liquid to be different due to the large surface tension of water, and such an energy deviation acts as a factor inhibiting the orientation of graphite using a magnetic field. Therefore, generally when a magnetic field is applied to the negative electrode slurry, the central portion of the negative electrode slurry with a flat exposed surface is realized with high orientation of graphite, while the edge portion region of the negative electrode slurry with a curved surface is realized with low orientation of graphite.

[0087] However, the negative electrode according to the present invention is manufactured through the above-described negative electrode manufacturing apparatus of the present invention, and the crystal planes of the carbon-based negative electrode active material contained in the edge region of the negative electrode slurry are aligned to have a high angle with respect to the surface of the negative electrode current collector. Therefore, the orientation and orientation uniformity of the entire negative electrode active layer are excellent.

[0088] Specifically, the negative electrode active layer of the negative electrode is divided into a flat region S1 located at the center in the width direction of the negative electrode active layer and having a uniform thickness, and a sliding region S2 located at the edge of the negative electrode active layer and having a thickness gradient. At this time, the carbon-based negative electrode active materials contained in the flat region S1 and the sliding region S2 respectively have a high degree of crystal plane orientation, and the degree of these orientations is uniform and can satisfy the following formula 1:

[0089] [Formula 1] 0.9 ≦ [O.I sliding / [O.I center ≦ 1.3

[0090] (In formula 1, O.I sliding represents the degree of alignment (O.I) in the sliding region, O.I center represents the degree of alignment (O.I) in the central region, The above degree of alignment (O.I) is the ratio (I 004 ) of the area (I 110 ) of the peak indicating the (0, 0, 4) crystal plane to the area (I 004 / I 110 ) of the peak indicating the (1, 1, 0) crystal plane when performing XRD measurement on the negative electrode active layer)

[0091] The crystal plane orientation of the carbonaceous negative electrode active material can be determined by crystal plane analysis of the carbonaceous negative electrode active material, such as X-ray diffraction. The degree of alignment (O.I) of the carbonaceous negative electrode active material represented by the above formula (1) is an index indicating the degree to which the crystal structure of the carbonaceous negative electrode active material is aligned in the direction during X-ray diffraction (XRD) measurement. More specifically, it indicates the degree to which the crystal plane showing the plane of the carbonaceous negative electrode active material is aligned with respect to the surface of the negative electrode current collector. For example, when the negative electrode active layer contains graphite as the carbonaceous negative electrode active material, during X-ray diffraction measurement on the electrode sheet, peaks are shown at 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°. These represent the (0,0,2) plane, (1,0,0) plane, (1,0,1)R plane, (1,0,1)H plane, (0,0,4) plane, and (1,1,0) plane among the crystal planes of the graphite contained in the negative electrode active layer. Generally, in the case of graphite, graphene layers are placed on the a-axis and b-axis planes, and such graphene layers are stacked along the c-axis, resulting in a hexagonal or rhombohedral crystal structure. Here, the above crystal plane peaks are peaks indicating the plane characteristics of such a crystal structure. Also, the peak appearing at 2θ = 43.4 ± 0.2° may be considered as the peak corresponding to the (1,0,1)R plane of the carbonaceous negative electrode active material overlapping with the (1,1,1) plane of the negative electrode current collector, for example, copper (Cu). Therefore, it can be excluded when determining the degree of alignment.

[0092] The present invention can measure the degree of alignment (O.I) of a carbon-based negative electrode active material by the area ratio of the peak at 2θ = 54.7 ± 0.2° showing the (0,0,4) plane and the peak at 2θ = 77.5 ± 0.2° showing the (1,1,0) plane, specifically, the ratio of the areas obtained by integrating the intensities of the above peaks. The (0,0,4) plane appearing at 2θ = 54.7 ± 0.2° shows the thickness direction characteristics (c-axis direction characteristics) of the layered structure in which graphite layers are stacked, and the (1,1,0) plane appearing at 2θ = 77.5 ± 0.2° shows the planar characteristics (a / b-axis direction characteristics) of the stacked graphite layers. Therefore, the smaller the peak of the (0,0,4) plane showing the thickness direction characteristics of the graphite layer plane, and the larger the peak of the (1,1,0) plane showing the planar characteristics of the graphite layer, the higher the angle at which the graphite plane is aligned with respect to the surface of the negative electrode current collector. That is, the closer the value of the above degree of alignment (O.I) is to 0, the closer the angle or inclination of the graphite layer plane with respect to the surface of the negative electrode current collector is to 90°, and the larger the value, the closer the inclination with respect to the surface of the negative electrode current collector is to 0° or 180°.

