Sacrificial positive electrode material with reduced gas generation and method of making

Abstract

The present invention relates to a sacrificial positive electrode material having reduced gas generation and a method for producing the same, wherein in the method for producing the sacrificial positive electrode material, calcination of a raw material mixture is performed in a non-reactive gas atmosphere containing a small amount of oxygen (O2) gas and under a humidity satisfying a specific range, thereby enabling reduction of the generation of gas, particularly oxygen (O2) gas, generated in an electrode assembly upon charging of a battery, and thus the effects of improving the stability and life of a battery containing the electrode assembly are excellent.

Description

Technical Field

[0001] The present invention relates to a method for preparing a sacrificial positive electrode material and a sacrificial positive electrode material prepared according to the method, the sacrificial positive electrode material having reduced gas generation during charging of a battery by controlling humidity and gas conditions when calcining a raw material mixture.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0024248 filed on February 23, 2021, and Korean Patent Application No. 10-2022-0007852 filed on January 19, 2022, the entire contents of which are incorporated herein by reference as a part of this specification. Background Art

[0003] In recent years, with the increasing demand for high-capacity electrode materials, irreversible additives are also required to have higher irreversible capacities. However, the development of positive electrode additives with such high irreversible capacities does have limitations.

[0004] On the other hand, conventional irreversible additives (such as Li6CoO4) are generally prepared by reacting cobalt oxide with excess lithium oxide. At this time, byproducts that do not participate in the reaction (such as unreacted lithium oxide (Li2O)) remain in the final irreversible additive, which may cause oxidation during the charge / discharge process, thereby generating oxygen inside the battery. The resulting oxygen may cause volume expansion, etc., and may be a major factor leading to battery performance degradation.

[0005] Furthermore, when preparing a slurry composition for electrode production, byproducts such as lithium oxide may react with binder components, increasing viscosity or causing gelation of the composition. This makes it difficult to uniformly apply the electrode composition for forming the active material layer, leading to deterioration in battery characteristics.

[0006] Therefore, due to the above problems, there is a continuous need to develop a cathode additive having higher reversible capacity while generating a small amount of oxygen during charge / discharge of a battery due to a small amount of residual byproducts such as lithium oxide.

[0007] Related literature

[0008] Korean Patent Publication No. 2019-0078392 Summary of the Invention

[0009] [Technical Issues]

[0010] Therefore, an object of the present invention is to provide a positive electrode additive, a positive electrode and a lithium secondary battery including the same, which have a higher irreversible capacity while generating a small amount of oxygen during the charge and discharge process of the battery due to a small amount of residual by-products such as lithium oxide.

[0011] [Technical solution]

[0012] In order to solve the above problems, in one embodiment, the present invention provides a method for preparing a sacrificial positive electrode material, wherein the method comprises the steps of calcining a raw material mixture of lithium oxide (Li2O) and cobalt oxide (CoO) in an inert gas atmosphere containing oxygen at a partial pressure of 1% or less to prepare a lithium cobalt metal oxide represented by the following chemical formula (1):

[0013] The relative humidity (RH) during calcination is below 20%,

[0014] [Chemical Formula 1]

[0015] Li x Co (1-y) M y O 4-z A z

[0016] in,

[0017] M is at least one selected from the group consisting of Ti, Al, Zn, Zr, Mn, and Ni,

[0018] A is a halogen that replaces oxygen,

[0019] x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.001.

[0020] Here, the calcination may be performed in an inert gas atmosphere having a relative humidity of 0.1% to 15% and containing oxygen at a partial pressure of 0.1% to 1%.

[0021] In addition, the calcination temperature may be 500°C to 800°C.

[0022] In addition, the raw material mixture of lithium oxide (Li 2 O) and cobalt oxide (CoO) may be a mixture in which lithium oxide (Li 2 O) and cobalt oxide (CoO) are mixed in a molar ratio of 2 to 4:1.

