Positive electrode for lithium secondary battery and lithium secondary battery comprising the same

Abstract

The present invention provides a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same. In the positive electrode, a positive electrode additive represented by Chemical Formula 1 is contained in a positive electrode mixture layer, and control is performed on a specific X-ray diffraction (XRD) and / or extended X-ray absorption fine structure (EXAFS) peak such that cobalt remaining in the positive electrode mixture layer after initial charging to SOC 100% has a specific oxidation number, thereby improving a side reaction caused by an irreversible additive, i.e., the positive electrode additive, and reducing the amount of gas such as oxygen generated during charging / discharging. Accordingly, the lithium secondary battery has an excellent effect of improving battery safety and electrical performance.

Description

Technical Field

[0001] This invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery comprising the same.

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2021-0071866, filed on June 3, 2021, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] With the technological advancements and increasing demands of mobile devices, the need for secondary batteries as energy sources is rapidly growing. Among these secondary batteries, lithium-ion batteries, characterized by high energy density, high operating potential, long cycle life, and low self-discharge rate, have been extensively studied, commercialized, and applied in various fields.

[0004] Recently, with the increasing use of lithium-ion batteries as an energy source for medium to large-scale devices such as electric vehicles, there is a growing need for high-capacity, high-energy-density, and low-cost lithium-ion batteries, as well as for irreversible additives used in the electrodes with higher irreversible capacity. However, there are indeed limitations in developing cathode additives with such high irreversible capacity.

[0005] On the other hand, conventional irreversible additives such as Li6CoO4 are typically prepared by reacting excess lithium oxide with a metal oxide such as cobalt oxide. The irreversible additives prepared as described above are structurally unstable and generate a large amount of oxygen (O2) during charging. Furthermore, during the initial charging of the secondary battery, i.e., battery activation, if the irreversible additive reaction is incomplete and residues remain, reactions may occur during subsequent charging / discharging processes, causing side reactions or generating large amounts of oxygen in the battery. The oxygen generated, as described above, can cause volume expansion of the electrode components, becoming one of the main factors leading to battery performance degradation.

[0006]

[0007] Furthermore, during the preparation of the slurry composition used to manufacture the electrode, byproducts such as lithium oxide may react with the binder components, leading to increased viscosity or gelation of the composition. As a result, it becomes difficult to uniformly coat the electrode composition used to form the active material layer, and the battery characteristics deteriorate.

[0008] Therefore, in order to improve the safety and electrical performance of lithium secondary batteries, it is necessary to develop technologies that can reduce side reactions caused by irreversible additives or the generation of gases such as oxygen (O2) during charging / discharging.

[0009] [Related Technical Documents]

[0010] [Patent Literature]

[0011] Korean Unexamined Patent Application Publication No. 10-2019-0078392 Summary of the Invention

[0012] Technical issues

[0013] Therefore, the present invention aims to provide a positive electrode for a lithium secondary battery and a lithium secondary battery, wherein the positive electrode for the lithium secondary battery and the lithium secondary battery can reduce the amount of side reactions caused by irreversible additives and gases such as oxygen (O2) generated during charging / discharging, thereby achieving excellent battery safety and high charging / discharging capacity.

[0014] Technical solution

[0015] To address the above problems, one aspect of the present invention provides a positive electrode for a lithium secondary battery, the positive electrode comprising:

[0016] Positive current collector, and

[0017] A positive electrode mixture layer is disposed on a positive electrode current collector and contains a positive electrode active material and a positive electrode additive represented by the following chemical formula 1.

[0018] The positive electrode mixture layer, in X-ray diffraction (XRD) measurements after initial charging to 100% SOC, exhibits one or more peaks at 19.1±0.5°, 36.6±0.5°, 38.7±0.5°, 42.4±0.5°, and 44.8±0.5° (represented by 2θ).

[0019] [Chemical Formula 1]

[0020] Li p Co (1-q) M 1 q O4

[0021] In chemical formula 1,

[0022] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0023] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0024] Here, the positive electrode mixture layer can satisfy the following Equation 1 in X-ray diffraction (XRD) measurements after initial charging to 100% SOC:

[0025] [Formula 1]

[0026] 0.2 ≤ P1 / P2 ≤ 1.5

[0027] In Formula 1,

[0028] P1 represents the highest intensity of the peak present at 42.4 ± 0.5°, and

[0029] P2 represents the highest intensity of the peak present at 44.8 ± 0.5°.

[0030] Furthermore, in the extended X-ray absorption fine structure (EXAFS) analysis of the positive electrode mixture layer after initial charging to SOC 100%, there may be peaks at one or more of and .

[0031] Furthermore, the positive electrode additive contained in the positive electrode mixture layer may have a tetragonal structure with a space group of P42 / nmc.