[0093] For example, in the negative electrode according to the present invention, the crystal plane of the carbon-based negative electrode active material contained in the flat region S1 of the negative electrode active layer is aligned at a high angle with respect to the negative electrode current collector, and the degree of alignment (O.I) can be 0.1 to 1.5. Specifically, the above degree of alignment (O.I) can be 0.1 to 1.2, 0.1 to 1.0, 0.1 to 0.5, 0.15 to 0.6, 0.15 to 0.5, 0.2 to 0.5, 0.4 to 0.7, 0.3 to 0.5, 0.4 to 0.9, 0.5 to 0.9, 0.6 to 1.0, 0.7 to 1.0, 0.9 to 1.2, or 0.8 to 1.1. The fact that the degree of alignment (O.I) of the above carbon-based negative electrode active material is 1.5 or less means that when the carbon-based negative electrode active material contains graphite, the crystal plane meaning the graphite layer plane is aligned at a high angle / inclination with respect to the negative electrode current collector, for example, an angle / inclination of 60° or more, 70° or more, 70 to 90°, 80 to 90°, 65 to 85°, or 70 to 85°.

[0094] In addition, the negative electrode according to the present invention not only has a generally low degree of alignment (O.I) of the carbon-based negative electrode active material contained in the negative electrode active layer, but also has excellent uniformity in the degree of alignment (O.I), and satisfies the above formula 1 in the range of 0.9 to 1.3 (that is, 0.9 ≤ [O.I sliding / [O.I center ≤ 1.3). Specifically, the negative electrode active layer of the negative electrode satisfies the above formula 1 in the range of 0.9 to 1.2 (that is, 0.9 ≤ [O.I sliding / [O.I center ≤ 1.2), 0.9 to 1.1 (that is, 0.9 ≤ [O.I sliding / [O.I center ≤ 1.1), 1.0 to 1.3 (that is, 1.0 ≤ [O.I sliding / [O.I center ≤ 1.3), 1.0 to 1.2 (that is, 1.0 ≤ [O.I sliding / [O.I center ≤ 1.2), 1.1 to 1.2 (that is, 1.1 ≤ [O.I sliding / [O.I center ≤ 1.2), 1.2 to 1.3 (that is, 1.2 ≤ [O.I sliding / [O.I center ≤ 1.3), or 1.0 to 1.15 (that is, 1.0 ≤ [O.I sliding / [O.I center ≤ 1.15).

[0095] The above formula 1 represents the ratio of the degree of alignment (O.I) of the carbon-based negative electrode active material contained in the flat region S1 and the sliding region S2 of the negative electrode active layer, and the closer the ratio is to 1, the smaller the deviation.

[0096] The negative electrode manufactured using the conventionally used negative electrode manufacturing apparatus has a phenomenon in which the degree of alignment (O.I sliding ) of the carbon-based negative electrode active material contained in the sliding region of the negative electrode active layer appears to be more than about 1.5 times higher than the degree of alignment (O.I center ) of the carbon-based active material contained in the flat region. The sliding region S2 of the negative electrode active layer can be introduced with a negative electrode tab during the manufacture of the negative electrode. However, the degree of alignment (O.I sliding) is the degree of alignment (O.I center ) of the carbon-based negative electrode active material contained in the flat region S1. When it is higher than this, the sliding region S2 may have relatively lower lithium mobility and electron mobility compared to the flat region S1, so the electrical resistance of the negative electrode tab increases, and the charge-discharge characteristics of the negative electrode may deteriorate.

[0097] However, the negative electrode according to the present invention can minimize the alignment deviation of the carbon-based negative electrode active materials contained in the flat region S1 and the sliding region S2 of the negative electrode active layer by adjusting the alignment ratio of the carbon-based active materials contained in the flat region S1 and the sliding region S2 of the negative electrode active layer to 0.7 to 1.3. Therefore, the negative electrode can uniformly implement lithium mobility and electron mobility in the negative electrode active layer, and thereby can further improve the charge-discharge characteristics of the negative electrode.

[0098] On the other hand, the flat region S1 of the negative electrode active layer is derived from the central portion S1 of the negative electrode slurry during negative electrode manufacturing, has a flat exposed surface shape, and is a region where the average thickness of the negative electrode active layer is uniform, and may have a length ratio of 95% or more of the total length based on the width direction. The flat region is a region that constitutes most of the negative electrode active layer, and may have a length ratio of 96% or more, 97% or more, 98% or more, 99% or more, 99.5% or more, 99% to 99.9%, or 99.5% to 99.99% of the total length based on the width direction of the negative electrode active layer.