[0023] In addition, the lithium oxide (Li 2 O) may have an average particle size (D50) of 10 μm to 30 μm.

[0024] Furthermore, when measured by X-ray diffraction analysis, the sacrificial positive electrode material prepared by the above preparation method may satisfy at least one of the following formulas 1 and 2:

[0025] [Formula 1] A / B ≤ 0.1

[0026] [Formula 2] C / D ≤ 0.35

[0027] in,

[0028] A represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 18.9 ± 0.1°,

[0029] B represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 19.2 ± 0.1°,

[0030] C represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 38.5 ± 0.1°,

[0031] D represents the intensity of the strongest peak among peaks appearing in the range of 2θ=47.9±0.1°.

[0032] In one embodiment, the present invention further provides an electrode assembly, comprising a positive electrode, wherein the positive electrode comprises:

[0033] a positive electrode current collector; and

[0034] a positive electrode mixture layer on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material, a conductive material, an organic binder polymer, and a sacrificial positive electrode material;

[0035] The sacrificial positive electrode material includes a lithium cobalt metal oxide represented by the following Chemical Formula 1, and satisfies at least one of Formulas 1 and 2 when measured by X-ray diffraction analysis:

[0036] [Chemical Formula 1]

[0037] Li x Co (1-y) M y O 4-z A z

[0038] in,

[0039] M is at least one selected from the group consisting of Ti, Al, Zn, Zr, Mn, and Ni,

[0040] A is a halogen that replaces oxygen,

[0041] x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.001,

[0042] [Formula 1] A / B ≤ 0.1

[0043] [Formula 2] C / D ≤ 0.35

[0044] wherein,

[0045] A represents the intensity of the strongest peak among peaks appearing in the range of 2θ = 18.9 ± 0.1°,

[0046] B represents the intensity of the strongest peak among peaks appearing in the range of 2θ = 19.2 ± 0.1°,

[0047] C represents the intensity of the strongest peak among peaks appearing in the range of 2θ = 38.5 ± 0.1°,

[0048] D represents the intensity of the strongest peak among peaks appearing in the range of 2θ = 47.9 ± 0.1°.

[0049] Here, the positive active material can be a lithium complex 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).

[0050] Further, the content of the sacrificial positive material can be 0.001 to 5.0 parts by weight, based on 100 parts by weight of the positive active material.

[0051] Further, in one embodiment, the present application provides a lithium secondary battery comprising the electrode assembly.

[0052] Advantages

[0053] In the method of producing a sacrificial positive material according to the present application, the calcination of the raw material mixture is performed under a non-reactive gas atmosphere containing a small amount of oxygen (O2) gas and a humidity satisfying a specific range, whereby the generation of gas, particularly oxygen (O2) gas, generated in the electrode assembly at the time of charging of the battery can be reduced, whereby the effect of improving the stability and the life of the battery containing the electrode assembly is excellent. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is a graph showing the X-ray diffraction of a sacrificial positive material according to the humidity condition at the time of calcination of a raw material mixture.

[0055] Figure 2 is a graph showing the X-ray diffraction of a sacrificial positive material according to the oxygen partial pressure at the time of calcination of a raw material mixture.

[0056] Figure 3 is a graph showing the amount of generated gas according to the number of times of charging / discharging at 45°C for each oxygen partial pressure at the time of calcination of a raw material mixture.

[0057] Figure 4It is a graph showing the amount of generated gas according to the storage time (unit: week) at 60° C. for each oxygen partial pressure when the raw material mixture is calcined.

[0058] Figure 5 is a graph showing initial charge / discharge curves of a positive electrode including a sacrificial positive electrode material according to humidity conditions when a raw material mixture is calcined.

[0059] Figure 6 is a graph showing initial charge / discharge curves of a positive electrode including a sacrificial positive electrode material according to the oxygen partial pressure when a raw material mixture is calcined. DETAILED DESCRIPTION

[0060] Because the present invention is capable of various changes and embodiments, specific embodiments will be described in detail in the detailed description.

