Sacrificial cathode material and lithium secondary battery comprising the same

Abstract

The present invention relates to a sacrificial cathode material, a cathode comprising the same, and a lithium secondary battery having the same, wherein the sacrificial cathode material is doped with a specific metal, and the defect formation energy of the metal according to density functional theory (DFT) is controlled within a specific range, so that a high initial charge / discharge efficiency can be achieved during initial charge / discharge, and the amount of gas additionally generated in the later stage of charge / discharge is reduced, thereby having the excellent advantage of an effect of improving the stability and charge / discharge performance of a battery comprising the same.

Description

Technical Field

[0001] The present invention relates to a sacrificial cathode material and a lithium secondary battery comprising the sacrificial cathode material, the sacrificial cathode material being doped with a metal (M) such as Zn, Ge, Mg or Si and having a metal (M) defect formation energy controlled to a specific level.

[0002] This application claims priority based on Korean Patent Application No. 10-2021-0024259, dated February 23, 2021, the entire contents of which are disclosed in the document are incorporated herein by reference. Background Technology

[0003] In recent years, the demand for secondary batteries as energy sources has been increasing rapidly. Among these secondary batteries, lithium secondary batteries, which have high energy density and voltage, long cycle life and low self-discharge rate, have been commercialized and are widely used.

[0004] Although graphite is primarily used as the anode material in lithium-ion batteries, its low capacity per unit mass (372 mAh / g) makes it difficult to increase the overall capacity of lithium-ion batteries. Therefore, to improve the capacity of lithium-ion batteries, non-carbon anode materials that form intermetallic compounds with lithium, such as silicon, tin, and their oxides, have been developed and used as non-carbon anode materials with higher energy densities than graphite. However, with these non-carbon anode materials, although the capacity is high, the initial efficiency is low, resulting in large lithium consumption and significant irreversible capacity loss during the initial charge / discharge period.

[0005] In this regard, a method has been proposed to overcome irreversible capacity loss of the negative electrode by using a material that can provide a lithium-ion source or reservoir for the positive electrode material and has electrochemical activity after the initial cycle without degrading the overall performance of the battery. Specifically, as a sacrifice of the positive electrode material or an irreversible additive (or over-discharge inhibitor), it is known to apply, for example, an oxide containing excess lithium (such as Li6CoO4) to the positive electrode.

[0006] However, sacrificial cathode materials or irreversible additives have unstable structures and may cause oxidation during the battery activation phase and subsequent charge / discharge processes, thereby generating oxygen inside the battery. This generated oxygen can lead to volume expansion and may be one of the main factors causing battery performance degradation.

[0007] Therefore, there is a need to develop a sacrificial cathode material that exhibits high charge / discharge capacity.

[0008] Literature in related fields

[0009] Korean Patent Publication No. 10-2019-0059115 Summary of the Invention

[0010] [Technical Issues]

[0011] Therefore, the object of the present invention is to provide a sacrificial cathode material and a cathode and a lithium secondary battery comprising the sacrificial cathode material, wherein the sacrificial cathode material achieves high initial charge / discharge efficiency while improving the irreversible capacity loss generated at the negative electrode during the initial charge / discharge, and reduces the amount of additional gas generated during subsequent charge / discharge.

[0012] [Technical Solution]

[0013] To address the aforementioned problems, in one embodiment, the present invention provides a sacrificial cathode material comprising lithium cobalt oxide represented by the following chemical formula 1, and

[0014] According to density functional theory (DFT), the defect formation energy of metal (M) is -4.0 eV to -8.5 eV.

[0015] [Chemical Formula 1]

[0016] Li x Co( 1-y) M y O4

[0017] in,

[0018] M is selected from at least one of the following: Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si.

[0019] x and y are 5≤x≤7 and 0.05≤y≤0.6.

[0020] In this case, in chemical formula 1, M can be at least one selected from Mg, Ge and Si, and y can be 0.2≤y≤0.4.

[0021] Furthermore, the defect formation energy of the metal M in the sacrificial cathode material, according to density functional theory (DFT), can be from -4.9 eV to -6.4 eV.

[0022] Furthermore, the sacrificial cathode material can have a tetragonal crystal structure with space group P42 / nmc.

[0023] Furthermore, the sacrificial cathode material can have a density of 5 × 10⁻⁶. -4 S / cm to 1×10 -2 Powder conductivity in S / cm.

