阅读说明：本技术 用于锂二次电池的负极和包括该负极的锂二次电池 (Negative electrode for lithium secondary battery and lithium secondary battery including the same ) 是由 李珍宪 金洪廷 严惠悧 李相俊 林大燮 于 2020-04-17 设计创作，主要内容包括：本发明涉及一种用于锂二次电池的负极和包括该负极的锂二次电池。用于锂二次电池的负极包括集流体以及形成在集流体上并且包括碳基负极活性物质的负极活性物质层,其中,负极活性物质层具有三个层或更多个层的多层结构,并且负极活性物质层中的至少一个层是发散度(DD)为19或更大的取向层,DD由下式1定义：[式1]发散度(DD)＝(I-(a)/I-(总))×100(在式1中,I-(a)是使用CuKα射线通过XRD测量的非平面角度处的峰强度的总和,I-(总)是使用CuKα射线通过XRD测量的所有角度处的峰强度的总和)。(The present invention relates to an anode for a lithium secondary battery and a lithium secondary battery including the same. The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer formed on the current collector and including a carbon-based negative electrode active material, wherein the negative electrode active material layer has a multilayer structure of three or more layersAnd at least one layer in the anode active material layer is an alignment layer having a divergence (DD) of 19 or more, the DD being defined by the following formula 1: [ formula 1]Divergence (DD) ═ I a /I General assembly ) X 100 (in formula 1, I) a Is the sum of the peak intensities at non-planar angles measured by XRD using CuK alpha rays, I General assembly Is the sum of the peak intensities at all angles measured by XRD using CuK α rays).)

1. An anode for a lithium secondary battery, comprising:

a current collector; and

a negative electrode active material layer formed on the current collector and including a carbon-based negative electrode active material,

wherein the anode active material layer has a multilayer structure of three or more layers,

at least one of the anode active material layers is an alignment layer having a DD (divergence) value of 19 or more as defined by equation 1:

[ equation 1]

DD (divergence) ═ I_a/I_{General assembly})×100

(in the case of equation 1,

I_ais the sum of the peak intensities at non-planar angles measured by XRD using CuK alpha rays, and

I_{general assembly}Is the sum of the peak intensities at all angles measured by XRD using CuK α rays).

2. The anode for a lithium secondary battery according to claim 1, wherein the active material layer is a multilayer structure of three layers or five layers.

3. The anode for a lithium secondary battery according to claim 1, wherein the anode active material layer of the multilayer structure having three or more layers includes an inner layer in contact with the current collector, a surface layer, and at least one intermediate layer between the inner layer and the surface layer, and the surface layer is the alignment layer having the DD value of 19 or more.

4. The anode for a lithium secondary battery according to claim 1, wherein the alignment layer has a DD value of 19 to 60.

5. The negative electrode for a lithium secondary battery according to claim 1, wherein the I_aIs the sum of peak intensities at 42.4 ± 0.2 °, 43.4 ± 0.2 °, 44.6 ± 0.2 ° and 77.5 ± 0.2 ° measured by XRD using CuK α ray,

said I_{General assembly}Is the sum of peak intensities at 26.5 ± 0.2 °, 42.4 ± 0.2 °, 43.4 ± 0.2 °, 44.6 ± 0.2 °, 54.7 ± 0.2 ° and 77.5 ± 0.2 ° measured by XRD using CuK α rays.

6. The anode for a lithium secondary battery according to claim 1, wherein the peak intensity is a peak integrated area value.

7. The anode for a lithium secondary battery according to claim 1, wherein at least one layer of the anode active material layers is an alignment layer having the DD value of 19 or more, and at least one layer is a non-alignment layer having the DD value of less than 19.

8. The negative electrode for a lithium secondary battery according to claim 1, wherein the peak intensity ratio I of the negative electrode at the (002) plane to the (110) plane is measured by XRD using CuK α ray₍₀₀₂₎/I₍₁₁₀₎Is 50 to 300.

9. The negative electrode for a lithium secondary battery according to claim 1, wherein the oriented layer has a peak intensity ratio I at a (002) plane to a (110) plane as measured by XRD using CuK α rays₍₀₀₂₎/I₍₁₁₀₎Is 10 to 200.

10. The negative electrode for a lithium secondary battery according to claim 7, wherein the non-oriented layer has a peak intensity ratio I at a (002) plane to a (110) plane as measured by XRD using CuK α rays₍₀₀₂₎/I₍₁₁₀₎Is 200 to 500.

11. The anode for a lithium secondary battery according to claim 1, wherein the anode active material layer has a total thickness of 100 μm to 1000 μm.

12. The negative electrode for a lithium secondary battery according to claim 1, wherein the carbon-based negative electrode active material is artificial graphite or a mixture of artificial graphite and natural graphite.

13. The anode for a lithium secondary battery according to claim 1, wherein the anode active material layer further comprises a Si-based anode active material, a Sn-based anode active material, lithium vanadium oxide, or a combination thereof.

14. A lithium secondary battery comprising:

the negative electrode according to any one of claims 1 to 13;

a positive electrode; and

an electrolyte.

15. The lithium secondary battery according to claim 14, wherein the lithium secondary battery is a high power battery.

Technical Field

The present invention relates to an anode for a lithium secondary battery and a lithium secondary battery including the same.

Background

Lithium secondary batteries have recently received attention as power sources for small portable electronic devices, and the lithium secondary batteries use organic electrolyte solutions, and thus the discharge voltage of the lithium secondary batteries is twice or more higher than that of conventional batteries using alkaline aqueous solutions, and thus the lithium secondary batteries have high energy density.

For a positive active material of a rechargeable lithium battery, an oxide including lithium and a transition metal to have a structure capable of intercalating/deintercalating lithium ions, such as LiCoO, has been mainly used₂、LiMn₂O₄、LiNi_1-xCo_xO₂(0<x<1) And the like.

For the anode active material, various carbon-based materials capable of intercalating/deintercalating lithium ions (such as artificial graphite, natural graphite, hard carbon, etc.) have been used, and in order to obtain a high capacity, a non-carbon-based anode active material (such as silicon or tin) has recently been studied.

