Anode for lithium secondary battery and lithium secondary battery including same

Abstract

An anode for a lithium secondary battery, according to one embodiment of the present disclosure, comprises: an anode current collector; a first anode mixture layer formed on at least one surface of the anode current collector and comprising a first carbon-based active material comprising artificial graphite and natural graphite; and a second anode mixture layer formed on the first anode mixture layer and comprising a second carbon-based active material comprising artificial graphite, wherein the first anode mixture layer and the second anode mixture layer each comprise a silicon-based active material, and the first anode mixture layer has a greater OI value, according to formula 1 below, than the second anode mixture layer. [Formula 1] OI = I004 / I110 (In formula 1, OI is the crystal orientation index according to an XRD measurement, I004 is the peak intensity of the (004) plane when the XRD measurement is performed for an anode mixture layer, and I110 is the peak intensity of the (110) plane when the XRD measurement is performed for the mixture layer.)

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 including artificial graphite and natural graphite; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second carbon-based active material including artificial graphite, wherein the first negative electrode mixture layer and the second negative electrode mixture layer each include a silicon-based active material, and wherein the first negative electrode mixture layer has an OI value according to the following Equation 1 that is greater than that of the second negative electrode mixture layer.

[0007] [Formula 1]

[0008] OI = I 004 / I 110

[0009] (In the above formula 1, 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 (110) plane peak intensity during XRD measurement of the composite layer.)

[0010] In some implementations, the first cathode composite layer may have an OI value of 9 to 18.

[0011] In some implementations, the second cathode composite layer may have an OI value of 1 to 8.

[0012] In some embodiments, the first carbon-based active material may have a Raman R value according to Equation 2 that is greater than that of the second carbon-based active material.

[0013] [Formula 2]

[0014] Raman R = I D / I G

[0015] (In the above equation 2, 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.)

[0016] In some embodiments, the first carbon-based active material may have a Raman R value of 0.11 to 0.50.

[0017] In some embodiments, the second carbon-based active material may have a Raman R value of 0.01 to 0.10.

[0018] In some embodiments, the content of artificial graphite in the first negative electrode composite layer may be from 50 wt% to 90 wt%, and the content of natural graphite in the first negative electrode composite layer may be from 10 wt% to 50 wt%.

[0019] In some embodiments, the first carbon-based active material may have a bimodal form, and the second carbon-based active material may have a single particle form.

[0020] In some embodiments, the first carbon-based active material may not be surface coated.

[0021] 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.

[0022] In some embodiments, the first cathode composite layer may further include a first conductive material, the second cathode composite layer may further include a second conductive material, and the first conductive material and the second conductive material may be different from each other.

[0023] In some implementations, the Raman R value of the first conductive material may have a Raman R value according to Equation 2 below that is greater than that of the second conductive material.

[0024] [Formula 2]

[0025] Raman R = I D / I G

[0026] (In the above equation 2, 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.)

[0027] In some implementations, the Raman R value of the first challenge material may be from 0.1 to 1.8.

[0028] In some implementations, the Raman R value of the second challenge material may be from 0.01 to 0.09.

[0029] 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.

[0030] According to one embodiment of the present disclosure, a negative electrode for a lithium secondary battery having excellent energy density can be provided.

[0031] According to another embodiment of the present disclosure, a negative electrode for a lithium secondary battery having excellent rapid charging characteristics can be provided.

[0032] According to another embodiment of the present disclosure, the resistance value of a negative electrode for a lithium secondary battery can be reduced.

[0033] 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.

[0034] Figure 2 is a schematic cross-sectional view showing the structure of a negative electrode for a lithium secondary battery according to one embodiment.

[0035] 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.

[0036] In this specification, the 'orientation' of 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 an active material means a low-oriented active material with a small orientation, and a relatively larger OI value means a high-oriented active material with a large orientation.

[0037] 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.

[0038] 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 secure a high level of energy density of the anode.