[0024] In one embodiment, the present invention provides a positive electrode, the positive electrode comprising:

[0025] Positive current collector; and

[0026] A positive electrode mixture layer on the positive current collector, the positive electrode mixture layer containing a positive electrode active material, a conductive material, an organic binder polymer and a sacrificial positive electrode material;

[0027] The sacrificial cathode material comprises lithium cobalt oxide represented by the following chemical formula 1, and the defect formation energy of the metal (M) according to density functional theory (DFT) is -4.0 eV to -8.5 eV:

[0028] [Chemical Formula 1]

[0029] Li x Co( 1-y) M y O4

[0030] in,

[0031] M is selected from at least one of the following: Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si.

[0032] x and y are 5≤x≤7 and 0.05≤y≤0.6.

[0033] Here, based on 100 parts by weight of the positive electrode active material, the content of the sacrificial positive electrode material can be from 0.001 to 5.0 parts by weight.

[0034] Furthermore, based on 100 parts by weight of the entire positive electrode mixture layer, the content of the conductive material can be from 0.5 to 10 parts by weight.

[0035] In addition, the conductive material may include at least one carbon-based material selected from the following: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

[0036] In addition, the positive electrode active material may contain 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).

[0037] In addition, the average thickness of the positive electrode mixture layer can be from 100 μm to 200 μm.

[0038] Furthermore, the resistance value of the positive electrode can change by less than 10% after 30 charge / discharge cycles, relative to the resistance value during the initial charge / discharge period.

[0039] Furthermore, in one embodiment, the present invention provides an electrode assembly comprising the aforementioned positive electrode.

[0040] Furthermore, in one embodiment, the present invention provides a lithium secondary battery comprising the electrode assembly.

[0041] [Beneficial Effects]

[0042] The sacrificial cathode material according to the present invention is doped with a specific metal, and the defect formation energy of the metal can be controlled within a specific range according to density functional theory (DFT), so that high initial charge / discharge efficiency can be achieved during the initial charge / discharge period, and the amount of additional gas generated in the later stages of charge / discharge can be reduced, thereby having the advantage of effectively improving the stability and charge / discharge performance of the battery containing the cathode. Attached Figure Description

[0043] Figure 1 This shows that for lithium cobalt oxide (Li) doped with x A graph showing the initial charge capacity of each type of metal in CoO4 (5≤x≤7). Detailed Implementation

[0044] Because the present invention can have various variations and various implementation schemes, specific implementation schemes will be described in detail in the detailed description.

[0045] However, this is not intended to limit the invention to the specific embodiments, and should be understood to include all variations, equivalents and alternatives contained within the spirit and scope of the invention.

[0046] In this invention, it should be understood that the terms "comprising" or "having" are intended to explicitly state the presence of the described features, numbers, steps, operations, components, ingredients or combinations thereof, but do not exclude the presence or addition of one or more other features or numbers, steps, operations, components or combinations thereof.

[0047] Furthermore, in this invention, when a portion of a layer, film, region, plate, etc., is described as being "on" another portion, this includes not only the case where the portion is "directly" "on" the other portion, but also the case where there are other portions in between. Conversely, when a portion of a layer, film, region, plate, etc., is described as being "below" another portion, this includes both the case where there are other portions in between and the case where it is "directly" "below" the other portion. Additionally, in this document, the reference to "deposited on" can include not only being disposed on the upper part, but also being disposed on the lower part.

[0048] The invention will be described in more detail below.

[0049] Sacrificial cathode material

[0050] In one embodiment, the present invention provides a sacrificial cathode material comprising: lithium cobalt oxide represented by the following chemical formula 1, and

[0051] According to density functional theory (DFT), the defect formation energy of metal (M) is -4.0 eV to -8.5 eV.

[0052] [Chemical Formula 1]

[0053] Li x Co( 1-y) M y O4

[0054] in,

[0055] M is selected from at least one of the following: Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si.

[0056] x and y are 5≤x≤7 and 0.05≤y≤0.6.

[0057] The sacrificial cathode material according to the present invention comprises lithium cobalt metal oxide represented by Chemical Formula 1 as a major component. Here, "major component" may refer to 80% by weight or more, 90% by weight or more, 95% by weight or more, or 97.5% by weight or more based on the total weight of the sacrificial cathode material, and in some cases, when the sacrificial cathode material is entirely composed of lithium cobalt metal oxide represented by Chemical Formula 1, that is, the "major component" may refer to 100% by weight.

[0058] Lithium cobalt metal oxide represented by chemical formula 1 has the ability to release large amounts of lithium ions. x The structure of CoO4 (5≤x≤7) has one or more metals selected from Al, Fe, Zn, Ti, W, Mg, Ge, Mn and Si at the cobalt position. Specifically, it may have a structure doped with one or more metals selected from Mg, Ge and Si.

