Anode for lithium secondary battery and lithium secondary battery including same

Abstract

An anode for a lithium secondary battery according to an embodiment of the present disclosure includes: an anode current collector: a first anode mixture layer formed on at least one surface of the anode current collector and containing a first carbon-based active material; and a second anode mixture layer formed on the first anode mixture layer and containing a second carbon-based active material and a silicon-based active material, wherein the first anode mixture layer has a Raman R value according to equation 1, which is smaller than that of the second anode mixture layer. [Equation 1] Raman R = ID / IG (where, ID represents the peak intensity value in the absorption region of 1350 to 1380 cm-1 , and IG represents the peak intensity value in the absorption region of 1580 to 1600 cm-1)

Description

Anode for lithium secondary battery and lithium secondary battery including same

[0001] The present disclosure relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Recently, extensive research has been conducted on electric vehicles (EVs) as a potential replacement for fossil fuel-powered vehicles like gasoline and diesel, a major source of air pollution. Lithium secondary batteries, with their high discharge voltage and output stability, are primarily used as power sources for these EVs. Consequently, the need for high-energy-density lithium secondary batteries is increasing, and active research and development is underway to develop high-capacity cathodes for these batteries.

[0003] One aspect of the present disclosure is to provide a negative electrode for a lithium secondary battery having a high energy density.

[0004] Another aspect of the present disclosure is to provide a negative electrode for a lithium secondary battery having a low resistance value.

[0005] Another aspect of the present disclosure is to provide a negative electrode for a lithium secondary battery having excellent rapid charging characteristics.

[0006] According to one embodiment of the present disclosure, a negative electrode for a lithium secondary battery comprises: a negative electrode current collector; a first negative electrode mixture layer formed on at least one surface of the negative electrode current collector and including a first carbon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second carbon-based active material and a silicon-based active material, wherein the first negative electrode mixture layer has a Raman R value according to the following formula 1 that is smaller than that of the second negative electrode mixture layer.

[0007] [Formula 1]

[0008] Raman R = I D / I G

[0009] (In the above equation 1, I Dis 1350 to 1380 cm -1 is the peak intensity value of the absorption region, and I G is 1580 to 1600 cm -1 (This is the peak intensity value of the absorption region.)

[0010] In some implementations, the first negative electrode composite layer may not include a silicon-based active material.

[0011] In some implementations, the first cathode composite layer may have an OI value according to Equation 2 that is greater than that of the second cathode composite layer.

[0012] [Formula 2]

[0013] OI = I 004 / I 110

[0014] (In the above formula 2, OI is the crystal orientation index according to XRD measurement, and I 004 is the peak intensity of the (004) plane in the XRD measurement of the cathode composite layer, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the negative electrode composite layer.

[0015] In some implementations, the first cathode composite layer may have an OI value of 9 to 18.

[0016] In some implementations, the second cathode composite layer may have an OI value of 1 to 8.

[0017] In some implementations, the first cathode composite layer can have a Raman R value of 0.15 to 0.27.

[0018] In some implementations, the second cathode composite layer can have a Raman R value of 0.281 to 0.55.

[0019] In some embodiments, the first carbon-based active material and the second carbon-based active material may each independently comprise artificial graphite.

[0020] In some embodiments, the first carbon-based active material may further include natural graphite.

[0021] In some embodiments, the first carbon-based active material may not be surface coated.

[0022] In some embodiments, the second carbon-based active material may be surface-coated with at least one selected from the group consisting of hard carbon, soft carbon, heavy oil, and pitch.

[0023] A lithium secondary battery according to one embodiment of the present disclosure includes a negative electrode for a lithium secondary battery according to any one of the above-described embodiments.

[0024] According to one embodiment of the present disclosure, a negative electrode for a lithium secondary battery having excellent energy density can be provided.

[0025] According to another embodiment of the present disclosure, a negative electrode for a lithium secondary battery having excellent rapid charging characteristics can be provided.

[0026] According to another embodiment of the present disclosure, the resistance value of a negative electrode for a lithium secondary battery can be reduced.

[0027] Figure 1 is a drawing conceptually showing a basal plane corresponding to a basal plane and an edge plane formed by the edges of each of the basal planes in a carbon-based active material having a parallel-layered structure.

[0028] Figure 2 is a schematic cross-sectional view showing the structure of a negative electrode for a lithium secondary battery according to one embodiment.

[0029] Hereinafter, unless otherwise specifically defined, when a part such as a layer, film, thin film, region, or plate is said to be “on” or “over” another part, this may include not only the case where it is “directly on” the other part, but also the case where there is another part in between.

[0030] In this specification, the 'orientation' of the composite layer and the active material is the peak intensity (I) of the (004) plane according to XRD measurement. 004 ) and peak intensity (I) on the (110) side 110 ) refers to a characteristic represented by the 'Orientation Index (OI)' value determined by the peak intensity ratio, which is the ratio between the two. For example, a relatively smaller OI value of the composite layer and active material indicates a composite layer and active material with a low degree of orientation and a small degree of orientation, and a relatively larger OI value indicates a composite layer and active material with a high degree of orientation and a large degree of orientation.

[0031] To realize a high-capacity and high-energy-density secondary battery, according to one implementation example, a silicon-based active material with a higher discharge capacity (1500 mAh / g) than graphite (350 mAh / g) can be applied to the negative electrode for a lithium secondary battery. When a silicon-based active material with such a high discharge capacity is applied together with a carbon-based active material such as graphite, the loading weight (LW) of the negative electrode active material layer can also be reduced, thereby further increasing the energy density.

[0032] However, since silicon-based active materials have a slow lithium ion diffusion rate and a large volume expansion rate compared to carbon-based active materials, it is difficult to secure excellent rapid charging characteristics and lifespan characteristics of an anode including a silicon-based active material. According to one embodiment, a low-oriented carbon-based active material having a low crystal orientation index (OI) value can be included together with a silicon-based active material to improve the rapid charging characteristics. However, since it is difficult to roll the low-oriented carbon-based active material to a high density, even if it is used, it may be difficult to improve the energy density of the anode to a high level.

[0033] In this regard, according to one implementation example, the above problems can be substantially solved. With reference to FIGS. 1 and 2, implementation examples of the present disclosure are described in detail below.

[0034] Figure 1 is a drawing conceptually showing a basal plane corresponding to a basal plane and an edge plane formed by the edges of each of the basal planes in a carbon-based active material having a parallel-layered structure.

[0035] Figure 2 is a schematic cross-sectional view showing the structure of a negative electrode for a lithium secondary battery according to one embodiment.

[0036] Cathode for lithium secondary batteries

[0037] A negative electrode (100) for a lithium secondary battery according to one embodiment may include a negative electrode current collector (10), a first negative electrode composite layer (21) formed on at least one surface of the negative electrode current collector (10), and a second negative electrode composite layer (22) formed on the first negative electrode composite layer (21).

