Positive electrode for secondary battery and secondary battery comprising the same

Abstract

The present application makes it possible to make the distribution of the binder uniform in the thickness direction of the electrode active material layer by applying a double-layer coating method when manufacturing an electrode having the same thickness, and to keep the binder resin in the lower portion of the positive electrode active material layer, thus having the effect of improving the adhesion strength. In addition, by making the composition of the positive electrode material different in the upper portion and the lower portion of the positive electrode, and in particular by injecting a sacrificial positive electrode material into only the lower portion, the electrochemical characteristics of the battery can be improved.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2021-0136984, filed in Korea on October 14, 2021; Korean Patent Application No. 10-2020-0132967, filed in Korea on October 14, 2020; and Korean Patent Application No. 10-2020-0186566, filed in Korea on December 29, 2020. The present invention relates to a positive electrode for a secondary battery. The present invention also relates to a secondary battery comprising the positive electrode. Background Technology

[0002] Thanks to the development of high-output, high-energy-density batteries, secondary batteries, including lithium-ion batteries, have been applied in a variety of fields, from powering portable electronic devices such as laptops, mobile phones, digital cameras and camcorders to electric vehicles.

[0003] To improve the energy density and high-rate characteristics of such secondary batteries and develop high-capacity batteries, it has been proposed to use cathode materials including Ni-rich lithium composite oxide materials and anode materials including silicon-based (silicon and / or silicon oxide) materials. Furthermore, when using Ni-rich lithium composite oxides as the cathode material, lithium nickel oxide (LNO, such as Li₂NiO₂) with high irreversible capacity is used as a sacrificial cathode material. However, a disadvantage of LNO sacrificial cathode materials is their high cost, leading to increased production costs. Additionally, there is a need for sacrificial cathode materials with higher charging capacity and irreversible capacity compared to LNO.

[0004] Meanwhile, the electrodes of secondary batteries are typically formed by coating an electrode slurry onto an electrode current collector in a single step. Here, the binder contained in the electrode slurry is not uniformly dispersed within the coated electrode active material layer, but rather floats on the surface of the electrode active material layer. In this case, the battery exhibits increased resistance due to the binder, thus undesirably leading to degradation of battery performance. This problem becomes more severe as the loading of electrode active material increases. Furthermore, the formation of conventional monolayer electrodes has limitations in achieving improved battery performance if battery performance can be improved by positioning the electrode material at specific portions of the electrode (e.g., the lower or upper layer of the electrode).

[0005] Therefore, it is necessary to develop electrodes with multiple electrode active material layers, each containing suitable electrode materials, in order to develop high-capacity secondary batteries with increased electrode active material capacity and maximized performance improvement of secondary batteries. Summary of the Invention

[0006] Technical issues

[0007] This invention is designed to solve the problems of related technologies. Therefore, this invention aims to provide a positive electrode for a secondary battery, which includes a layer of positive electrode active material having a uniform binder distribution in the thickness direction. This invention also aims to provide a positive electrode for a secondary battery comprising a plurality of positive electrode active material layers, each containing a suitable positive electrode active material by using positive electrode active materials of different compositions in the upper and lower portions of the positive electrode.

[0008] Furthermore, this invention aims to provide a battery comprising a sacrificial positive electrode material to compensate for the irreversible capacity generated when using Ni-rich lithium composite oxide materials as the positive electrode active material, and to reduce gas generation. Specifically, this invention aims to provide a positive electrode for a secondary battery comprising a sacrificial positive electrode material disposed in the lower portion of the positive electrode to prevent the sacrificial positive electrode material from contacting air and deteriorating.

[0009] Finally, the present invention aims to provide a battery that uses single-walled carbon nanotubes (SWCNTs) as a conductive material in order to ensure the conductivity of the silicon-based anode.

[0010] It is readily understood that the objects and advantages of the present invention can be achieved by means shown in the appended claims and combinations thereof.

[0011] Technical solution

[0012] According to a first embodiment of the present invention, a positive electrode for a secondary battery is provided, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a lower layer disposed on the surface of the current collector and an upper layer disposed on the lower layer, the upper layer comprising a first positive electrode active material, a conductive material and a binder resin, the lower layer comprising a second positive electrode active material, a sacrificial positive electrode material, a conductive material and a binder resin, and the first positive electrode active material and the second positive electrode active material each comprising at least one compound selected from the following chemical formula 1:

[0013] [Chemical Formula 1]

[0014] LiNi 1-x M x O2

[0015] M includes at least one of Mn, Co, Al, Cu, Fe, Mg, B and Ga, and x is 0-0.5.

[0016] According to a second embodiment of the present invention, a positive electrode for a secondary battery as defined in the first embodiment is provided, wherein the sacrificial positive electrode material in the lower layer comprises at least one of Li6CoO4 and a compound represented by the following chemical formula 2:

[0017] [Chemical Formula 2]

[0018] Li6Co 1-x Zn x O4

[0019] Where x is 0-1.

[0020] According to a third embodiment of the present invention, a positive electrode for a secondary battery as defined in the first or second embodiment is provided, wherein the sacrificial positive electrode material comprises a material selected from Li6CoO4 and Li6Co. 0.7 Zn 0.3 At least one of O4.

[0021] According to a fourth embodiment of the present invention, a positive electrode for a secondary battery as defined in any one of the first to third embodiments is provided, wherein the amount of the sacrificial positive electrode material is 1-20 wt% based on 100 wt% of the lower layer.

[0022] According to a fifth embodiment of the present invention, a positive electrode for a secondary battery as defined in any one of the first to fourth embodiments is provided, wherein the amount of the sacrificial positive electrode material is 10% by weight or less based on 100% by weight of the entire positive electrode active material layer.

[0023] According to a sixth embodiment of the present invention, a positive electrode for a secondary battery as defined in any one of the first to fifth embodiments is provided, wherein x in chemical formula 1 is 0-0.15.

[0024] According to a seventh embodiment of the present invention, a positive electrode for a secondary battery as defined in any one of the first to sixth embodiments is provided, wherein M in chemical formula 1 includes at least two of Co, Al and Mn.

[0025] According to an eighth embodiment of the present invention, a positive electrode for a secondary battery as defined in any one of the first to seventh embodiments is provided, wherein the positive electrode active material represented by chemical formula 1 is LiNi. 1-x (Co,Mn,Al) x O2, in which Al exists at an atomic ratio of 0.001-0.02 based on Ni.