[0099] Here, the "width direction of the negative electrode active layer" may mean a direction perpendicular to the running direction (x-axis direction) of the negative electrode current collector during negative electrode manufacturing, and may be the same as the direction from one surface where the negative electrode tab is formed to the opposite surface in the manufactured negative electrode. The present invention can further increase the output and energy density of the lithium secondary battery of the negative electrode by adjusting the length ratio of the flat region S1 to the above range.

[0100] In addition, the sliding region S2 of the negative electrode active layer is derived from the edge portion S2 of the negative electrode slurry during negative electrode manufacturing, has a curved exposed surface shape, and refers to a region having a gradient in which the average thickness of the negative electrode active layer decreases as it progresses outward in the width direction.

[0101] At this time, the sliding region S2 can be sequentially and continuously arranged on both sides of the flat region S1. In some cases, stamping (or notching) of the electrode sheet is performed during the negative electrode manufacturing process, and it can be sequentially and continuously arranged only on one side of the flat region S1.

[0102] In addition, the sliding region S2 may have a length ratio of 5% or less of the total length in the width direction of the negative electrode active layer. Specifically, the sliding region S2 may have a length ratio of 4% or less, 3% or less, 2% or less, 1% or less, 0.5% or less, 0.01% - 1%, or 0.01% - 0.5% of the total length in the width direction of the negative electrode active layer in consideration of the energy density of the negative electrode. The above length ratio is the total length ratio provided based on the width direction of the negative electrode active layer. When the sliding region S2 is provided on both sides of the flat region S1, the length ratio of each sliding region may be halved to 1 / 2 of the above ratio.

[0103] In addition, the sliding region S2 may have a thickness gradient in which the thickness decreases as it goes outward, so that the exposed surface with a curved surface shape may have a predetermined inclination angle with respect to the negative electrode current collector. For example, the sliding region S2 may have an inclination angle of 70° or more with respect to the negative electrode current collector, specifically 75° or more, 80° or more, 85° or more, 70° - 85°, 75° - 80°, 70° - 75°. By adjusting the inclination angle of the exposed surface of the sliding region S2 with respect to the negative electrode current collector within the above range, the present invention can prevent the N / P ratio from reversing at the end of the electrode assembly assembled with the positive electrode and can further improve the adhesive force with the separator at the end of the negative electrode.

[0104] Furthermore, the average thickness of the negative electrode active layer can be 100 μm to 300 μm, specifically 100 μm to 250 μm, or 130 μm to 190 μm, and the above average thickness can be the same as the average thickness of the flat region. By adjusting the average thickness of the negative electrode active layer within the above range, the present invention can uniformly align the crystal planes of the carbon-based negative electrode active material contained in each region, thereby improving the high-rate charge and discharge performance and energy density of the battery including the negative electrode.

[0105] Further, the negative electrode active layer may have a structure in which two separate layers are laminated according to the battery model to which the negative electrode of the present invention is applied and the use of the product, but is not limited thereto.

[0106] Specifically, the negative electrode according to the present invention may have a structure in which a first negative electrode active layer is provided on a negative electrode current collector, and a second negative electrode active layer is provided on the first negative electrode active layer. At this time, the first negative electrode active layer and the second negative electrode active layer each contain a carbon-based negative electrode active material, and the carbon-based negative electrode active materials contained in each layer may be the same or different. When the negative electrode active layer having a two-layer structure is provided on the negative electrode current collector, the composition of each negative electrode active layer can be easily controlled. Therefore, not only can an active material excellent in the energy efficiency of the battery be applied as the negative electrode active material to improve the electrical performance of the negative electrode, but also problems generated thereby (for example, a decrease in the interfacial adhesive force between the negative electrode current collector and the negative electrode active layer) can be improved and / or prevented. There is an advantage that a composition of the negative electrode active layer is possible.

[0107] Further, the negative electrode active layer contains a carbon-based negative electrode active material as a negative electrode active material in order to exhibit electrical activity through a reversible oxidation-reduction reaction during charging and discharging of the battery.

[0108] The carbon-based negative electrode active material means a material mainly composed of carbon atoms, and such a carbon-based negative electrode active material may include graphite. The graphite may include any one or more of natural graphite and artificial graphite.

[0109] As an example, the carbon-based negative electrode active material may include a mixed graphite obtained by mixing natural graphite and artificial graphite. In this case, the mixed graphite may be obtained by mixing natural graphite and artificial graphite at a weight ratio of 10 to 50:50 to 90, or 10 to 30:70 to 90. By adjusting the content ratio of natural graphite and artificial graphite as described above, the mixed graphite can prevent the adhesive force between the negative electrode current collector and the negative electrode active layer from being reduced by natural graphite of less than 10 parts by weight with respect to the total weight, and can prevent the charge and discharge capacity of the negative electrode from being reduced by natural graphite of more than 50 parts by weight.

