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

Abstract

The present invention relates to a positive electrode for a lithium secondary battery and a lithium secondary battery including the same. The positive electrode contains a positive electrode additive represented by Chemical Formula 1 in a positive electrode composite layer. After initial charging to an SOC of 100%, specific X-ray diffraction peaks and / or extended X-ray absorption fine structure (EXAFS) analysis peaks are controlled so that the cobalt remaining in the positive electrode composite layer has a specific oxidation number. This improves side reactions caused by the positive electrode additive as an irreversible additive and reduces the amount of gases such as oxygen generated during charge and discharge, thereby improving the battery safety and electrical performance of the lithium secondary battery.

Description

Technical Field

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

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0071866 filed on June 3, 2021, and all contents disclosed in the literature of the Korean patent application are included as part of this specification.

Background Art

[0003] With the development of technologies and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has been rapidly increasing. Among such secondary batteries, lithium secondary batteries having a high energy density, an operating potential, a long cycle life, and a low self-discharge rate have been commercialized and widely used.

[0004] Recently, as lithium secondary batteries are used as a power source for medium and large-sized devices such as electric vehicles, higher capacity, higher energy density, and lower cost of lithium secondary batteries have been further required, and even for irreversible additives used in electrodes, it is required to have a higher irreversible capacity. However, the current situation is that there are limitations in the development of positive electrode additives having such a high irreversible capacity.

[0005] On the other hand, conventional irreversible additives such as Li 6 CoO 4 are generally produced by reacting an excessive amount of metal oxides such as lithium oxide and cobalt oxide. The irreversible additive produced in this way is structurally unstable, and as charging progresses, oxygen gas (O 2) It generates a large amount of substances such as [substances not specified in the original], but when the non-reversible additive does not completely react and remains during the initial charging of the secondary battery, that is, during the activation of the battery, a reaction occurs during the subsequent charge-discharge process, generating side reactions and a large amount of oxygen gas inside the battery. The oxygen gas generated in this way can induce volume expansion of the electrode assembly and act as one of the main factors leading to a decrease in battery performance.

[0006]

Chem.

[0007] In addition, by-products such as the lithium oxide can react with the binder component and the like during the production of the slurry composition for electrode manufacturing, causing an increase in the viscosity or gelation of the composition. As a result, when applying the electrode composition for forming the active material layer, it is difficult to achieve uniform coating, and there is a problem that the characteristics of the battery deteriorate.

[0008] Therefore, in order to improve the safety and electrical performance of the lithium secondary battery, the development of a technology that can reduce side reactions caused by non-reversible additives and gas generation such as oxygen (O 2 ) is required.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] From this, the object of the present invention is to provide a positive electrode for a lithium secondary battery and a lithium secondary battery in which side reactions caused by non-reversible additives are improved, the amount of gas generation such as oxygen (O 2 ) generated during the charge-discharge process is reduced, and excellent battery safety and high charge-discharge capacity can be realized.

Means for Solving the Problem

[0011] In order to solve the problems as described above, In one embodiment, the present invention provides a positive electrode current collector, a positive electrode composite material layer located 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, After initial charging to SOC 100%, the positive electrode composite material layer provides a positive electrode for a lithium secondary battery having at least one peak appearing 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 during X-ray diffraction (XRD) measurement:

[0012] [Chemical Formula 1] Li p Co (1-q) M 1 q O 4

[0013] In the Chemical Formula 1, M 1 is one or more elements selected from the group consisting of 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, p and q are 5 ≦ p ≦ 7 and 0 ≦ q ≦ 0.5, respectively.

[0014] Here, after initial charging to SOC 100%, the positive electrode composite material layer can satisfy the following Formula 1 during X-ray diffraction (XRD) measurement:

[0015] [Formula 1] 0.2 ≦ P1 / P2 ≦ 1.5

[0016] In the Formula 1, P1 represents the intensity of the peak with the largest intensity existing at 42.4 ± 0.5°, P2 represents the intensity of the peak with the largest intensity existing at 44.8 ± 0.5°.

[0017] Further, after initial charging to SOC 100%, the positive electrode composite material layer may have a peak at any one or more of 1.4 ± 0.5 Å, 2.4 ± 0.5 Å, 4.45 ± 0.5 Å, 4.6 ± 0.5 Å, 5.1 ± 0.1 Å, and 5.2 ± 0.1 Å during extended X-ray absorption fine structure (EXAFS) analysis.

[0018] Further, the positive electrode additive contained in the positive electrode composite material layer may have a tetragonal structure with a space group of P4 2 / nmc.

[0019] Further, the positive electrode additive may be contained in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the positive electrode composite material layer.