Disclosure of Invention

Technical problem

One embodiment provides an anode for a lithium secondary battery, which exhibits excellent physical properties such as good adhesion and good electrolyte impregnation.

Another embodiment provides a lithium secondary battery including the anode.

Technical scheme

An embodiment provides an anode for a lithium secondary battery including: a current collector; and an anode active material layer including a carbon-based anode active material, wherein the anode active material layer has a multilayer structure of three or more layers, and at least one layer in the anode active material layer is an alignment layer having a DD (divergence) value of 19 or more as defined by equation 1.

[ equation 1]

DD (divergence) ═ I_a/I_{General assembly})×100

(in the case of equation 1,

I_ais the sum of the peak intensities at non-planar angles measured by XRD using CuK alpha rays, and

I_{general assembly}Is the sum of the peak intensities at all angles measured by XRD using CuK α rays. )

The active material layer may be a multilayer structure of three layers or five layers.

The negative active material layer having a multilayer structure of three or more layers may have an inner layer in contact with a current collector, a surface layer, and at least one intermediate layer between the inner layer and the surface layer, and the surface layer may be an alignment layer having a DD value of 19 or more.

The alignment layer may have a DD value of 19 to 60.

I_aMay be the sum of peak intensities at 42.4 ± 0.2 °, 43.4 ± 0.2 °, 44.6 ± 0.2 ° and 77.5 ± 0.2 ° of 2 θ measured by XRD using CuK α ray, and I_{General assembly}May be 26.5 ± 0.2 °, 42.4 ± 0.2 °, 43.4 ± 0.2 °, 44.6 ± 0.2 °, 54.7 ±) as measured by XRD using CuK α raysThe sum of the peak intensities at 0.2 ° and 77.5 ± 0.2 °.

The peak intensity may be a peak integrated area value.

At least one layer of the anode active material layer may be an alignment layer having a DD value of 19 or more, and at least one layer may be a non-alignment layer having a DD value of less than 19.

When measured by XRD using CuK α ray, the peak intensity ratio of the negative electrode at the (002) plane to the (110) plane (i.e., I)₍₀₀₂₎/I₍₁₁₀₎) And may be 50 to 300.

When measured by XRD using CuK α rays, the peak intensity ratio of the orientation layer at the (002) plane to the (110) plane (i.e., I)₍₀₀₂₎/I₍₁₁₀₎) May be 10 to 200. When measured by XRD using CuK α ray, the peak intensity ratio of the non-oriented layer at the (002) plane to the (110) plane (i.e., I-₍₀₀₂₎/I₍₁₁₀₎) May be 200 to 500.

The anode active material layer may have a total thickness of 100 μm to 1000 μm.

The second carbon-based negative active material may be artificial graphite or a mixture of artificial graphite and natural graphite.

In addition, the anode active material layer may further include a Si-based anode active material, a Sn-based anode active material, lithium vanadium oxide, or a combination thereof.

Another embodiment provides a lithium secondary battery including a negative electrode, a positive electrode including a positive electrode active material; and an electrolyte.

The lithium secondary battery may be used for high power.

Other embodiments are included in the detailed description below.

Advantageous effects

The anode for a lithium secondary battery according to one embodiment may provide a lithium secondary battery exhibiting excellent battery performance.

Drawings

FIG. 1 is a schematic diagram illustrating an orientation according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing a structure of an anode according to an embodiment of the present invention.

Fig. 3 is a schematic view of the orientation of the negative electrode according to an embodiment of the present invention.

Fig. 4 is a schematic view illustrating a structure of a lithium secondary battery according to an embodiment.

Detailed Description

Hereinafter, embodiments of the present invention are described in detail. However, these embodiments are exemplary, the present invention is not limited thereto, and the present invention is defined by the scope of the claims.

The anode according to one embodiment of the present invention includes a current collector and an anode active material layer formed on the current collector and including a carbon-based anode active material, the anode active material layer having a multilayer structure of three or more layers, and at least one layer of the anode active material layer is an alignment layer having a DD (Divergence of Divergence) value of 19 or more.

The DD value may be defined by equation 1.

[ equation 1]

DD (divergence) ═ I_a/I_{General assembly})×100

In the case of the equation 1, the,

I_ais the sum of the peak intensities at non-planar angles measured by XRD using CuK alpha rays,

I_{general assembly}Is the sum of the peak intensities at all angles measured by XRD using CuK α rays.

Here, when measured by XRD using CuK α rays, the non-planar angles represent 42.4 ± 0.2 °, 43.4 ± 0.2 °, 44.6 ± 0.2 °, and 77.5 ± 0.2 °, that is, the (100) plane, (101) R plane, (101) H plane, and (110) plane. Generally, graphite has a structure classified into a diamond structure and a hexagonal structure having an ABAB type lamination order according to the lamination order of graphene layers, the R face represents the diamond structure, and the H face represents the hexagonal structure.

In addition, when measured by XRD using CuK α rays, peaks at all angles (representing 2 θ ═ 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 °, that is, (002), (100), (101) R, (101) H, (004), and (110) planes, and 2 θ ═ 43.4 ± 0.2 ° can also be considered to occur because a peak of the (101) R plane of the carbon-based material overlaps with another peak of the (111) plane of the current collector (e.g., Cu).

Typically, the peak intensity indicates the height of the peak or the integrated area of the peak, and according to an embodiment, the peak intensity indicates the integrated area of the peak.

In the examples, XRD was measured under measurement conditions of a scanning speed (°/S) of 0.044 to 0.089 and a step size (°/step) of 0.013 to 0.039 by using CuK α rays as target rays, but the monochromator was removed in order to improve peak intensity resolution.

The DD value indicates that the anode active material included in the anode active material layer is oriented at a predetermined angle, and a larger value indicates that the anode active material is well oriented. That is, as schematically shown in fig. 1, when the anode active material 3 is oriented at an angle (α) to one side of the substrate 1, the angle (α) increases as the DD value increases. Further, the DD value is maintained after charge and discharge.

In one embodiment, the DD value may be 19 to 60, or may be 19 to 40. The DD value of the alignment layer satisfying the above range indicates that the anode active material is aligned at a predetermined angle, which is maintained after charge and discharge.