[0110] In addition, although the form of the carbonaceous negative electrode active material is not particularly limited, it preferably has a spherical graphite granule form formed by aggregation of a plurality of flaky graphites. Examples of the flaky graphite include, in addition to natural graphite and artificial graphite, mesophase-fired carbon (bulk mesophase) using tar pitch as a raw material, cokes (raw coke, green coke, pitch coke, needle coke, petroleum coke, etc.) graphitized ones, etc. In particular, as the carbonaceous negative electrode active material, it is preferable to use a plurality of highly crystalline natural graphites assembled. Further, one graphite granule can be formed by aggregation of 2 to 100, preferably 3 to 20, flaky graphites.

[0111] In addition, the carbonaceous negative electrode active material can exhibit an average particle diameter (D 50 ) of 0.5 μm to 20 μm, specifically, an average particle diameter (D 50 ) of 0.5 μm to 15 μm, 0.5 μm to 10 μm, 5 μm to 20 μm, 10 μm to 20 μm, 12 μm to 18 μm, 2 μm to 7 μm, 0.5 μm to 5 μm, or 1 μm to 3 μm.

[0112] The average particle diameter of graphite can be more advantageous as the particle diameter is made smaller in order to maximize the degree of disorder in the expansion direction for each particle so as to prevent expansion of the particles due to charging of lithium ions. However, when the particle diameter of graphite is less than 0.5 μm, a large amount of binder may be required due to an increase in the number of particles per unit volume. On the other hand, when the maximum particle diameter exceeds 20 μm, the expansion becomes intense and as charge and discharge are repeated, the inter-particle binding property and the binding property between the particles and the current collector decrease, and the cycle characteristics may be greatly reduced.

[0113] Furthermore, the negative electrode according to the present invention may contain a predetermined silicon-based negative electrode active material together with a carbon-based negative electrode active material in the negative electrode active layer. The silicon-based negative electrode active material is a material containing silicon (Si) as a main component, and may include silicon (Si) particles, silicon monoxide (SiO), silicon dioxide (SiO2) particles, silicon carbide (SiC), or a mixture thereof. In some cases, the silicon (Si)-containing particles may mean those further containing silicon carbide (SiC) particles together with silicon (Si) particles, silicon monoxide (SiO), and / or silicon dioxide (SiO2) particles.

[0114] Also, the silicon-based negative electrode active material may be contained in an amount of 0.5 parts by weight to 30 parts by weight, specifically 1 part by weight to 9 parts by weight, 3 parts by weight to 7 parts by weight, 11 parts by weight to 19 parts by weight, 13 parts by weight to 17 parts by weight, 10 parts by weight to 30 parts by weight, 20 parts by weight to 30 parts by weight, 15 parts by weight to 25 parts by weight, or 9 parts by weight to 22 parts by weight, based on 100 parts by weight of the total negative electrode active material. By adjusting the contents of the carbon-based negative electrode active material and the silicon-based negative electrode active material contained in the negative electrode active material within the above ranges, the present invention can improve the charge capacity per unit mass while reducing the lithium consumption amount and the irreversible capacity loss during the initial charge and discharge of the battery.

[0115] On the other hand, the negative electrode active layer according to the present invention may further selectively contain a conductive material, a binder, other additives, etc., as necessary, together with the carbon-based negative electrode active material as the main component.

[0116] The conductive material may include one or more of carbon black such as acetylene black and ketjen black, carbon nanotubes, carbon fibers, etc., but is not limited thereto.

[0117] As an example, the negative electrode active layer may contain carbon black, carbon nanotubes, carbon fibers, etc. as the conductive material alone or in combination.

[0118] At this time, the content of the conductive material can be 0.1 part by weight to 10 parts by weight with respect to 100 parts by weight of the entire negative electrode active layer, specifically, it can be 0.1 part by weight to 8 parts by weight, 0.1 part by weight to 5 parts by weight, 0.1 part by weight to 3 parts by weight, 2 parts by weight to 6 parts by weight, or 0.5 part by weight to 2 parts by weight. By controlling the content of the conductive material within the above range, the present invention can prevent the resistance of the negative electrode from increasing and the charging capacity from decreasing due to a low content of the conductive material, and can also prevent problems such as a decrease in the charging capacity due to a decrease in the content of the negative electrode active material caused by an excessive amount of the conductive material, or a decrease in the rapid charging characteristics due to an increase in the loading amount of the negative electrode active layer.