[0038] The first negative electrode composite layer (21) may include a first carbon-based active material. The second negative electrode composite layer (22) may include a second carbon-based active material and a silicon-based active material.

[0039] The above first cathode composite layer (21) may have a Raman R value according to the following equation 1 that is smaller than that of the second cathode composite layer (22).

[0040] [Formula 1]

[0041] Raman R = I D / I G

[0042] In the above equation 1, I D is 1350 to 1380 cm -1 is the peak intensity value of the absorption region, and I G is 1580 to 1600 cm -1 This is the peak intensity value of the absorption region.

[0043] The above Raman R value is a parameter indicating the relative crystallinity of a material, and the above I D The values ​​represent the peak intensity of the region associated with the amorphous state, and the above I GThe value represents the peak intensity in the region related to the crystalline state. Therefore, the larger the Raman R value, the lower the crystallinity of the material, and the smaller the Raman R value, the higher the crystallinity of the material. The peak intensity may refer to the maximum peak height within a specific wavenumber range.

[0044] Specifically, the Raman R value of the first negative electrode mixture layer (21) may be from about 0.15 to about 0.27, and the Raman R value of the second negative electrode mixture layer (22) may be from about 0.281 to about 0.55. More specifically, the Raman R value of the first negative electrode mixture layer (21) may be from about 0.16 to about 0.26, and the Raman R value of the second negative electrode mixture layer (22) may be from about 0.29 to about 0.3.

[0045] When the Raman R values ​​of the first negative electrode mixture layer (21) and the second negative electrode mixture layer (22) are adjusted within the above-described range, a high-density negative electrode mixture layer with a relatively high degree of crystallinity and a low porosity can be arranged in the lower layer of the multilayered negative electrode, thereby improving the energy density of the negative electrode, and a low-density negative electrode mixture layer with a relatively low degree of crystallinity and a high porosity can be arranged in the upper layer, thereby facilitating the entry and exit of lithium ions, thereby improving the rapid charging characteristics of the negative electrode.

[0046] The above first cathode composite layer (21) may have an OI value according to the following equation 2 that is greater than that of the above second cathode composite layer (22).

[0047] [Formula 2]

[0048] OI = I 004 / I 110

[0049] In the above equation 2, OI is the crystal orientation index according to XRD measurement, and I 004 is the peak intensity of the (004) plane in the XRD measurement of the cathode composite layer, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the negative electrode composite layer.

[0050] A negative electrode (100) for a lithium secondary battery has a multilayer structure and includes a negative electrode mixture layer (20) on a negative electrode current collector (10). The negative electrode mixture layer (20) may include a first negative electrode mixture layer (21) and a second negative electrode mixture layer (22). The first negative electrode mixture layer (21) may be an active material layer (lower layer) on one side adjacent to the negative electrode current collector (10), and the second negative electrode mixture layer (22) may be an active material layer (upper layer) formed on the first negative electrode mixture layer (21) and relatively spaced from the negative electrode current collector (10) and adjacent to the electrolyte.

[0051] According to one embodiment, a negative electrode (100) for a lithium secondary battery may include a first negative electrode mixture layer (21) and a second negative electrode mixture layer (22), which are carbon-based active materials having different orientations, respectively, the first carbon-based active material and the second carbon-based active material. Specifically, the first negative electrode mixture layer (21), which is a lower layer, may be a highly oriented negative electrode mixture layer having a relatively high crystal orientation index (OI) value, including the first carbon-based active material having a relatively high crystal orientation index (OI) value, and the second negative electrode mixture layer (22), which is an upper layer, may be a low-oriented negative electrode mixture layer having a relatively low crystal orientation index (OI) value, including the second carbon-based active material having a relatively low crystal orientation index (OI) value. Hereinafter, the negative electrode mixture layer and the crystal orientation index (OI) of the carbon-based active material will be described in more detail.

[0052] The above crystal orientation index (OI) is the peak intensity (I) shown on the (004) plane during XRD measurement of the negative electrode composite layer. 004 ) and peak intensity (I) appearing on the (110) plane 110 ) as a ratio between the crystal orientation (Orientation Index; OI) values. In addition, the crystal orientation index (OI) is the peak intensity (I) shown on the (004) plane when measuring the XRD for the active material. 004 ) and peak intensity (I) appearing on the (110) plane 110) is the ratio between the crystal orientation index (OI) values. Specifically, I 004 It can be the peak intensity value of the (004) plane that appears at an angle of 2θ = 54.7±0.2° when measuring XRD using CuKα rays for the negative electrode composite layer and active material, and I 110 It may be the peak intensity value of the (110) plane that appears at an angle of 2θ = 77.5±0.2° when measuring XRD using CuKα rays for the negative electrode composite layer and active material. In general, the peak intensity value means the height value of the peak or the integrated area value of the peak, and the above I 004 and I 110 can be calculated as the integral area value of the peak.

[0053] Meanwhile, referring to Fig. 1, carbon-based active materials (1) such as artificial graphite generally include carbon layers in which hexagonal rings composed of six carbon atoms are connected in a plane, and the carbon layers are stacked in parallel to each other. In such carbon-based active materials (1), the basal plane (2) corresponds to the basal plane in the carbon layer having a parallel stacked structure, and the edge plane (3) refers to a plane (edge ​​plane) formed by the edges of each of the basal planes coming together.

[0054] During the charging and discharging process of a secondary battery, the intercalation and deintercalation phenomena, in which lithium ions are stored and released in a carbon-based active material (1), mainly occur through edge planes (3). Therefore, as the number of these edge planes (3) increases, the intercalation and deintercalation of lithium ions during the charging process become easier, and the rapid charging characteristics can also be improved.

[0055] In this regard, the crystal orientation index (OI) value determined by XRD measurement of the carbon-based active material (1) refers to the peak intensity of the (110) plane compared to the (004) plane, and the smaller the OI value of the carbon-based active material (1), the more likely it is to have a structure in which the number of edge planes (3) is relatively larger compared to the base plane (2). This is because the smaller the crystal orientation index (OI) value, the more disordered the crystal arrangement is, thereby increasing the number of edge planes (3) through which lithium ions can enter and exit. Therefore, the lower the crystal orientation index (OI) value of the carbon-based active material included in the negative electrode, the easier it is for lithium ions to enter and exit through many edge planes (3), and thus the better the rapid charging characteristics can be.

[0056] However, as the orientation decreases, the hardness of the carbon-based active material increases, making it practically difficult to roll low-orientation carbon-based active materials at high densities. Consequently, increasing the rolling density of anodes containing low-orientation carbon-based active materials is difficult, and there are limitations in manufacturing high-energy-density anodes for lithium secondary batteries.