[0039] 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.

[0040] 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.

[0041] Figure 2 is a schematic cross-sectional view showing the structure of a negative electrode for a lithium secondary battery according to one embodiment.

[0042] Cathode for lithium secondary batteries

[0043] A negative electrode (100) for a lithium secondary battery according to one embodiment of the present disclosure 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).

[0044] The first negative electrode composite layer (21) includes a first carbon-based active material, the second negative electrode composite layer (22) includes a second carbon-based active material, and the first negative electrode composite layer and the second negative electrode composite layer may each include a silicon-based active material.

[0045] The above first carbon-based active material may have an OI value according to the following equation 1 that is greater than that of the above second carbon-based active material.

[0046] [Formula 1]

[0047] OI = I 004 / I 110

[0048] In the above formula 1, OI is the crystal orientation index according to XRD measurement, and I 004 is the peak intensity of the (004) plane in XRD measurement for carbon-based active materials, and I 110 is the peak intensity of the (110) plane in XRD measurements for carbon-based active materials.

[0049] 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.

[0050] According to one embodiment of the present disclosure, 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 include 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 include the second carbon-based active material having a relatively low crystal orientation index (OI) value. Hereinafter, the crystal orientation index (OI) of the carbon-based active material will be described in more detail.

[0051] The above 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 ) as a ratio, which means the orientation index (OI) value. 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 active material, and I 110 It can 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 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Accordingly, a negative electrode (100) for a lithium secondary battery according to one embodiment of the present disclosure has a multilayer structure, and may include carbon-based active materials with different orientations for each layer, thereby exhibiting excellent rapid charging characteristics and energy density. Specifically, a first negative electrode mixture layer (21) includes the first carbon-based active material, a second negative electrode mixture layer (22) includes the second carbon-based active material, and the first carbon-based active material may have a greater OI value than the second carbon-based active material.

[0057] That is, the first negative electrode mixture layer (21), which is the lower layer, can be rolled at a high density by including the first carbon-based active material having a relatively high orientation with an orientation index (OI) value, and thus the negative electrode (100) can secure a high energy density. In addition, the second negative electrode mixture layer (22), which is the upper layer, can include the second carbon-based active material having a relatively low orientation with an orientation index (OI) value, so that lithium ions can easily enter and exit the negative electrode mixture layer adjacent to the electrolyte in which a large amount of lithium ions exist, and thus the negative electrode (100) can secure excellent rapid charging characteristics. Accordingly, the first negative electrode mixture layer (21) can have a higher OI value than the second negative electrode mixture layer (22).

[0058] 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.

[0059] 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.

[0060] More specifically, the first cathode composite layer (21) may have an OI value of about 15 to about 17, and the second cathode composite layer (22) may have an OI value of about 3 to about 5.

[0061] 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.

[0062] The OI value of the first carbon-based active material may be about 2.1 to about 5, and the OI value of the second carbon-based active material may be about 1 to about 2.1.

[0063] The first carbon-based active material may include artificial graphite and natural graphite, and the second carbon-based active material may include artificial graphite. The OI values ​​of the artificial graphite and natural graphite included in the first carbon-based active material may be higher than the OI value of the artificial graphite included in the second carbon-based active material. For example, the artificial graphite included in the first carbon-based active material may have an OI value of about 3 to about 5, the natural graphite included in the first carbon-based active material may have an OI value of 2.1 to 3, and the artificial graphite included in the second carbon-based active material may have an OI value of about 1 to about 2.1.

[0064] When the crystal orientation index (OI) values ​​of the first carbon-based active material and the second carbon-based active material 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 negative electrode can be appropriately controlled within different ranges, so that the rapid charging characteristics, energy density, etc. of the negative electrode can all be excellent.

[0065] Meanwhile, the first carbon-based active material may have a Raman R value according to Equation 2 below that is greater than that of the second carbon-based active material.