[0032] Furthermore, the content of the positive electrode additive may be 0.01 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0033] Furthermore, the positive electrode active material contained in the positive electrode mixture layer may be a lithium metal composite oxide represented by the following Chemical Formula 2:

[0034] [Chemical Formula 2]

[0035] Li x [Ni y Co z Mn w M 2 v O u

[0036] In Chemical Formula 2,

[0037] M 2 is one or more elements selected from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0038] x, y, z, w, v, and u are 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5, respectively.

[0039] Furthermore, the positive electrode mixture layer may further comprise one or more conductive materials selected from the following: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0040] Here, the content of conductive material can be 0.5 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

[0041] Furthermore, another aspect of the present invention provides a lithium secondary battery comprising the positive electrode, the negative electrode, and a separator disposed between the positive electrode and the negative electrode as described above.

[0042] Here, the negative electrode may include: a negative electrode current collector; and a negative electrode mixture layer disposed on the negative electrode current collector and containing carbon material and silicon material as negative electrode active materials.

[0043] In addition, the carbon material contained in the negative electrode mixture layer may include one or more selected from the following: natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black, acetylene black, Ketjen black and carbon fiber.

[0044] In addition, the silicon material contained in the negative electrode mixture layer may include one or more of silicon (Si) particles and silicon oxide (SiOx, 1≤x≤2) particles.

[0045] Furthermore, the content of silicon material can be 1 to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

[0046] Beneficial effects

[0047] In the positive electrode for lithium secondary batteries according to the present invention, the positive electrode mixture layer contains a positive electrode additive represented by Chemical Formula 1, and specific X-ray diffraction (XRD) and / or extended X-ray absorption fine structure (EXAFS) peaks are controlled so that the cobalt remaining in the positive electrode mixture layer after initial charging to 100% SOC has a specific oxidation number, thereby improving side reactions caused by irreversible additives, i.e., positive electrode additives, and reducing the amount of gases such as oxygen generated during charging / discharging. Therefore, the lithium secondary battery has excellent effects in improving battery safety and electrical performance. Attached Figure Description

[0048] Figure 1 This is an XRD pattern showing the positive electrode mixture layer of the positive electrode for a lithium secondary battery according to the present invention after being charged to 100% SOC.

[0049] Figure 2 Transmission electron microscopy (TEM) images and figures are shown of the positive electrode mixture layer contained in the positive electrode for lithium secondary batteries according to the present invention after being charged to 100% SOC.

[0050] Figure 3 The EXAFS analysis plot of the positive electrode mixture layer for lithium secondary batteries according to the present invention after being charged to 100% SOC is shown. Detailed Implementation

[0051] The present invention can have various variations and instances, and specific examples are shown in the accompanying drawings and described in detail in specific embodiments.

[0052] However, it should be understood that the present invention is not limited to the specific embodiments, but includes all variations, equivalents or alternatives within the spirit and scope of the present invention.

[0053] The terms “comprising,” “including,” and “having” as used herein indicate the presence of the features, quantities, steps, operations, components, or elements or combinations thereof described in the specification, but it should be understood that these terms do not exclude the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, elements, or combinations thereof.

[0054] Furthermore, when a portion of a layer, film, region, or plate is disposed "on" another portion, this includes not only the case where one portion is disposed "directly" on the other portion, but also the case where another portion is inserted in between. Conversely, when a portion of a layer, film, region, or plate is disposed "below" another portion, this includes not only the case where one portion is disposed "directly" below the other portion, but also the case where another portion is inserted in between. Moreover, in this application, "on" includes not only the case where it is disposed on the upper part, but also the case where it is disposed on the lower part.

[0055] Furthermore, the term "major component" as used herein can refer to a component that has a content of 50% by weight or more, 60% by weight or more, 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more relative to the total weight of the composition or a particular component, and in some cases, when the major component constitutes the entire composition or a particular component, its content can be 100% by weight.

[0056] Furthermore, the "Ah" used in this article refers to the capacity unit of lithium secondary batteries, also known as "ampere-hour," which refers to the current output per hour. For example, when the battery capacity is "3000mAh," it means that the battery can discharge at a current of 3000mA for 1 hour.

[0057] The invention will be described in more detail below.

[0058] Positive electrode for lithium secondary batteries

[0059] In one embodiment of the present invention, the positive electrode for a lithium secondary battery comprises:

[0060] Positive current collector, and

[0061] A positive electrode mixture layer, wherein the positive electrode mixture layer is disposed on a positive electrode current collector and contains a positive electrode active material and a positive electrode additive represented by the following chemical formula 1,

[0062] The positive electrode mixture layer exhibits one or more peaks at 19.1±0.5°, 36.6±0.5°, 38.7±0.5°, 42.4±0.5°, and 44.8±0.5° (represented by 2θ) in X-ray diffraction (XRD) measurements after initial charging to 100% SOC.

[0063] [Chemical Formula 1]

[0064] Li p Co (1-q) M 1 q O4

[0065] In chemical formula 1,

[0066] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0067] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0068] The positive electrode for a lithium secondary battery according to the present invention has a structure in which a mixture layer is formed on a positive electrode current collector, wherein the positive electrode mixture layer has a structure comprising a positive electrode active material and a positive electrode additive.