[0020] At the same time, the positive electrode active material contained in the positive electrode composite material layer may be a lithium metal composite oxide represented by the following Chemical Formula 2:

[0021] [Chemical Formula 2] Li x [Ni y Co z Mn w M 2 v O u

[0022] In Chemical Formula 2, M 2 is one or more elements selected from the group consisting of 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, 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.

[0023] Further, the positive electrode composite material layer may further contain one or more conductive materials selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, and carbon fibers.

[0024] At this time, the content of the conductive material may be 0.5 to 5 parts by weight with respect to 100 parts by weight of the positive electrode composite material layer.

[0025] Further, in one embodiment, the present invention provides a lithium secondary battery including the positive electrode according to the present invention described above, a negative electrode, and a separator positioned between the positive electrode and the negative electrode.

[0026] Here, the negative electrode may include a negative electrode current collector and a negative electrode composite material layer located on the negative electrode current collector and containing a carbon material and a silicon material as negative electrode active materials.

[0027] Further, the carbon material contained in the negative electrode composite material layer may include one or more selected from the group consisting of natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fibers.

[0028] Further, the silicon material contained in the negative electrode composite material layer may include one or more of silicon (Si) particles and silicon oxide (SiOx, 1 ≦ x ≦ 2) particles.

[0029] Further, the silicon material may be contained in an amount of 1 to 20 parts by weight with respect to 100 parts by weight of the negative electrode composite material layer.

Advantages of the Invention

[0030] The positive electrode for a lithium secondary battery according to the present invention contains a positive electrode additive represented by Chemical Formula 1 in the positive electrode composite material layer. After initial charging to SOC 100%, by controlling specific X-ray diffraction peaks and / or extended X-ray absorption fine structure (EXAFS) analysis peaks so that the cobalt remaining in the positive electrode composite material layer has a specific oxidation number, side reactions caused by the positive electrode additive as an irreversible additive are improved, and the amount of gas generation such as oxygen generated during the charge-discharge process is reduced. Therefore, the battery safety and electrical performance of the lithium secondary battery are excellently improved.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0032] The present invention can be subjected to various changes and may have various embodiments. However, specific embodiments will be described in detail in the detailed description.

[0033] However, this is not intended to limit the present invention to specific embodiments, and it should be understood to include all changes, equivalents, and alternatives included in the spirit and technical scope of the present invention.

[0034] In the present invention, terms such as "comprising" or "having" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood not to preclude in advance the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0035] Also, in the present invention, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only the case where it is "directly on" the other part, but also the case where there are other parts in between. Conversely, when a part such as a layer, film, region, plate, etc. is described as being "under" another part, this includes not only the case where it is "directly under" the other part, but also the case where there are other parts in between. Also, in the present application, being "disposed on" may include not only the upper part but also the case of being disposed in the lower part.

[0036] Also, in the present invention, the "main component" means 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 with respect to the total weight of the composition or a specific component, and in some cases, when constituting the entire composition or specific component, that is, it can also mean 100% by weight.

[0037] Also, in the present invention, "Ah" is a unit of the capacity of a lithium secondary battery, called "ampere-hour", and means the current amount per unit time. For example, if the battery capacity is "3000 mAh", it means that it can be discharged with a current of 3000 mA for 1 hour.

[0038] Hereinafter, the present invention will be described in more detail.

[0039] Positive electrode for lithium secondary battery In one embodiment, the present invention a positive electrode current collector, A positive electrode composite material layer which is located on the positive electrode current collector and contains a positive electrode active material and a positive electrode additive represented by the following Chemical Formula 1: After initial charging to SOC 100%, the positive electrode composite material layer provides a positive electrode for a lithium secondary battery having at least one of the peaks appearing 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 during X-ray diffraction (XRD) measurement:

[0040] [Chemical Formula 1] Li p Co (1-q) M 1 q O 4

[0041] In Chemical Formula 1, M 1 is one or more elements selected from the group consisting of 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, p and q are 5 ≦ p ≦ 7 and 0 ≦ q ≦ 0.5, respectively.

[0042] The positive electrode for a lithium secondary battery according to the present invention has a structure in which a composite material layer is formed on a positive electrode current collector, and the positive electrode composite material layer has a configuration including a positive electrode active material and a positive electrode additive.

[0043] At this time, the positive electrode active material can be a lithium composite transition metal oxide containing two or more elements selected from the group consisting of 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:

[0044] [Chemical Formula 2] Li x [Ni y Co z Mnw M 2 v O u

[0045] In Chemical Formula 2, M 2 is one or more elements selected from the group consisting of 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, x, y, z, w, v, and u may each be 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.