[0057] Accordingly, a negative electrode (100) for a lithium secondary battery according to one embodiment has a multilayer structure, and may include carbon-based active materials having different orientations for each layer, thereby exhibiting excellent rapid charging characteristics and energy density. Specifically, the first negative electrode mixture layer (21) includes the first carbon-based active material, the second negative electrode mixture layer (22) includes the second carbon-based active material, and the first carbon-based active material may have a larger OI value than the second carbon-based active material. Accordingly, the first negative electrode mixture layer (21) may have a larger OI value than the second negative electrode mixture layer (22).

[0058] That is, since the first negative electrode mixture layer (21), which is the lower layer, is a highly oriented negative electrode mixture layer having a relatively large crystal orientation index (OI) value, it can be rolled at a high density, and accordingly, the negative electrode (100) can secure a high energy density. In addition, since the second negative electrode mixture layer (22), which is the upper layer, is a low oriented negative electrode mixture layer having a relatively small crystal orientation index (OI) value, it is easy for lithium ions to enter and exit the negative electrode mixture layer adjacent to the electrolyte where a large amount of lithium ions exist, and thus the negative electrode (100) can secure excellent rapid charging characteristics.

[0059] Specifically, the first negative electrode mixture layer (21) may have an OI value of about 9 to about 18. When the OI value of the first negative electrode mixture layer (21) is less than 9, the lower negative electrode mixture layer may have a low orientation and high hardness, which may make rolling difficult, and it may be difficult to improve the energy density of the negative electrode. When the OI value of the first negative electrode mixture layer (21) is more than 18, the lower negative electrode mixture layer may have a high orientation, which may make intercalation and deintercalation of lithium ions difficult, thereby deteriorating the rapid charging characteristics of the negative electrode.

[0060] Specifically, the second negative electrode mixture layer (22) may have an OI value of about 1 to about 8. When the OI value of the second negative electrode mixture layer (22) is less than 1, the upper negative electrode mixture layer may have a low orientation and high hardness, which may make rolling difficult, and it may be difficult to improve the energy density of the negative electrode. When the OI value of the second negative electrode mixture layer (22) is greater than 8, the upper negative electrode mixture layer may have a high orientation, which may make intercalation and deintercalation of lithium ions difficult, thereby deteriorating the rapid charging characteristics of the negative electrode.

[0061] More specifically, the first cathode composite layer (21) may have an OI value of about 13 to about 16, and the second cathode composite layer (22) may have an OI value of about 3 to about 5.

[0062] When the crystal orientation index (OI) values ​​of the first negative electrode composite layer (21) and the second negative electrode composite layer (22) are each within the above-described range, the orientation, hardness, etc. of the carbon-based active material included in each negative electrode composite layer in the multilayer structure can be appropriately controlled within different ranges, so that the rapid charging characteristics, energy density, etc. of the negative electrode can all be excellent.

[0063] For example, the first carbon-based active material and the second carbon-based active material may each independently be at least one carbon-based active material selected from artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon.

[0064] Specifically, considering the ease of controlling the orientation of the negative electrode composite layer and the active material, the first carbon-based active material and the second carbon-based active material may each independently include artificial graphite.

[0065] The above first carbon-based active material may further include natural graphite. When the first carbon-based active material includes natural graphite, electrode adhesion and resistance characteristics may be improved.

[0066] In one embodiment, the first carbon-based active material may include artificial graphite and natural graphite, and the second carbon-based active material may include only artificial graphite.

[0067] The weight-based content of artificial graphite in the first carbon-based active material may be greater than or equal to the weight-based content of natural graphite. Specifically, the weight ratio of artificial graphite and natural graphite in the first carbon-based active material may be from 5:5 to 9:1. More specifically, the weight ratio of artificial graphite and natural graphite in the first carbon-based active material may be from 6:4 to 8:2. When the weight ratio of artificial graphite and natural graphite in the first carbon-based active material is within the above-described range, both the energy density and rapid charging characteristics of the negative electrode can be improved.

[0068] In one embodiment, the first carbon-based active material and the second carbon-based active material may each include only artificial graphite.

[0069] Meanwhile, the second carbon-based active material may be surface-coated with at least one selected from the group consisting of hard carbon, soft carbon, heavy oil, and pitch. For example, the artificial graphite included in the second carbon-based active material may be surface-coated with at least one selected from the group consisting of soft carbon, heavy oil, and pitch. Accordingly, the hardness of the second carbon-based active material may be improved, thereby improving the rapid charging characteristics and resistance characteristics of the negative electrode.

[0070] The weight ratio of artificial graphite and natural graphite in the first negative electrode mixture layer may be about 5:5 to about 9:1. Specifically, the weight ratio of artificial graphite and natural graphite in the first negative electrode mixture layer may be about 6:4 to about 8:2. When the weight ratio of artificial graphite and natural graphite in the first negative electrode mixture layer is within the above-described range, electrode adhesion and resistance characteristics may be improved. If the weight ratio of artificial graphite and natural graphite in the first negative electrode mixture layer exceeds the above-described range, the life characteristics and rapid charging characteristics of the negative electrode may be inferior.

[0071] The first carbon-based active material may not be surface-coated. Specifically, the artificial graphite included in the first carbon-based active material is not surface-coated with hard carbon, soft carbon, heavy oil, or pitch, so that side reactions with the electrolyte are minimal and the high-temperature storage characteristics of the negative electrode may be excellent. When the first carbon-based active material is surface-coated with at least one selected from the group consisting of hard carbon, soft carbon, heavy oil, and pitch, it may be difficult to roll the negative electrode mixture layer to a high density, which may lower the energy density of the negative electrode.

[0072] The content of the first carbon-based active material in the first negative electrode composite layer (21) may be about 90 to about 98 wt%. In addition, the content of the second carbon-based active material in the second negative electrode composite layer (22) may be about 60 to about 90 wt%.

[0073] The content of the silicon-based active material in the second negative electrode composite layer (22) may be about 10 to about 40 wt%. Specifically, the content of the silicon-based active material in the second negative electrode composite layer (22) may be about 10 to about 20 wt%.

[0074] Meanwhile, the first negative electrode composite layer (21) may only include the first carbon-based active material as the active material. That is, the first negative electrode composite layer (22) may not include a silicon-based active material.

[0075] When the first negative electrode mixture layer (21) does not include a silicon-based active material and the content and ratio of the silicon-based active material in the second negative electrode mixture layer (22) are within the above-described range, the first negative electrode mixture layer (21) formed on one surface adjacent to the negative electrode current collector (10) does not include a silicon-based active material, thereby preventing problems such as detachment of the active material layer due to volume expansion, and improving the life characteristics of the negative electrode (100). In addition, since the second negative electrode mixture layer (22) includes a silicon-based active material having a lower lithium ion diffusion rate than a carbon-based active material within the above-described range, the negative electrode (100) can secure high-capacity characteristics, rapid charging characteristics, etc.