[0119] In addition, the binder is a component that helps bind the negative electrode active material and the conductive material, etc., and bind to the current collector, and can be preferably applied within a range that does not reduce the electrical physical properties of the electrode. Specifically, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene butadiene rubber (SBR), and fluorine rubber may include any one or more of them.

[0120] The content of the binder can be 0.1 part by weight to 10 parts by weight with respect to 100 parts by weight of the entire negative electrode active layer, specifically, it can be 0.1 part by weight to 8 parts by weight, 0.1 part by weight to 5 parts by weight, 0.1 part by weight to 3 parts by weight, or 2 parts by weight to 6 parts by weight. By controlling the content of the binder contained in the negative electrode active layer within the above range, the present invention can prevent the adhesive force of the active layer from decreasing due to a low content of the binder, or the electrical physical properties of the electrode from decreasing due to an excessive amount of the binder.

[0121] Further, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, fired carbon, etc. can be used. In the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Further, the average thickness of the negative electrode current collector can be preferably applied in the range of 1 μm to 500 μm in consideration of the conductivity and total thickness of the manufactured negative electrode.

[0122] <Method for manufacturing negative electrode for lithium secondary battery>

[0123] Furthermore, in one embodiment, the present invention provides a method for manufacturing a negative electrode for a lithium secondary battery.

[0124] Specifically, the method for manufacturing the negative electrode includes a step of applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector, and a step of applying a magnetic field to the applied negative electrode slurry using the negative electrode manufacturing apparatus of the present invention and drying it to form a negative electrode active layer.

[0125] In the method for manufacturing a negative electrode according to the present invention, by applying a negative electrode slurry containing a carbon-based negative electrode active material onto a negative electrode current collector and applying a magnetic field to the surface of the applied negative electrode slurry, the carbon-based negative electrode active material in the negative electrode slurry can be aligned to have a high angle with respect to the surface of the negative electrode current collector. Thereafter, the negative electrode slurry containing the continuously aligned carbon-based negative electrode active material is dried to form a negative electrode active layer, whereby a negative electrode can be manufactured.

[0126] Here, the step of applying the negative electrode slurry is a step of discharging and coating a negative electrode slurry containing a carbon-based negative electrode active material on the surface of a moving negative electrode current collector, and it is not particularly limited as long as it is a method commonly applied in the art and can be applied. Preferably, the die coating method can be used. The die coating method can be performed by a slot die provided with a shim for controlling the discharge conditions of the negative electrode slurry. In this case, by controlling the shape of the shim, etc., the loading amount, coating thickness, etc. of the negative electrode slurry applied on the negative electrode current collector can be easily controlled.

[0127] Further, the step of forming the negative electrode active layer can be performed by applying a magnetic field to the negative electrode slurry applied using the negative electrode manufacturing apparatus according to the present invention and drying it.

[0128] The magnetic field application can be performed by an orientation unit of the manufacturing apparatus disposed above and below the negative electrode current collector coated with the negative electrode slurry. Here, the degree of alignment (O.I) of the carbon-based negative electrode active material contained in the negative electrode slurry can be adjusted by the intensity of the applied magnetic field, the time exposed to the magnetic field, etc. Therefore, the magnetic field application can be performed under predetermined magnetic field intensity and time conditions.

[0129] As an example, the magnetic field can be applied at an intensity of 2,000 G (Gauss) to 9,000 G (Gauss), more specifically, 2,000 G to 8,000 G, 2,000 G to 7,000 G, 2,000 G to 6,000 G, 4,000 G to 9,000 G, 4,000 G to 7,000 G, 6,000 G to 9,000 G, 2,500 G to 5,500 G, 3,000 G to 5,500 G, 3,500 G to 5,500 G, 4,000 G to 5,500 G, 3,500 G to 4,500 G, or 4,500 G to 5,000 G.

[0130] As another example, the magnetic field can be applied for 5 seconds to 60 seconds, specifically, 10 seconds to 60 seconds, 10 seconds to 30 seconds, 30 seconds to 60 seconds, 40 seconds to 50 seconds, 15 seconds to 35 seconds, or 10 seconds to 50 seconds.

[0131] For example, the magnetic field can be applied to the negative electrode slurry at a strength of 4,700 ± 100 G for 12 to 33 seconds.

[0132] Also, the drying of the negative electrode slurry may vary in drying timing and method depending on the position where the negative electrode slurry is applied. Specifically, the edge portion of the negative electrode slurry is pre-dried by light energy simultaneously or continuously with the application of the magnetic field, and then the entire surface of the negative electrode slurry can be completely dried by thermal energy immediately after the application of the magnetic field. A more detailed description of this is the same as the content described in the above-mentioned negative electrode manufacturing apparatus, so it is omitted.