[0026] According to a ninth embodiment of the present invention, a lithium-ion secondary battery is provided, comprising a positive electrode, a negative electrode, an insulating membrane disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is the same as defined in any one of the first to eighth embodiments, and the negative electrode comprises a silicon-based compound as a negative electrode active material and a conductive material including a linear conductive material.

[0027] According to a tenth embodiment of the present invention, a lithium-ion secondary battery as defined in the ninth embodiment is provided, wherein the silicon-based compound includes at least one of the compounds represented by chemical formula 3 below:

[0028] [Chemical Formula 3]

[0029] SiO x

[0030] Where x is equal to or greater than 0 and less than 2.

[0031] According to the eleventh embodiment of the present invention, a lithium-ion secondary battery as defined in the tenth embodiment is provided, wherein x is 0.5-1.5.

[0032] According to the twelfth embodiment of the present invention, a lithium-ion secondary battery as defined in any one of the ninth to eleventh embodiments is provided, wherein the linear conductive material includes at least one selected from single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and graphene.

[0033] According to the thirteenth embodiment of the present invention, a lithium-ion secondary battery as defined in any one of the ninth to twelfth embodiments is provided, wherein the linear conductive material includes single-walled carbon nanotubes (SWCNTs).

[0034] Beneficial effects

[0035] The present invention provides the following effects.

[0036] 1) According to the present invention, when manufacturing positive electrodes with the same thickness, the adhesive can be uniformly distributed in the thickness direction of the electrode active material layer by using a double-layer coating process, and the adhesive resin in the lower part of the positive electrode active material layer is retained in the lower part to provide an effect of improved adhesion.

[0037] 2) The electrochemical properties of the battery can be improved by using cathode materials with different compositions in the upper and lower portions of the cathode (especially by introducing sacrificial cathode materials only into the lower portion).

[0038] 3) In addition, the secondary battery of the present invention uses lithium cobalt oxide (in which cobalt is partially replaced by Zn) as a sacrificial positive electrode material to supplement the irreversible capacity of the battery, and the lithium cobalt oxide is used as a gas scavenger to reduce gas generation in the battery.

[0039] 4) The secondary battery of the present invention comprises a nickel-rich lithium composite oxide as the positive electrode active material and a silicon oxide as the negative electrode active material, thus enabling the manufacture of a high-capacity battery.

[0040] 5) Finally, the secondary battery of the present invention uses single-walled carbon nanotubes (SWCNTs) as the negative electrode conductive material to ensure that the conductivity of the silicon oxide-containing negative electrode reaches a level sufficient to operate the battery. Attached Figure Description

[0041] The accompanying drawings illustrate preferred embodiments of the invention and, together with the foregoing disclosure, serve to provide a further understanding of the technical features of the invention. Therefore, the invention is not to be construed as limited to the drawings. Furthermore, for clarity, the shape, size, scale, or proportion of some constituent elements in the drawings may be exaggerated.

[0042] Figure 1 This is a graph showing the change in the charging capacity of the battery in Example 1 over time (weeks).

[0043] Figure 2 This is a graph showing the change in discharge capacity of the battery in Example 1 over time (weeks).

[0044] Figure 3 This is a graph showing the change in the charging capacity of the battery of Comparative Example 1 over time (weeks).

[0045] Figure 4 This is a graph showing the change in discharge capacity of the battery of Comparative Example 1 over time (weeks).

[0046] Figure 5 and Figure 6 The changes in Li6CoO4 over time are shown due to exposure to air, decomposition, and the generation of various byproducts.

[0047] Figure 7 The graph shows the capacity retention rate of Example 2-1 and Comparative Examples 2 and 3 as a function of the number of cycles.

[0048] Figure 8 This is a graph showing the capacity retention rate of Examples 2-1 and 2-2 as a function of the number of cycles.

[0049] Figures 9 to 11 The graph shows the capacity retention rate of Example 3 and Comparative Examples 4 and 5 as a function of C-rate and cycle number. Detailed Implementation

[0050] Preferred embodiments of the invention will be described in detail below with reference to the accompanying drawings. Before the description, it should be understood that, based on the principle of allowing inventors to appropriately define terminology for best explanation, the terminology used in the specification and appended claims should not be construed as limited to its general and dictionary meanings, but rather as being interpreted based on the meanings and concepts corresponding to the technical aspects of the invention. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention; thus, it should be understood that other equivalents and modifications can be made thereto without departing from the scope of the invention.

[0051] Throughout the specification, the statement "a portion includes an element" does not preclude the presence of any additional elements, but rather indicates that the portion may further include other elements.

[0052] As used herein, the terms “about,” “substantially,” etc., when implying an acceptable degree of preparation and material error unique to the claimed meaning, are used to mean from or to the claimed value and to prevent unethical infringers from improperly using the claimed disclosure, including the accurate or absolute values ​​provided to aid in understanding the disclosure.

[0053] As used in this article, the expression "A and / or B" means "A, B, or both of them".

[0054] The specific terms used in the following description are for illustrative purposes and not for limitation. Terms such as “right,” “left,” “top,” and “bottom” indicate their orientation in the accompanying drawings. Terms such as “inward” and “outward” indicate directions toward and away from the geometric center of the respective device, system, and its components, respectively. “Front,” “back,” “top,” and “bottom,” as well as related words and expressions, indicate their location and points in the accompanying drawings and should not be limiting. Such terms include the words listed above, their derivatives, and words with similar meanings.

[0055] In one aspect, the present invention relates to a positive electrode for a secondary battery. As used herein, the term "secondary battery" refers to a device that converts chemical energy into electrical energy through an electrochemical reaction and is rechargeable. Specific examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, nickel-metal hydride batteries, etc.

[0056] According to the present invention, the positive electrode includes a positive current collector and a positive active material layer formed on at least one surface of the current collector, wherein the positive active material layer comprises a positive active material, a conductive material and an adhesive resin.

[0057] According to an embodiment of the present invention, the positive electrode active material layer has a multilayer structure including a lower layer and an upper layer. The lower layer refers to the layer disposed on the surface of the current collector and in contact with the current collector. The upper layer refers to the layer disposed on the surface of the lower layer and facing the separator during battery manufacturing. According to an embodiment of the present invention, at least one additional electrode active material layer may be disposed between the upper and lower layers.

[0058] The upper layer comprises a positive electrode active material, a conductive material, and a binder resin. The lower layer comprises a positive electrode active material, a sacrificial positive electrode material, a conductive material, and a binder resin. Preferably, the upper layer does not contain a sacrificial positive electrode material. In other words, in the positive electrode of the present invention, the sacrificial positive electrode material is prepared in a manner that does not expose the top portion of the positive electrode active material layer. According to embodiments of the present invention, the additional electrode active material layer may or may not contain a sacrificial positive electrode material. Preferably, the additional electrode active material layer does not contain a sacrificial positive electrode material.