[0076] The silicon-based active material included in the second negative electrode composite layer (22) is not particularly limited, but may be SiO depending on the purpose of designing the negative electrode of the multilayer structure. x (0 <x<2)의 화학식으로 표현되는 화합물인 규소산화물계 활물질, SiC의 화학식으로 표현되는 화합물인 Si-C 복합체 등의 탄화규소계 활물질, 및 이들의 조합에서 적절히 선택될 수 있다.

[0077] In general, Si-C composites have high capacity and low resistance characteristics compared to existing silicon oxide-based active materials, but during the charge / discharge process, the structural collapse of the active material may cause a short circuit (isolation) phenomenon between the Si-C composite and the carbon-based active material, which may reduce the life characteristics of the battery. Therefore, by applying a Si-C composite having high capacity and low resistance characteristics to the second negative electrode composite layer (22), high energy density can also be secured at the same time. That is, the second negative electrode composite layer (22) may include a silicon carbide-based active material as the silicon-based active material.

[0078] The first negative electrode mixture layer (21) may further include a first conductive material, and the second negative electrode mixture layer (22) may further include a second conductive material. The first conductive material and the second conductive material are used to provide conductivity to the electrode and maintain the structure of the electrode, and any conductive material that does not cause side reactions with other elements of the secondary battery may be used. Examples thereof include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone, or a mixture of two or more may be used. Specifically, the first conductive material and the second conductive material may each include carbon nanotubes (CNTs). Carbon nanotubes (CNTs) have higher electron mobility than existing conductive materials such as carbon black, enabling high energy density even with a small amount. In addition, they have high strength due to their stable structure, and can substantially alleviate volume expansion of silicon-based active materials. Therefore, when the first conductive material and the second conductive material include carbon nanotubes (CNTs), the energy density, life characteristics, resistance characteristics, etc. of the negative electrode (100) can be further improved.

[0079] The first conductive material and the second conductive material may be different from each other. Specifically, the negative electrode (100) for the lithium secondary battery may apply conductive materials with different characteristics to each layer of the negative electrode having a multilayer structure. In this regard, the characteristics of the first conductive material and the second conductive material may be adjusted as follows.

[0080] The Raman R value of the first conductive material may have a greater Raman R value than that of the second conductive material. A detailed description of the Raman R value is omitted as it overlaps with the description described above.

[0081] The Raman R value of the first conductive material may be from about 0.1 to about 1.8, and the Raman R value of the second conductive material may be from about 0.01 to about 0.09. Specifically, the Raman R value of the first conductive material may be from about 0.3 to about 1.0, and the Raman R value of the second conductive material may be from about 0.01 to about 0.05.

[0082] The first conductive material may include a multi-walled carbon nanotube (MWCNT), and the second conductive material may include a single-walled carbon nanotube (SWCNT).

[0083] When the Raman R value, type, etc. of the first conductive material and the second conductive material are applied as described above, a conductive material having relatively low dispersibility and large particle size can be included in the first negative electrode mixture layer (21) adjacent to the negative electrode current collector (10) having relatively high energy density to form a conductive path between the current collector and the electrode layer, and at the same time, micropores can be formed in the electrode layer to increase ionic conductivity. In addition, a conductive material having high crystallinity and excellent conductivity and dispersibility can be included in the second negative electrode mixture layer (22) having relatively low energy density to form and maintain a conductive path within the electrode layer, thereby further improving rapid charging characteristics.

[0084] The content of the first conductive material in the first negative electrode mixture layer may be greater than or equal to the content of the second conductive material in the second negative electrode mixture layer. Specifically, the content of the first conductive material in the first negative electrode mixture layer may be about 0.3 to about 5 wt%, and the content of the second conductive material in the second negative electrode mixture layer may be about 0.01 to about 0.3 wt%. Specifically, the content of the first conductive material in the first negative electrode mixture layer may be about 0.3 to about 3 wt%, about 0.35 to about 1 wt%, or about 0.4 to about 0.6 wt%, and the content of the second conductive material in the second negative electrode mixture layer may be about 0.05 to about 0.15 wt%.

[0085] When the content characteristics of the first conductive agent and the second conductive agent are adjusted as described above, the conductive agent content of the first negative electrode mixture layer (21) formed on one surface adjacent to the negative electrode current collector (10) is adjusted to be relatively high, thereby increasing the contact point between the negative electrode current collector (10) and the first negative electrode mixture layer (21). When this contact point is increased, the resistance between the negative electrode (100) and the negative electrode current collector (10) can be reduced, and even if the negative electrode (100) expands during use, the contact point between the negative electrode current collector (10) and the negative electrode (100) can be maintained. In addition, by adjusting the conductive material content of the second negative electrode mixture layer (22) to be relatively small, the content of the conductive material included in the entire negative electrode (100) can be reduced, thereby ensuring economic feasibility, and by increasing the content of the active material in the negative electrode mixture layer (20), the negative electrode (100) having the same energy density can be implemented with a relatively low loading weight. In addition, the problem of the interface resistance and life characteristics of the negative electrode (100) deteriorating due to blocking of pores when an excessive amount of conductive material is included in the upper layer can be alleviated.

[0086] The first cathode composite layer (21) and the second cathode composite layer (22) may each further include a binder.

[0087] The binder is not particularly limited as long as it is a compound that serves to attach the components within the negative electrode mixture layer (20) well to each other and to attach the negative electrode mixture layer (20) well to the negative electrode current collector (10), and for example, it may be at least one rubber-based binder selected from the group consisting of styrene-butadiene rubber (SBR), fluorine-based rubber, ethylene propylene rubber, butyl acrylate rubber, butadiene rubber, isoprene rubber, acrylonitrile rubber, acrylic rubber, and silane-based rubber; a cellulose-based binder such as carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, methylcellulose, or an alkali metal salt thereof; a water-soluble polymer-based binder such as a polyacrylic acid (PAA)-based binder, a polyvinyl alcohol (PVA)-based binder, and a polyvinyl alcohol-polyacrylic acid copolymer (PVA-PAA Copolymer)-based binder; and combinations thereof. Specifically, the binder may include styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), and combinations thereof.

[0088] The content of the binder in the first negative electrode mixture layer (21) may be greater than or equal to the content of the binder in the second negative electrode mixture layer (22). Specifically, the ratio between the content of the binder in the first negative electrode mixture layer (21) and the content of the binder in the second negative electrode mixture layer (22) may be from about 9:1 to about 5:5. More specifically, the ratio between the content of the binder in the first negative electrode mixture layer (21) and the content of the binder in the second negative electrode mixture layer (22) may be from about 8.5:1.5 to about 7:3.

[0089] If the content of the above binder is too low, the adhesive strength of the first negative electrode mixture layer (21) adjacent to the negative electrode current collector (10) may be reduced, which may cause problems such as scrap generation and mixture layer detachment during the notching process. On the other hand, if the content of the binder is too high throughout the negative electrode (100), the electrical resistance may increase, which may deteriorate the battery characteristics. Accordingly, if the content of the binder included in the first negative electrode mixture layer (21), which is the lower layer, is adjusted relatively high, the binder content throughout the negative electrode can be lowered while substantially alleviating the occurrence of the above-described problem, thereby also alleviating the increase in electrical resistance.