When the DD value of the alignment layer is greater than 19, the negative electrode active material is not horizontally aligned with respect to the current collector, but is sufficiently aligned to easily transfer lithium ions, that is, the negative electrode active material is arranged at a predetermined angle with respect to the current collector, for example, it indicates that the (002) plane of graphite is arranged at an angle greater than 0 degrees (°) and less than 90 degrees (°), which indicates that non-alignment is controlled, and the DD value of less than 19 increases direct current internal resistance, drastically deteriorates rate performance (particularly high rate performance), and deteriorates cycle life characteristics. In addition, the DD value of 19 or more and 60 or less does not indicate that the negative active material is substantially vertically oriented with respect to the current collector, and if it is vertically oriented, disadvantages such as deformation of the battery may occur as the charge and discharge processes are repeated.

The anode active material layer may have a multi-layer structure of three or more layers, and in one embodiment, the anode active material layer may have a multi-layer structure of three to five layers. In the multilayer structure, at least one layer may be an alignment layer having a DD value of 19 or more.

Here, the negative active material layer having a multilayer structure of three or more layers may include an inner layer contacting the current collector, a surface layer, and at least one intermediate layer between the inner layer and the surface layer, and it is desirable that the surface layer is an alignment layer having a DD value of 19 or more. When shown based on fig. 2, the anode 30 has a structure in which a current collector 32, an inner layer 34, an intermediate layer 36, and a surface layer 38 are sequentially stacked, where the surface layer 38 is an alignment layer having a DD value of 19 or more.

When the surface layer is an orientation layer, that is, has a high degree of orientation of the anode active material, the anode active material is not oriented horizontally and parallel with respect to the current collector, but is positioned in a standing state at a predetermined angle with respect to the current collector, which allows easy impregnation of the electrolyte into the anode active material layer, thereby easily transporting lithium ions, and shortening the transport path, and therefore, the resulting anode can be suitably used as a high-power battery, and can exhibit excellent high-rate performance characteristics.

If the surface layer is not an orientation layer, i.e., is a non-orientation layer indicating non-dispersion in various ways in which the negative active material is oriented horizontally and parallel with respect to the current collector or positioned vertically with respect to the current collector, impregnation of the electrolyte may be deteriorated and a transport path of lithium ions may be increased, and thus, it may be unsuitable for use as a high power battery.

In the anode active material layer, at least one layer may be an alignment layer having a DD value of 19 or more, and at least one layer may be a non-alignment layer having a DD value of less than 19. As such, when the anode active material layer has a multilayer structure of three or more layers and has both an alignment layer and a non-alignment layer, uniformity of reaction in the same layer can be ensured, and migration of the binder during drying can be suppressed, so that cohesion at the boundary portion between the alignment layer and the non-alignment layer can be increased to improve adhesion, electronic resistance of the active material layer (including the active material, the binder, and the optional conductive material, and referred to as the active material layer on the current collector) can also be reduced, and ionic resistance of the anode can be reduced. Even if the anode active material layer has a multilayer structure, if an oriented portion and a non-oriented portion are present together in the same layer but not in separate layers, during drying, migration of a binder occurs in the oriented portion/non-oriented portion, resulting in a decrease in adhesiveness, the ion resistance of the anode may increase, and impregnation of an electrolyte in the oriented portion is different from impregnation in the non-oriented portion, resulting in an increase in reaction non-uniformity, and local non-uniformity of thickness at the time of full charge and precipitation of lithium during charge at a high rate.

Further, even if the anode active material layer has a multilayer structure and has an alignment layer and a non-alignment layer, if the structure is a two-layer structure (i.e., one alignment layer and one non-alignment layer), it is difficult to suppress the migration of the binder during drying, so that the ionic resistance and the electronic resistance of the active material layer in the electrode may increase.

According to one embodiment, the anode active material layer may include three or more layers, or three to five layers, and if the number of layers is an odd number, when the surface is referred to as a first layer, the alignment layer may correspond to the first layer, a third layer, and a fifth layer, and the non-alignment layer may correspond to the second layer and a fourth layer.

Further, when the anode active material layer includes four layers, the first layer and the fourth layer may be alignment layers, and the second layer and the third layer may be non-alignment layers.

When measured by XRD using CuK α ray, the peak intensity ratio of the negative electrode at the (002) plane to the (110) plane (i.e., I)₍₀₀₂₎/I₍₁₁₀₎) And may be 50 to 300. When the negative electrode is in I₍₀₀₂₎/I₍₁₁₀₎When the above range is satisfied, reduction in internal resistance, improvement in high rate performance and cycle life characteristics, and reduction in the active material layer in the electrode can be obtained.

Further, when measured by XRD using CuK α rays, the peak intensity ratio of the oriented layer in the (002) plane to the (110) plane (i.e., I;)₍₀₀₂₎/I₍₁₁₀₎) May be 10 to 200. When aligning layer I₍₀₀₂₎/I₍₁₁₀₎Satisfy the aboveIn the range, reduction in internal resistance, improvement in high rate performance and cycle life characteristics, and reduction in the active material layer in the electrode can be obtained.

When measured by XRD using CuK α ray, the peak intensity ratio of the non-oriented layer at the (002) plane to the (110) plane (i.e., I-₍₀₀₂₎/I₍₁₁₀₎) May be 200 to 500. When not in alignment layer I₍₀₀₂₎/I₍₁₁₀₎When included in this range, the contact of the active material particles with each other may be increased to lower the impedance of the active material in the electrode.

In an embodiment, the DD value is not the peak at the non-plane relative to the peak at all angles, and therefore is not compared to the I₍₀₀₂₎/I₍₁₁₀₎Associated, therefore, I of 50 to 300₍₀₀₂₎/I₍₁₁₀₎It is not intended that the DD values of the first and second layers are within the above-mentioned ranges.