[0059] According to embodiments of the present invention, the positive electrode active material comprises a Ni-rich lithium composite oxide represented by the following chemical formula 1:

[0060] [Chemical Formula 1]

[0061] LiNi 1-x M x O2

[0062] M includes at least one of Mn, Co, Al, Cu, Fe, Mg, B, and Ga. Preferably, M can be at least two of Co, Al, and Mn. In Formula 1, the value of x can be 0-0.5, preferably 0-0.3, and more preferably 0-0.15. According to embodiments of the present invention, M may include at least one of Co, Mn, and Al. According to embodiments of the present invention, the positive electrode active material may be LiNi. 1-x (Co,Mn,Al) x O2, in which Al can exist at an atomic ratio of 0.001-0.02 based on Ni.

[0063] Preferably, based on 100% by weight of positive electrode active material, the positive electrode active material layer contains more than 90% by weight of a Ni-rich lithium composite oxide of Formula 1.

[0064] According to one embodiment of the present invention, the upper layer and the lower layer each independently comprise a Ni-rich lithium composite oxide of Formula 1, which comprises at least 90% by weight of a positive electrode active material based on 100% by weight.

[0065] If necessary, in addition to the Ni-rich lithium composite oxide represented by Formula 1, the positive electrode active material may also contain any of the following: layered compounds, such as lithium manganese composite oxides (LiMn2O4, LiMnO2, etc.), lithium cobalt oxides (LiCoO2), and lithium nickel oxides (LiNiO2), or those compounds substituted with one or more transition metals; lithium manganese oxides, such as those derived from the formula Li... 1+x Mn 2-x Those represented by O4 (where x is 0-0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); lithium vanadium oxide, such as LiV3O8, LiV3O4, V2O5, or Cu2V2O7; and those represented by the chemical formula LiNi. 1-x M x Ni-type lithium nickel oxide represented by O2 (where M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x is 0.01-0.3); LiMn 2-x M x Lithium manganese composite oxides represented by O2 (where M is Co, Ni, Fe, Cr, Zn or Ta, and x is 0.01-0.1) or Li2Mn3MO8 (where M is Fe, Co, Ni, Cu or Zn); LiMn2O4 in which Li is partially substituted by alkaline earth metal ions; disulfides; and Fe2(MoO4)3; or mixtures of two or more of them.

[0066] The adhesive resin may include PVDF-type polymers and / or acrylic polymers. According to embodiments of the invention, the PVDF-type polymer may include at least one copolymer of vinylidene fluoride and a comonomer, and mixtures thereof. According to one embodiment, specific examples of monomers include fluorinated monomers and / or chlorinated monomers. Non-limiting examples of fluorinated monomers include at least one selected from: vinyl fluoride; trifluoroethylene (TrFE); vinyl chlorofluorocarbon (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), or perfluoro(propyl vinyl) ether (PPVE); perfluoro(1,3-dioxane); perfluoro(2,2-dimethyl-1,3-dioxane) (PDD); etc., and at least one of these fluorinated monomers may be used. According to embodiments of the present invention, the PVDF-type polymer may include at least one selected from polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-co-chlorotrifluoroethylene (PVDF-CTFE), polyvinylidene fluoride-co-tetrafluoroethylene (PVDF-TFE), and polyvinylidene fluoride-co-trifluoroethylene (PVDF-TrFE). For example, the PVDF-type polymer may include at least one selected from PVDF-HFP, PVDF-CTFE, and PVDF-TFE. Preferably, the PVDF-type polymer may include at least one selected from PVDF-HFP and PVDF-CTFE. According to the present invention, the acrylic polymer includes (meth)acrylic acid polymers. (Meth)acrylate polymers include (meth)acrylates as monomers, and non-limiting examples of monomers include butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, tert-butyl (meth)acrylate, amyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate, etc., and these monomers can be used alone or in combination.

[0067] Specifically, the conductive material may include any one selected from graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives, or a mixture of two or more thereof. More specifically, the conductive material may include any one selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium dioxide, or a mixture of two or more of these conductive materials.

[0068] Sacrificial cathode materials are used to provide lithium, which can be used to meet the lithium demand caused by the irreversible electrochemical reaction at the negative electrode during initial charging. As mentioned above, Si-based materials are used for the negative electrode and combined with Ni-rich lithium composite metal oxides (Ni-rich positive electrode active materials) as positive electrode active materials to obtain high-capacity secondary batteries. Here, due to the irreversible electrochemical reaction at the negative electrode, such sacrificial cathode materials are needed to easily provide lithium at the positive electrode.

[0069] According to embodiments of the present invention, the sacrificial cathode material may include a cobalt-containing lithium composite oxide to supplement the irreversible capacity of the Ni-rich cathode active material. According to embodiments of the present invention, the cobalt-containing lithium composite oxide may include Li6CoO4 and at least one of the compounds represented by the following chemical formula 2:

[0070] [Chemical Formula 2]

[0071] Li6Co 1-x Zn x O4

[0072] x can have a value between 0 and 1. Preferably, x is greater than 0. For example, the sacrificial cathode material may include Li6CoO4 and Li6Co. 0.7 Zn 0.3 At least one of O4.

[0073] Meanwhile, sacrificial cathode materials readily react with water or carbon dioxide in the air to produce byproducts such as Li6C, CoO, LiOH, Co(OH)2, and Li2CO3. See also Figure 5 and Figure 6 It can be seen that when Li6CoO4 is left to stand in air, various byproducts are formed within 1-7 hours. Figure 5 In this context, all values ​​are expressed as a percentage (%), representing the weight percentage of each component based on the total weight of byproducts generated in each test run. Figure 6 The results of the Fourier transform infrared (FT-IR) spectra of the byproducts are shown. Figure 6 In the diagram, bar (1) represents Li6CoO4, bar (2) represents Li2CO3, bar (3) represents Co(OH)2, and bar (4) represents CoO. This includes... Figure 6 The main bars in the structure were identified, and the detection results of each component were also identified at a specific wavelength (WL). In this document, according to the invention, the sacrificial cathode material is arranged in a manner that prevents it from being present in the uppermost (or most uppermost) layer of the electrode active material layer and is located in the lowermost (or most lowermost) layer of the electrode active material layer, in order to prevent the sacrificial cathode material from contacting air.