[0090] The content of the binder in the first negative electrode mixture layer (21) may be about 2.5 to about 5.0 wt%. In addition, the content of the binder in the second negative electrode mixture layer (22) may be about 0.1 to about 2.5 wt%. Specifically, the content of the binder in the first negative electrode mixture layer (21) may be about 3.0 to about 4.0 wt%, and the content of the binder in the second negative electrode mixture layer (22) may be about 1.0 to about 2.0 wt%.

[0091] When the content of the binder per negative electrode composite layer is within the above-described range, the negative electrode (100) having a multilayer structure can have excellent flexibility, adhesiveness, etc., so that problems such as electrode detachment during the process or cracking or electrode detachment during the charge / discharge process can be substantially alleviated, and low resistance characteristics can also be secured.

[0092] The loading weight (LW) ratio of the first negative electrode mixture layer (21) and the second negative electrode mixture layer (22) may be about 2:8 to about 8:2. In addition, the loading weight of the first negative electrode mixture layer (21) may be about 1.5 to about 9.5 mg / cm 2 It can be, and the loading weight of the second cathode composite layer (22) is about 1.5 to about 9.5 mg / cm 2 It could be.

[0093] The above loading weight (LW) means the amount of the negative electrode composite layer (20) formed on the negative electrode current collector (10), i.e., the layer including the active material, binder, conductive material, etc., formed on the negative electrode current collector (10), expressed in units of weight per area. In this case, the area is based on the area of ​​the negative electrode current collector (10), and the weight is based on the weight of the entire formed negative electrode composite layer (20).

[0094] When the loading weight (LW) value, ratio, etc. of the first negative electrode composite layer (21) and the second negative electrode composite layer (22) are within the above-described range, a negative electrode (100) having a multilayer structure with excellent capacity characteristics, life characteristics, and rapid charging characteristics can be provided.

[0095] As the negative electrode current collector (10), a material selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and a combination thereof can be appropriately used.

[0096] The method for manufacturing the above-mentioned negative electrode (100) for a lithium secondary battery is not particularly limited, and can be performed by a method such as (1) a 'double coating' process in which the slurries of the upper and lower layers are sequentially applied, (2) a 'simultaneous coating' process in which the slurries of the upper and lower layers are simultaneously applied. For example, the 'two-coating' process may be manufactured by applying a first negative electrode slurry containing a first solvent, the first carbon-based active material, the silicon-based active material, the binder, and the first conductive agent onto a negative electrode current collector (10) by a method such as bar coating, casting, or spraying, and drying at about 70 to about 100° C. to form a first negative electrode mixture layer (21), and then applying a second negative electrode slurry containing a second solvent, the second carbon-based active material, the silicon-based active material, the binder, and the second conductive agent onto the first negative electrode mixture layer (21) by a method such as bar coating, casting, or spraying, and drying at about 70 to about 100° C.

[0097] The solvent may be, for example, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. The amount of the solvent used is sufficient to dissolve or disperse the active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the composition for forming the negative electrode mixture layer, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter to form the negative electrode mixture layer.

[0098] lithium secondary battery

[0099] A lithium secondary battery according to one embodiment may include the anode for a lithium secondary battery described above. For example, the lithium secondary battery may include a cathode, an anode, and a separator interposed between the cathode and the anode. The anode may be an anode for a secondary battery according to any one of the embodiments described above.

[0100] The positive electrode may include a positive electrode current collector and a positive electrode composite layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may include stainless steel, nickel, aluminum, titanium, or an alloy thereof. The positive electrode current collector may also include aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver. The positive electrode current collector may have a thickness of, but is not limited to, 10 to 50 μm, for example.

[0101] The above positive electrode active material layer may include a positive electrode active material. The positive electrode active material may include a compound capable of reversibly intercalating and deintercalating lithium ions.

[0102] According to exemplary embodiments, the positive electrode active material may include a lithium-nickel metal oxide. The lithium-nickel metal oxide may further include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0103] In some embodiments, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1.

[0104] [Chemical Formula 1]

[0105] Li x Ni a M b O 2+z

[0106] In Chemical Formula 1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b≤0.4, -0.5≤z≤0.1 may be satisfied. As described above, M may include Co, Mn, and / or Al.

[0107] The chemical structure represented by Chemical Formula 1 represents the bonding relationship included in the layered structure or crystal structure of the positive electrode active material and does not exclude other additional elements. For example, M includes Co and / or Mn, and Co and / or Mn can serve as the main active element of the positive electrode active material together with Ni. Chemical Formula 1 is provided to express the bonding relationship of the above main active elements and should be understood as a formula encompassing the introduction and substitution of additional elements.

[0108] In one embodiment, auxiliary elements may be further included in addition to the main active element to enhance the chemical stability of the positive electrode active material or the layered structure / crystal structure. The auxiliary elements may be incorporated into the layered structure / crystal structure to form bonds, and in this case, it should be understood that they are also included within the chemical structure range represented by Chemical Formula 1.

[0109] The auxiliary element may include, for example, at least one of Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. The auxiliary element may also act as an auxiliary active element that contributes to the capacity / output activity of the positive electrode active material together with Co or Mn, for example, Al.

[0110] For example, the positive electrode active material or the lithium-nickel metal oxide may include a layered structure or crystal structure represented by the following chemical formula 1-1.

[0111] [Chemical Formula 1-1]

[0112] Li x Ni a M1 b1 M2 b2 O 2+z

[0113] In Chemical Formula 1, M1 may include Co, Mn, and / or Al. M2 may include the auxiliary elements described above. In Chemical Formula 1-1, 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, -0.5≤z≤0.1 may be satisfied.

[0114] The above-described positive electrode active material may further include a coating element or doping element. For example, elements substantially identical to or similar to the above-described auxiliary elements may be used as the coating element or doping element. For example, the above-described elements may be used singly or in combination of two or more.

[0115] The above coating element or doping element may be present on the surface of the lithium-nickel metal oxide particle, or may penetrate through the surface of the lithium-nickel metal composite oxide particle and be included in the bonding structure represented by the above chemical formula 1 or chemical formula 1-1.

[0116] The above positive electrode active material may include a nickel-cobalt-manganese (NCM) lithium oxide. In this case, an NCM lithium oxide with an increased nickel content may be used.

[0117] Ni can be provided as a transition metal associated with the output and capacity of a lithium secondary battery. Therefore, by employing a high-content (High-Ni) composition as described above in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0118] However, as the Ni content increases, the long-term storage stability and lifespan stability of the cathode or secondary battery may relatively deteriorate, and side reactions with the electrolyte may also increase. However, according to exemplary embodiments, the inclusion of Co can maintain electrical conductivity, while improving lifespan stability and capacity retention characteristics through Mn.