Further, the total thickness of the anode active material layer may be 100 μm to 1000 μm. In this manner, the anode active material layer can be formed with a maximum thickness of 1000 μm which is greatly larger than the general maximum thickness of 70 μm of the anode active material layer. The anode active material layer is a multilayer structure of three or more layers, which is desirable if the total thickness of all the active material layers falls within this range, but the thickness of each layer is not limited. In one embodiment, the anode active material layer is formed in a multi-layer structure of three or more layers, where the DD value of the surface layer is controlled to 19 or more to improve impregnation of the electrolyte, and thus high-rate charge and discharge can be effectively performed even if a thick layer is formed, and thus, it can be suitably applied to a high power battery.

In one embodiment, the DD value is obtained by: charging and discharging a rechargeable lithium battery including a negative electrode; disassembling the battery to obtain a negative electrode when the battery is completely discharged; and measuring the negative electrode by XRD. Here, the charge and discharge are performed once to twice at about 0.1C to about 0.2C.

The negative electrode may have a BET specific surface area of less than about 5.0m²In terms of/g, or about 0.6m²G to about 2.0m²(ii) in terms of/g. When the BET specific surface area of the negative electrode is less than about 5.0m²At the time of/g, can improveElectrochemical cycle life characteristics of the battery. In an embodiment, BET may be measured in a nitrogen adsorption method by the following steps: charging and discharging a lithium secondary battery including a negative electrode; fully discharging the battery to less than or equal to about 3V; disassembling the battery to obtain a negative electrode; cutting the negative electrode into a predetermined size; and placing the cut negative electrode into a BET sample holder.

The negative electrode may have about 6mg/cm²To about 65mg/cm²Cross-sectional load level (L/L).

In the negative electrode active material, the carbon-based negative electrode active material may be artificial graphite or a mixture of artificial graphite and natural graphite. When the anode active material is a crystalline carbon-based material (such as artificial graphite or a mixture of natural graphite and artificial graphite), the crystalline carbon-based material has more developed crystalline characteristics than the amorphous carbon-based active material, and thus the orientation characteristics of the carbon material in the electrode with respect to an external magnetic field can be further improved. The artificial graphite or the natural graphite may be amorphous, plate-shaped, flake-shaped, spherical, fibrous, or a combination thereof without particular limitation. Further, the artificial graphite is mixed with the natural graphite in a ratio of about 70 wt% to 30 wt% to about 95 wt% to 5 wt%.

In addition, the anode active material layer may include at least one non-carbon-based material from among a Si-based anode active material, a Sn-based anode active material, or a lithium vanadium oxide anode active material. When the anode active material layer further includes these materials (i.e., a carbon-based anode active material as the first anode active material and a non-carbon-based material as the second anode active material), the first anode active material and the second anode active material may be mixed in a weight ratio of about 50:50 to about 99: 1.

The Si-based negative active material may be Si, Si-C composite, or SiO_x(0<x<2) And an Si-Q alloy (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, but is not Si), and the Sn-based negative electrode active material is selected from the group consisting of Sn, SnO, and₂Sn-R alloy (wherein R is selected from alkali metal, alkaline earth metal, group 13 element, and group 14 element)Elements of group 15, group 16, transition metals, rare earth elements, and combinations thereof, but not Si), and the like, and the Sn-based negative electrode active material is also selected from at least one of them and SiO₂A mixture of (a). The elements Q and R may be selected from Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po and combinations thereof.

In the anode active material layer, the amount of the anode active material may be about 95 wt% to about 99 wt% based on the total weight of each layer, so that it may be about 95 wt% to about 99 wt% based on the total weight of the anode active material layer.

The anode active material layer includes a binder, and may further include a conductive material. In the anode active material layer, the amount of the binder may be about 1 wt% to about 5 wt% based on the total weight of the anode active material layer. In addition, when the conductive material is further included, about 90 wt% to about 98 wt% of the negative active material, about 1 wt% to about 5 wt% of the binder, and about 1 wt% to about 5 wt% of the conductive material may be included.

The binder improves the binding property of the negative electrode active material particles to each other and the binding property of the negative electrode active material particles to the current collector. The binder may be a non-aqueous binder, an aqueous binder, or a combination thereof.

The non-aqueous binder may be an ethylene propylene copolymer, polyacrylonitrile, polystyrene, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

The aqueous binder may be styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber (ABR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluoro rubber, ethylene oxide containing polymers, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

When an aqueous binder is used as the negative electrode binder, a cellulose-based compound may also be used as a thickener to provide viscosity. The cellulosic compound comprises one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose or their alkali metal salts. The alkali metal may be Na, K or Li. The thickener may be included in an amount of about 0.1 parts by weight to about 3 parts by weight, based on 100 parts by weight of the anode active material.

A conductive material is included to provide electrode conductivity, and any electrically conductive material may be used as the conductive material unless it causes a chemical change. Examples of conductive materials may be: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, and the like; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, or the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

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

The negative electrode according to one embodiment may be prepared by applying a magnetic field while coating the negative active material composition on a current collector. Preparation of an anode active material layer (for example, an anode active material layer having three layers) will be described with reference to fig. 3.

As shown in fig. 3, the current collector 1 is disposed on the magnet 7, and a first layer composition including the negative active material 3 is coated on the current collector 1. After the first layer composition was applied, drying was performed to prepare a first layer U1. Thereafter, a second layer composition including a negative active material was coated on the first layer and dried to prepare a second layer U2, and a third layer composition including a negative active material was coated on the second layer and dried to prepare a third layer U3.

The anode active material 3 included in the third layer U3 is an alignment layer in which the anode active material is aligned at a predetermined angle with respect to the current collector, and since a surface layer as the alignment layer is an important factor, fig. 3 shows only the anode active material 3 aligned in the third layer U3, and does not show the alignment state of the anode active material included in the first and second layers.

The magnet may have a magnetic field strength of about 1000 gauss to about 10000 gauss. In addition, the negative active material composition may be coated on the current collector and maintained for about 3 seconds to about 9 seconds, i.e., the negative active material composition may be exposed to the magnetic field for about 3 seconds to about 9 seconds.

When such magnetic field application is performed, particularly when the coating process is performed while moving the current collector, the magnetic field (magnetic flux) formed by the magnet may be formed perpendicularly with respect to the current collector, but since the magnetic field according to the coating speed (speed of moving the current collector) is formed at a predetermined angle as a vector function, the negative active materials included in the first layer composition and the second layer composition may stand up on the surface of the current collector, i.e., be oriented at a predetermined angle on the surface of the current collector.