[0074] According to an embodiment of the present invention, the amount of sacrificial cathode material present in 100% by weight of the lower layer can be about 1-20% by weight. Alternatively, the amount of sacrificial cathode material present in 100% by weight of the entire cathode active material layer can be less than 10% by weight.

[0075] According to an embodiment of the present invention, the particle size (D) of the sacrificial cathode material Li6CoO4 is... 50 The particle size can be larger than that of the positive electrode active material particles (D). 50 Specifically, the particle size (D) of the sacrificial cathode material 50 The size can be 10-25μm.

[0076] According to embodiments of the present invention, the sacrificial cathode material serves as a sacrificial cathode material capable of supplementing the irreversible capacity in the secondary battery, and can also serve as a gas scavenger capable of reducing gas generation during battery operation. Therefore, since the secondary battery of the embodiments of the present invention includes a sacrificial cathode material, capacity degradation can be prevented while reducing gas generation.

[0077] In the positive electrode active material layer, the ratio of the content of positive electrode active material to the content of binder resin can be 80:20-99:1 in the upper and lower layers, respectively.

[0078] Meanwhile, in the case of the lower layer, based on 100% by weight, it may contain 0.4-1.5% by weight of conductive material. In the case of the upper layer, based on 100% by weight, it may contain 0.4-1.0% by weight of conductive material. In the case of the lower layer, since Li6CoO4, used as a sacrificial cathode material, has a larger particle size and lower conductivity compared to the cathode active material, the content of conductive material in the lower layer needs to be increased compared to the content of conductive material in the upper layer.

[0079] Meanwhile, according to an embodiment of the present invention, based on the total thickness of the 100% positive electrode active material layer, the thickness of the lower layer can be 40-60%.

[0080] There are no particular restrictions on the current collector, as long as it has high conductivity and does not cause any chemical changes in the corresponding battery. Specific examples of current collectors include stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, silver, etc.

[0081] For example, the positive electrode of the present invention can be obtained by forming a lower layer on one surface of the current collector and forming an upper layer on the surface of the lower layer.

[0082] There are no particular restrictions on the method of manufacturing the positive electrode, as long as it can produce a positive electrode with the above-mentioned structure.

[0083] For example, first, a suitable solvent is prepared, and binder resin, conductive material, positive electrode active material, and sacrificial positive electrode material are introduced into it to prepare a slurry for the lower layer. The order in which the components are introduced can be appropriately determined by taking into account the dispersibility of each component. Next, the slurry for the lower layer is applied to the surface of the current collector and then dried. The lower layer can be formed on both surfaces of the current collector, or selectively formed on one surface of the current collector.

[0084] Then, the upper layer is formed on the surface of the prepared lower layer.

[0085] In the case of the upper layer, a solvent is prepared, and a binder resin, a conductive material, and a positive electrode active material are introduced into it to prepare a slurry for the upper layer. The order in which the components are introduced can be appropriately determined by taking into account the dispersibility of each component. Next, the slurry for the upper layer is applied to the surface of the lower layer and then dried.

[0086] Non-limiting examples of solvents include any one selected from the group consisting of water, acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane, or a mixture of two or more thereof. The lower layer is then applied to the surface of the current collector using a slurry.

[0087] The slurry can be coated using conventional coating processes known to those skilled in the art, and specific examples of coating processes include various processes such as dip coating, die coating, roll coating, comma coating, Meyer bar coating, reverse roll coating, gravure coating, or combinations thereof. Conventional drying processes (e.g., natural drying and forced-air drying) can be used to dry the slurry without particular limitation.

[0088] Meanwhile, according to an embodiment of the present invention, the upper slurry can be applied after the lower slurry is applied and before the lower slurry is dried, and then the upper and lower slurries can be introduced into the drying step simultaneously.

[0089] In another aspect of the invention, a secondary battery comprising the aforementioned positive electrode is provided. The secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and an electrolyte, wherein the positive electrode has the aforementioned structural features.

[0090] In another aspect of the invention, an electrochemical device comprising the positive electrode and a secondary battery comprising the electrochemical device are provided.

[0091] A secondary battery is a device that converts chemical energy into electrical energy through an electrochemical reaction and is rechargeable. Specific examples of secondary batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. According to the present invention, the secondary battery is preferably a lithium-ion secondary battery. Therefore, the electrochemical device will be explained below using a lithium-ion secondary battery as an example. A lithium-ion secondary battery includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The lithium-ion secondary battery will now be explained in detail with reference to each constituent element.

[0092] According to the present invention, the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the current collector and containing a negative electrode active material, a conductive material and an adhesive resin.

[0093] According to an embodiment of the present invention, the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may comprise graphite and a silicon-based compound as the negative electrode active material, wherein the graphite and silicon-based compound may be used in a weight ratio of 70:30 to 99:1. According to an embodiment of the present invention, the silicon-based compound may comprise silicon and / or silicon oxide. According to an embodiment of the present invention, the silicon oxide may comprise at least one compound represented by the following chemical formula 3:

[0094] [Chemical Formula 3]

[0095] SiO x

[0096] Where 0 ≤ x < 2. In the case of SiO2 (x = 2 in chemical formula 3), it does not react with lithium ions and therefore cannot store lithium. Therefore, it is preferable that x is less than 2. In particular, considering the structural stability of the electrode active material, 0.5 ≤ x ≤ 1.5.

[0097] Furthermore, according to embodiments of the present invention, the silicon-based compound may further include a carbon coating that at least partially or completely covers the surface of the active material particles. The carbon coating serves as a protective layer, suppressing volume expansion of the negative electrode active material particles containing the silicon-based compound and preventing side reactions with the electrolyte. The amount of carbon coating present in the silicon-based compound may be 0.1-10% by weight, preferably 3-7% by weight. Within the above-defined range, the carbon coating preferably prevents side reactions with the electrolyte while controlling the volume expansion of the negative electrode active material particles containing the silicon-based compound to a high level.

[0098] Furthermore, according to embodiments of the present invention, the negative electrode active material particles containing silicon-based compounds can have a particle size of 3-10 μm (D 50 ). When the particle size (D 50When the particle size is less than 3 μm, the negative electrode active material particles have a high specific surface area, providing an increased surface area for reaction with the electrolyte. This increases the likelihood of side reactions with the electrolyte during charging / discharging, leading to battery life degradation. On the other hand, when the particle size (D...) is less than 3 μm, the negative electrode active material particles have a high specific surface area, providing an increased surface area for reaction with the electrolyte. This increases the likelihood of side reactions with the electrolyte during charging / discharging, resulting in decreased battery life. 50 When the particle size is greater than 10 μm, the negative electrode active material particles exhibit large volume changes caused by volume expansion / contraction, which may cause them to break or fracture, leading to problems of battery performance degradation and reduction.