[0069] Here, the positive electrode active material can be a lithium composite transition metal oxide containing two or more elements selected from the following: nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), zinc (Zn), titanium (Ti), magnesium (Mg), chromium (Cr), and zirconium (Zr). For example, the positive electrode active material can be a lithium metal composite oxide represented by the following chemical formula 2, capable of reversible intercalation and deintercalation:

[0070] [Chemical Formula 2]

[0071] Li x [Ni y Co z Mn w M 2 v ]O u

[0072] In Chemical Formula 2,

[0073] M 2 is one or more elements selected from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0074] x, y, z, w, v, and u are respectively 1.0 ≤ x ≤ 1.30, 0.1 ≤ y < 0.95, 0.01 < z ≤ 0.5, 0.01 < w ≤ 0.5, 0 ≤ v ≤ 0.2, and 1.5 ≤ u ≤ 4.5.

[0075] The lithium metal composite oxide represented by Chemical Formula 2 is a metal oxide containing lithium, nickel, cobalt, and manganese, and in some cases, may have a form in which different transition metals (M 2 ) are doped. For example, the positive electrode active material may include one or more compounds selected from the following: LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.05 Mn 0.05 O2, LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2, and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O2. As an example, in the positive electrode active material, as the lithium metal composite oxide represented by Chemical Formula 2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O2, or LiNi 0.8 Co 0.1 Mn 0.1Al0.05 O`2 can be used alone or in combination.

[0076] In addition, relative to 100 parts by weight of the positive electrode mixture layer, the content of the positive electrode active material can be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight.

[0077] Furthermore, the cathode mixture layer may include a cathode additive that imparts irreversible capacity and a cathode active material that exhibits electroactivity, wherein the cathode additive may include lithium cobalt oxide represented by the following chemical formula 1:

[0078] [Chemical Formula 1]

[0079] Li p Co (1-q) M 1 q O4

[0080] In chemical formula 1,

[0081] M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and

[0082] p and q are 5≤p≤7 and 0≤q≤0.5, respectively.

[0083] The positive electrode additive can contain excess lithium to provide lithium for the lithium consumption caused by irreversible chemical and physical reactions at the negative electrode during initial charging, thereby increasing charging capacity, reducing irreversible capacity, and improving lifetime characteristics.

[0084] In cathode additives, the lithium-ion content of the cathode additive represented by Formula 1 can be higher than that of commonly used nickel-containing oxides in the art. This replenishes the lithium-ions lost during the initial activation of the battery through irreversible reactions, thus significantly improving the battery's charge / discharge capacity. Furthermore, compared to commonly used iron- and / or manganese-containing oxides in the art, there are no side reactions caused by transition metal dissolution during battery charging / discharging, resulting in excellent battery stability. Examples of lithium cobalt oxides represented by Formula 1 may include Li6CoO4, Li6Co... 0.5 Zn 0.5 O4 and Li6Co 0.7 Zn 0.3 O4.

[0085] Furthermore, the average particle size of the lithium cobalt oxide represented by Chemical Formula 1 can be from 0.1 to 10 μm, specifically from 0.1 to 8 μm; 0.1 to 5 μm; 0.1 to 3 μm; 0.5 to 2 μm; 0.1 to 0.9 μm; 0.1 to 0.5 μm; 0.6 to 0.9 μm; 1 to 4 μm; 1.5 to 3.5 μm; 4 to 6 μm; 5 to 10 μm; or 6 to 9 μm. By controlling the average particle size of the lithium cobalt oxide of the present invention within the above range, the irreversible activity of the lithium cobalt oxide may increase, and the decrease in the powder conductivity of the lithium cobalt oxide can be prevented.

[0086] Furthermore, the lithium cobalt oxide represented by Chemical Formula 1 can have a tetragonal crystal structure, and within this tetragonal crystal structure, it can be included in the P42 / nmc space group having a twisted tetrahedral structure composed of cobalt and oxygen elements. Because the cathode additive has a twisted tetrahedral structure composed of cobalt and oxygen elements, this structure is unstable, and the cathode may be damaged by side reactions with moisture (H2O) in the air during manufacturing, leading to deterioration of the battery's electrical performance. However, in this invention, by using a binder with low affinity for water as the binder for the composite layer, damage to the cathode additive can be minimized, thereby further improving the electrical performance and lifespan of the lithium secondary battery.

[0087] Furthermore, relative to 100 parts by weight of the positive electrode mixture layer, the content of the positive electrode additive can be 0.01 to 5 parts by weight, specifically 0.01 to 4 parts by weight; 0.01 to 3 parts by weight; 0.01 to 2 parts by weight; 0.1 to 1 part by weight; 0.5 to 2 parts by weight; 1 to 3 parts by weight; 2 to 4 parts by weight; 1.5 to 3.5 parts by weight; 0.5 to 1.5 parts by weight; 1 to 2 parts by weight; 0.1 to 0.9 parts by weight; or 0.3 to 1.2 parts by weight.