[0066] [Formula 2]

[0067] Raman R = I D / I G

[0068] In the above equation 2, 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.

[0069] 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 G The 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.

[0070] For example, the Raman R value of the first carbon-based active material may be from about 0.11 to about 0.50, and the Raman R value of the second carbon-based active material may be from about 0.01 to about 0.10.

[0071] The first carbon-based active material may include artificial graphite and natural graphite, and the second carbon-based active material may include artificial graphite. The Raman R values ​​of the artificial graphite and natural graphite included in the first carbon-based active material may be higher than the Raman R value of the artificial graphite included in the second carbon-based active material. For example, the Raman R value of the artificial graphite included in the first carbon-based active material may be about 0.10 to about 0.15, the Raman R value of the natural graphite included in the first carbon-based active material may be about 0.30 to about 0.50, and the Raman R value of the artificial graphite included in the second carbon-based active material may be about 0.01 to about 0.10.

[0072] When the Raman R values ​​of the first carbon-based active material and the second carbon-based active material are adjusted within the above-described range, a high-density carbon-based active material having a relatively high degree of crystallinity and a low porosity can be included in the lower layer of the multilayered negative electrode to improve the energy density of the negative electrode, and a low-density energy carbon-based active material having a relatively low degree of crystallinity and a high porosity can be included in the upper layer to facilitate the entry and exit of lithium ions, thereby improving the rapid charging characteristics of the negative electrode.

[0073] The first carbon-based active material and the second carbon-based active material are not particularly limited as long as they can satisfy the above-described OI values, etc. For example, the first carbon-based active material and the second carbon-based active material may 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.

[0074] Specifically, considering the ease of controlling the orientation of the active material, etc., the first carbon-based active material and the second carbon-based active material may each include artificial graphite.

[0075] More specifically, the first carbon-based active material may include artificial graphite and natural graphite, and the second carbon-based active material may include artificial graphite.

[0076] The above first carbon-based active material can include natural graphite, thereby reducing cell resistance and improving electrode adhesion.

[0077] 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.

[0078] The content of artificial graphite in the first negative electrode mixture layer may be 50 to 90 wt%, and the content of natural graphite in the first negative electrode mixture layer may be 10 to 50 wt%. When the content of artificial graphite and the content of natural graphite in the first negative electrode mixture layer are within the above-described ranges, cell resistance may be reduced and electrode adhesion may be improved. When the content of natural graphite in the first negative electrode mixture layer exceeds the above-described range, cell resistance may increase and lifespan may be deteriorated. When the content of natural graphite in the first negative electrode mixture layer is less than the above-described range, the effect of improving electrode adhesion and the effect of reducing cell resistance may be insufficient.

[0079] 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.

[0080] In addition, the first carbon-based active material may have a bimodal form in which primary particles and secondary particles are mixed, and the second carbon-based active material may have a single particle form. Here, the secondary particle means a particle in which a plurality of primary particles (for example, more than 10) are assembled or aggregated to form substantially a single particle, and the single particle form may mean excluding the secondary particle. However, the single particle form does not exclude a case in which 2 to 10 single particles are attached or adhered to each other to have a substantially single body form (for example, a structure converted into a single particle).

[0081] Meanwhile, the first negative electrode composite layer (21), which is the lower layer, can be rolled at a high density by including the first carbon-based active material in a bimodal form with excellent rolling characteristics, and thus the negative electrode (100) can secure a high energy density. In addition, the second negative electrode composite layer (22), which is the upper layer, includes the second carbon-based active material in a single particle form with excellent rapid charging characteristics, and thus the negative electrode (100) can secure excellent rapid charging characteristics.

[0082] 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. 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, thereby improving hardness and providing excellent rapid charging characteristics.

[0083] 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.

[0084] 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 80 to about 90 wt%.