In particular, when the coating process is performed while moving the current collector, a magnetic field (magnetic flux) formed by the magnet may be vertically formed with respect to the current collector, but since the magnetic field according to the coating speed (speed of moving the current collector) is formed at a predetermined angle as a vector function, the negative active material included in the negative active material composition may stand up on the surface of the current collector, that is, be oriented at a predetermined angle on the surface of the current collector.

Here, even though the same magnetic field is applied to the first layer preparation, the second layer preparation, and the third layer preparation, the viscosities of the first layer composition, the second layer composition, and the third layer composition are adjusted to form the first layer, the second layer, and the third layer having DD values different from each other. That is, in the preparation of a multilayer structure of three or more layers, it is desirable to adjust the viscosity of the composition for preparing the layers to an alignment layer or a non-alignment layer to prepare each layer.

The viscosity of the composition should be 2000cps or more and less than 4000cps at room temperature (about 20 ℃ to about 25 ℃) for preparing a layer to be formed into an alignment layer, and should be 4000cps to 5000cps at room temperature (about 20 ℃ to about 25 ℃) for preparing a layer to be formed into a non-alignment layer. In particular, the layer prepared may be an alignment layer having a DD value of 19 or more when the viscosity of the composition falls in a range of 2000cps or more and less than 4000cps at room temperature (about 20 ℃ to about 25 ℃), and more particularly, the layer prepared may be an alignment layer having a DD value of 19 to 60 when the viscosity of the composition falls in a range of 2000cps to 3500cps at room temperature (about 20 ℃ to about 25 ℃).

Further, when the viscosity of the composition is 4000cps to 5000cps at room temperature (about 20 ℃ to about 25 ℃), the prepared layer may be a non-oriented layer having a DD value of less than 19.

As such, if they are outside this range, the desired degree of orientation is not obtained.

The composition may be prepared by mixing a negative electrode active material, a binder, and a conductive material in a solvent.

The negative electrode active material, the binder, and the conductive material are the same as described above. The solvent may be an organic solvent such as N-methylpyrrolidone or water, and when an aqueous binder is used as the binder, the solvent may be water.

A lithium secondary battery according to another embodiment includes an anode, a cathode, and an electrolyte.

The lithium secondary battery may be a battery for high power. In other words, the lithium secondary battery can be effectively applied to electronic devices requiring high power, such as electric power tools, electric vehicles, vacuum cleaners, and the like. The reason is that the lithium secondary battery including the anode according to the embodiment can easily release heat generated during charge and discharge, and particularly, when it is applied to a high capacity battery and an electronic device for high power, deterioration due to heat can be suppressed, and it can be effectively used as a high power battery. In addition, the lithium secondary battery can easily release heat according to charge and discharge, and can suppress an increase in the battery temperature, thereby effectively improving cycle life characteristics, particularly at high rates.

The high power battery may be a cylindrical pouch-shaped battery or a stacked battery. In addition, the cylindrical battery may be a 18650 battery (diameter of 18mm, height of 65mm) and a 21700 battery (diameter of 21mm, height of 70mm), but is not limited thereto.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode active material may include a lithiated intercalation compound that reversibly intercalates and deintercalates lithium ions. Specifically, one or more complex oxides of lithium and a metal selected from cobalt, manganese, nickel, and a combination thereof may be used. More specifically, a compound represented by one of the following chemical formulas may be used. Li_aA_1-bX_bD₂(0.90≤a≤1.8，0≤b≤0.5)；Li_aA_1-bX_bO_2-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aE_1-bX_bO_2-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aE_2-bX_bO_4-cD_c(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05)；Li_aNi_1-b-cCo_bX_cD_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.5，0<α≤2)；Li_aNi_1-b-cCo_bX_cO_2-αT_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cCo_bX_cO_2-αT₂(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cMn_bX_cD_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α≤2)；Li_aNi_1-b-cMn_bX_cO_2-αT_α(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_1-b-cMn_bX_cO_2-αT₂(0.90≤a≤1.8，0≤b≤0.5，0≤c≤0.05，0<α<2)；Li_aNi_bE_cG_dO₂(0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0.001≤d≤0.1)；Li_aNi_bCo_cMn_dG_eO₂(0.90≤a≤1.8，0≤b≤0.9，0≤c≤0.5，0≤d≤0.5，0.001≤e≤0.1)；Li_aNiG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aCoG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn_1-bG_bO₂(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn₂G_bO₄(0.90≤a≤1.8，0.001≤b≤0.1)；Li_aMn_1-gG_gPO₄(0.90≤a≤1.8，0≤g≤0.5)；QO₂；QS₂；LiQS₂；V₂O₅；LiV₂O₅；LiZO₂；LiNiVO₄；Li_(3-f)J₂(PO₄)₃(0≤f≤2)；Li_(3-f)Fe₂(PO₄)₃(0≤f≤2)；Li_aFePO₄(0.90≤a≤1.8)。

In the above formula, A is selected from the group consisting of Ni, Co, Mn and combinations thereof; x is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; d is selected from O, F, S, P and combinations thereof; e is selected from Co, Mn and combinations thereof; t is selected from F, S, P and combinations thereof; g is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and combinations thereof; q is selected from Ti, Mo, Mn and combinations thereof; z is selected from Cr, V, Fe, Sc, Y and combinations thereof; and J is selected from V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Further, the compound may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and an oxycarbonate of the coating element. The compound used for the coating layer may be amorphous or crystalline. The coating element included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. The coating layer may be provided by a method using these elements in a compound so as not to adversely affect the properties of the positive electrode active material, for example, the method may include any coating method (such as spraying, dipping, etc.), but is not described in more detail since it is well known in the related art.

In the positive electrode, the content of the positive electrode active material may be 90 wt% to 98 wt% based on the total weight of the positive electrode active material layer.

In an embodiment, the positive electrode active material layer may further include a binder and a conductive material. Here, the binder and the conductive material may be included in an amount of about 1 wt% to about 5 wt%, respectively, based on the total amount of the positive electrode active material layer.