[0119] The content of Ni (e.g., the mole fraction of nickel among the total moles of nickel, cobalt, and manganese) in the NCM-based lithium oxide may be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the content of Ni may be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0120] In some embodiments, the positive electrode active material may include a lithium cobalt oxide-based active material, a lithium manganese oxide-based active material, a lithium nickel oxide-based active material, or a lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0121] In some embodiments, the positive electrode active material may include, for example, a Mn-rich active material, an LLO (Li rich layered oxide) / OLO (Over Lithiated Oxide) active material, or a Co-less active material having a chemical structure or crystal structure represented by Chemical Formula 2.

[0122] [Chemical Formula 2]

[0123] p[Li2MnO3]·(1-p)[Li q JO2]

[0124] In chemical formula 2, 0 <p<1이고, 0.9≤q≤1.2이며, J는 Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg 및 B 중 적어도 하나의 원소를 포함할 수 있다.

[0125] A separator may be interposed between the anode and cathode. The separator may be configured to prevent electrical short-circuiting between the anode and cathode and to allow ion flow. Depending on the embodiment, the thickness of the separator may be 10 μm to 20 μm, but the present disclosure is not limited thereto.

[0126] For example, the separator may include a porous polymer film or a porous non-woven fabric. The porous polymer film may include a polyolefin polymer such as an ethylene polymer, a propylene polymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer. The porous non-woven fabric may include high-melting-point glass fibers, polyethylene terephthalate fibers, and the like. The separator may also include a ceramic material. For example, inorganic particles may be coated on the polymer film or dispersed within the polymer film to improve heat resistance.

[0127] The above-mentioned separator may have a single-layer or multi-layer structure including the above-mentioned polymer film and / or non-woven fabric.

[0128] Lithium secondary batteries, such as those described above, have excellent rapid charging characteristics, high capacity characteristics, life characteristics, and resistance characteristics, and thus can be very useful as a power source for electric vehicles (EVs).

[0129] Examples and Comparative Examples

[0130] 1) Carbon-based active materials

[0131] First artificial graphite, first natural graphite, and second artificial graphite were prepared for application as carbon-based active materials in Examples and Comparative Examples, respectively, and the first artificial graphite, first natural graphite, and second artificial graphite were applied differently as the first carbon-based active material and the second carbon-based active material, respectively, according to Examples and Comparative Examples. The physical properties of the first artificial graphite, first natural graphite, and second artificial graphite are shown in Table 1 below.

[0132] At this time, the peak intensity value for calculating the crystal orientation index (OI) value of the carbon-based active material was measured using an XRD device (PANalytical Empyrean) with CuKα line as the target line. At this time, the measurement conditions were 2θ = 10° to 80°, scan speed (° / S) = 3, and step size 0.025° / step.

[0133] In addition, the Raman R value of the carbon-based active material was calculated from the Raman spectrum measured using a Raman spectrometer (RENISHAW Invia). At this time, I D Among the spectra measured at an excited wavelength of 532 nm using the above Raman spectrometer, 1360 cm -1 Based on the peak intensity value in , I G Using the above Raman spectrometer, the spectrum measured at an excited wavelength of 532 nm was 1580 cm -1 The peak intensity value was used as the standard. In addition, the measurement conditions were three scans and 30 seconds of laser exposure time.

[0134] (004) Peak intensity (I)(004) )(110) Peak intensity (I) (110) ) Crystal orientation index (OI) (I (004) / I (110) ) Raman R value (I D / I G ) 1st artificial graphite 1409140073.520.13 1st natural graphite 5488134462.450.34 2nd artificial graphite 870741702.090.10

[0135] 2) Manufacturing of cathode

[0136] A first negative electrode slurry including a first carbon-based active material, a binder, and a first conductive agent; and a second negative electrode slurry including a second carbon-based active material, a silicon-based active material, a binder, and a second conductive agent were each prepared. Thereafter, the first negative electrode slurry was applied onto a copper foil as a negative electrode current collector and dried at 80°C to form a first negative electrode mixture layer, and a second negative electrode slurry was applied onto the first negative electrode mixture layer and dried at 80°C to form a second negative electrode mixture layer, thereby preparing negative electrodes for lithium secondary batteries of Examples and Comparative Examples. At this time, the loading weight (LW) ratio of the first negative electrode mixture layer and the second negative electrode mixture layer was applied as 5:5.

[0137] At this time, artificial graphite and natural graphite were applied differently according to the examples and comparative examples as the first carbon-based active material and the second carbon-based active material. Specifically, whether the first negative electrode mixture layer included artificial graphite and natural graphite, whether the second negative electrode mixture layer included artificial graphite and natural graphite, the content ratio of artificial graphite and natural graphite in the first negative electrode mixture layer, and the content ratio of artificial graphite and natural graphite in the second negative electrode mixture layer are shown in Table 2 below, respectively. In addition, single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were applied differently according to the examples and comparative examples as the first conductive material and the second conductive material, and silicon oxide-based active material (SiOx; 0 <x<2)을 적용하고, 바인더로 카르복시메틸셀룰로오스(CMC) 및 스티렌-부타디엔 고무(SBR)를 적용하였다. 또한, 제1 음극 합제층 내 제1 탄소계 활물질의 함량은 95.8중량%, 제2 음극 합제층 내 제2 탄소계 활물질의 함량은 86중량%로 하였으며, 제1 음극 합제층 내 바인더의 함량은 3.7중량%, 제2 음극 합제층 내 규소계 활물질 및 바인더의 함량은 각각 12중량% 및 1.9중량%로 하였다.

[0138] The crystal orientation index (OI) of the first negative electrode mixture layer and the second negative electrode mixture layer of the examples and comparative examples, the Raman R values ​​of the first negative electrode mixture layer and the second negative electrode mixture layer, the Raman R values ​​of the first conductive material and the second conductive material, and the contents of the first conductive material and the second conductive material are shown in Table 3 below, respectively.

[0139] At this time, the peak intensity values ​​for calculating the crystal orientation index (OI) values ​​of the first cathode composite layer and the second cathode composite layer were measured using an XRD device (PANalytical Empyrean) with CuKα rays as the target line. At this time, the measurement conditions were 2θ = 10° to 80°, scan speed (° / S) = 3, and step size 0.025° / step.

[0140] In addition, the Raman R values ​​of the first cathode composite layer, the second cathode composite layer, and the conductive material were calculated from the Raman spectra measured using a Raman spectrometer (RENISHAW Invia). At this time, I D Among the spectra measured at an excited wavelength of 532 nm using the above Raman spectrometer, 1360 cm -1 Based on the peak intensity value in , I G Using the above Raman spectrometer, the spectrum measured at an excited wavelength of 532 nm was 1580 cm -1 The peak intensity value was used as the standard. In addition, the measurement conditions were three scans and 30 seconds of laser exposure time.