[0099] Meanwhile, the graphite may include at least one selected from artificial graphite and natural graphite. Natural graphite may include coarse natural graphite, such as crystalline graphite, flake graphite, or amorphous graphite, or spheroidized natural graphite. Crystalline and flake graphite exhibit substantially perfect crystals, while amorphous graphite exhibits lower crystallinity. Considering electrode capacity, crystalline and flake graphite with high crystallinity can be used. For example, flake graphite can be used after spheroidization. In the case of spheroidized natural graphite, its particle size can be 5-30 μm, preferably 10-25 μm.

[0100] In this paper, artificial graphite is typically prepared via a graphitization process, which involves sintering raw materials, such as coal tar, coal tar pitch, and petroleum-based heavy oil, at temperatures above 2500°C. Following this graphitization, the resulting product undergoes particle size adjustment, such as pulverization and secondary particle formation, making it suitable for use as a negative electrode active material.

[0101] Typically, synthetic graphite comprises crystals randomly distributed within particles, exhibiting lower sphericity and a slightly sharper shape compared to natural graphite. This synthetic graphite can be supplied in powder, flake, block, plate, or rod forms, but preferably with a degree of isotropic microcrystalline orientation, allowing for a reduction in lithium-ion migration distance to improve output characteristics. With this in mind, synthetic graphite can be in flake and / or plate shapes.

[0102] The artificial graphite used in embodiments of the present invention includes commercially available mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers (MPCF), bulk graphitized artificial graphite, powdered graphitized artificial graphite, etc. The particle size of the artificial graphite can be 5-30 μm, preferably 10-25 μm.

[0103] The specific surface area of ​​synthetic graphite can be determined using the BET (Brunauer-Emmett-Teller) method. For example, the specific surface area can be determined using a porosity analyzer (e.g., Belserp-II mini, Bell Japan Inc.) via a nitrogen adsorption flow-based BET 6-point method. This is also applicable to the determination of the specific surface area of ​​natural graphite as described below.

[0104] The tap density of synthetic graphite can range from 0.7 to 1.1 g / cc, particularly from 0.8 to 1.05 g / cc. When the tap density is less than 0.7 g / cc (outside the range specified above), the contact area between particles is insufficient, leading to deterioration of adhesion and a reduction in capacity per unit volume. When the tap density is greater than 1.1 g / cc, the tortuosity of the electrode and the wettability of the electrolyte may decrease, undesirably resulting in deterioration of output characteristics during charging / discharging.

[0105] In this paper, tap density can be determined as follows: using an instrument IV-1000 available from COPLEY Co., 50 g of the precursor is introduced into a 100 cc cylinder and struck together with a SEISHIN (KYT-4000) testing instrument, and the cylinder is subjected to 3000 strikes. This method is applicable to the determination of tap density of natural graphite as described below.

[0106] In addition, the average particle size (D) of artificial graphite 50 The average particle size (D) of artificial graphite can range from 8 to 30 μm, particularly 12 to 25 μm. 50 When the average particle size is less than 8 μm, it has an increased specific surface area, leading to a decrease in the initial efficiency of the secondary battery and thus a reduction in battery performance. When the average particle size (D...) is less than 8 μm, it has an increased specific surface area, leading to a decrease in the initial efficiency of the secondary battery and a reduction in battery performance. 50 When the thickness is greater than 30 μm, it can reduce adhesion and packing density, resulting in a decrease in capacity.

[0107] For example, the average particle size of artificial graphite can be determined using laser diffraction. Laser diffraction typically allows for the determination of particle sizes ranging from submicron to several millimeters, providing results with high reproducibility and high resolution. The average particle size of artificial graphite (D...) 50 The average particle size (D) of artificial graphite can be defined as the particle size at the 50% mark of its particle size distribution. For example, the average particle size of artificial graphite is... 50 The following method can be used to determine the particle size distribution: Artificial graphite is dispersed in an ethanol / water solution. The resulting product is introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves are applied at a frequency of approximately 28 kHz and an output of 60 W. The average particle size (D) at 50% of the particle size distribution measured by the analyzer is then calculated. 50 This also applies to determining the particle size of any component other than artificial graphite.

[0108] According to embodiments of the present invention, the conductive material may include any one selected from graphite, carbon black, carbon fiber or metal fiber, metal powder, conductive whiskers, conductive metal oxide, activated carbon, and polyphenylene derivatives, or a mixture of two or more thereof. More specifically, the conductive material may include any one selected from the group consisting of natural graphite, artificial graphite, Super-P, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, Denka black, aluminum powder, nickel powder, zinc oxide, potassium titanate, and titanium dioxide, or a mixture of two or more of these conductive materials.

[0109] Specifically, according to the present invention, considering that the negative electrode active material comprises a high content of silicon-based compounds, the conductive material used for the negative electrode preferably comprises at least one linear conductive material, such as carbon nanotubes, preferably single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), or graphene, which are in linear or surface contact. When silicon-based compounds are used as negative electrode active materials, the electrode capacity can be increased, but the compounds exhibit large volume changes due to charging / discharging, resulting in high Li consumption and the formation of a thick solid electrolyte interphase (SEI) film on the surface, leading to separation between particles. Therefore, such silicon-based compounds exhibit lower electrochemical efficiency compared to carbonaceous negative electrode materials (e.g., graphite). Therefore, the contact between easily separable material (e.g., Si) particles can be enhanced, and lifetime characteristics can be improved by introducing linear conductive materials (e.g., SWCNTs). According to embodiments of the present invention, the linear conductive material may have a length of 0.5-100 μm. For example, SWCNTs may have an average length of 2-100 μm, and MWCNTs may have an average length of 0.5-30 μm. Meanwhile, linear conductive materials can have a cross-sectional diameter of 1-70 nm.

[0110] There are no particular restrictions on the current collector, as long as it has high conductivity and does not cause any chemical changes in the corresponding battery. For example, stainless steel, copper, aluminum, nickel, titanium, calcined carbon, or copper, aluminum, or stainless steel with surface treatments such as carbon, nickel, titanium, or silver can be used. Although there are no particular restrictions on the thickness of the current collector, its currently used thickness can range from 3 to 500 μm.