The binder improves the binding property of the positive electrode active material particles to each other and the binding property of the positive electrode active material particles to the current collector. Examples of the binder may be polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like, but are not limited thereto.

A conductive material is included to provide electrode conductivity, and any electrically conductive material may be used as the conductive material unless it causes a chemical change. Examples of the conductive material include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, and the like; metal-based materials including metal powders or metal fibers of copper, nickel, aluminum, silver, or the like; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

The current collector may use Al, but is not limited thereto.

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

The non-aqueous organic solvent serves as a medium for transporting ions participating in the electrochemical reaction of the battery.

The non-aqueous organic solvent may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, or aprotic solvents.

The carbonate-based solvent may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), and the like. The ester solvent may include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decalactone, mevalonolactone, caprolactone, and the like. The ether solvent may include dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like. In addition, the ketone solvent may include cyclohexanone and the like. The alcohol solvent may include ethanol, isopropanol, etc., and examples of the aprotic solvent include nitriles such as R — CN (where R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1, 3-dioxolane, sulfolane, etc.

The organic solvents may be used alone or as a mixture. When the organic solvent is used in a mixture, the mixing ratio may be controlled according to desired battery performance, and may be well known to those skilled in the related art.

In addition, the carbonate-based solvent may include a mixture of cyclic carbonates and chain carbonates. The cyclic carbonate and the chain carbonate are mixed together in a volume ratio of about 1:1 to about 1:9, and when the mixture is used as an electrolyte, it may have enhanced properties.

The organic solvent may include an aromatic hydrocarbon solvent in addition to the carbonate-based solvent. Here, the carbonate-based solvent and the aromatic hydrocarbon-based solvent may be mixed together in a volume ratio of about 1:1 to about 30: 1.

The aromatic hydrocarbon solvent may be an aromatic hydrocarbon compound represented by chemical formula 1.

[ chemical formula 1]

(in chemical formula 1, R₁To R₆The same or different and selected from hydrogen, halogen, C1 to C10 alkyl, haloalkyl, and combinations thereof. )

Specific examples of the aromatic hydrocarbon solvent may be selected from benzene, fluorobenzene, 1, 2-difluorobenzene, 1, 3-difluorobenzene, 1, 4-difluorobenzene, 1,2, 3-trifluorobenzene, 1,2, 4-trifluorobenzene, chlorobenzene, 1, 2-dichlorobenzene, 1, 3-dichlorobenzene, 1, 4-dichlorobenzene, 1,2, 3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1, 2-diiodobenzene, 1, 3-diiodobenzene, 1, 4-diiodobenzene, 1,2, 3-triiodobenzene, 1,2, 4-triiodobenzene, toluene, fluorotoluene, 2, 3-difluorotoluene, 2, 4-difluorotoluene, 2, 5-difluorotoluene, 2,3, 4-trifluorotoluene, 2,3, 5-trifluorotoluene, chlorotoluene, and the like, 2, 3-dichlorotoluene, 2, 4-dichlorotoluene, 2, 5-dichlorotoluene, 2,3, 4-trichlorotoluene, 2,3, 5-trichlorotoluene, iodotoluene, 2, 3-diiodotoluene, 2, 4-diiodotoluene, 2, 5-diiodotoluene, 2,3, 4-triiodotoluene, 2,3, 5-triiodotoluene, xylene, and combinations thereof.

The electrolyte may further include an additive of vinylene carbonate, an ethylene carbonate-based compound represented by chemical formula 2, or propane sultone to improve cycle life.

[ chemical formula 2]

(in chemical formula 2, R₇And R₈Are the same or different and may each independently be hydrogen, halogen, Cyano (CN), Nitro (NO)₂) And fluoro C1 to C5 alkyl, with the proviso that R₇And R₈At least one of (A) is halogen, Cyano (CN), Nitro (NO)₂) Or fluoro C1 to C5 alkyl, and R₇And R₈Not both hydrogen. )

Examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of the additive for improving cycle life can be flexibly used within a suitable range.

The lithium salt dissolved in the organic solvent supplies lithium ions to the battery, allows the lithium secondary battery to perform a basic operation, and improves the transport of lithium ions between the positive electrode and the negative electrode. Examples of lithium salts include those selected from LiPF₆、LiBF₄、LiSbF₆、LiAsF₆、LiN(SO₂C₂F₅)₂、Li(CF₃SO₂)₂N、LiN(SO₃C₂F₅)₂、Li(FSO₂)₂Lithium bis (fluorosulfonyl) imide: LiFSI), LiC₄F₉SO₃、LiClO₄、LiAlO₂、LiAlCl₄、LiN(C_xF_2x+1SO₂)(C_yF_2y+1SO₂) (wherein x and y are natural numbers, for example, integers of 1 to 20), LiCl, LiI and LiB (C)₂O₄)₂At least one supporting salt of (lithium bis (oxalato) borate: LiBOB). The concentration of the lithium salt may range from about 0.1M to about 2.0M. When the lithium salt is included in the above concentration range, the electrolyte may have excellent performance and lithium ion mobility due to optimal electrolyte conductivity and viscosity.

The lithium secondary battery may further include a separator between the anode and the cathode according to the kind of the battery. Examples of suitable membrane materials include polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof (such as polyethylene/polypropylene bi-layer membranes, polyethylene/polypropylene/polyethylene tri-layer membranes, and polypropylene/polyethylene/polypropylene tri-layer membranes).

Fig. 4 is an exploded perspective view of a lithium secondary battery according to an embodiment. The lithium secondary battery according to the embodiment may be a cylindrical battery.

Referring to fig. 4, the lithium secondary battery 100 is a cylindrical battery, and includes an anode 112, a cathode 114, and a separator 113, an electrolyte (not shown) impregnated into the anode 112, the cathode 114, and the separator 113, a battery case 120, and a sealing member 140 accommodating the battery case 120.

Such a lithium secondary battery 100 is manufactured by the following steps: sequentially stacking the anode 112, the separator 113, and the cathode, winding them in a spiral form; and accommodated in the battery case 120.

Examples of the invention

Hereinafter, examples of the present invention and comparative examples are described. However, these examples should not be construed as limiting the scope of the invention in any way.