[0059] At this point, the metal doping amount can be 5 to 60 mole fractions (i.e., 0.05 ≤ y ≤ 0.6), specifically 10 to 50 mole fractions (0.1 ≤ y ≤ 0.5), 15 to 50 mole fractions (0.15 ≤ y ≤ 0.5), 15 to 45 mole fractions (0.15 ≤ y ≤ 0.45), 20 to 40 mole fractions (0.2 ≤ y ≤ 0.4), or 25 to 35 mole fractions (0.25 ≤ y ≤ 0.35). In this invention, by controlling the metal doping amount within the above mole fraction range, the structural distortion of lithium cobalt oxide can be mitigated, thereby further improving structural stability.

[0060] Furthermore, the lithium cobalt metal oxide represented by Formula 1 can have a tetragonal crystal structure, wherein it can have the space group P42 / nmc. Typically, lithium cobalt metal oxides with a tetragonal crystal structure are structurally unstable due to distortion of the tetragonal crystal structure formed by cobalt and oxygen elements, and this structural instability leads to the generation of oxygen-containing gases even during charging after battery activation. However, in the sacrificial cathode material of the present invention, at least one metal selected from Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si is doped at the cobalt sites of the lithium cobalt oxide (LixCoO4, 5≤x≤7) to have a doped structure, thereby exhibiting a reduction in gas generation even when containing the lithium cobalt metal oxide represented by Formula 1 with a tetragonal crystal form.

[0061] Furthermore, in sacrificial cathode materials, the defect formation energy of the metal (M) according to density functional theory (DFT) can be controlled to meet a specific range. Specifically, the defect formation energy of the metal (M) according to density functional theory (DFT) in sacrificial cathode materials can be -4.0 to -8.5 eV, more specifically -4.0 to -7.0 eV, -4.0 to -6.5 eV, -4.5 to -7.0 eV, -4.9 to -6.4 eV, -5.0 to -6.0 eV, -4.5 to -5.6 eV, -5.0 to -5.5 eV, -5.5 to -5.9 eV, or -6.0 to -6.5 eV. The defect formation energy of metal (M) refers to the energy required to generate crystallographic defects due to the doping of metal (M) in lithium cobalt oxide (LixCoO4, 5≤x≤7). In this invention, by controlling the defect formation energy of (M) within the above range, the structural stability of the sacrificial cathode material can be improved, and the amount of gas generated during the initial charging / discharging and the amount of accumulated gas thereafter can be reduced.

[0062] Furthermore, in sacrificial cathode materials, the powder conductivity of lithium cobalt metal oxide represented by chemical formula 1 can reach 5 × 10⁻⁶. -4 S / cm to 1×10 -2 S / cm, specifically 5×10 -4 S / cm to 1×10 -3 S / cm, 5×10 -4 S / cm to 1×10 -2 S / cm, 5×10 -4 S / cm up to 5×10 -3 S / cm, 8×10 -4 S / cm up to 9×10 -3 S / cm, 1×10 -3 S / cm to 8×10 -3 S / cm, 6.0×10-3 S / cm up to 7.5×10 -3 S / cm or 3.5×10 -3 S / cm up to 6.5×10 -3 S / cm. The powder conductivity of the sacrificial cathode material can be determined based on the properties of lithium cobalt oxide (Li). x CoO4, 5≤x≤7)(the lithium cobalt oxide has 10 -7 By adjusting the amount of metal (M) doping at the cobalt position (significantly low powder conductivity below S / cm), the manufacturing conditions of the sacrificial cathode material, etc., and by adjusting the powder conductivity within the above range, it is possible to further improve the charge / discharge capacity while reducing the amount of gas generated during battery charging.

[0063] As described above, the sacrificial cathode material according to the present invention comprises a lithium cobalt metal oxide represented by chemical formula 1 doped with a specific metal, thereby enabling high initial charge / discharge efficiency during initial charging / discharging and reducing the amount of additional gas generated in the later stages of charging / discharging. Therefore, it has the advantage of excellent effect in improving the stability and charge / discharge performance of the battery containing the cathode.

[0064] positive electrode

[0065] In one embodiment, the present invention provides a positive electrode, the positive electrode comprising:

[0066] Positive current collector; and

[0067] A positive electrode mixture layer on the positive current collector, the positive electrode mixture layer containing a positive electrode active material, a conductive material, an organic binder polymer, and a sacrificial positive electrode material, and

[0068] The sacrificial cathode material comprises lithium cobalt oxide represented by the following chemical formula 1, and the defect formation energy of the metal (M) according to density functional theory (DFT) is -4.0 eV to -8.5 eV.