[0133] The method for manufacturing a negative electrode according to the present invention may further include a step of rolling the dried negative electrode slurry. The step of rolling is a step of increasing the density of the negative electrode active layer by applying pressure to the dried negative electrode slurry using a roll press or the like. At this time, the rolling can be performed under temperature conditions higher than room temperature.

[0134] Specifically, the rolling can be performed at a temperature of 40°C to 100°C, more specifically 60°C to 100°C, 75°C to 100°C, 85°C to 100°C, 50°C to 90°C, 60°C to 80°C, 65°C to 90°C, 40°C to 70°C, or 40°C to 60°C.

[0135] Also, the rolling can be performed at a rolling speed of 2 m / s to 7 m / s, more specifically 2 m / s to 6.5 m / s, 2 m / s to 6 m / s, 2 m / s to 5.5 m / s, 2 m / s to 5 m / s, 2 m / s to 4.5 m / s, 2 m / s to 4 m / s, 2.5 m / s to 4 m / s, 2.5 m / s to 3.5 m / s, 3.5 m / s to 5 m / s, 5 m / s to 7 m / s, 5.5 m / s to 6.5 m / s, or 6 m / s to 7 m / s.

[0136] Further, the rolling can be performed under pressure conditions of 50 MPa to 200 MPa, specifically, under pressure conditions of 50 MPa to 150 MPa, 50 MPa to 100 MPa, 100 MPa to 200 MPa, 150 MPa to 200 MPa, or 80 MPa to 140 MPa.

[0137] The present invention can increase the energy density of the negative electrode while minimizing the change in the alignment degree of the carbon-based negative electrode active material contained in the negative electrode active layer formed by performing rolling of the dried negative electrode slurry under the above temperature, speed, and / or pressure conditions.

[0138] Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples.

[0139] However, the following Examples and Experimental Examples are illustrative of the present invention, and the content of the present invention is not limited to the following Examples and Experimental Examples.

[0140] Examples 1 to 6 and Comparative Examples 1 to 2. Production of negative electrode for lithium secondary battery

[0141] First, natural graphite and artificial graphite were respectively prepared as carbon-based negative electrode active materials, and a negative electrode slurry was produced using the prepared carbon-based negative electrode active materials.

[0142] Specifically, mixed graphite obtained by mixing natural graphite and artificial graphite at a weight ratio of 2:8 was prepared as the negative electrode active material, carbon black was prepared as the conductive material, and carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) were prepared as the binder. Then, 95 parts by weight of mixed graphite, 1 part by weight of carbon black, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 2.5 parts by weight of styrene-butadiene rubber (SBR) were mixed with water so that the solid content was 50% to produce a negative electrode slurry.

[0143] Once the negative electrode slurry was prepared, it was cast onto a copper thin plate (thickness: 10 μm, length in the width direction: about 550 mm) being roll-to-roll transferred (transfer speed: 5 m / min) using a die coater. The negative electrode slurry (average thickness: 180 μm to 200 μm, length in the width direction: 500 mm) was cast. A magnetic field of 6,000 ± 100 G was applied to the negative electrode slurry cast on the copper thin plate using a negative electrode manufacturing apparatus for 15 to 30 seconds and dried to form a negative electrode active layer. Here, with respect to the formed negative electrode active layer, a region having a length ratio of 98.5% based on the length in the width direction of the negative electrode active layer was set as a flat region at the center, and regions arranged at a total length ratio of 1.5% on both sides of the flat region (each having a length ratio of 0.75%) were set as sliding regions. Then, the negative electrode active layer was rolled at 50 ± 1 °C under a pressure of 100 to 150 MPa and a transfer speed of 3 m / s to manufacture a negative electrode for a lithium secondary battery.

[0144] However, the negative electrode manufacturing apparatus used for magnetic field application and drying of the negative electrode slurry has a first magnet part and a second magnet part respectively arranged above and below the copper thin plate, and the ratio of the width direction lengths of the first magnet part and the second magnet part based on the width direction length of the negative electrode slurry (1) was adjusted as shown in Table 1.

[0145] In addition, the negative electrode manufacturing apparatus includes a first drying part including a far-infrared dryer (output density: 150 kW / m 2 and 180 kW / m 2 ) on the side surface of the width direction edge of the first magnet part, and includes a second dryer including a hot air dryer on the outlet side of the orientation part (that is, the first magnet part and the second magnet part). At this time, the light irradiation region of the far-infrared dryer of the first drying part was adjusted to be the edge part of the negative electrode slurry. Further, the negative electrode manufacturing apparatus adjusted (2) whether to include the first drying part, (3) the position of the first drying part in the first magnet part (the first section / the second section / the third section), (4) the arrangement form of the first drying part, and (5) the separation distance between the outlet of the orientation part and the inlet of the second drying part as shown in Table 1 below.