[0046] 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 doped with other transition metals (M 2 ). For example, the positive electrode active material may include one or more compounds selected from the group consisting of LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.9 Co 0.05 Mn 0.05 O 2 , LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 O 2 and LiNi 0.7 Co 0.1 Mn 0.1 Al 0.1 O 2 . As an example, the positive electrode active material is a 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 O 2 and LiNi 0.8 Co 0.1 Mn 0.1 Al 0.05 O 2 etc. can be used alone or in combination respectively.

[0047] Also, the content of the positive electrode active material may be 85 to 95 parts by weight with respect to 100 parts by weight of the positive electrode composite material layer, specifically, it may be 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.

[0048] Also, the positive electrode composite material layer includes a positive electrode additive that imparts an irreversible capacity, together with a positive electrode active material that exhibits electrical activity. The positive electrode additive may include lithium cobalt oxide represented by the following Chemical Formula 1:

[0049] [Chemical Formula 1] Li p Co (1-q) M 1 q O 4

[0050] In Chemical Formula 1, M 1 is one or more elements selected from the group consisting of 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, p and q are 5 ≤ p ≤ 7 and 0 ≤ q ≤ 0.5 respectively.

[0051] The positive electrode additive contains an excessive amount of lithium and can provide lithium for lithium consumption generated by an irreversible chemical and physical reaction at the negative electrode during initial charging. As a result, the charging capacity of the battery can be increased, the irreversible capacity can be decreased, and the life characteristics can be improved.

[0052] Among them, the cathode additive represented by the chemical formula 1 has a higher lithium ion content compared to nickel-containing oxides commonly used in the industry, and can replenish the lithium ions lost in the irreversible reaction during the initial activation of the battery, so that the charge-discharge capacity of the battery can be significantly improved. In addition, compared with iron and / or manganese-containing oxides commonly used in the industry, there is no side reaction caused by the elution of transition metals during the charge and discharge of the battery, so there is an advantage of excellent battery stability. Such lithium cobalt oxide represented by the chemical formula 1 includes, for example, Li 6 CoO 4 、Li 6 Co 0.5 Zn 0.5 O 4 、Li 6 Co 0.7 Zn 0.3 O 4 and the like.

[0053] In addition, the average particle size of the lithium cobalt oxide represented by the chemical formula 1 may be 0.1 to 10 μm, specifically, 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, 4 to 6 μm, or 6 to 9 μm. By controlling the average particle size of the lithium cobalt oxide within the above range, the present invention can enhance the irreversible activity of the lithium cobalt oxide and prevent the reduction of the powder electrical conductivity of the lithium cobalt oxide.

[0054] In addition, the lithium cobalt oxide represented by the chemical formula 1 may have a tetragonal crystal structure. Among them, it may be included in the space group of P4 2 / nmc having a distorted tetrahedral structure formed by cobalt and oxygen elements. The cathode additive having a distorted tetrahedral structure has a distorted tetrahedral structure formed by cobalt and oxygen atoms and is structurally unstable. Therefore, during the manufacture of the cathode, moisture (H 2There is a risk of damage due to side reactions such as (O), which may cause a decrease in the electrical performance of the battery. However, in the present invention, since a binder having low affinity for water can be used as the binder of the composite material layer to minimize the damage of the positive electrode additive, the electrical performance and life of the lithium secondary battery can be further improved.

[0055] At the same time, the positive electrode additive may be contained in an amount of 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, based on 100 parts by weight of each positive electrode composite material layer.

[0056] Moreover, the positive electrode for a lithium secondary battery according to the present invention can exhibit specific peaks at specific intensities during X-ray diffraction (XRD) measurement after initial charging at SOC 100%.

[0057] As an example, after initial charging at SOC 100%, the positive electrode for a lithium secondary battery can exhibit one or more of the peaks appearing 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 during X-ray diffraction (XRD) measurement of the positive electrode composite material layer.

[0058] As another example, after initial charging at SOC 100%, the positive electrode for a lithium secondary battery can be shown at 42.4 ± 0.5° and 44.8 ± 0.5° represented by 2θ during X-ray diffraction (XRD) measurement of the positive electrode composite material layer, and the peak can satisfy the following formula 1:

[0059] [Formula 1] 0.2 ≦ P1 / P2 ≦ 1.5

[0060] In the above formula 1, P1 represents the intensity of the peak with the largest intensity existing at 42.4 ± 0.5°, P2 represents the intensity of the peak with the highest intensity existing at 44.8 ± 0.5°.

[0061] Specifically, the positive electrode for the lithium secondary battery can satisfy that the formula 1 is 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).