[0088] Furthermore, the positive electrode for lithium secondary batteries according to the present invention can show a specific peak with a specific intensity in XRD measurements after initial charging to 100% SOC.

[0089] In one example, the positive electrode of a lithium secondary battery, after initial charging to 100% SOC, can show one or more peaks in XRD measurements of the positive electrode mixture layer at 19.1±0.5°, 36.6±0.5°, 38.7±0.5°, 42.4±0.5°, and 44.8±0.5°, represented by 2θ.

[0090] In another example, the positive electrode of a lithium secondary battery, after initial charging to 100% SOC, exhibits peaks at 42.4 ± 0.5° and 44.8 ± 0.5° in XRD measurements of the positive electrode mixture layer, expressed in terms of 2θ, and these peaks satisfy the following Equation 1:

[0091] [Formula 1]

[0092] 0.2 ≤ P1 / P2 ≤ 1.5

[0093] In Formula 1,

[0094] P1 represents the highest intensity of the peak present at 42.4 ± 0.5°, and

[0095] P2 represents the highest intensity of the peak present at 44.8 ± 0.5°.

[0096] Specifically, the positive electrode for lithium secondary batteries can satisfy Formula 1 within the following ranges: 0.2 to 1.2 (i.e., 0.2 ≤ P1 / P2 ≤ 1.2); 0.2 to 1.0 (i.e., 0.2 ≤ P1 / P2 ≤ 1.0); 0.5 to 1.3 (i.e., 0.5 ≤ P1 / P2 ≤ 1.3); 0.4 to 1.1 (i.e., 0.4 ≤ P1 / P2 ≤ 1.1); 0.6 to 1.0 (i.e., 0.6 ≤ P1 / P2 ≤ 1.0); 0.5 to 0.95 (i.e., 0.5 ≤ P1 / P2 ≤ 0.95); or 0.7 to 0.99 (i.e., 0.7 ≤ P1 / P2 ≤ 0.99).

[0097] This peak represents the cobalt oxide remaining in the cathode mixture layer after initial charging to 100% SOC. Specifically, the peak represents the peak of CoO with an oxidation number of 2; the peak of Co3O4 with an oxidation number of 8 / 3; and / or the peak of Li2Co2O4 with an oxidation number of 3. In the cathode for lithium secondary batteries according to the present invention, the oxidation number of cobalt (Co) remaining in the cathode mixture layer can be controlled, so that one or more XRD peaks may appear after initial charging to 100% SOC, while the peaks satisfy Formula 1. Therefore, the cathode of the present invention can prevent additional side reactions occurring at the cathode during initial charging, i.e., activation of the lithium secondary battery, and reduce the amount of gases such as oxygen (O2) generated during charging / discharging.

[0098] Furthermore, in the extended X-ray absorption fine structure (EXAFS) analysis of the K absorption edge of cobalt (Co) contained in the cathode mixture layer after initial charging to 100% SOC according to the present invention, in... and Peaks can be present at any or multiple locations within a given element.

[0099] This peak represents the combination between cobalt (Co) and the surrounding oxygen (O) and / or transition metals, indicating the presence of CoO, LiCoO2 and / or Co3O4 in the cathode mixture layer, and the intensity of the peak can be adjusted by the oxidation number of cobalt (Co) in the cathode mixture layer contained in the cathode initially charged to 100% SOC.

[0100] Furthermore, in the positive electrode for lithium-ion batteries, the oxidation number and / or degree of cobalt (Co) contained in the positive electrode mixture layer can be controlled under initial charging conditions. For example, the positive electrode for lithium-ion batteries can have a structure in which a three-step charging process is carried out continuously, i.e., one-step to three-step activation. More specifically, the initial charging step can be performed through the following steps:

[0101] First activation step: Apply a current of 0.05C to 0.2C to charge the lithium secondary battery to below 30% SOC;

[0102] The second activation step involves applying a current of 0.3C to 0.5C to charge the lithium-ion battery, which has undergone the first activation step, to a state of charge (SOC) greater than 30% and less than 70%; and

[0103] The third activation step: Apply a current of 0.6C to 0.9C to charge the lithium secondary battery that has undergone the second activation step to a state of charge (SOC) of over 70%.

[0104] In one example, the positive electrode for a lithium secondary battery can be manufactured through the following steps:

[0105] First activation step: During the initial charge, apply a current of 0.08C to 0.15C to charge the lithium secondary battery to below 30% SOC;

[0106] The second activation step involves applying a current of 0.35C to 0.45C to charge the lithium-ion battery that has undergone the first activation step to a state of charge (SOC) greater than 30% and less than 70%; and

[0107] The third activation step: Apply a current of 0.65C to 0.8C to charge the lithium secondary battery that has undergone the second activation step to a state of charge (SOC) of over 70%.

[0108] On the other hand, in addition to the positive electrode active material and positive electrode additives, the positive electrode mixture layer may further contain conductive materials, binders or additives.