[0146]

Table 1

[0147] Experimental Example

[0148] The orientation and orientation uniformity of the carbon-based negative electrode active material contained in the negative electrode active layer of the negative electrode according to the present invention were evaluated.

[0149] Specifically, for the negative electrodes manufactured in Examples 1 to 6 and Comparative Examples 1 and 2, X-ray diffraction spectroscopy (XRD) was performed on the flat region and the sliding region of the negative electrode active layer to measure the spectrum. At this time, the measurement conditions for the above X-ray diffraction (XRD) are as follows:

[0150] - Target: Cu(Kα-ray) graphite monochromator - Slit: Divergence slit = 1°, Receiving slit = 0.1 mm, Scattering slit = 1° - Measurement area: (1,1,0) plane: 76.5° < 2θ < 78.5° (0,0,4) plane: 53.5° < 2θ < 56.0°

[0151] From the spectrum measured under the above conditions, the alignment degree of the carbon-based negative electrode active material for each region according to Equation 2 was calculated, and the ratio of the alignment degree (O.I sliding ) in the sliding region to the alignment degree (O.I center ) in the flat region was calculated. The results are shown in Table 2.

[0152] [Equation 2] O.I = I 004 / I 110

[0153] In Equation 2, I 004 represents the area of the peak indicating the (0,0,4) crystal plane during the X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer, and I 110 represents the area of the peak indicating the (1,1,0) crystal plane during the X-ray diffraction spectroscopy (XRD) measurement of the negative electrode active layer.

[0154] [Table 2]

[0155] As shown in Table 2 above, it can be seen that the negative electrode for a lithium secondary battery according to the present invention is excellent in the orientation of the carbon-based negative electrode active material contained in the negative electrode active layer and has high orientation uniformity.

[0156] Specifically, the negative electrode of the comparative example without the first drying part has an alignment degree (O.I center ) of the carbon-based negative electrode active material contained in the flat region of the negative electrode active layer exceeding 2.5, and the alignment degree ratio of the flat region and the sliding region showing the orientation uniformity of the carbon-based negative electrode active material is shown to be 1.5 or more.

[0157] On the other hand, the negative electrode of the example provided with the first drying part has an alignment degree (O.I center ) of the carbon-based negative electrode active material contained in the flat region of the negative electrode active layer less than 2.4, and the alignment degree ratio of the flat region and the sliding region showing the orientation uniformity of the carbon-based negative electrode active material is shown to be 1.3 or less.

[0158] Further, in the negative electrode of the example, i) the length in the width direction of the magnet part is longer than the length in the width direction of the negative electrode slurry, ii) the first drying part is arranged in a form mixed with the unit magnet in the second section of the magnet part, and iii) it was confirmed that the higher the angle at which the plane crystal plane of the carbon-based negative electrode active material contained in the negative electrode active layer is uniformly aligned perpendicular to the negative electrode current collector as the separation distance between the orientation part and the second drying part is narrower.

[0159] From these results, it can be seen that the negative electrode manufacturing apparatus according to the present invention can highly embody the crystal plane orientation of the carbon-based negative electrode active material contained in the sliding region of the negative electrode active layer, and thus can manufacture a negative electrode excellent in the overall orientation and orientation uniformity of the negative electrode active layer. Further, it can be seen that the manufactured negative electrode is uniformly excellent in the lithium mobility and electron mobility of the negative electrode active layer, and thus has excellent charge and discharge performance.

[0160] In the above, the preferred embodiments of the present invention have been described. However, those skilled in the art or those with ordinary knowledge in the art can understand that the present invention can be variously modified and changed without departing from the spirit and technical scope of the present invention described in the claims described below.

[0161] Therefore, the technical scope of the present invention is not limited to the content described in the summary of the invention in the specification, and can be defined by the claims.