[0069] [Chemical Formula 1]

[0070] Li x Co( 1-y) M y O4

[0071] in,

[0072] M is selected from at least one of the following: Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si.

[0073] x and y are 5≤x≤7 and 0.05≤y≤0.6.

[0074] The positive electrode according to the present invention has a structure in which a positive electrode mixture layer is formed on a positive electrode current collector, wherein the positive electrode mixture layer comprises: the sacrificial positive electrode material and the positive electrode active material of the present invention described above; a conductive material; and an organic binder polymer, and the positive electrode has a high charge / discharge capacity and has an excellent effect of reducing the gas generated during battery charging / discharging, especially oxygen (O2).

[0075] 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 include: layered compounds, such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or layered compounds replaced by one or more transition metals; with the formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides such as Li2CuO2; vanadium oxides such as LiV3O8, Li3VO4, V2O5, and Cu2V2O7; and LiNi 1-x M x Ni-site type lithium nickel oxides represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); and those represented by the formula LiMn 2-x M x Lithium manganese composite oxides represented by O2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu or Zn); and LiNi x Mn 2-x O4 represents lithium manganese composite oxides with a spinel structure; LiMn2O4, in which a portion of the Li is replaced by alkaline earth metal ions; disulfide compounds; Fe2(MoO4)3, etc.

[0076] Furthermore, based on 100 parts by weight of the positive electrode active material, the content of the sacrificial positive electrode material can be from 0.001 to 5.0 parts by weight. More specifically, based on 100 parts by weight of the positive electrode active material, the content of the sacrificial positive electrode material can be from 0.001 to 4.0 parts by weight, 0.001 to 3.0 parts by weight, 0.001 to 2.0 parts by weight, 0.001 to 1.0 parts by weight, 0.01 to 2.0 parts by weight, 0.05 to 2.0 parts by weight, 0.1 to 2.0 parts by weight, or 0.1 to 1.5 parts by weight.

[0077] In addition, based on 100 parts by weight of positive electrode active material, the content of conductive material can be 1 to 20 parts by weight, specifically 1 to 10 parts by weight, 1 to 5 parts by weight, 3 to 8 parts by weight, or 2 to 5 parts by weight.

[0078] Furthermore, there are no particular limitations on the conductive material, as long as it is conductive and does not cause chemical changes in the battery. For example, the following can be used: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorinated carbon; metal powders, such as aluminum powder and nickel powder; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials, such as polyphenylene derivatives.

[0079] In addition, the organic binder polymer is a component that helps to bond the active material with the conductive material and with the current collector, and the content of the organic binder polymer can be 1 to 20 parts by weight based on 100 parts by weight of the positive electrode active material, specifically 1 to 10 parts by weight, 1 to 5 parts by weight, 3 to 8 parts by weight or 2 to 5 parts by weight.

[0080] In addition, examples of organic adhesive polymers include: polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers.

[0081] In addition to the positive electrode active material, conductive material, and organic binder polymer, the positive electrode may also contain filler to suppress positive electrode expansion in the positive electrode mixture layer. There are no particular restrictions on the filler when it is a fibrous material that does not cause chemical changes in the battery. Specifically, as fillers, olefin polymers such as polyethylene or polypropylene and fibrous materials such as glass fiber or carbon fiber can be used.

[0082] As an example, based on 100 parts by weight of lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), the cathode mixture layer may contain 1 part by weight of sacrificial cathode material (Li6Co). 0.7 Zn 0.3 O4), 5 parts by weight of acetylene black as a conductive material, and 10 parts by weight of adhesive (PVdF).

[0083] In addition, the average thickness of the cathode mixture layer can be from 100 μm to 200 μm, specifically from 120 μm to 180 μm, from 140 μm to 170 μm, or from 150 μm to 200 μm.

[0084] In addition, the positive electrode mixture layer can be a single layer or a multilayer structure with two or more layers. In the case of a multilayer structure with two or more layers, the content of the sacrificial positive electrode material contained in the positive electrode mixture layer can be different. The type and / or content of the positive electrode active material, conductive material and binder can be the same or different.

[0085] As an example, the positive electrode mixture layer can have a bilayer structure in which a first mixture layer and a second mixture layer are stacked sequentially on the positive electrode current collector, and is based on 100 parts by weight of lithium nickel cobalt manganese oxide (LiNi). 0.8 Co 0.1 Mn 0.1 O2), the first mixture layer may contain 1 part by weight of sacrificial cathode material (Li6Co). 0.7 Zn 0.3 O4), 5 parts by weight of acetylene black as a conductive material, and 10 parts by weight of binder (PVdF), and based on 100 parts by weight of lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2 The second mixture layer may contain 2 parts by weight of sacrificial cathode material (Li6Co). 0.7 Zn 0.3 O4), 5 parts by weight of acetylene black as a conductive material, and 9 parts by weight of adhesive (PVdF).