[0085] The content of the silicon-based active material in the first negative electrode mixture layer (21) may be about 0.1 to about 6 wt%. Specifically, the content of the silicon-based active material in the second negative electrode mixture layer (22) may be about 1 to about 4 wt%. The content of the silicon-based active material in the second negative electrode mixture layer (22) may be about 8 to about 20 wt%. Specifically, the content of the silicon-based active material in the second negative electrode mixture layer (22) may be about 10 to about 15 wt%.

[0086] When the content and ratio of the silicon-based active material in the first negative electrode composite layer (21) and the second negative electrode composite layer (22) are within the above-described ranges, the first negative electrode composite layer (21) formed on one surface adjacent to the negative electrode current collector (10) does not include a silicon-based active material, thereby alleviating 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 composite 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.

[0087] The silicon-based active material included in the first negative electrode composite layer (21) and 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.

[0088] In general, Si-C composites have high capacity and low resistance characteristics compared to existing silicon oxide-based active materials, but due to structural collapse of the active material during the charge / discharge process, a short circuit (isolation) phenomenon may occur between the Si-C composite and the carbon-based active material, which may deteriorate the life characteristics of the battery. Therefore, when a silicon oxide-based active material with relatively less structural collapse during the charge / discharge process is applied to the first negative electrode composite layer (21), problems such as short circuit (isolation) phenomenon between the carbon-based active material and the silicon oxide-based active material in the electrode, unlike when a Si-C composite is applied, can be alleviated, and at the same time, a high energy density can be secured at the same time by applying a Si-C composite with relatively high capacity and low resistance characteristics to the second negative electrode composite layer (22). That is, the first negative electrode composite layer (21) may include a silicon oxide-based active material as the silicon-based active material, and the second negative electrode composite layer (22) may include a silicon carbide-based active material as the silicon-based active material.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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).

[0094] When the Raman R value, type, etc. of the first conductive material and the second conductive material are applied as described above, by including a conductive material with relatively low crystallinity in the first negative electrode mixture layer (21) adjacent to the negative electrode current collector (10), problems such as electrode detachment due to volume expansion of the silicon-based active material can be substantially alleviated. In addition, by including a conductive material with high crystallinity and excellent conductivity and dispersibility in the second negative electrode mixture layer (22) having relatively low energy density, a conductive path can be formed and maintained within the electrode layer, thereby further improving the rapid charging characteristics.

[0095] 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%.

[0096] 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.

[0097] The first cathode composite layer (21) and the second cathode composite layer (22) may each further include a binder.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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%.

[0102] 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.

[0103] 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.

[0104] 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).

[0105] 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.

[0106] 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.

[0107] The method for manufacturing the negative electrode (100) for a lithium secondary battery of the present disclosure is not particularly limited, and may 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.

[0108] 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.

[0109] lithium secondary battery

[0110] A lithium secondary battery according to one embodiment of the present disclosure 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.

[0111] 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.

[0112] 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.

[0113] 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).

[0114] 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.

[0115] [Chemical Formula 1]

[0116] Li x Ni a M b O 2+z

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] [Chemical Formula 1-1]

[0123] Li x Ni a M1 b1 M2 b2 O 2+z

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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).

[0132] 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.

[0133] [Chemical Formula 2]

[0134] p[Li2MnO3]·(1-p)[Li q JO2]

[0135] 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.

[0136] 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.

[0137] For example, the separator may include a porous polymer film or a porous nonwoven 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 nonwoven 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.

[0138] The above-mentioned separator may have a single-layer or multi-layer structure including the above-mentioned polymer film and / or non-woven fabric.

[0139] 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).

[0140] Examples and Comparative Examples

[0141] 1) Carbon-based active materials

[0142] 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 first artificial graphite, first natural graphite, and second artificial graphite were applied differently as first and second carbon-based active materials, 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.

[0143] 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.

[0144] 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.

[0145] (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

[0146] 2) Manufacturing of cathode

[0147] A first negative electrode slurry including a first carbon-based active material, a silicon-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.