[0061] However, this is not intended to limit the present invention to specific embodiments, and should be construed as including all variations, equivalents, and substitutes included within the spirit and scope of the present invention.

[0062] In the present invention, it should be understood that the terms "including" or "having" are intended to clarify the existence of the described features, numbers, steps, operations, parts, ingredients or their combinations, but do not exclude the existence or addition of one or more other features or numbers, steps, operations, parts and their combinations.

[0063] Furthermore, in the present invention, when a portion of a layer, film, region, plate, or the like 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 another portion exists therebetween. Conversely, when a portion of a layer, film, region, plate, or the like is described as being "under" another portion, this includes the case where another portion exists therebetween, as well as the case where the portion is "directly" "under" the other portion. Furthermore, herein, reference to being disposed "on" may include not only being disposed on an upper portion, but also being disposed on a lower portion.

[0064] In addition, in the present invention, "relative humidity (RH)" is expressed as a percentage (%) and is the ratio of the amount of water vapor currently contained in the air to the maximum saturated water vapor pressure that a constant volume of air can maintain, and can be expressed as a percentage of humidity in an electric furnace that calcines a raw material mixture.

[0065] In addition, in the present invention, "D 50 ” is the particle size at the point where the cumulative curve of the particle size distribution reaches 50% by volume when the cumulative curve is calculated with the total volume being 100%, and “D 50" refers to the particle size when the volume accounts for 50% by accumulating from the smallest particle size. The average particle size (D 50 ) can be measured, for example, by using laser diffraction, and laser diffraction is generally capable of measuring particle sizes in the submicron range to several mm, and can obtain results with high reproducibility and high resolution.

[0066] Hereinafter, the present invention will be described in more detail.

[0067] Method for preparing sacrificial positive electrode material

[0068] In one embodiment, the present invention provides a method for preparing a sacrificial positive electrode material, wherein the method comprises the steps of calcining a raw material mixture of lithium oxide (Li2O) and cobalt oxide (CoO) in an inert gas atmosphere containing oxygen at a partial pressure of 1% or less to prepare a lithium cobalt metal oxide represented by the following chemical formula (1):

[0069] [Chemical Formula 1]

[0070] Li x Co (1-y) M y O 4-z A z

[0071] in,

[0072] M is at least one selected from the group consisting of Ti, Al, Zn, Zr, Mn, and Ni,

[0073] A is a halogen that replaces oxygen,

[0074] x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.001.

[0075] The method for preparing a sacrificial positive electrode material according to the present invention relates to a method for preparing a lithium cobalt metal oxide represented by Chemical Formula 1 as a sacrificial positive electrode material, wherein the lithium cobalt metal oxide represented by Chemical Formula 1 has an inverse fluorite structure Li x CoO 4-z A z (provided that A is F or Cl, 5.4≤x≤6.8 and 0≤z≤0.0005), and in some cases, any one or more of Ti, Al, Zn, Zr, Mn and Ni may be doped in Li x CoO 4-z A z Specifically, the lithium cobalt metal oxide may include at least one selected from the following: Li6CoO4, Li6Co (1-y) Ti y O4、Li6Co (1-y) Aly O4、Li6Co (1-y) Zn y O4、Li6Co (1-y) Zr y O4、Li6Co (1-y) Mn y O4、Li6Co (1-y) Ni y O4 (provided that 0≤y≤0.4) and mixtures thereof.

[0076] A sacrificial positive electrode material comprising such a lithium cobalt metal oxide can be prepared by calcining a raw material mixture of lithium oxide (Li2O) and cobalt oxide (CoO) mixed in a molar ratio of 2 to 4:1, for example, 2.5 to 3.5:1 or 2.95 to 3.1:1, and when one or more oxides of Ti, Al, Zn, Zr, Mn and Ni are added to the raw material mixture, a lithium cobalt metal oxide doped with one or more of Ti, Al, Zn, Zr, Mn and Ni can be prepared.