[0141] First cathode composite layerSecond cathode composite layerArtificial graphiteNatural graphiteWeight ratio of artificial graphite and natural graphiteSurface coating of artificial graphiteArtificial graphiteNatural graphiteWeight ratio of artificial graphite and natural graphiteSurface coating of artificial graphiteExample 1O(First artificial graphite)X-XO(Second artificial graphite)XOExample 2O(First artificial graphite)O(First natural graphite)7:3XO(Second artificial graphite)XOExample 3O(Second artificial graphite)X-X0(Second artificial graphite)XOExample 4O(First artificial graphite)X-XO(First artificial graphite)XXExample 5O(First artificial graphite)O(First natural graphite)3:7XO(Second artificial graphite)XOExample 6O(No. 1 Artificial graphite) O (1st natural graphite) 9:1 X O (2nd artificial graphite) X O Example 7 O (1st artificial graphite) O (1st natural graphite) 7:3 00 (2nd artificial graphite) X O Comparative example 1 X O (1st natural graphite) - X O (2nd artificial graphite) X O Comparative example 2 O (2nd artificial graphite) O (1st natural graphite) 7:3 00 (2nd artificial graphite) X O Comparative example 3 O (1st artificial graphite) X - X O (2nd artificial graphite) O (1st natural graphite) 7:3 O

[0142] First cathode composite layerSecond cathode composite layerCrystal orientation index (OI)(I (004) / I (110) )Raman R value (I D / I G )1st Challenge Recrystallization Orientation Index (OI)(I (004) / I (110) )Raman R value (ID / I G ) Second challenge Raman R value (I D / I G ) Content (wt%) Raman R value (I D / I G ) Content (wt%) Example 1 15.5 50.25 0.35 0.5 4.24 0.29 0.0 20.1 Example 2 13.00 0.19 0.35 0.5 4.24 0.29 0.0 20.1 Example 3 4.5 50.15 0.35 0.5 4.24 0.29 0.0 20.1 Example 4 12.9 10.28 0.35 0.5 10.39 0.310.0 20.1 Example 58.34 0.130 .350.54.240.290.020.1Embodiment 623.000.290.350.54.240.290.020.1Embodiment 712.000.140.350.50.560.540.020.1Comparative Example 19.320.380.350.54.240.280.020.1Comparative Example 29.780.30.350.54.240.260.020.1Comparative Example 312.910.280.350.58.510.190.020.1

[0143] 2) Manufacturing of secondary batteries

[0144] Li[Ni], a Li-transition metal complex oxide, on aluminum foil 0.8 Co 0.1 Mn 0.1 ]O2 was applied and dried to manufacture a positive electrode, and a polyolefin separator was interposed between the positive electrode and the negative electrode manufactured above, and the manufactured secondary battery cell was placed in a pouch for secondary batteries. Then, an electrolyte solution in which 1 M LiPF6 was dissolved in a solvent mixed with ethylene carbonate (EC) and diethyl carbonate (DEC) was injected into the pouch for secondary batteries, and then sealed to manufacture a pouch-type lithium secondary battery. The manufactured pouch-type lithium secondary battery was applied as a secondary battery sample of the examples and comparative examples.

[0145] 3) Energy density evaluation

[0146] For the manufactured secondary battery samples, a pouch-type secondary battery (cell) with a large capacity of 20 Ah or more was manufactured using the same anode and cathode, and then the battery was charged at a constant current of 0.3 C until the voltage reached 4.2 V, and then charged at a constant voltage with a cut-off at a current of 0.05 C while maintaining 4.2 V in constant voltage mode. Thereafter, the battery was discharged at a constant current of 0.3 C until the voltage reached 2.5 V, and the discharge capacity (Ah) and energy (Wh) were measured, and the volume of each battery at a 4.2 V charge state was measured to calculate the volume-energy density, and the results are shown in Table 4 below.

[0147] 4) Resistance characteristic evaluation

[0148] For the secondary battery sample above, after adjusting the SOC to 50% at 25°C and allowing a rest period of 1 hour, the resistance characteristics were measured by discharging at a 1C current for 10 seconds, and the results are shown in Table 2. Specifically, the resistance value of the secondary battery sample was measured according to the following Equation 2, and the results are shown in Table 4.

[0149] [Formula 3]

[0150] R = (V0- V1) / I

[0151] In the above equation 3, R is the resistance value of the secondary battery, V0 is the voltage of the secondary battery measured after a rest period of 1 hour after adjusting the SOC to 50% at 25°C, V1 is the voltage of the secondary battery measured after discharging for 10 seconds with a 1C current, and I is the 1C current value.

[0152] 5) Evaluation of rapid charging life characteristics

[0153] For the secondary battery sample above, a cycle of charging for 17 minutes in the range of SOC 8-80% at 25℃ and discharging at 0.3C was repeated 300 times, and the discharge capacity retention rate compared to the initial discharge capacity was measured as a %, and the results are shown in Table 4.

[0154] Energy density (Wh / L) Resistance characteristics (mΩ) Fast charging life characteristics (%) Example 17050.9192.5 Example 26990.8893.3 Example 36820.8694.1 Example 47040.9585.4 Example 56930.8793.4 Example 67020.9887.9 Example 76910.8595.5 Comparative example 16860.8491.2 Comparative example 26920.9290.1 ​​Comparative example 37121.2368.2

[0155] Referring to Tables 1 to 4 above, in Comparative Examples 1 to 3, in which a low-density negative electrode mixture layer with a relatively low crystallinity and high porosity (i.e., a negative electrode mixture layer with a relatively high Raman R value) was placed in the lower layer and a high-density negative electrode mixture layer with a relatively high crystallinity and low porosity (i.e., a negative electrode mixture layer with a relatively low Raman R value) was placed in the upper layer, the rapid charge life characteristics, etc. were found to be relatively inferior.

[0156] On the other hand, in the case of Examples 1 to 7, in which a high-density negative electrode mixture layer with a relatively high crystallinity and low porosity (i.e., a negative electrode mixture layer with a relatively low Raman R value) was placed in the lower layer and a low-density negative electrode mixture layer with a relatively low crystallinity and high porosity (i.e., a negative electrode mixture layer with a relatively high Raman R value) was placed in the upper layer, it was shown that the energy density and resistance characteristics were excellently secured, and the rapid charge life characteristics were relatively excellent.

[0157] It is believed that the energy density of the negative electrode is improved because the lower layer of the multilayer structure negative electrode includes a high-density negative electrode composite layer with relatively high crystallinity and low porosity, and the upper layer includes a low-density negative electrode composite layer with relatively low crystallinity and high porosity, which facilitates the entry and exit of lithium ions, thereby improving the rapid charging characteristics of the negative electrode.