[0148] At this time, carbon-based active materials were applied differently in the first negative electrode composite layer and the second negative electrode composite layer according to the examples and comparative examples as shown in Table 2 below, and single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were applied differently as the first conductive material and the second conductive material according to the examples and comparative examples, and silicon-based active materials were silicon oxide-based active materials (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 93.8중량%, 제2 음극 합제층 내 제2 탄소계 활물질의 함량은 86 중량%로 하였으며, 제1 음극 합제층 내 규소계 활물질 및 바인더의 함량은 각각 2 중량% 및 3.7 중량%, 제2 음극 합제층 내 규소계 활물질 및 바인더의 함량은 각각 12중량% 및 1.9중량%로 하였다. 한편, 하드카본으로 표면 코팅된 인조 흑연을 표면 코팅된 탄소계 활물질로 사용하였다.

[0149] The crystal orientation index (OI) of the first electrode mixture layer and the second electrode mixture layer applied to the negative electrode mixture layer of the examples and comparative examples, the Raman R values ​​of the first and second conductive materials, and the contents of the first and second conductive materials are shown in Table 3 below, respectively.

[0150] In addition, the Raman R value of the challenge 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.

[0151] First cathode composite layerSecond cathode composite layerArtificial graphiteNatural graphiteWeight ratio of artificial graphite and natural graphiteArtificial graphiteSurface coatingArtificial graphiteNatural graphiteArtificial graphiteSurface coatingExample 1O(First artificial graphite)O(First natural graphite)7:3XO(Second artificial graphite)XOExample 2O(First artificial graphite)O(First natural graphite)7:3XO(First artificial graphite)XOExample 3O(Second artificial graphite)O(First natural graphite)7:3XO(Second artificial graphite)XOExample 4O(First artificial graphite)O(First natural graphite)7:3XO(Second artificial graphite)XOExample 5O(1st artificial graphite)O(1st natural graphite)3:7XO(2nd artificial graphite)XOExample 6O(1st artificial graphite)O(1st natural graphite)9:1XO(2nd artificial graphite)XOExample 7O(1st artificial graphite)O(1st natural graphite)7:3OO(2nd artificial graphite)XOComparative example 1O(2nd artificial graphite)O(1st natural graphite)7:3XO(1st artificial graphite)XO

[0152] First cathode composite layer (lower layer)Second cathode composite layer (upper layer)First electrode composite layerCrystal orientation index (OI)(I (004) / I (110) )1st challenge agent2nd electrode composite layer crystal orientation index (OI)(I (004) / I (110) ) The second challenge material R value (I D / I G ) content (wt%) Raman R value (I D / I G ) Content (wt%) Example 116.000.350.54.240.020.1 Example 216.000.350.513.60.020.1 Example 34.550.350.54.240.020.1 Example 416.000.350.54.550.350.1 Example 58.340.350.54.240.020.1 Example 623.000.350.54.240.020.1 Example 712.000.350.50.560.020.1 Comparative Example 14.550.350.513.60.020.1

[0153] 3) Manufacturing of secondary batteries

[0154] Li[Ni], a Li-transition metal complex oxide, on aluminum foil 0.8 Co 0.1 Mn0.1 ]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.

[0155] 4) Energy density evaluation

[0156] 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.

[0157] 5) Resistance characteristic evaluation

[0158] 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.

[0159] [Formula 3]

[0160] R = (V0- V1) / I

[0161] 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.

[0162] 6) Evaluation of rapid charging life characteristics

[0163] 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.