[0086] Furthermore, when the positive electrode mixture layer has a double-layer structure in which a first mixture layer and a second mixture layer are stacked sequentially on the positive electrode current collector, each layer can satisfy the following equation 1:

[0087] [Formula 1]

[0088] 0.05≤SCM 1st / SCM 2nd ≤0.9

[0089] in,

[0090] SCM 1st This represents the content of cathode additives contained in the first cathode mixture layer.

[0091] SCM 2nd This represents the content of cathode additives contained in the second cathode mixture layer.

[0092] Formula 1 shows the proportion of cathode additives contained in the first cathode mixture layer and the second cathode mixture layer, as well as the content of cathode additives contained in the second cathode mixture layer, i.e., the content of lithium cobalt oxide represented by Formula 1. Formula 1 implies that the content of cathode additives contained in the first cathode mixture layer is lower than the content of cathode additives contained in the second cathode mixture layer. The cathode mixture layer according to the present invention can satisfy Formula 1 above, with a content of 0.05 to 0.9 (e.g., 0.05 ≤ SCM). 1st / SCM 2nd ≤0.9), specifically 0.1 to 0.9 (e.g., 0.1≤SCM). 1st / SCM 2nd ≤0.9), 0.2 to 0.8 (e.g., 0.2≤SCM) 1st / SCM 2nd ≤0.8), 0.3 to 0.7 (e.g., 0.3≤SCM) 1st / SCM 2nd ≤0.7) or 0.4 to 0.8 (e.g., 0.4 ≤ SCM) 1st / SCM 2nd ≤0.8). By satisfying the conditions of Equation 1, the cathode mixture layer according to the present invention can further improve the irreversible reaction efficiency of the cathode additive during the initial charging, thereby reducing the gas generated by charging / discharging after the initial charging / discharging.

[0093] Furthermore, there are no particular limitations on the positive electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., can be used. In the case of aluminum or stainless steel, carbon, nickel, titanium, silver, etc., can be used for surface treatment. Additionally, fine irregularities can be formed on the surface of the positive electrode current collector to improve the adhesion of the positive electrode active material, and various forms such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics are possible. Furthermore, considering the conductivity and total thickness of the positive electrode to be prepared, the average thickness of the positive electrode current collector can be appropriately applied in the range of 3 μm to 500 μm.

[0094] Furthermore, the positive electrode according to the present invention can possess excellent electrical performance by incorporating the above-described structure. Specifically, the positive electrode can have low electrode resistance at room temperature (23±2°C), and the change in electrode resistance can be very small even after repeated charging / discharging of the battery, thereby improving battery life.

[0095] For example, relative to the electrode resistance value during the initial charge / discharge (e.g., activation step), after 30 charge / discharges, the rate of change of the resistance value of the positive electrode can be 10% or less. For example, after the initial charge / discharge and 30 charge / discharges, the rate of change of the electrode resistance value of the positive electrode can be 8% or less, 6% or less, 4% or less, or 3% or less.

[0096] Electrode assembly

[0097] In addition, in one embodiment, the present invention provides an electrode assembly comprising the above positive electrode.

[0098] The electrode assembly according to the present invention can have a structure comprising the above positive electrode, negative electrode, and a separator interposed between the positive electrode and the negative electrode, and in some cases, may not include a separator.

[0099] Here, the negative electrode can be manufactured by coating a negative electrode active material on a negative electrode current collector, drying and pressing, and if necessary, may optionally further include a conductive material, an organic binder polymer, a filler, etc. as described above.

[0100] In addition, as the negative electrode active material, for example, the following can be used: graphite having a fully layered crystal structure (such as natural graphite) and soft carbon having a layered crystal structure with low crystallinity (graphene structure; a structure in which the hexagonal honeycomb planes of carbon are arranged in layers), and graphite-based materials such as hard carbon, artificial graphite, expanded graphite, carbon fiber, non-graphitized carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc., in which carbon and these structures are mixed with an amorphous part; metal composite oxides such as Li x Fe2O3(0≤x≤1), Li x WO2(0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me': Al, B, P, Si, Group 1 elements of the periodic table, Group 2 and Group 3 elements, and halogens; 0 < x ≤ 1; 1 ≤ y ≤ 3; 1 ≤ z ≤ 8); lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; titanium oxide; lithium titanium oxide, etc.