[0077] Here, the temperature for performing calcination is not particularly limited and can be applied as long as the mixed metal oxide can be converted into the lithium cobalt metal oxide represented by Chemical Formula 1. Specifically, the calcination temperature may be 500° C. to 800° C., more specifically 500° C. to 700° C., 600° C. to 800° C., 600° C. to 750° C., 650° C. to 800° C., 630° C. to 770° C., or 660° C. to 740° C.

[0078] In addition, calcination can be carried out under an inert gas atmosphere containing a small amount of oxygen, wherein the inert gas atmosphere containing a small amount of oxygen is, for example, an argon (Ar) gas or nitrogen (N2) gas atmosphere containing oxygen at a partial pressure of less than 1%, 0.1 to 1%, 0.5 to 1%, 0.2 to 0.8%, 0.5 to 0.9% or 0.2 to 0.6%.

[0079] In the present invention, by controlling the content of oxygen contained in the inert gas during the calcination of the raw material mixture within the above range, it is possible to prevent an increase in gas generation during charge and discharge due to an excessively low oxygen partial pressure, and to prevent a decrease in the initial charge capacity of the battery due to an excessive amount of oxygen.

[0080] In addition, the humidity during calcination may be a relative humidity (RH) of 20% or less, specifically a relative humidity (RH) of 0.1% to 20%, 0.1% to 18%, 0.1% to 15%, 1% to 15%, 0.5% to 12%, 1% to 12%, 4% to 12%, 7% to 12%, 0.5% to 10%, 0.5% to 7%, or 3% to 8%.

[0081] By controlling the humidity during calcination of the raw material mixture within such a range, the present invention can prevent the ratio of the lithium cobalt metal oxide represented by Chemical Formula 1 contained in the prepared sacrificial positive electrode material from being reduced due to a significantly low humidity of less than 0.01%, and can overcome the problem of a reduction in the initial charge capacity of the battery due to excessive humidity.

[0082] For example, in the method for preparing a sacrificial positive electrode material according to the present invention, calcination can be performed at a temperature of 670° C. to 730° C. in an argon (Ar) gas or nitrogen (N2) gas atmosphere containing oxygen at a partial pressure of 0.2 to 0.8% for 2 to 20 hours.

[0083] Conventionally, a sacrificial positive electrode material comprising lithium cobalt metal oxide represented by Chemical Formula 1 has an inverse fluorite structure through a calcination process, and the sacrificial positive electrode material having an inverse fluorite structure has the following problem: during charge / discharge, a large amount of gas containing oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), etc. is generated.

[0084] However, by calcining the raw material mixture containing lithium oxide (Li2O) and cobalt oxide (CoO) under the conditions where a small amount of oxygen is mixed with an inert gas and the relative humidity (RH) satisfies the above range, the sacrificial positive electrode material prepared according to the present invention can prevent the highly reactive lithium oxide (Li2O) from remaining, thereby increasing the ratio of the lithium cobalt metal oxide represented by Chemical Formula 1 in the synthesized sacrificial positive electrode material, and further reducing the amount of gas generated when the battery is used while maintaining or increasing the charge / discharge capacity of the battery.

[0085] For example, in the sacrificial cathode material prepared according to the present invention, the ratio of the lithium cobalt metal oxide represented by Chemical Formula 1 is increased so that at least one of the following Formulas 1 and 2 may be satisfied when X-ray diffraction measurement is performed:

[0086] [Formula 1] A / B ≤ 0.1

[0087] [Formula 2] C / D ≤ 0.35

[0088] in,

[0089] A represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 18.9 ± 0.1°,

[0090] B represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 19.2 ± 0.1°,

[0091] C represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 38.5 ± 0.1°,

[0092] D represents the intensity of the strongest peak among peaks appearing in the range of 2θ=47.9±0.1°.