[0164] Energy density (Wh / L) Resistance characteristics (mΩ) Fast charging life characteristics (%) Example 1700 0.90 92.7 Example 2705 0.94 81.5 Example 3689 0.91 93.0 Example 4701 0.97 74.3 Example 5693 0.93 93.3 Example 6702 0.98 72.9 Example 7691 0.95 80.5 Comparative example 1688 0.99 70.3

[0165] Referring to Tables 1 to 4 above, in Comparative Example 1, which includes a relatively low-oriented carbon-based active material in the first negative electrode mixture layer (lower layer) and a relatively high-oriented carbon-based active material in the second negative electrode mixture layer (upper layer), the energy density, resistance characteristics, and rapid charge life characteristics were found to be relatively inferior to those of Examples 1 to 7. This is believed to be because the conductive path is not properly formed due to the increase in pores in the first negative electrode mixture layer (lower layer) including a low-oriented carbon-based active material, and the second negative electrode mixture layer (upper layer), which is subjected to excessive pressure during electrode rolling to match the energy density, includes a highly oriented carbon-based active material, making it difficult for lithium ions to enter and exit.

[0166] Meanwhile, Example 2, which has a relatively high orientation with an OI value of more than 8 in the upper second negative electrode mixture layer in contact with the electrolyte, showed relatively poor resistance characteristics and rapid charging characteristics compared to Example 1 because lithium ions were relatively difficult to enter and exit from the upper layer. In addition, Example 3 showed that the energy density was relatively inferior to Example 1 because both the upper and lower negative electrode mixture layers had OI values ​​of less than 9, which corresponds to a relatively low orientation. In addition, Example 4, which includes a conductive material with a relatively high Raman R value in the second negative electrode mixture layer (upper layer), showed that the OI value of the upper negative electrode mixture layer was relatively high compared to Example 1, and the rapid charging characteristics were relatively poor compared to Example 1.

[0167] In addition, in the case of Example 5, which has a relatively low orientation because the lower first negative electrode mixture layer has an OI value of less than 9, the energy density was found to be inferior compared to Example 1. In addition, in the case of Example 6, which has an excessively high orientation because the lower first negative electrode mixture layer has an OI value of more than 18, the rapid charging performance was found to be inferior compared to Example 1. On the other hand, in the case of Example 7, which has a relatively low orientation because the upper second negative electrode mixture layer has an OI value of less than 1, the energy density was found to be inferior compared to Example 1.

[0168] Considering these results, it is judged that when the lower first negative electrode mixture layer, as in Example 1, appropriately includes a highly oriented carbon-based active material and a conductive material with excellent dispersibility, and the upper second negative electrode mixture layer appropriately includes a low oriented carbon-based active material and a conductive material with 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.

[0169] 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.

[0170] The present disclosure may also relate to the following aspects:

[0171] 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 including artificial graphite and natural graphite; and a second negative electrode mixture layer formed on the first negative electrode mixture layer and including a second carbon-based active material including artificial graphite, wherein the first negative electrode mixture layer and the second negative electrode mixture layer each include a silicon-based active material, and the first negative electrode mixture layer may have an OI value according to the following Equation 1 that is greater than that of the second negative electrode mixture layer.

[0172] [Formula 1]

[0173] OI = I 004 / I 110

[0174] (In the above formula 1, 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 (110) plane peak intensity during XRD measurement of the composite layer.)

[0175] Side 2) In side 1, the first cathode composite layer may have an OI value of 9 to 18.

[0176] Side 3) In side 1 or 2, the second cathode composite layer may have an OI value of 1 to 8.

[0177] Aspect 4) In any one of aspects 1 to 3, the first carbon-based active material may have a Raman R value according to the following equation 2 that is greater than that of the second carbon-based active material.

[0178] [Formula 2]

[0179] Raman R = I D / I G

[0180] (In the above equation 2, 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.)

[0181] Aspect 5) In aspect 4, the first carbon-based active material may have a Raman R value of 0.11 to 0.50.

[0182] Aspect 6) In aspect 4 or 5, the second carbon-based active material may have a Raman R value of 0.01 to 0.10.

[0183] Side 7) In any one of Sides 1 to 6, the content of artificial graphite in the first negative electrode composite layer may be 50 wt% to 90 wt%.