[0062] The peak is the cobalt oxide remaining in the positive electrode composite layer after initial charging at SOC 100%, specifically, CoO with an oxidation number of 2, Co 3 O 4 and / or Li with an oxidation number of 3 2 Co 2 O 4 shown by the peak, and the positive electrode for the lithium secondary battery according to the present invention has the oxidation number of cobalt (Co) remaining in the positive electrode composite layer controlled, shows one or more of the peaks as an X-ray diffraction (XRD) peak after initial charging at SOC 100%, and can satisfy the formula 1 at the same time. Through this, the positive electrode of the present invention can prevent side reactions that further occur in the positive electrode during initial charging of the lithium secondary battery, that is, after activation, and at the same time, can reduce the amount of gas generation such as oxygen (O 2 ) generated during the charge-discharge process.

[0063] Also, the positive electrode for the lithium secondary battery according to the present invention may have a peak at any one or more of 1.4 ± 0.5 Å, 2.4 ± 0.5 Å, 4.45 ± 0.5 Å, 4.6 ± 0.5 Å, 5.1 ± 0.1 Å, and 5.2 ± 0.1 Å during extended X-ray absorption fine structure (EXAFS) analysis of the K absorption edge of cobalt (Co) contained in the positive electrode composite layer after initial charging at SOC 100%.

[0064] The peak is a peak where cobalt (Co) shows a bond with surrounding oxygen (O) and / or transition metals. In the positive electrode composite material layer, CoO, LiCoO 2 and / or Co 3 O 4 exists, and the intensity of the peak can be adjusted by the oxidation number of cobalt (Co) in the positive electrode composite material layer provided on the positive electrode initially charged to SOC 100%.

[0065] Moreover, the positive electrode for the lithium secondary battery can control the oxidation number and / or the degree of oxidation of cobalt (Co) contained in the positive electrode composite material layer through the initial charging conditions. For example, the positive electrode for the lithium secondary battery may have a configuration in which a three-stage charging process, that is, activation stages 1 to 3, is continuously performed during initial charging. More specifically, the initial charging stage includes an activation stage 1 in which a current of 0.05C to 0.2C is applied to the lithium secondary battery and charged to SOC 30% or less, an activation stage 2 in which a current of 0.3C to 0.5C is applied to the lithium secondary battery in which activation stage 1 has been performed and charged to more than SOC 30% and less than 70%, and an activation stage 3 in which a current of 0.6C to 0.9C is applied to the lithium secondary battery in which activation stage 2 has been performed and charged to SOC 70% or more.

[0066] As an example, the positive electrode for the lithium secondary battery includes an activation stage 1 in which a current of 0.08C to 0.15C is applied to the lithium secondary battery during initial charging and charged to SOC 30% or less, an activation stage 2 in which a current of 0.35C to 0.45C is applied to the lithium secondary battery in which activation stage 1 has been performed and charged to more than SOC 30% and less than 70%, and an activation stage 3 in which a current of 0.65C to 0.8C is applied to the lithium secondary battery in which activation stage 2 has been performed and charged to SOC 70% or more, and can be manufactured by performing these steps.

[0067] On the other hand, the positive electrode composite material layer may further include a conductive material, a binder, an additive, etc. together with the positive electrode active material and the positive electrode additive.

[0068] At this time, the conductive material can be used to improve the performance such as the electrical conductivity of the positive electrode, and may include one or more selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, and carbon fibers. For example, the conductive material may include acetylene black.

[0069] Also, the conductive material may be 0.5 to 5 parts by weight with respect to 100 parts by weight of the positive electrode composite material layer. Specifically, it may be 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, 1 to 3 parts by weight, or 25.

[0070] Also, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride - hexafluoropropylene copolymer (PVdF - co - HFP), polyvinylidene fluoride (PVdF), polyacrylonitrile, polymethyl methacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0071] Also, the binder may be included in an amount of 1 to 10 parts by weight with respect to 100 parts by weight of the entire positive electrode composite material layer. Specifically, it may be included in an amount of 2 to 8 parts by weight, or 1 to 5 parts by weight.

[0072] At the same time, the average thickness of the positive electrode composite material layer is not particularly limited, but specifically, it may be 50 μm to 300 μm. More specifically, it may be 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0073] In addition, for the positive electrode, as the positive electrode current collector, one having high conductivity can be used without inducing a chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, etc. can be used. In the case of aluminum or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Further, the positive electrode current collector can also form fine irregularities on its surface to enhance the adhesive force of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric body, etc. are possible. Also, the average thickness of the current collector can be appropriately applied in the range of 3 to 500 μm in consideration of the conductivity and the total thickness of the positive electrode to be manufactured.