[0101] Furthermore, there are no particular limitations on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, nickel, titanium, calcined carbon, etc., can be used. In the case of copper or stainless steel, carbon, nickel, titanium, silver, etc., can be used for surface treatment. Similar to the positive electrode current collector, fine irregularities can be formed on the surface of the negative electrode current collector to enhance adhesion to the negative electrode active material, and various forms such as films, sheets, foils, meshes, porous materials, foams, non-woven materials, etc., are possible. Moreover, 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 μm to 500 μm.

[0102] Furthermore, the separator is positioned between the negative and positive electrodes and utilizes an insulating film with 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, polyethylene, etc., can be used. In some cases, composite separators can be used where inorganic / organic particles are coated onto a porous polymer substrate (such as sheets or nonwoven fabrics) using an organic binder polymer. When a solid electrolyte, such as a polymer, is used as the electrolyte, the solid electrolyte can also serve as the separator. Furthermore, the average pore size of the separator can be from 0.01 μm to 10 μm, and the average thickness can be from 5 μm to 300 μm.

[0103] On the other hand, the electrode assembly can be wound in the form of a roll and stored in a cylindrical battery, a prismatic battery or a pouch battery, or it can be stored in a pouch battery in a folded or stacked and folded form, but is not limited thereto.

[0104] Lithium secondary batteries

[0105] Furthermore, in one embodiment, the present invention provides a lithium secondary battery comprising the above-described electrode assembly.

[0106] The lithium secondary battery according to the present invention can have a structure in which the electrode components are impregnated with an electrolyte containing lithium salt.

[0107] In this case, the lithium salt-containing electrolyte can be composed of an electrolyte and a lithium salt, and non-aqueous organic solvents, organic solid electrolytes, inorganic solid electrolytes, etc. can be used as the electrolyte.

[0108] As non-aqueous organic solvents, for example, 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, or ethyl propionate can be used.

[0109] As organic solid electrolytes, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyalginate-lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, and polymer materials containing ion-dissociating groups can be used.

[0110] As an inorganic solid electrolyte, nitrides, halides, sulfates, etc. of Li can be used, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, and Li3PO4-Li2S-SiS2.

[0111] Lithium salts are materials that are readily soluble in non-aqueous electrolytes, and examples include 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, lithium imide, etc.

[0112] In addition, to improve charge / discharge characteristics, flame retardancy, etc., pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (condensed) glycol dimethyl ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, and N-substituted substances can be added to the electrolyte. Examples of nonflammable materials include oxaliplatinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. In some cases, to impart nonflammability, halogenated solvents such as carbon tetrachloride and trifluoroethylene may be further included, and carbon dioxide gas may be further included to improve high-temperature storage properties. Additionally, fluoroethylene carbonate (FEC) and propylene sulfonate lactone (PRS) may be further included.

[0113] Furthermore, in one embodiment, the present invention provides a battery module comprising the aforementioned secondary battery as a unit battery, and provides a battery pack comprising the battery module.

[0114] The battery pack can be used as a power source for medium to large-sized devices that require high-temperature stability, long cycle life, and high rate capability. Specific examples of such medium to large-sized devices include: power tools powered by electric motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), etc.; electric two-wheeled vehicles, including electric bicycles (E-bicycles) and electric scooters (E-scooters); electric golf carts; and systems for storing electricity. More specifically, specific examples of such medium to large-sized devices include, but are not limited to, hybrid electric vehicles (HEVs).

[0115] Preferred implementation scheme

[0116] The present invention will be described in detail below through examples.

[0117] 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.

[0118] Examples 1 to 11: Preparation of sacrificial cathode materials

[0119] Lithium oxide (Li₂O), cobalt oxide (CoO), and metal oxide (MO) as shown in Table 1 were added to the reactor and dry-mixed uniformly for about 30 minutes using a mixer. Then, the prepared raw material mixture was placed in an electric furnace and calcined at about 700 ± 10 °C for 10 hours under argon (Ar) atmosphere to obtain lithium cobalt oxide (Li₆CoO) as a sacrificial cathode material. 1-y M y O4).

[0120] At this point, the molar ratio of lithium oxide to cobalt oxide fed into the reactor was 1:3.0 to 3.03. The types of metal oxides (MO) and the molar ratio of cobalt oxide to metal oxides (MO) are shown in Table 1 below. For each sacrificial material prepared, the defect formation energy of the doped metal (M) and the powder conductivity were analyzed.