(example 1: three-layer Structure having first layer as alignment layer and surface layer (third layer))

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the first layer having a viscosity (at 25 ℃) of 3000 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the second layer having a viscosity (at 25 ℃) of 4000 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the third layer having a viscosity (at 25 ℃) of 2000 cps.

A Cu foil was disposed on a magnet having a magnetic field strength of 4000 gauss, and a negative active material slurry for a first layer was coated on the Cu foil while moving the Cu foil to be exposed to the magnetic field for 9 seconds and dried to form a first layer having a thickness of 40 μm on one side.

Thereafter, the negative active material slurry for the second layer was coated on the first layer, exposed to a magnetic field for 9 seconds, and dried to prepare a second layer having a thickness of 40 μm, and the negative active material slurry for the third layer was coated on the second layer, exposed to a magnetic field for 9 seconds, and dried to prepare a third layer having a thickness of 50 μm.

After the first layer, the second layer and the third layer were formed, a load level (L/L) to one surface was 15mg/cm²The pressing is performed for the negative electrode.

96 wt% LiCoO₂2 wt% of ketjen black and 2 wt% of polyvinylidene fluoride were mixed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive active material slurry was coated on an Al current collector, dried and pressed to prepare a positive electrode.

A18650 type cylindrical lithium secondary battery cell, which had a capacity of 550mAh and a current density of 4.70mAh/cm, was fabricated using a negative electrode, a positive electrode, and an electrolyte²The full cell of (3). Here, by using a mixed solvent of ethylene carbonate and diethyl carbonate (in a volume ratio of 50:50) and dissolving 1MLiPF therein₆To prepare the electrolyte.

(example 2: four-layer Structure having first layer as alignment layer and surface layer (fourth layer))

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the first layer having a viscosity (at 25 ℃) of 3000 cps.

97.8 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 0.7 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the second layer having a viscosity (at 25 ℃) of 4000 cps.

98.2 wt% of artificial graphite, 0.3 wt% of styrene butadiene rubber, and 1.5 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the third layer having a viscosity (at 25 ℃) of 4000 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the fourth layer having a viscosity (at 25 ℃) of 2000 cps.

A Cu foil was placed on a magnet having a magnetic field strength of 4000 gauss, and a negative active material slurry for the first layer was coated on the Cu foil while moving the Cu foil to be exposed to the magnetic field for 9 seconds and dried to form a first layer having a thickness of 30 μm on one side.

Thereafter, the negative active material slurry for the second layer was coated on the first layer, exposed to a magnetic field for 9 seconds, and dried to prepare a second layer having a thickness of 30 μm, the negative active material slurry for the third layer was coated on the second layer, exposed to a magnetic field for 9 seconds, and dried to prepare a third layer having a thickness of 30 μm, and the negative active material slurry for the fourth layer was coated on the third layer, exposed to a magnetic field for 9 seconds, and dried to prepare a fourth layer having a thickness of 40 μm.

After the first layer, the second layer, the third layer and the fourth layer were formed, a load level (L/L) to one surface was 15mg/cm²The pressing is performed for the negative electrode.

Using this anode, a lithium secondary battery was manufactured by the same steps as those in example 1.

(example 3: five-layer Structure having first layer, third layer and surface layer (fifth layer) as alignment layer)

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the first layer having a viscosity (at 25 ℃) of 3000 cps.

97.5 wt% of artificial graphite, 1.2 wt% of styrene butadiene rubber, and 1.3 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the second layer having a viscosity (at 25 ℃) of 4000 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the third layer having a viscosity (at 25 ℃) of 3000 cps.

98.2 wt% of artificial graphite, 0.3 wt% of styrene butadiene rubber, and 1.5 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the fourth layer having a viscosity (at 25 ℃) of 4000 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the fifth layer having a viscosity (at 25 ℃) of 2000 cps.

A Cu foil was placed on a magnet having a magnetic field strength of 4000 gauss, and a negative active material slurry for the first layer was coated on the Cu foil while moving the Cu foil to be exposed to the magnetic field for 9 seconds and dried to form a first layer having a thickness of 30 μm on one side.

Thereafter, the negative active material slurry for the second layer was coated on the first layer, exposed to a magnetic field for 9 seconds, and dried to prepare a second layer having a thickness of 30 μm, the negative active material slurry for the third layer was coated on the second layer, exposed to a magnetic field for 9 seconds, and dried to prepare a third layer having a thickness of 30 μm, the negative active material slurry for the fourth layer was coated on the third layer, exposed to a magnetic field for 9 seconds, and dried to prepare a fourth layer having a thickness of 30 μm, the negative active material slurry for the fifth layer was coated on the fourth layer, exposed to a magnetic field for 9 seconds, and dried to prepare a fifth layer having a thickness of 30 μm.

After the first layer, the second layer, the third layer, the fourth layer and the fifth layer were formed, a load level (L/L) to one surface was 15mg/cm²The pressing is performed for the negative electrode.

Using this anode, a lithium secondary battery was manufactured by the same steps as those in example 1.

(comparative example 1: double layer Structure of alignment layer and non-alignment layer)

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the first layer having a viscosity (at 25 ℃) of 4500 cps.

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1.0 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry for the second layer having a viscosity (at 25 ℃) of 2500 cps.

A Cu foil was disposed on a magnet having a magnetic field strength of 4000 gauss, and a negative active material slurry for a first layer was coated on the Cu foil while moving the Cu foil to be exposed to the magnetic field for 3 seconds, and dried to form a first layer having a thickness of 60 μm on one side.

Thereafter, the anode active material slurry for the second layer was coated on the first layer, exposed to a magnetic field for 9 seconds, and dried to prepare a second layer having a thickness of 70 μm.

After the first layer and the second layer were formed, a load level (L/L) to one surface was 15mg/cm²The pressing is performed for the negative electrode.

Using this anode, a lithium secondary battery was manufactured by the same steps as those in example 1.

(comparative example 2: presenting oriented and non-oriented portions in the same layer)

97.5 wt% of artificial graphite, 1.5 wt% of styrene butadiene rubber, and 1 wt% of carboxymethyl cellulose were mixed with an aqueous solvent to prepare a negative active material slurry having a viscosity (at 25 ℃) of 3000 cps.