[0074] Lithium secondary battery Moreover, in one embodiment of the present invention, There is provided a lithium secondary battery including the positive electrode according to the present invention described above, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0075] The lithium secondary battery according to the present invention includes the positive electrode of the present invention as described above and can exhibit excellent characteristics in battery safety and electrical performance. Such a lithium secondary battery according to the present invention has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0076] Here, for the negative electrode, a negative electrode active material is applied, dried, and pressed on a negative electrode current collector to manufacture a negative electrode composite material layer, and if necessary, the same conductive material, organic binder polymer, additive, etc. as those of the positive electrode can be selectively further included.

[0077] Further, the negative electrode active material may contain, for example, a carbon material and a silicon material. The carbon material means a carbon material mainly composed of carbon atoms. Such carbon materials include graphite having a perfect layered crystal structure like natural graphite, soft carbon having a low-crystalline layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), hard carbon in which such a structure is mixed with an amorphous part, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotube, fullerene, activated carbon, graphene, carbon nanotube, etc. It may preferably contain one or more selected from the group consisting of natural graphite, artificial graphite, graphene, and carbon nanotube. More preferably, the carbon material contains natural graphite and / or artificial graphite, and may contain one or more of graphene and carbon nanotube together with the natural graphite and / or artificial graphite. In this case, the carbon material may contain 50 to 95 parts by weight of graphene and / or carbon nanotube based on 100 parts by weight of the whole carbon material. More specifically, it may contain 60 to 90 parts by weight, or 70 to 80 parts by weight of graphene and / or carbon nanotube based on 100 parts by weight of the whole carbon material.

[0078] Further, the silicon material is particles mainly containing silicon (Si) as a metal component, and may contain one or more of silicon (Si) particles and silicon oxide (SiO X , 1≦X≦2) particles. As an example, the silicon material may contain silicon (Si) particles, silicon monoxide (SiO) particles, silicon dioxide (SiO 2 ) particles, or a mixture of these particles.

[0079] Further, the silicon material may have a form in which crystalline particles and amorphous particles are mixed, and the proportion of the amorphous particles may 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 with respect to 100 parts by weight of the entire silicon material. By controlling the proportion of the amorphous particles contained in the silicon material within the above range, the present invention can improve the thermal stability and flexibility without degrading the electrical properties of the electrode.

[0080] Further, the negative electrode active material contains a carbon material and a silicon material, and may be contained in an amount of 1 to 20 parts by weight, specifically 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 with respect to 100 parts by weight of the negative electrode binder layer.

[0081] By adjusting the contents of the carbon material and the silicon material contained in the negative electrode active material within the above range, the present invention can reduce the lithium consumption amount and the irreversible capacity loss during the initial charge and discharge of the battery, and improve the charge capacity per unit mass.

[0082] As an example, the negative electrode active material may contain 95 ± 2 parts by weight of graphite and 5 ± 2 parts by weight of a mixture in which silicon monoxide (SiO) particles and silicon dioxide (SiO 2 ) particles are uniformly mixed with respect to 100 parts by weight of the negative electrode active material. By adjusting the contents of the carbon material and the silicon material contained in the negative electrode active material within the above range, the present invention can reduce the lithium consumption amount and the irreversible capacity loss during the initial charge and discharge of the battery, and improve the charge capacity per unit mass.

[0083] Further, the negative electrode binder layer may have an average thickness of 100 μm to 200 μm, specifically 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0084] Further, the negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, fired carbon, etc. can be used. In the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used. Also, similar to the positive electrode current collector, the negative electrode current collector can also have fine irregularities formed on its surface to strengthen the bonding force with the negative electrode active material, and various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc. are possible. Further, the average thickness of the negative electrode current collector can be appropriately applied in the range of 3 to 500 μm in consideration of the conductivity and total thickness of the manufactured negative electrode.

[0085] Also, the separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used. The separator is not particularly limited as long as it is commonly used in the art. Specifically, sheets or non-woven fabrics made of chemical-resistant and hydrophobic polypropylene, glass fibers, polyethylene, etc. can be used. In some cases, a composite separator in which inorganic particles / organic particles are coated on a porous polymer substrate such as the sheet or non-woven fabric with an organic binder polymer can also be used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte can also serve as the separator. Further, the pore diameter of the separator is on average 0.01 to 10 μm, and the thickness may be on average 5 to 300 μm.

[0086] On the other hand, the positive electrode and the negative electrode may be wound in a jelly roll form and housed in a cylindrical battery, a prismatic battery or a pouch-type battery, or may be housed in a pouch-type battery in a folding or stack-and-fold form, but is not limited thereto.

[0087] Also, the lithium salt-containing electrolyte according to the present invention may be composed of an electrolyte and a lithium salt, and as the electrolyte, non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. can be used.

[0088] Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxymethane, dioxolane derivative, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, ethyl propionate, etc.