[0121] Specifically, for the defect formation energy of metal (M), density functional theory (DFT) was used for calculation, and Vienna Ab initio Simulation Package (Molecular Dynamics Simulation Package, VASP) was used as a projection-enhanced wave (PAW) method for DFT calculation to calculate the structure and energy of atoms and electrons; the Perdew, Burke and Ernzerhof (PBE) model method based on the generalized gradient approximation (GGA) was used to calculate the electron exchange correlation function; the kinetic energy cutoff was set to 500 eV; and the 2×2×3 Monkhorst-Pack method was used for the surface of each metal (M).

[0122] In addition, ② to measure the powder conductivity of the sacrificial cathode materials, each prepared sacrificial cathode material was compressed to prepare powder. Then, for the prepared powder, the sheet resistance of each sacrificial cathode material was measured using a powder resistivity measuring instrument with a 4-point probe method, according to changes in volume and pressure. The powder conductivity of the sacrificial cathode material was calculated using the measured volume and input mass. The measurement results are shown in Table 1 below.

[0123] [Table 1]

[0124]

[0125] Comparative Examples 1 to 3: Preparation of Sacrificial Cathode Materials

[0126] In addition to adjusting i) the type of metal oxide (MO) mixed with lithium oxide (Li₂O) and cobalt oxide (CoO) and ii) the molar ratio of cobalt oxide to metal oxide as shown in Table 2 below to obtain lithium cobalt oxide (Li₆Co) as a sacrificial cathode material, 1-y M y Apart from O4), Comparative Examples 1 to 3 were performed in the same manner as in Example 1.

[0127] At this point, the defect formation energy of ① the doped metal (M) and the powder conductivity of ② the prepared sacrificial cathode material were analyzed in the same manner as in the examples, and the results are shown in Table 2 below.

[0128] [Table 2]

[0129]

[0130] Experimental Example

[0131] To evaluate the performance of the sacrificial cathode material prepared in this invention, the following experiments were conducted.

[0132] A) Initial charge / discharge capacity and efficiency evaluation

[0133] N-methylpyrrolidone solvent was placed in a homogenizer, and each of the sacrificial cathode materials, acetylene black conductive materials, modified silanol binders and dispersants prepared in Examples 1 to 11 and Comparative Examples 1 to 3 were added at a weight ratio of 95:3:1.7:0.3. The mixture was then mixed at 3000 rpm for 60 minutes to prepare a pre-dispersion.

[0134] The prepared pre-dispersion was mixed with the positive electrode active material, so that based on 100 parts by weight of the positive electrode active material (LiNi), 0.6 Co 0.2 Mn 0.2 The positive electrode material content was 2 parts by weight (O2), and the positive electrode active material, PVdF as a binder, and carbon black as a conductive material were mixed in N-methylpyrrolidone solvent and placed in a homogenizer at a weight ratio of 96:1:3. The mixture was then dispersed at 3000 rpm for 80 minutes to prepare a positive electrode slurry. The prepared positive electrode slurry was coated on one surface of an aluminum current collector, dried at 100°C, and rolled to manufacture the positive electrode.

[0135] The positive electrode and lithium metal counter electrode are used to manufacture a type 2032 coin cell battery. A separator made of porous polyethylene (PE) membrane (thickness: about 16 μm) is placed between the positive electrode and the lithium metal counter electrode, and an electrolyte is injected to manufacture a half-cell coin cell battery.

[0136] In this case, E2DVC is used as the electrolyte. Here, "E2DVC" is a carbonate electrolyte, and refers to a solution obtained by mixing lithium hexafluorophosphate (LiPF6, 1.0M) and ethylene carbonate (VC, 2% by weight) in a mixed solution of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:1:1 (volume ratio).

[0137] For the manufactured coin batteries, the initial charge / discharge capacity was measured by performing an initial charge / discharge (formation) at 25°C under a reference capacity of 200mAh / 200mAh, and the efficiency was calculated based on the measured initial charge / discharge capacity. The results are shown in Table 3 below.

[0138] [Table 3]

[0139]

[0140] As shown in Table 3, it can be seen that the sacrificial cathode material according to the present invention has a high initial charge capacity during the initial charge / discharge period and exhibits a high initial charge / discharge efficiency.

[0141] B) Evaluation of gas generation after initial charging / discharging

[0142] The previously used coin cell battery was repeatedly charged and discharged 50 times at 0.3C / 0.3C and 45°C, and the amount of gas generated during each charge / discharge cycle was measured to calculate the cumulative amount of gas generated after the initial charge / discharge. The results are shown in Table 4 below.