Two magnets having a magnetic field of 4000 gauss were fixed in the width direction of the electrode at predetermined intervals, and a Cu foil was disposed on the magnets, and a negative active material slurry for the first layer was coated on the Cu foil while moving the Cu foil to be exposed to the magnetic field for 9 seconds, and dried to form a first layer having a thickness of 130 μm on one side. In the prepared coating, any portion that is directly on the magnet and is affected by the magnetic field is prepared as an oriented portion, and any portion that is located between two magnets (i.e., between one magnet and the other magnet) and is not affected by the magnetic field is prepared as a non-oriented portion.

After the coating was formed, the load level (L/L) was 15mg/cm for one surface²The pressing is performed for the negative electrode.

Using this anode, a lithium secondary battery was manufactured by the same steps as those in example 1.

Measurement of X-ray diffraction characteristics

The lithium secondary batteries according to examples 1 to 3 and comparative examples 1 and 2 were charged and discharged twice at 0.1C and were completely discharged to 2.75V at 0.1C. The fully discharged battery cells were disassembled to obtain the negative electrodes. For these negative electrodes, an X' Pert (panalytical b.v.) XRD apparatus using CuK α rays as target rays was used, but in order to improve peak intensity resolution, the monochromator apparatus was removed. Here, the measurement is performed under the conditions that 2 θ is 10 ° to 80 °, the scanning speed (°/S) is 0.06436, and the step size is 0.026 °/step.

From the measured XRD results, DD values of the entire anode active material layer and the first layer were calculated, and the results are shown in table 1.

The areas of peaks shown at 2 θ ═ 26.5 ± 0.2 ° ((002) plane), 42.4 ± 0.2 ° ((100) plane), 43.4 ± 0.2 ° ((101) R plane), 44.6 ± 0.2 ° ((101) H plane), 54.7 ± 0.2 ° ((004) plane), and 77.5 ± 0.2 ° ((110) plane) were measured, and the sum of peak areas shown at 2 θ ═ 42.4 ± 0.2 ° ((100) plane), 43.4 ± 0.2 ° ((101) R plane), 44.6 ± 0.2 ° ((101) H plane), and 77.5 ± 0.2 ° ((110) plane) was measured as I_aThe sum of the peak areas shown at 2 θ ═ 26.5 ± 0.2 ° ((002) plane), 42.4 ± 0.2 ° ((100) plane), 43.4 ± 0.2 ° ((101) R plane), 44.6 ± 0.2 ° ((101) H plane), 54.7 ± 0.2 ° ((004) plane), and 77.5 ± 0.2 ° ((110) plane) is taken as the sum of the peak areas shown as I_{General assembly}And DD (I) is obtained by calculation from these values_{General assembly}/I_a). The results are shown in Table 2.

In addition, calculate I₍₀₀₄₎/I₍₀₀₂₎And I₍₁₁₀₎/I₍₀₀₄₎And the results are shown in table 2. In particular, the peak at 43.4 ± 0.2 ° appears because the peak of the (101) R face of graphite overlaps with another peak of the (111) face of the Cu current collector.

Evaluation of Rate-Performance characteristics

The lithium secondary batteries according to examples 1 to 3 and comparative examples 1 to 2 were charged once at each C-rate of 0.2C, 0.5C, 1C, 1.5C, and 2.0C, and the capacity ratio of the respective C-rates to 0.2C was measured. The results are shown in Table 3.

TABLE 1

As shown in table 1, the DD values of the negative electrodes according to examples 1 to 3 were 28.9 to 31.1, and the DD values of the first and third layers of example 1, the first and fourth layers of example 2, and the first, third, and fifth layers of example 3 fell within a range of 19 to 60, which indicated an alignment layer.

TABLE 2

As shown in Table 2, the peak intensity ratio I of the negative electrode₍₀₀₂₎/I₍₁₁₀₎Falls within the range of 50 to 300, and the peak intensity ratio I of the alignment layer₍₀₀₂₎/I₍₁₁₀₎Falling within the range of 10 to 200.

TABLE 3

As shown in table 3, examples 1 to 3, in which the surface layer is an alignment layer and the active material layer includes three or more layers, exhibited excellent high-rate charge and discharge characteristics. However, comparative example 1 having two layers regardless of the inclusion of the alignment layer and comparative example 2 in which the alignment part and the non-alignment part are formed in one layer instead of separate layers show deteriorated high-rate charge-discharge cycle life characteristics.

BET evaluation

The lithium secondary battery cells according to examples 1 to 3 and comparative examples 1 and 2 were charged and discharged at 0.1C and completely discharged to 3V, and then disassembled to obtain an anode. The negative electrodes were used to obtain respective samples of 5cm × 5cm size, the samples were cut into 0.5cm × 0.5cm size and placed in BET sample holders, and their BET was measured by nitrogen adsorption, and the results are shown in table 4.

TABLE 4

	BET(m2/g)
		Example 1	0.71
Example 2	0.72
		Example 3	0.69
Comparative example 1	0.75
		Comparative example 2	0.73

Evaluation of cycle life characteristics

The full cells of examples 1 to 3 and comparative examples 1 and 2 were constant current/constant voltage charged under the conditions of 1.0C, 4.4V, and 0.1C cutoff, respectively, suspended for 5 minutes, and constant current discharged under the conditions of 1.0C and 3.0V cutoff and suspended for 5 minutes as one cycle, which was repeated 300 times. The capacity retention rate depending on the charge-discharge cycle was evaluated by calculating the discharge capacity ratio of the discharge capacity per cycle to the discharge capacity of the first cycle.

The results are shown in Table 5.

TABLE 5

	Cycle characteristics (%)
		Example 1	80
Example 2	79.5
		Example 3	78.9
Comparative example 1	70.5
		Comparative example 2	62.1

As shown in table 5, the batteries according to examples 1 to 3 including the negative electrode in which the active material layer includes three or more layers and the surface layer is the alignment layer exhibited superior cycle life characteristics, as compared to the battery having two active material layers (comparative example 1) or the battery having one layer in which the alignment portion and the non-alignment portion are formed (comparative example 2).

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