[0111] The adhesive resin may include polymers conventionally used for electrodes in the art. Non-limiting examples of adhesive resins include, but are not limited to: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, ethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylates, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, or carboxymethyl cellulose, etc.

[0112] There are no particular limitations on the membrane, as long as it is conventionally used as a membrane in secondary batteries. Any membrane can be used without particular limitation, as long as it has electrical insulation properties, provides ion conduction channels, and can be used as a membrane in electrochemical devices in the art. For example, porous sheets containing polymer materials (e.g., polymer membranes or nonwoven fabrics) can be used as membranes. According to embodiments of the invention, the membrane may also include a heat-resistant coating containing inorganic particles or the like on the surface of the porous sheet.

[0113] There are no particular limitations on the method for fabricating the electrode assembly. For example, once the positive electrode, negative electrode, and separator are fabricated, they are stacked sequentially to fabricate the electrode assembly. The electrode assembly is then introduced into a suitable housing and an electrolyte is injected into it to obtain a battery.

[0114] According to the present invention, the electrolyte is having A + B - Salts of structure, in which A + Including, for example, Li + Na + K + Or combinations thereof, such as alkali metal cations, B - Including PF6 - BF4 - Cl-, Br - I-, ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 -Or combinations thereof, such as anions, wherein the salt is dissolved or dissociated in an organic solvent, said organic solvent including propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), ester compounds, or mixtures thereof. However, the invention is not limited thereto.

[0115] In another aspect of the invention, a battery module comprising a battery containing the electrode assembly as a unit cell is provided, a battery pack comprising the battery module, and a device comprising the battery pack as a power source is provided. Specific examples of this device may include, but are not limited to: electric tools driven by an electric motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; two-wheeled electric vehicles, including electric bicycles (E-bikes) and electric scooters (E-scooters); electric golf carts; power storage systems; and so on.

[0116] The embodiments will now be described more fully to facilitate a clear understanding of the invention. However, the embodiments described below may be presented in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided to make the invention thorough and complete, and to fully convey the scope of the invention to those skilled in the art.

[0117] Example 1 (Double-layer positive electrode)

[0118] 1) Preparation of the positive electrode

[0119] First, the positive electrode active material (LiNi) 0.89 Co 0.07 Mn 0.04 Al 0.01 O2, binder (PVDF), conductive material (carbon nitride CNT), and sacrificial cathode material (Li6CoO4) were introduced into NMP at a weight ratio of 96.65:1.34:0.84:1.17 to prepare a slurry (70% by weight solids) for forming the lower cathode active material layer. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to form the lower layer of the electrode active material. Next, the cathode active material (LiNi) was... 0.89 Co 0.01 Mn 0.1O2, binder (PVDF), and conductive material (B.CNT) were introduced into NMP at a weight ratio of 98.74:0.66:0.6 to prepare a slurry (70% by weight solids) for forming the upper positive electrode active material layer. The slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0120] The ratio of the thickness of the upper electrode active material layer to the thickness of the lower electrode active material layer is 5:5, and the total thickness of the electrode active material layer is 150 μm.

[0121] 2) Battery manufacturing

[0122] A porous membrane (10 μm) made of polyethylene was prepared as the separator. The positive electrode, separator, and lithium metal were sequentially introduced into the coin cell, and an electrolyte was injected into it to obtain the cell. The electrolyte was prepared as follows: ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed in a weight ratio of 2:1:2.5:4.5, and LiPF6 was introduced into it at a concentration of 1.4 M.

[0123] Comparative Example 1

[0124] First, the positive electrode active material (LiNi) 0.89 Co 0.07 Mn 0.04 Al 0.01 O2, a binder (PVDF), a conductive material (acetylene black), and a sacrificial cathode material (Li6CoO4) were introduced into NMP at a weight ratio of 97.11:1.0:0.72:1.17 to prepare a slurry (70% by weight solids) for forming the positive electrode active material layer. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the positive electrode.

[0125] Next, the negative electrode was prepared in the same manner as in Example 1, and the negative and positive electrodes were used in the same manner as in Embodiment 1 to obtain a battery.

[0126] Evaluation of capacity retention

[0127] The batteries of Example 1 and Comparative Example 1 were left to stand at 10% relative humidity for 4 weeks, and the charge / discharge characteristics and capacity retention of each battery were evaluated weekly. The batteries were charged to 4.25V at 0.2C in constant current (CC) / constant voltage (CV) mode with a cutoff current of 50mA, and discharged to 2.5V at 0.2C, and the charge / discharge cycle was repeated under these conditions. Testing was conducted at room temperature (25°C). Figure 1 and Figure 2 This is a graph showing the charge / discharge capacity of Example 1. Figure 3 and Figure 4This is a graph showing the charge / discharge capacity of Comparative Example 1, wherein the charge / discharge capacity was measured immediately after manufacturing each battery and after allowing each battery to rest for 1 to 4 weeks. See also Figures 1 to 4 As can be seen, because the sacrificial cathode material is disposed in the lower layer of the electrode active material layer, it can be prevented from contacting water. Therefore, the battery of Example 1 shows a delay in cathode degradation and a small capacity change during charge / discharge cycles.

[0128] Meanwhile, Table 1 below shows the changes in water content and Li2CO3 content in the positive electrode active material layer, which were measured by allowing the positive electrodes obtained in Example 1 and Comparative Example 1 to stand at 10% relative humidity for 4 weeks. As can be seen from Table 1, compared with the positive electrode of Comparative Example 1, the positive electrode of Example 1 shows a lower water content and Li2CO3 content, as well as a lower increase over time.

[0129] Table 1

[0130]

[0131] Example 2-1

[0132] 1) Preparation of the positive electrode

[0133] First, the positive electrode active material (LiNi) 0.89 Co 0.01 Mn 0.1 O2, binder (PVDF), conductive material (acetylene black), and sacrificial cathode material (Li6CoO4) were introduced into NMP at a weight ratio of 97.00:1.12:0.60:1.28 to prepare a slurry (70% by weight solids) for forming the lower cathode active material layer. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to form the lower layer of the electrode active material. Next, the cathode active material (LiNi) was... 0.89 Co 0.01 Mn 0.1 O2, a binder (PVDF), and a conductive material (acetylene black) were introduced into NMP at a weight ratio of 98.74:0.66:0.6 to prepare a slurry (70% by weight solids) for forming the upper positive electrode active material layer. This slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0134] 2) Preparation of the negative electrode

[0135] A slurry (45% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (single-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.78:1.15:0.12:0.95. The negative electrode active material is composed of artificial graphite (D...) in a weight ratio of 90:10. 50 Approximately 15μm in diameter; specific surface area: approximately 0.9m². 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2 A mixture of (g) was prepared. The slurry was applied to copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode.