[0089] Examples of the organic solid electrolyte include polyethylene derivative, polyethylene oxide derivative, polypropylene oxide derivative, phosphate ester polymer, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymer materials containing ionic dissociation groups, etc.

[0090] Examples of the inorganic solid electrolyte include nitrides, halides, sulfates, etc. of Li such as Li 3 N, LiI, Li 5 Ni 2 、Li 3 N-LiI-LiOH, LiSiO 4 、LiSiO 4 -LiI-LiOH, Li 2 SiS 3 、Li 4 SiO 4 、Li 4 SiO 4 -LiI-LiOH, Li 3 PO 4 -Li 2 S-SiS 2 etc.

[0091] The lithium salt is a substance that is easily soluble in the non-aqueous electrolyte. For example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, (CF 3 SO 2 ) 2 NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4-phenylborate, imide, etc. can be used.

[0092] In addition, for the purpose of improving charge and discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added to the electrolytic solution. In some cases, for imparting non-flammability, it may further contain a halogen-containing solvent such as carbon tetrachloride and vinylidene fluoride, and for improving high-temperature storage characteristics, it may further contain carbon dioxide gas, and it may further contain FEC (Fluoro-Ethylene Carbonate), PRS (Propene sultone), etc.

[0093] Hereinafter, the present invention will be described in more detail based on examples and experimental examples.

[0094] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0095] Examples 1-2 and Comparative Examples 1-4. Manufacture of Lithium Secondary Batteries (A) Manufacture of positive electrode for lithium secondary battery Inject N-methylpyrrolidone into a homomixer, and for 100 parts by weight of the positive electrode slurry solid content, as the positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O 2 97 parts by weight and, as the positive electrode additive, Li 6 CoO 4 or Li 6 Co 0.7 Zn 0.3 O 4 0.8 part by weight, 0.7 part by weight of a mixture (75:25 wt. / wt.) of carbon nanotubes (average size: 60±10 nm) and Denka black (average size: 2±0.5 μm) as the conductive material, and 1.5 parts by weight of PVdF as the binder were weighed and added, and mixed at 2,000 rpm for 60 minutes to produce a positive electrode slurry for a lithium secondary battery. After applying the produced positive electrode slurry to one side of an aluminum current collector, it was dried at 100°C and rolled to produce a positive electrode. At this time, the total thickness of the positive electrode mixture layer was 130 μm, and the total thickness of the produced positive electrode was about 200 μm.

[0096] (B) Manufacture of lithium secondary battery For 100 parts by weight of the negative electrode slurry solid content, 84 parts by weight of natural graphite as the negative electrode active material and 14 parts by weight of silicon (SiOx, where 1≦x≦2) particles, and 2 parts by weight of styrene-butadiene rubber (SBR) as the binder were prepared, and the negative electrode slurry was prepared in the same manner as the method for producing the positive electrode slurry. At this time, the graphite used in the production of the negative electrode mixture layer was natural graphite (average particle size: 0.01~0.5 μm), and the silicon (SiOx) particles used had an average particle size of 0.9~1.1 μm. After applying the prepared negative electrode slurry to one side of a copper current collector, it was dried at 100°C and rolled to produce a negative electrode. At this time, the total thickness of the negative electrode mixture layer was 150 μm, and the total thickness of the produced negative electrode was about 250 μm.

[0097] A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was laminated so as to be interposed between the prepared positive electrode and negative electrode, and E2DVC was injected as an electrolyte to assemble a battery in a full cell form. Here, "E2DVC" is a kind of carbonate-based electrolyte, and ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio) mixture, to which lithium hexafluorophosphate (LiPF 6 , 1.0 M) and vinyl carbonate (VC, 2 wt%) were mixed solutions.

[0098] The manufactured full cell was initially charged at 22 ± 2 °C under the current conditions shown in Table 1 below to manufacture a lithium secondary battery.

[0099]

Table 1

[0100] Experimental Example. In order to evaluate the performance of the positive electrode for a lithium secondary battery according to the present invention, the following experiments were conducted.

[0101] (A) Analysis of cobalt oxidation number in initially charged positive electrode composite layer The positive electrodes were disassembled from the lithium secondary batteries manufactured in Examples 1 to 2 and Comparative Examples 1 to 4, and the positive electrode composite layer was peeled off from the disassembled positive electrodes to prepare samples. X-ray diffraction (XRD), transmission electron microscopy (TEM), and extended X-ray absorption fine structure (EXAFS) analysis were performed on each of the prepared samples, and the results are shown in FIGS. 1 to 3 below.