[0158] Meanwhile, referring to Examples 1 and 2, Example 2 including natural graphite was found to have better energy density, resistance characteristics, and rapid charge life characteristics than Example 1 not including natural graphite. This is believed to be because natural graphite improved the electrode adhesion and resistance characteristics of the first negative electrode mixture layer.

[0159] In addition, Example 3, in which the lower first negative electrode composite layer contained the second artificial graphite and thus had a relatively low OI value and thus low-orientation characteristics, showed a lower energy density compared to Examples 1 and 2. In addition, Example 4, in which the upper second negative electrode composite layer contained the first artificial graphite without surface coating and thus had a high OI value and thus high-orientation characteristics, showed inferior rapid charging performance compared to Examples 1 and 2.

[0160] Meanwhile, Example 5, which had a higher content of the first natural graphite than the first artificial graphite included in the lower first negative electrode mixture layer, had a low OI value of the first negative electrode mixture layer, resulting in a large low-orientation characteristic and a low energy density. In addition, Example 6, which had a higher content of the first artificial graphite than the first natural graphite included in the lower first negative electrode mixture layer, had a high OI value of the first negative electrode mixture layer, resulting in a large high-orientation characteristic and a low rapid charging performance. In addition, Example 7, which includes artificial graphite on the surface of both the first negative electrode mixture layer and the second negative electrode mixture layer, had a low energy density because the OI values ​​of the negative electrode mixture layers were low and thus the low-orientation characteristic was present.

[0161] Considering these results, it is judged that when a first negative electrode mixture layer having a relatively high crystallinity and a low porosity and a high density and high orientation is disposed at the bottom as in Examples 1 and 2, the first negative electrode mixture layer appropriately includes a conductive material having excellent dispersibility, and a second negative electrode mixture layer having a relatively low crystallinity and a high porosity and a low density and low orientation is disposed at the top, and appropriately includes a conductive material having excellent conductivity, it is possible to provide a negative electrode for a lithium secondary battery having excellent energy density, resistance characteristics, and rapid charging characteristics, and a lithium secondary battery including the same.

[0162] While the embodiments of the present disclosure have been described in detail above, they are merely exemplary, and those skilled in the art will understand that various modifications and equivalent alternative embodiments are possible. Therefore, the true scope of technical protection of the present disclosure should be determined by the technical spirit of the appended claims.

[0163] The present disclosure may also relate to the following aspects:

[0164] Aspect 1) A negative electrode for a lithium secondary battery comprises: a negative electrode current collector; a first negative electrode mixture layer formed on at least one surface of the negative electrode current collector and including a first carbon-based active material; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second carbon-based active material and a silicon-based active material, wherein the first negative electrode mixture layer may have a Raman R value according to the following Equation 1 that is smaller than that of the second negative electrode mixture layer.

[0165] [Formula 1]

[0166] Raman R = I D / I G

[0167] (In the above equation 1, I D is 1350 to 1380 cm -1 is the peak intensity value of the absorption region, and I Gis 1580 to 1600 cm -1 (This is the peak intensity value of the absorption region.)

[0168] Side 2) In side 1, the first negative electrode composite layer may not include a silicon-based active material.

[0169] Side 3) In side 1 or 2, the first cathode composite layer may have an OI value according to the following formula 2 that is greater than that of the second cathode composite layer.

[0170] [Formula 2]

[0171] OI = I 004 / I 110

[0172] (In the above formula 2, OI is the crystal orientation index according to XRD measurement, and I 004 is the peak intensity of the (004) plane in the XRD measurement of the cathode composite layer, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the negative electrode composite layer.

[0173] Side 4) In side 3, the first cathode composite layer may have an OI value of 9 to 18.

[0174] Side 5) In side 3 or 4, the second cathode composite layer may have an OI value of 1 to 8.

[0175] Side 6) In any one of Sides 1 to 5, the first cathode composite layer may have a Raman R value of 0.15 to 0.27.

[0176] Side 7) In any one of Sides 1 to 6, the second cathode composite layer may have a Raman R value of 0.281 to 0.55.

[0177] Aspect 8) In any one of aspects 1 to 7, the first carbon-based active material and the second carbon-based active material may each independently include artificial graphite.

[0178] Aspect 9) In any one of aspects 1 to 8, the first carbon-based active material may further include natural graphite.

[0179] Side 10) In any one of sides 1 to 9, the first carbon-based active material may not be surface-coated.

[0180] Side 11) In any one of sides 1 to 10, the second carbon-based active material may be surface-coated with at least one selected from the group consisting of hard carbon, soft carbon, heavy oil, and pitch.

[0181] Aspect 12) A lithium secondary battery may include a negative electrode for a lithium secondary battery according to any one of aspects 1 to 11.

[0182] [Explanation of symbols]

[0183] 1: Carbon-based active material 2: Basel plain

[0184] 3: Edge plane 10: Negative current collector

[0185] 20: Cathode composite layer 21: First cathode composite layer

[0186] 22: Second negative electrode composite layer 100: Negative electrode for lithium secondary battery

[0187] As described above, the features of the present invention can be applied in whole or in part to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

Claims

1. Negative current collector; A first negative electrode composite layer formed on at least one surface of the negative electrode current collector and including a first carbon-based active material; and A second negative electrode composite layer formed on the first negative electrode composite layer and including a second carbon-based active material and a silicon-based active material, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has a Raman R value according to the following formula 1 that is smaller than that of the second negative electrode composite layer. [Formula 1] Raman R = I D / I G (In the above equation 1, I D is 1350 to 1380 cm -1 is the peak intensity value of the absorption region, and I G is 1580 to 1600 cm -1 (is the peak intensity value of the absorption region).

2. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer does not contain a silicon-based active material.

3. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has an OI value according to the following formula 2 that is greater than that of the second negative electrode composite layer. [Formula 2] OI = I 004 / I 110 (In the above formula 2, OI is the crystal orientation index according to XRD measurement, and I 004 is the peak intensity of the (004) plane in the XRD measurement of the cathode composite layer, and I 110 is the peak intensity of the (110) plane in the XRD measurement of the cathode composite layer.) 4. In paragraph 3, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has an OI value of 9 to 18.

5. In paragraph 3, A negative electrode for a lithium secondary battery, wherein the second negative electrode composite layer has an OI value of 1 to 8.

6. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has a Raman R value of 0.15 to 0.

27.

7. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the second negative electrode composite layer has a Raman R value of 0.281 to 0.

55.

8. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first carbon-based active material and the second carbon-based active material each independently contain artificial graphite.

9. In paragraph 6, A negative electrode for a lithium secondary battery, wherein the first carbon-based active material further comprises natural graphite.

10. In paragraph 1, The above first carbon-based active material is a negative electrode for a lithium secondary battery that is not surface-coated.

11. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the second carbon-based active material is surface-coated with at least one selected from the group consisting of hard carbon, soft carbon, heavy oil, and pitch.

12. A lithium secondary battery comprising a negative electrode for a lithium secondary battery according to any one of claims 1 to 11.

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