Explanation of Reference Numerals

[0162] 10: Negative electrode manufacturing apparatus 20: Transfer section 30: Coating section 110: Alignment section 110a and 110b: First magnet section and second magnet section 111a and 111b: Plurality of unit magnets 112a and 112b: Support section 120: Drying section 121: First drying section 122: Second drying section S: Negative electrode slurry S1: Flat region of the negative electrode slurry S2: Sliding region of the negative electrode slurry G: Carbon-based negative electrode active material C: Negative electrode current collector M: Magnetic field E: Light energy 111a-1 and 111b-1: First section of the first magnet section and second magnet section and / or unit magnets included in this section 111a-2 and 111b-2: Second section of the first magnet section and second magnet section and / or unit magnets included in this section 111a-3 and 111b-3: Third section of the first magnet section and second magnet section and / or unit magnets included in this section 111a’ and 111b’: Unit magnets forming a row with the first drying section on the edge side surfaces of the second section of the first magnet section and second magnet section

Claims

1. An aligning section for applying a magnetic field to the upper and lower portions of an electrode sheet coated with a carbon-based negative electrode active material slurry, and a drying section for drying the negative electrode active material slurry of the electrode sheet to which the magnetic field is applied by the aligning section, the drying section includes a first drying section and a second drying section, and the first drying section preliminarily dries the edge portion of the negative electrode active material slurry when a magnetic field is applied to the electrode sheet by the aligning section, the second drying section dries the entire surface of the negative electrode active material slurry after the magnetic field application by the aligning section is completed. A manufacturing apparatus for a negative electrode of a lithium secondary battery.

2. The aligning section includes a first magnet section and a second magnet section respectively disposed on the upper and lower portions of the electrode sheet, the first magnet section and the second magnet section include a plurality of unit magnets arranged along the transfer direction and the width direction of the electrode sheet. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to Claim 1.

3. The first magnet section and the second magnet section have a length of 0.5 m to 10 m along the transfer direction of the electrode sheet. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to Claim 2.

4. The first magnet section and the second magnet section each have a width direction length ratio of 105% to 150% based on the width direction length of the negative electrode active material slurry. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to Claim 2.

5. The first drying section is disposed alone at the width direction edge of the magnet section along the transfer direction of the electrode sheet, or is arranged to form a column by being mixed with the unit magnets at the width direction edge of the magnet section. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to any one of Claims 2 to 4.

6. The first magnet section and the second magnet section are each based on the point where the electrode sheet is introduced along the transfer direction of the electrode sheet, a first section corresponding to a magnet section length ratio of 0% to 10%, a second section corresponding to a magnet section length ratio of 10% to 90%, and a third section corresponding to a magnet section length ratio of 90% to 100%, the first drying section is disposed in the second section of any one of the first magnet section and the second magnet section. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to Claim 5.

7. The first drying section includes one or more of an ultraviolet dryer, a near-infrared dryer, and a far-infrared dryer. The manufacturing apparatus for a negative electrode of a lithium secondary battery according to Claim 1.

8. The manufacturing apparatus for a negative electrode for a lithium secondary battery according to claim 1, wherein the second drying unit is disposed adjacent to the end of the alignment unit where the electrode sheet applied with a magnetic field is carried out.

9. The manufacturing apparatus for a negative electrode for a lithium secondary battery according to claim 1, wherein the second drying unit includes one or more of a hot air dryer, a vacuum oven, and a heater.

10. A negative electrode current collector, and a negative electrode active layer provided on at least one surface of the negative electrode current collector and containing a carbon-based negative electrode active material. A negative electrode for a lithium secondary battery manufactured by the manufacturing apparatus according to claim 1.

11. The negative electrode active layer is divided into a flat region located at the center in the width direction of the negative electrode active layer and having a uniform thickness, and a sliding region located at the edge of the negative electrode active layer and having a thickness gradient. The flat region and the sliding region of the negative electrode active layer satisfy the following formula 1, and the negative electrode for a lithium secondary battery according to claim 10: [Formula 1] 0.9 ≤ [O.I ｓｌｉｄｉｎｇ / [O.I ｃｅｎｔｅｒ ≤ 1.3 In formula 1, O.I ｓｌｉｄｉｎｇ represents the degree of alignment (O.I) in the sliding region, O.I ｃｅｎｔｅｒ represents the alignment degree (O.I) in the flat region, The degree of alignment (O.I) is the ratio (I ００４ / ) of the area (I １１０ ) of the peak indicating the (0, 0, 4) crystal plane to the area (I ００４ ) of the peak indicating the (1, 1, 0) crystal plane during XRD measurement with respect to the negative electrode active layer. １１０ ) is shown.

12. The flat region of the negative electrode active layer has an alignment degree (O.I ｃｅｎｔｅｒ ), which is 0.1 to 1.

5. The negative electrode for a lithium secondary battery according to claim 11.

13. The flat region of the negative electrode active layer has a ratio of 95% or more of the total length in the width direction of the negative electrode active layer, and The sliding region of the negative electrode active layer has a ratio of 5% or less of the total length in the width direction of the negative electrode active layer, and the negative electrode for a lithium secondary battery according to claim 11.

14. The carbon-based negative electrode active material includes one or more of natural graphite and artificial graphite, and the negative electrode for a lithium secondary battery according to claim 10.

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