[0143] [Table 4]

[0144] Cumulative gas production [mL / g] Example 1 4.5 Example 2 5.3 Example 3 6.1 Example 4 5.7 Example 5 7.1 Example 6 6.6 Example 7 5.8 Example 8 5.1 Example 9 4.9 Example 10 4.4 Example 11 4.1 Comparative Example 1 13.0 Comparative Example 2 9.7 Comparative Example 3 7.8

[0145] It can be seen that, in the case of the sacrificial cathode material according to the present invention, the amount of gas generated due to charging / discharging after the initial charging / discharging is reduced.

[0146] Specifically, it can be seen that the cumulative gas generation amount of the sacrificial cathode material in the embodiment due to charging / discharging after the initial charging / discharging is low, below 7.5 mL / g, while the sacrificial cathode material in the comparative example has a high cumulative gas generation amount of more than 7.5 mL / g.

[0147] These results show that when the sacrificial cathode material according to the present invention is doped with a specific metal, and the defect formation energy of the metal according to density functional theory (DFT) is controlled within a specific range, high initial charge / discharge efficiency can be achieved during initial charge / discharge, and the amount of additional gas generated in the later stages of charge / discharge can be reduced. This has the advantage of significantly improving the stability and charge / discharge performance of the battery containing the cathode.

[0148] Although the invention has been described above with reference to preferred embodiments thereof, those skilled in the art or of ordinary skill in the art should understand that various modifications and variations can be made thereto without departing from the spirit and scope of the invention as set forth in the appended claims.

[0149] Therefore, the technical scope of this invention should not be limited to the content described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A sacrificial cathode material, said sacrificial cathode material comprising lithium cobalt oxide represented by the following chemical formula 1, and According to density functional theory (DFT), the defect formation energy of metal M is -4.0 eV to -8.5 eV. The sacrificial cathode material has a tetragonal crystal structure with space group P42 / nmc. The defect formation energy of metal M according to density functional theory (DFT) is calculated as follows: the structure and energy of atoms and electrons are calculated using the ViennaAb initio Simulation Package as the projection-enhanced wave (PAW) method; the electron exchange correlation function is calculated using the Perdew, Burke, and Ernzerhof (PBE) model method based on the generalized gradient approximation (GGA); the kinetic energy cutoff is set to 500 eV; and for the surface of metal M, the 2×2×3 Monkhorst-Pack method is used. [Chemical Formula 1] Li x Co (1-y) M y O4 in, M is selected from at least one of the following: Al, Fe, Zn, Ti, W, Mg, Ge, Mn, and Si. x and y are 5≤x≤7 and 0.05≤y≤0.

6.

2. The sacrificial cathode material according to claim 1, wherein, M is selected from one or more of the following: Mg, Ge, and Si.

3. The sacrificial cathode material according to claim 1, wherein, In Equation 1, y is 0.2≤y≤0.

4.

4. The sacrificial cathode material according to claim 1, wherein, The defect formation energy of the sacrificial cathode material, according to density functional theory (DFT), is -4.9 eV to -6.4 eV for the metallic M.

5. The sacrificial cathode material according to claim 1, wherein the sacrificial cathode material has a density of 5 × 10⁻⁶. -4 S / cm to 1×10 - 2 Powder conductivity in S / cm The powder conductivity is obtained by compressing the sacrificial cathode material to prepare powder, and then measuring the sheet resistance of the sacrificial cathode material according to volume and pressure using a powder resistance characteristic measuring instrument with a 4-point probe method, and calculating the powder conductivity of the sacrificial cathode material using the measured volume and input mass.

6. A positive electrode, said positive electrode comprising: Positive current collector; and A positive electrode mixture layer on the positive current collector, the positive electrode mixture layer containing a positive electrode active material, a conductive material, an organic binder polymer, and the sacrificial positive electrode material as described in claim 1.

7. The positive electrode according to claim 6, wherein, Based on 100 parts by weight of the positive electrode active material, the content of the sacrificial positive electrode material is from 0.001 parts by weight to 5.0 parts by weight.

8. The positive electrode according to claim 6, wherein, Based on 100 parts by weight of the entire positive electrode mixture layer, the content of the conductive material is from 0.5 parts by weight to 10 parts by weight.

9. The positive electrode according to claim 6, wherein, The conductive material includes one or more carbon-based materials selected from the following: natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

10. The positive electrode according to claim 6, wherein, The positive electrode active material is 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).

11. The positive electrode according to claim 6, wherein, The average thickness of the positive electrode mixture layer is 100 μm to 200 μm.

12. An electrode assembly comprising the positive electrode of claim 6.

13. A lithium secondary battery comprising the electrode assembly of claim 12.

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