[0109] Here, conductive materials can be used to improve the performance of the positive electrode, such as conductivity, and can include one or more selected from: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers. For example, conductive materials may include acetylene black.

[0110] In addition, the content of conductive material may be 0.5 to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer, specifically 0.5 to 4 parts by weight; 0.5 to 3 parts by weight; 0.5 to 1 part by weight; 0.5 to 2 parts by weight or 1 to 3 parts by weight.

[0111] In addition, the adhesive may include one or more resins selected from: polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. In one example, the adhesive may include polyvinylidene fluoride.

[0112] In addition, the content of the binder may be 1 to 10 parts by weight, specifically 2 to 8 parts by weight or 1 to 5 parts by weight, relative to 100 parts by weight of the positive electrode mixture layer.

[0113] In addition, there is no particular limitation on the average thickness of the cathode mixture layer, but it can be 50 to 300 μm, more specifically 100 to 200 μm; 80 to 150 μm; 120 to 170 μm; 150 to 300 μm; 200 to 300 μm; or 150 to 190 μm.

[0114] Furthermore, in the positive electrode, materials with high conductivity that do not cause chemical changes in the battery can be used as the positive electrode current collector. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can be used as the positive electrode current collector, and in the case of aluminum or stainless steel, aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver can also be used. In addition, the positive electrode current collector can have fine irregularities formed on its surface to improve the adhesion of the positive electrode active material, and can be formed in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Furthermore, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the current collector can be appropriately applied within the range of 3 to 500 μm.

[0115] Lithium secondary batteries

[0116] Furthermore, in one embodiment of the present invention, a lithium secondary battery is provided, the battery comprising the positive electrode, the negative electrode and the separator inserted between the positive electrode and the negative electrode as described above according to the present invention.

[0117] The lithium secondary battery according to the present invention comprises the positive electrode described above, thereby exhibiting excellent characteristics such as battery safety and electrical performance. The lithium secondary battery of the present invention has a structure comprising the aforementioned positive electrode; a negative electrode; and a separator inserted between the positive and negative electrodes.

[0118] Here, for the negative electrode, the negative electrode mixture layer is formed by coating a negative electrode active material onto a negative electrode current collector, drying and pressing it, and like the positive electrode, the negative electrode may selectively contain conductive materials, organic binder polymers or additives as needed.

[0119] Furthermore, the negative electrode active material may include, for example, carbon materials and silicon materials. Carbon materials refer to carbon materials containing carbon atoms as a major component, and examples of such carbon materials may include: graphite with a fully layered crystal structure, such as natural graphite; soft carbon with a low-crystallinity layered crystal structure (graphene structure; wherein hexagonal honeycomb planes of carbon are arranged in layers); and hard carbon wherein the above structures are mixed with amorphous portions; artificial graphite; expanded graphite; carbon nanofibers; non-graphitized carbon; carbon black; acetylene black; Ketjen black; carbon nanotubes; fullerenes; activated carbon; and graphene, preferably selected from one or more of natural graphite, artificial graphite, graphene, and carbon nanotubes. More preferably, the carbon material includes natural graphite and / or artificial graphite, and may also include any one or more of graphene and carbon nanotubes in addition to natural graphite and / or artificial graphite. In this case, the carbon material may contain 50 to 95 parts by weight, more specifically 60 to 90 parts by weight or 70 to 80 parts by weight of graphene and / or carbon nanotubes, relative to a total of 100 parts by weight of carbon material.

[0120] Furthermore, silicon materials are particles containing silicon (Si) as the main component, which is a metallic component, and may contain silicon (Si) particles and silicon oxide (SiO). X The silicon material may contain one or more of the following: (1 ≤ X ≤ 2) particles. In one instance, the silicon material may comprise silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO2) particles, or mixtures thereof.

[0121] Furthermore, the silicon material can be in the form of a mixture of crystalline and amorphous particles, and based on a total of 100 parts by weight of all silicon material, the proportion of amorphous particles can be 50 to 100 parts by weight, specifically 50 to 90 parts by weight, 60 to 80 parts by weight, or 85 to 100 parts by weight. In this invention, by controlling the proportion of amorphous particles contained in the silicon material within the above range, thermal stability and flexibility can be improved without reducing the electrical performance of the electrode.

[0122] In addition, the negative electrode active material contains carbon material and silicon material, and based on 100 parts by weight of the negative electrode mixture layer, the content of silicon material can be 1 to 20 parts by weight, particularly 5 to 20 parts by weight; 3 to 10 parts by weight; 8 to 15 parts by weight; 13 to 18 parts by weight; or 2 to 7 parts by weight.

[0123] In this invention, by adjusting the content of carbon and silicon materials contained in the negative electrode active material to the above-mentioned range, lithium consumption and irreversible capacity loss during the initial charging / discharging of the battery can be reduced, and the charging capacity per unit mass can also be improved.