[0184] Aspect 8) In any one of aspects 1 to 7, the first carbon-based active material may have a bimodal form, and the second carbon-based active material may have a single particle form.

[0185] Side 9) In any one of sides 1 to 8, the first carbon-based active material may not be surface-coated.

[0186] Side 10) In any one of Sides 1 to 9, 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.

[0187] Side 11) In any one of Sides 1 to 10, the first cathode composite layer further includes a first conductive material, the second cathode composite layer further includes a second conductive material, and the first conductive material and the second conductive material may be different from each other.

[0188] Side 12) In side 11, the Raman R value of the first conductive material may have a Raman R value according to the following equation 2 that is greater than that of the second conductive material.

[0189] [Formula 2]

[0190] Raman R = I D / I G

[0191] (In the above equation 2, 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.)

[0192] Side 13) In side 12, the Raman R value of the first conductive material may be 0.1 to 1.8.

[0193] Side 14) In side 12 or 13, the Raman R value of the second conductive material may be 0.01 to 0.09.

[0194] Aspect 15) A lithium secondary battery may include a negative electrode for a lithium secondary battery according to any one of aspects 1 to 14.

[0195] [Explanation of symbols]

[0196] 1: Carbon-based active material 2: Basel plain

[0197] 3: Edge plane 10: Negative current collector

[0198] 20: Cathode composite layer 21: First cathode composite layer

[0199] 22: Second negative electrode composite layer 100: Negative electrode for lithium secondary battery

[0200] 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 including artificial graphite and natural graphite; and A second negative electrode composite layer formed on the first negative electrode composite layer and including a second carbon-based active material including artificial graphite, The first negative electrode composite layer and the second negative electrode composite layer each contain a silicon-based active material, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has an OI value according to the following Equation 1 greater than that of the second negative electrode composite layer. [Formula 1] OI = I 004 / I 110 (In the above formula 1, 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 (110) plane peak intensity during XRD measurement of the composite layer.) 2. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first negative electrode composite layer has an OI value of 9 to 18.

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

4. In paragraph 1, A negative electrode for a lithium secondary battery, wherein the first carbon-based active material has a Raman R value according to the following equation 2 that is greater than that of the second carbon-based active material. [Formula 2] Raman R = I D / I G (In the above equation 2, 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).

5. In paragraph 4, A negative electrode for a lithium secondary battery, wherein the first carbon-based active material has a Raman R value of 0.11 to 0.

50.

6. In paragraph 4, A negative electrode for a lithium secondary battery, wherein the second carbon-based active material has a Raman R value of 0.01 to 0.

10.

7. In paragraph 1, The content of artificial graphite in the first cathode composite layer is 50 wt% to 90 wt%, A negative electrode for a lithium secondary battery, wherein the content of natural graphite in the first negative electrode composite layer is 10 to 50 wt%.

8. In paragraph 1, The above first carbon-based active material has a bimodal form, A negative electrode for a lithium secondary battery, wherein the second carbon-based active material has a single particle form.

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

10. 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.

11. In paragraph 1, The first cathode composite layer further includes a first conductive material, The second cathode composite layer further includes a second conductive material, A negative electrode for a lithium secondary battery, wherein the first conductive material and the second conductive material are different from each other.

12. In paragraph 11, A negative electrode for a lithium secondary battery, wherein the Raman R value of the first conductive material is greater than that of the second conductive material according to the following equation 2. [Formula 2] Raman R = I D / I G (In the above equation 2, 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).

13. In paragraph 12, A negative electrode for a lithium secondary battery, wherein the Raman R value of the first challenge material is 0.1 to 1.

8.

14. In paragraph 12, A negative electrode for a lithium secondary battery, wherein the Raman R value of the second challenge material is 0.01 to 0.

09.

15. A lithium secondary battery comprising a negative electrode for a lithium secondary battery according to any one of claims 1 to 14.

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