[0102] In addition, X-ray diffraction (XRD) analysis was performed using a Rigaku X-ray diffractometer, scanning at a wavelength of 1.5406 Å (Cu Ka radiation, 40 kV, 100 mA), and an X-ray diffraction pattern was obtained in the range of 2θ from 10° to 50° at a scanning speed of 5° / sec. Also, in the measured X-ray diffraction graph, the intensity P1 of the peak appearing at 2θ = 42.4 ± 0.5° and the intensity P2 of the peak appearing at 2θ = 44.8 ± 0.5° were measured, and the ratio P1 / P2 was calculated, and the results are shown in Table 2 below.

[0103] (B) Evaluation of cumulative gas generation amount generated during charge and discharge after initial charge For the lithium secondary batteries initially charged in Examples 1 to 2 and Comparative Examples 1 to 4, a degassing process was performed. Subsequently, after discharging to a cut-off voltage of 2 V at a discharge current of 0.1 C, 50 charge-discharge cycles were repeatedly performed on each secondary battery with the internal gas removed at 45 °C under the conditions of 4.5 V and 1.0 C. At this time, the amount of gas generated during each charge-discharge cycle was measured, and the cumulative gas amount generated after the initial charge-discharge was calculated, and the results are shown in Table 2 below.

[0104] (C) Evaluation of cycle life performance For the lithium secondary batteries initially charged in Examples 1 to 2 and Comparative Examples 1 to 4, a degassing process was performed. Subsequently, after discharging to a cut-off voltage of 2 V at a discharge current of 0.1 C, 100 charge-discharge cycles (n = 100) were performed at 25 °C under the conditions of a charge cut-off voltage of 4.25 V, a discharge cut-off voltage of 2.5 V, and 0.5 C / 0.5 C, and the capacity retention rate (%) was measured. At this time, the capacity retention rate was calculated using Equation 2 below, and the results are shown in Table 2 below:

[0105] [Equation 2] Capacity Retention Rate (%) = (Discharge Capacity during 100 Charge-Discharge Cycles / Discharge Capacity during 1 Charge-Discharge Cycle) × 100

[0106]

Table 2

[0107] Referring to Table 2 and FIGS. 1 to 3 above, the positive electrode for a lithium secondary battery according to the present invention has its X-ray diffraction peaks and / or extended X-ray absorption fine structure (EXAFS) analysis peaks controlled within a specific range after being charged to SOC 100%, indicating that the safety and electrical performance of the lithium secondary battery are improved.

[0108] Specifically, the lithium secondary battery manufactured in the example was confirmed to contain CoO, Co 3 O 4 and LiCoO 2 in the positive electrode composite material layer through transmission electron microscope (TEM) analysis. Also, the extended X-ray absorption fine structure (EXAFS) analysis results for the K absorption edge of cobalt (Co) in the positive electrode composite material layer showed peaks at interatomic distances (i.e., radial distances) of 1.4 ± 0.5 Å, 2.4 ± 0.5 Å, 4.45 ± 0.5 Å, 4.6 ± 0.5 Å, 5.1 ± 0.1 Å, and 5.2 ± 0.1 Å. These peaks indicate the peaks embodied by CoO, Co 3 O 4 and / or LiCoO 2 contained in the positive electrode composite material layer.

[0109] Furthermore, when the positive electrode composite material layer was measured by X-ray diffraction (XRD), peaks were shown at 2θ values of 19.1 ± 0.5°, 36.6 ± 0.5°, 38.7 ± 0.5°, 42.4 ± 0.5°, and 44.8 ± 0.5°. Among these, the ratio P1 / P2 of the intensities of the peaks appearing at 2θ = 42.4 ± 0.5° and 2θ = 44.8 ± 0.5° was shown to be approximately 0.8 to 0.9. Here, the peak appearing at 2θ = 44.8 ± 0.5° is the peak indicating the [4, 0, 0] crystal lattice of CoO, and the peak at 2θ = 42.4 ± 0.5° is the peak indicating the [2, 0, 0] crystal lattice of Co 3 O 4 These ratios mean the oxidation number and / or degree of oxidation of cobalt (Co) contained in the positive electrode composite material layer. Such results mean that in the positive electrode of the present invention, the oxidation number of cobalt (Co) present in the positive electrode composite material layer is adjusted within a specific range after the initial charge to SOC 100%.

[0110] Moreover, it was confirmed that in the lithium secondary battery of the embodiment provided with such a positive electrode, after degassing the gas generated during the initial charge and discharge, the amount of gas generated during charge and discharge was significantly reduced. Further, it was confirmed that the lithium secondary battery has a high initial charge capacity of 103 Ah or more and a high capacity retention rate of 95% or more.