[0124] In one example, relative to 100 parts by weight of the negative electrode active material, the negative electrode active material may comprise: 95 ± 2 parts by weight of graphite; and 5 ± 2 parts by weight of a mixture wherein silicon monoxide (SiO) particles and silicon dioxide (SiO2) particles are uniformly mixed. In this invention, by adjusting the content of carbon and silicon materials contained in the negative electrode active material to the above-mentioned range, lithium consumption and irreversible capacity loss during the initial charge / discharge process of the battery can be reduced, and the charge capacity per unit mass can also be improved.

[0125] In addition, the average thickness of the negative electrode mixture layer can be 100 to 200 μm, specifically 100 to 180 μm, 100 to 150 μm, 120 to 200 μm, 140 to 200 μm or 140 to 160 μm.

[0126] Furthermore, there are no particular limitations on the negative electrode current collector, as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, nickel, titanium, or calcined carbon can be used. In the case of copper or stainless steel, copper or stainless steel with a surface treated with carbon, nickel, titanium, or silver can be used. Moreover, like the positive electrode current collector, the negative electrode current collector has fine irregularities on its surface to enhance the adhesion of the positive electrode active material, and can be formed in various shapes such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics. Furthermore, considering the conductivity and total thickness of the negative electrode to be manufactured, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 500 μm.

[0127] Furthermore, an insulating film is used as the separator, which is inserted between the positive and negative electrodes and has high ion permeability and mechanical strength. There are no particular limitations on the separator, as long as it is commonly used in the art; specifically, sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene can be used. In some cases, composite separators can be used, wherein a porous polymer substrate such as a sheet or nonwoven fabric is coated with an organic binder polymer using inorganic / organic particles. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also act as a separator. Furthermore, the pore size of the separator can be from an average of 0.01 to 10 μm, and the thickness can be from an average of 5 to 300 μm.

[0128] On the other hand, the positive and negative electrodes can be wound and housed in a cylindrical, prismatic, or pouch-shaped battery in the shape of a roll, or they can be housed in a pouch-shaped battery in the form of folding or stacking and folding, but the present invention is not limited thereto.

[0129] Furthermore, the lithium-containing electrolyte according to the present invention can be composed of an electrolyte and a lithium salt, and as the electrolyte, a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte can be used.

[0130] As non-aqueous organic solvents, aprotic organic solvents such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate can be used.

[0131] As organic solid electrolytes, polymers such as polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyalginate lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymers containing ion-dissociating groups can be used.

[0132] As an inorganic solid electrolyte, lithium nitrides, halides, or sulfates can be used, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, or Li3PO4-Li2S-SiS2.

[0133] Lithium salts are materials that are readily soluble in non-aqueous electrolytes, and can be, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB. 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate or lithium imide.

[0134] In addition, to improve charge / discharge characteristics and flame retardancy, substances such as pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted compounds can be added to the electrolyte. The electrolyte may contain oxaliplatinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In some cases, to impart non-flammability, the electrolyte may further contain halogenated solvents such as carbon tetrachloride or trifluoroethylene, and to improve high-temperature storage performance, it may further contain carbon dioxide gas, and may also contain fluoroethylene carbonate (FEC) or propylene sulfonate lactone (PRS).

[0135] [Example]

[0136] The invention will be described in further detail below with reference to embodiments and experimental examples.

[0137] However, the following embodiments and experimental examples are only used to illustrate the present invention, and the content of the present invention is not limited to the following embodiments and experimental examples.

[0138] Manufacturing of lithium secondary batteries in Examples 1 and 2 and Comparative Examples 1 to 4

[0139] a) Manufacturing of positive electrodes for lithium secondary batteries

[0140] The positive electrode slurry for lithium secondary batteries is prepared as follows: N-methylpyrrolidone is injected into a homogenizer, and 97 parts by weight of positive electrode active material LiNi are weighed and added relative to 100 parts by weight of the solids of the positive electrode slurry. 0.6 Co 0.2 Mn 0.2 O2; 0.8 parts by weight of positive electrode additive Li6CoO4 or Li6Co 0.7 Zn 0.3 O4; 0.7 parts by weight of a conductive material, said conductive material being a mixture of carbon nanotubes (average size: 60 ± 10 nm) and tandoor black (average size: 2 ± 0.5 μm) (75:25 wt / wt); and 1.5 parts by weight of a binder PVdF, and the resulting mixture was mixed at 2,000 rpm for 60 minutes. The positive electrode was manufactured by coating the prepared positive electrode slurry onto one surface of an aluminum current collector, drying the slurry at 100°C, and rolling the resulting mixture. Here, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the manufactured positive electrode was approximately 200 μm.