[0136] 3) Battery manufacturing

[0137] A porous membrane (10 μm) made of polyethylene was prepared as a separator, and a lamination process was performed, which included sequentially stacking the positive electrode, separator, and lithium metal and pressing them at 80°C to obtain an electrode assembly. The electrode assembly was introduced into a cylindrical metal can (0.2C capacity, 3.0 Ah standard) of 18650 size and an electrolyte was injected to obtain a battery. The electrolyte was prepared as follows: ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed in a weight ratio of 2:1:2.5:4.5, and LiPF6 was introduced into it at a concentration of 1.4 M.

[0138] Example 2-2

[0139] The battery was obtained in the same manner as in Example 2-1, except that Li6Co was used. 0.7 Zn 0.3 O4 replaces Li6CoO4 as the sacrificial cathode material in the lower layer of the positive electrode active material layer.

[0140] Comparative Example 2

[0141] 1) Preparation of the positive electrode

[0142] First, the positive electrode active material (LiNi) 0.89 Co 0.01 Mn 0.1 O2, binder (PVDF), conductive material (acetylene black), and sacrificial cathode material (Li2NiO2) were introduced into NMP at a weight ratio of 94.28:1.12:0.60:4.0 to prepare a slurry (70% by weight solids) for forming the lower cathode active material layer. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to form the lower layer of the electrode active material. Next, the cathode active material (LiNiO2) was... 0.89 Co0.01 Mn 0.1 O2, a binder (PVDF), and a conductive material (acetylene black) were introduced into NMP at a weight ratio of 98.74:0.66:0.6 to prepare a slurry (70% by weight solids) for forming the upper positive electrode active material layer. This slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0143] 2) Preparation of the negative electrode

[0144] A slurry (45% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (multi-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.4:1.15:0.5:0.95. The negative electrode active material is composed of artificial graphite (D) in a weight ratio of 90:10. 50 Approximately 15μm in diameter; specific surface area: approximately 0.9m². 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2 A mixture of (g) was prepared. The slurry was applied to copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode.

[0145] 3) Battery manufacturing

[0146] The battery was obtained in the same manner as in Example 2-1.

[0147] Comparative Example 3

[0148] 1) Manufacturing of the positive electrode

[0149] The positive electrode was obtained in the same manner as in Comparative Example 2.

[0150] 2) Preparation of the negative electrode

[0151] A slurry (45% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (single-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.78:1.15:0.12:0.95. The negative electrode active material is composed of artificial graphite (D...) in a weight ratio of 90:10. 50 Approximately 15-16 μm, specific surface area: approximately 0.9 m² 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2 A mixture of (g) was prepared. The slurry was applied to copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode.

[0152] 3) Battery manufacturing

[0153] The battery was obtained in the same manner as in Example 1.

[0154] Example 3

[0155] 1) Manufacturing of the positive electrode

[0156] First, a slurry (70% by weight solids) for forming the lower positive electrode active material layer was prepared by introducing the positive electrode active material, binder (polyvinylidene fluoride, PVDF), conductive material (acetylene black), and sacrificial positive electrode material (Li6CoO4) into NMP at a weight ratio of 97.00:1.12:0.6:1.28. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60°C for 6 hours to form the lower layer of the electrode active material layer. Next, the positive electrode active material, binder (PVDF), and conductive material (acetylene black) were introduced into NMP at a weight ratio of 98.74:0.66:0.6 to prepare a slurry (70% by weight solids) for forming the upper positive electrode active material layer. This slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0157] The positive electrode active material is LiNi with a weight ratio of approximately 95:5. 0.89 Co 0.01 Mn 0.1 A mixture of O2 and Li2NiO2.

[0158] 2) Preparation of the negative electrode

[0159] A slurry (70% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (single-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.78:1.15:0.12:0.95. This slurry was applied to a copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode. The negative electrode active material was composed of artificial graphite (D) in a weight ratio of 84:16. 50 Approximately 15-16 μm, specific surface area: approximately 0.9 m² 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2 A mixture of (g) and (g).

[0160] 3) Battery manufacturing

[0161] A porous membrane (10 μm) made of polyethylene was prepared as a separator, and a lamination process was performed, which included sequentially stacking the positive electrode, separator, and negative electrode and pressing them at 80°C to obtain an electrode assembly. The electrode assembly was introduced into a 21700-size cylindrical metal can (0.2C capacity, 5.0 Ah standard) and an electrolyte was injected to obtain a battery. The electrolyte was prepared as follows: ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate were mixed in a weight ratio of 2:1:2.5:4.5, and LiPF6 was introduced into it at a concentration of 1.4 M.

[0162] Comparative Example 4

[0163] 1) Manufacturing of the positive electrode

[0164] First, a slurry (70% by weight solids) for forming the lower positive electrode active material layer was prepared by introducing the positive electrode active material, binder (polyvinylidene fluoride, PVDF), and conductive material (acetylene black) into NMP at a weight ratio of 98.28:1.12:0.6. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60°C for 6 hours to form the lower layer of the electrode active material layer. The positive electrode active material is LiNi containing approximately 95:5 by weight. 0.89 Co 0.01 Mn 0.1 A mixture of O2 and Li2NiO2. Next, the positive electrode active material (LiNi) is... 0.89 Co 0.01 Mn 0.1 O2, a binder (PVDF), and a conductive material (acetylene black) were introduced into NMP at a weight ratio of 98.74:0.66:0.6 to prepare a slurry (70% by weight solids) for forming the upper positive electrode active material layer. This slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0165] 2) Preparation of the negative electrode

[0166] A slurry (70% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (single-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.78:1.15:0.12:0.95. This slurry was applied to a copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode. The negative electrode active material was composed of artificial graphite (D) in a weight ratio of 90:10. 50 Approximately 15-16 μm, specific surface area: approximately 0.9 m² 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2A mixture of (g)

[0167] 3) Battery manufacturing

[0168] The battery was obtained in the same manner as in Example 2.