[0111] From such results, the positive electrode for a lithium secondary battery according to the present invention contains a positive electrode additive represented by Chemical Formula 1 in the positive electrode composite material layer, and after initial charging to SOC 100%, the cobalt remaining in the positive electrode composite material layer has a specific oxidation number. By controlling the specific X-ray diffraction peak and / or extended X-ray absorption fine structure (EXAFS) analysis peak, the side reaction caused by the positive electrode additive as an irreversible additive is improved, and the amount of gas generation such as oxygen generated during the charge and discharge process is reduced. It can be seen that the battery safety and electrical performance of the lithium secondary battery are improved.

[0112] As described above, the preferred embodiments of the present invention have been described with reference thereto. However, those skilled in the art or those having ordinary knowledge in the art can understand that the present invention can be variously modified and changed without departing from the spirit and technical scope of the present invention described in the claims to be described later.

[0113] Therefore, the technical scope of the present invention should not be limited to the content described in the detailed description of the specification, but should be determined by the claims.

Claims

1. a positive electrode current collector; a positive electrode composite material layer which is located on the positive electrode current collector and contains a positive electrode active material and a positive electrode additive represented by the following Chemical Formula 1; after initial charging to SOC 100%, when the positive electrode composite material layer is measured by X-ray diffraction (XRD), it satisfies the following Formula 1; [Formula 1] 0.4 ≦ P1 / P2 ≦ 1.5 In the above Formula 1, P1 represents the intensity of the peak with the highest intensity existing at 42.4 ± 0.5°; P2 represents the intensity of the peak with the highest intensity existing at 44.8 ± 0.5°; after initial charging to SOC 100%, when the positive electrode composite material layer is measured by X-ray diffraction (XRD), the positive electrode for a lithium secondary battery having peaks appearing 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; [Chemical Formula 1] Li ｐ Co （１－ｑ） M １ ｑ O ４ In the above Chemical Formula 1, M １ is one or more elements selected from the group consisting of 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, p and q are respectively 5 ≦ p ≦ 7 and 0 ≦ q ≦ 0.

5.

2. The positive electrode for a lithium secondary battery according to Claim 1, wherein the positive electrode composite material layer satisfies the following Formula 1 when measured by X-ray diffraction (XRD) after initial charging to SOC 100%; [Formula 1] 0.7 ≦ P1 / P2 ≦ 1.5 In the above Formula 1, P1 represents the intensity of the peak with the highest intensity existing at 42.4 ± 0.5°; P2 represents the intensity of the peak with the highest intensity existing at 44.8 ± 0.5°.

3. The positive electrode for a lithium secondary battery according to Claim 1, wherein the positive electrode composite material layer has a peak at any one or more of 1.4 ± 0.5 Å, 2.4 ± 0.5 Å, 4.45 ± 0.5 Å, 4.6 ± 0.5 Å, 5.1 ± 0.1 Å, and 5.2 ± 0.1 Å when analyzed by extended X-ray absorption fine structure (EXAFS) after initial charging to SOC 100%.

4. The positive electrode additive has a tetragonal structure with a space group of P4 ２ / nmc, and is the positive electrode for a lithium secondary battery according to claim 1.

5. The positive electrode for a lithium secondary battery according to Claim 1, wherein the positive electrode additive is contained in an amount of 0.01 part by weight to 5 parts by weight based on 100 parts by weight of the positive electrode composite material layer.

6. The electrode assembly for a lithium secondary battery according to Claim 1, 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 Mn ｗ M ２ ｖ O ｕ In the above Chemical Formula 2, M ２ is one or more elements selected from the group consisting of 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, 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, 1.5 ≦ u ≦ 4.

5.

7. The positive electrode composite layer further contains at least one conductive material selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, and carbon fibers. The positive electrode for a lithium secondary battery according to claim 1.

8. The content of the conductive material is 0.5 parts by weight to 5 parts by weight with respect to 100 parts by weight of the positive electrode composite layer. The positive electrode for a lithium secondary battery according to claim 7.

9. A lithium secondary battery comprising the positive electrode according to claim 1, a negative electrode, and a separator positioned between the positive electrode and the negative electrode.

10. The negative electrode includes a negative electrode current collector and a negative electrode composite layer positioned on the negative electrode current collector and containing a carbon material and a silicon material as negative electrode active materials. The lithium secondary battery according to claim 9.

11. The silicon material is contained in an amount of 1 part by weight to 20 parts by weight with respect to 100 parts by weight of the negative electrode composite layer. The lithium secondary battery according to claim 10.

12. The carbon material includes at least one selected from the group consisting of natural graphite, artificial graphite, graphene, carbon nanotubes, carbon black, acetylene black, ketjen black, and carbon fibers. The lithium secondary battery according to claim 10.

13. The silicon material includes at least one of silicon (Si) particles and silicon oxide (SiO x, 1 ≤ x ≤ 2) particles. The lithium secondary battery according to claim 10.

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