[0141] b) Manufacturing of lithium secondary batteries

[0142] Relative to 100 parts by weight of the solids of the negative electrode slurry, 84 parts by weight of natural graphite (a negative electrode active material) and 14 parts by weight of silicon oxide (SiOx, 1≤x≤2) particles were prepared; and 2 parts by weight of styrene-butadiene rubber (SBR) as a binder. The negative electrode slurry was prepared in the same manner as the positive electrode slurry. Here, the graphite used to form the negative electrode mixture layer was natural graphite (average particle size: 0.01 to 0.5 μm), and the average particle size of the silicon oxide (SiOx) particles was 0.9 to 1.1 μm. The negative electrode was manufactured by coating the prepared negative electrode slurry onto one surface of a copper current collector, drying the slurry at 100°C, and rolling the result. Here, the total thickness of the negative electrode mixture layer was 150 μm, and the total thickness of the manufactured negative electrode was approximately 250 μm.

[0143] The battery is assembled into a full-cell type by stacking a separator (thickness: approximately 16 μm) made of porous polyethylene (PE) membranes between the prepared positive and negative electrodes and injecting E2DVC as the electrolyte. Here, "E2DVC" refers to a carbonate electrolyte, which is a mixed solution in which lithium hexafluorophosphate (LiPF6, 1.0 M) and ethylene carbonate (VC, 2 wt%) are added to a mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0144] Lithium secondary batteries were manufactured by initially charging the manufactured full cells at 22±2°C under the conditions shown in Table 1 below.

[0145] [Table 1]

[0146]

[0147] Experimental Example

[0148] To evaluate the performance of the positive electrode for secondary batteries according to the present invention, the following experiment was conducted.

[0149] a) Analysis of cobalt oxide number in the positive electrode mixture layer during initial charging

[0150] Samples were prepared by removing the positive electrode from each of the lithium secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 4, and by peeling off the positive electrode mixture layer from the removed positive electrode. XRD, TEM, and EXAFS analyses were performed on each prepared sample, and the results are presented below. Figures 1 to 3 middle.

[0151] Furthermore, XRD analysis was performed using an XRD analyzer (Rigaku Corporation), and the wavelength was scanned at a scan rate of 5° / second within a 2θ range of 10° to 50°. XRD patterns were obtained using X-rays (Cu Kα radiation, 40 kV, 100 mA). Furthermore, in the measured X-ray diffraction patterns, the intensities (P1) of the peak appearing at 2θ = 42.4 ± 0.5° and the intensities (P2) of the peak appearing at 2θ = 44.8 ± 0.5° were measured to calculate their ratio (P1 / P2), and the results are shown in Table 2 below.

[0152] b) Evaluation of the cumulative gas generation during charging / discharging after initial charging

[0153] After degassing the initially charged lithium secondary batteries of Examples 1 and 2 and Comparative Examples 1 to 4, the lithium secondary batteries were discharged to a final voltage of 2V at a discharge current of 0.1C, and the secondary batteries from which the internal gas was removed were repeatedly charged / discharged 50 times at 45°C, 4.5V, and 1.0C. Here, the cumulative amount of gas generated after the initial charge / discharge was measured by measuring the amount of gas generated in each charge / discharge. The results are shown in Table 2 below.

[0154] c) Evaluation of cycle life performance

[0155] The lithium secondary batteries initially charged in Examples 1 and 2 and Comparative Examples 1 to 4 were degassed and discharged at a discharge current of 0.1C until the final voltage reached 2V. Then, the batteries were subjected to 100 charge / discharge cycles (n = 100) at 25°C, a charge termination voltage of 4.25V, a discharge termination voltage of 2.5V, and 0.5C / 0.5C conditions. The capacity retention rate [%) was then measured. The capacity retention rate was calculated using Formula 2 below, and the results are shown in Table 2 below:

[0156] [Formula 2]

[0157] Capacity retention (%) = (Discharge capacity at 100 charge / discharge cycles / Discharge capacity at initial charge / discharge cycles) × 100

[0158] [Table 2]

[0159]

[0160] Refer to Table 2 and Figures 1 to 3 It can be seen that after charging the lithium secondary battery according to the present invention to 100% SOC with a positive electrode, controlling the XRD peak and / or EXAFS peak within a specific range improves the safety and electrical performance of the lithium secondary battery.

[0161] Specifically, TEM analysis showed that in the lithium secondary battery prepared in the examples, the positive electrode mixture layer contained, for example, CoO, Co3O4, and LiCoO2 as cobalt oxides. Furthermore, EXAFS analysis of the K-absorption edge of cobalt (Co) revealed that the positive electrode mixture layer... and A peak is observed at the interatomic distance (i.e., radial distance). This peak is attributed to CoO, Co3O4, and / or LiCoO2 contained in the cathode mixture layer.

[0162] Furthermore, the cathode mixture layer exhibits peaks at 19.1±0.5°, 36.6±0.5°, 38.7±0.5°, 42.4±0.5°, and 44.8±0.5° (represented by 2θ) in XRD measurements. Among these peaks, the intensity ratio (P1 / P2) of the peak at 2θ = 42.4±0.5° to that at 2θ = 44.8±0.5° is approximately 0.8 to 0.9. Here, the peak at 2θ = 44.8±0.5° represents the [4,0,0] lattice of CoO, and the peak at 2θ = 42.4±0.5° represents the [2,0,0] lattice of Co3O4. Their ratio can represent the oxidation number and / or degree of oxidation of cobalt (Co) contained in the cathode mixture layer. This result indicates that in the positive electrode of the present invention, the oxidation number of cobalt (Co) present in the positive electrode mixture layer is adjusted to a specific range after initial charging to 100% SOC.