[0169] Comparative Example 5

[0170] 1) Manufacturing of the positive electrode

[0171] First, a slurry (70% by weight solids) for forming the positive electrode active material layer was prepared by introducing the positive electrode active material, binder (polyvinylidene fluoride, PVDF), and conductive material (acetylene black) into NMP at a weight ratio of 98.28:1.12:0.6. This slurry was applied to an aluminum foil (thickness: approximately 10 μm) and dried at 60°C for 6 hours to form the lower layer of the electrode active material layer. The positive electrode active material is LiNi containing approximately 95:5 by weight. 0.89 Co 0.01 Mn 0.1 A mixture of O2 and Li2NiO2. Next, the positive electrode active material (LiNi) is... 0.89 Co 0.01 Mn 0.1 O2, a binder (PVDF), and a conductive material (acetylene black) were introduced into NMP at a weight ratio of 98.28:1.12:0.6 to prepare a slurry (70% by weight solids) for forming the positive electrode active material layer. This slurry was applied to the surface of the lower layer and dried at 60°C for 6 hours to form the upper layer of the electrode active material layer.

[0172] 2) Preparation of the negative electrode

[0173] A slurry (70% by weight) for forming the negative electrode active material layer was prepared by introducing a negative electrode active material, a binder (PVDF), a conductive material (multi-walled carbon nanotubes, LG Chem.), and a thickener (carboxymethyl cellulose, CMC) into NMP at a weight ratio of 97.78:1.15:0.12:0.95. This slurry was applied to a copper foil (thickness: approximately 10 μm) and dried at 60 °C for 6 hours to prepare the negative electrode. The negative electrode active material was composed of artificial graphite (D...) in a weight ratio of 90:10. 50 Approximately 15-16 μm, specific surface area: approximately 0.9 m². 2 / g) and Si(D 50 Approximately 6μm, specific surface area: approximately 6m² 2 A mixture of (g) and (g).

[0174] 3) Battery manufacturing

[0175] The battery was obtained in the same manner as in Example 2.

[0176] (3) Evaluation of capacity retention

[0177] 1) Test 1

[0178] The batteries of Examples 2-1 and 2-2, and Comparative Examples 2 and 3, were charged / discharged, and their capacity retention was evaluated. Each battery was charged to 4.2V at 3A in constant current (CC) / constant voltage (CV) mode with a cutoff current of 50mA, and discharged to 2.5V at 10A, and the charge / discharge cycle was repeated under these conditions. Tests were conducted at room temperature (25°C). Results are in... Figure 7 As shown in the figure. It can be seen that, in the case of the battery of Example 2-1, it exhibits a higher capacity retention rate compared to the batteries of Comparative Example 2 and Comparative Example 3. Meanwhile, from Figure 8 It can be seen that the capacity retention rate of the battery in Example 2-2 is the same as that of the battery in Example 2-1.

[0179] 2) Test 2

[0180] The batteries of Example 3 and Comparative Examples 4 and 5 were charged / discharged, and their capacity retention was evaluated. Each battery was charged to 4.2V at 3A in constant current (CC) / constant voltage (CV) mode with a cutoff current of 50mA, and then discharged to 2.5V at 10A, 20A, and 30A, respectively, under the same conditions. The charge / discharge cycles were repeated. Tests were conducted at room temperature. Results were... Figures 9 to 11 As shown in the image. Figure 9 The results obtained after discharging each battery at 10A are shown. Figure 10 The results obtained after discharging each battery at 20A are shown. Figure 11 The results obtained after discharging each battery at 30A are shown. Figures 9 to 11 As can be seen, in the case of the battery of Example 3, it exhibits a higher capacity retention rate compared to the batteries of Comparative Examples 4 and 5.

Claims

1. A positive electrode for a secondary battery, comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. in, The positive electrode active material layer comprises a lower layer disposed on the surface of the current collector and an upper layer disposed on the lower layer. The upper layer comprises a first positive electrode active material, a conductive material, and an adhesive resin. The lower layer comprises a second positive electrode active material, a sacrificial positive electrode material, a conductive material, and an adhesive resin, and The first positive electrode active material and the second positive electrode active material each comprise at least one compound selected from those represented by Chemical Formula 1 below: [Chemical Formula 1] LiNi 1-x M x O2 In chemical formula 1, M includes at least one of Mn, Co, Al, Cu, Fe, Mg, B and Ga, and x is 0 to 0.5; The sacrificial cathode material in the lower layer includes at least one of Li6CoO4 and a compound represented by the following chemical formula 2: [Chemical Formula 2] Li6Co 1-x Zn x O4 In chemical formula 2, x is greater than 0 and less than 1.

2. The positive electrode for a secondary battery as described in claim 1, wherein, The upper layer does not contain sacrificial cathode material.

3. The positive electrode for a secondary battery as described in claim 1, wherein, The sacrificial cathode material includes materials selected from Li6CoO4 and Li6Co. 0.7 Zn 0.3 At least one of O4.

4. The positive electrode for a secondary battery as described in claim 1, wherein, Based on 100% by weight of the lower layer, the sacrificial cathode material is present in an amount of 1% to 20% by weight.

5. The positive electrode for a secondary battery as described in claim 1, wherein, Based on 100% by weight of the entire positive electrode active material layer, the amount of the sacrificial positive electrode material is less than 10% by weight.

6. The positive electrode for a secondary battery as described in claim 1, wherein, In chemical formula 1, x ranges from 0 to 0.

15.

7. The positive electrode for a secondary battery as described in claim 1, wherein, M in chemical formula 1 includes at least two of Co, Al, and Mn.

8. The positive electrode for a secondary battery as described in claim 1, wherein, The positive electrode active material represented by chemical formula 1 is LiNi 1-x (Co, Mn, Al) x O2, wherein Al exists in an atomic ratio of 0.001 to 0.02 based on Ni.

9. A lithium-ion secondary battery comprising a positive electrode, a negative electrode, an insulating membrane disposed between the positive electrode and the negative electrode, and an electrolyte. in, The positive electrode is the same as that defined in claim 1. The negative electrode comprises a silicon-based compound as the negative electrode active material and a conductive material including a linear conductive material.

10. The lithium-ion secondary battery as described in claim 9, wherein, The silicon-based compound includes at least one of the compounds represented by the following chemical formula 3: [Chemical Formula 3] Not. x In chemical formula 3, x is equal to or greater than 0 and less than 2.

11. The lithium-ion secondary battery of claim 10, wherein x in chemical formula 3 is from 0.5 to 1.

5.

12. The lithium-ion secondary battery as described in claim 9, wherein, The linear conductive material includes at least one selected from single-walled carbon nanotubes, multi-walled carbon nanotubes, and graphene.

13. The lithium-ion secondary battery as described in claim 9, wherein, The linear conductive material includes single-walled carbon nanotubes.

Images