[0163] Furthermore, it was confirmed that in the lithium secondary battery of the embodiment containing the above-described positive electrode, the amount of gas generated during charging / discharging is significantly reduced after degassing the gas generated during the initial charging / discharging. Furthermore, it was confirmed that the lithium secondary battery has a high initial charging capacity of 103 Ah or more and a high capacity retention rate of 95% or more.

[0164] Based on the above results, in the positive electrode for lithium secondary batteries according to the present invention, the positive electrode mixture layer contains a positive electrode additive represented by Chemical Formula 1, and specific XRD and / or EXAFS peaks are controlled so that the cobalt remaining in the positive electrode mixture layer after initial charging to 100% SOC has a specific oxidation number, thereby improving the side reactions caused by irreversible additives, i.e., positive electrode additives, and reducing the amount of gases such as oxygen generated during charging / discharging. Therefore, it can be seen that the battery safety and electrical performance of the lithium secondary battery are improved.

[0165] In the foregoing, although the invention has been described with reference to exemplary embodiments, those skilled in the art or of ordinary skill in the art should understand that various modifications and changes can be made to the invention without departing from the spirit and scope of the invention as set forth in the appended claims.

[0166] Therefore, the technical scope of the present invention is not limited to the contents described in the specific embodiments of the specification, but should be defined by the claims.

Claims

1. A positive electrode for a lithium secondary battery, the positive electrode being a positive electrode after initial charging to 100% SOC, the positive electrode comprising: A positive electrode current collector, and A positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material and a positive electrode additive represented by the following Chemical Formula 1, in, The positive electrode mixture layer has one or more peaks shown at 19.1±0.5°, 36.6±0.5°, 38.7±0.5°, 42.4±0.5° and 44.8±0.5° represented by 2θ in X-ray diffraction (XRD) measurement, [Chemical Formula 1] Li p Co (1-q) M 1 q O4 In Chemical Formula 1, M 1 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and p and q are 5≤p≤7 and 0≤q≤0.5, respectively, Wherein, the positive electrode mixture layer satisfies the following Formula 1 in X-ray diffraction (XRD) measurement: [Formula 1] 0.4≤P1 / P2≤1.5 In Formula 1, P1 represents the highest intensity of the peak existing at 42.4±0.5°, and P2 represents the highest intensity of the peak existing at 44.8±0.5°, Wherein, the positive electrode active material is a lithium metal composite oxide represented by the following Chemical Formula 2: [Chemical Formula 2] Li x [Ni y Co z Mr w M 2 v ]O u In Chemical Formula 2, M 2 It is selected from one or more elements chosen from the following: W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, v and u are 1.0≤x≤1.30, 0.1≤y<0.95, 0.01<z≤0.5, 0.01<w≤0.5, 0≤v≤0.2 and 1.5≤u≤4.5, respectively.

2. The positive electrode according to claim 1, wherein, The positive electrode mixture layer has peaks at any one or more of 1.4±0.5Å, 2.4±0.5Å, 4.45±0.5Å, 4.6±0.5Å, 5.1±0.1Å and 5.2±0.1Å in extended X-ray absorption fine structure (EXAFS) analysis.

3. The positive electrode according to claim 1, wherein, The positive electrode additive has a tetragonal structure with a space group of P42 / nmc.

4. The positive electrode according to claim 1, wherein, The content of the positive electrode additive is 0.01 parts by weight to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

5. The positive electrode according to claim 1, wherein, The positive electrode mixture layer further contains one or more conductive materials selected from the following: natural graphite, artificial graphite, carbon black, carbon nanotubes, graphene and carbon fiber.

6. The positive electrode according to claim 5, wherein, The content of the conductive material is 0.5 parts by weight to 5 parts by weight relative to 100 parts by weight of the positive electrode mixture layer.

7. A lithium secondary battery, the lithium secondary battery comprising: The positive electrode according to claim 1, A negative electrode, and A separator disposed between the positive electrode and the negative electrode.

8. The battery according to claim 7, wherein, The negative electrode comprises: A negative electrode current collector; and A negative electrode mixture layer disposed on the negative electrode current collector and containing a carbon material and a silicon material as negative electrode active materials.

9. The battery according to claim 8, wherein, The content of the silicon material is 1 part by weight to 20 parts by weight relative to 100 parts by weight of the negative electrode mixture layer.

10. The battery according to claim 8, wherein, The carbon material includes one or more selected from the following: natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black and carbon fiber.

11. The battery according to claim 8, wherein, The silicon material includes one or more of silicon (Si) particles and silicon oxide SiOx particles, where 1≤x≤2.

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