[0093] In Formulas 1 and 2, the peaks (B and D) appearing in the range of 2θ = 19.2 ± 0.1° and 47.9 ± 0.1° are realized by the crystals of the lithium cobalt metal oxide represented by Chemical Formula 1, and the peaks (A and C) appearing in the range of 2θ = 18.9 ± 0.1° and 2θ = 38.5 ± 0.1° are realized by impurities. The lower the intensity ratio of these peaks, i.e., "A / B" and "C / D", the higher the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1. In the sacrificial positive electrode material prepared according to the present invention, the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1 is increased to more than 98%, thereby satisfying A / B of 0.15 or less, specifically 0.12 or less, 0.1 or less, or 0.05 or less in X-ray diffraction measurement; and C / D of 0.3 or less, 0.25 or less, or 0.1 or less. In some cases, when the lithium cobalt metal oxide represented by Chemical Formula 1 occupies 100% of the sacrificial positive electrode, A / B and C / D may satisfy 0.

[0094] According to the method for preparing a sacrificial positive electrode material of the present invention, the raw material mixture is calcined in an inert gas atmosphere containing a small amount of oxygen (O2) gas and a relative humidity (RH) that meets a specific range, thereby reducing the gas generated in the electrode assembly during battery charging, especially the generation of oxygen (O2) gas, thereby excellently improving the stability and life of the battery containing the electrode assembly.

[0095] positive electrode

[0096] In one embodiment, the present invention provides a positive electrode comprising:

[0097] a positive electrode current collector; and

[0098] a positive electrode mixture layer on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material, a conductive material, an organic binder polymer and a sacrificial positive electrode material,

[0099] The sacrificial positive electrode material is prepared according to the preparation method, includes a lithium cobalt metal oxide represented by the following Chemical Formula 1, and satisfies at least one of Formulas 1 and 2 when measured by X-ray diffraction analysis:

[0100] [Chemical Formula 1]

[0101] Li x Co (1-y) M y O 4-z A z

[0102] in,

[0103] M is at least one selected from the group consisting of Ti, Mg, Al, Zn, Zr, Mn, and Ni,

[0104] A is a halogen that replaces oxygen,

[0105] x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.001.

[0106] [Formula 1] A / B ≤ 0.1

[0107] [Formula 2] C / D ≤ 0.35

[0108] in,

[0109] A represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 18.9 ± 0.1°,

[0110] B represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 19.2 ± 0.1°,

[0111] C represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 38.5 ± 0.1°,

[0112] D represents the intensity of the strongest peak among peaks appearing in the range of 2θ=47.9±0.1°.

[0113] The positive electrode according to the present invention has a structure in which a positive electrode mixture layer is formed on a positive electrode collector, wherein the positive electrode mixture layer comprises: a sacrificial positive electrode material prepared according to the preparation method of the present invention, and the sacrificial positive electrode material contains a lithium cobalt metal oxide represented by Chemical Formula 1; a positive electrode active material; a conductive material; and an organic binder polymer, thereby achieving an excellent effect in reducing gases generated during charge / discharge of the battery, especially oxygen (O2) gas.

[0114] Here, the positive electrode active material may 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 may include: a layered compound such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or a layered compound substituted with one or more transition metals; a formula of Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO4 (wherein x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2, etc.; lithium copper oxides such as Li2CuO2; vanadium oxides such as LiV3O8, Li3VO4, V2O5, Cu2V2O7; 1-x Mx Ni-site lithium nickel oxide represented by O2 (wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); 2-x M x Lithium manganese composite oxide represented by Li2Mn3MO8 (wherein M=Fe, Co, Ni, Cu or Zn); LiNi x Mn 2-x O4 represents a lithium manganese composite oxide having a spinel structure; LiMn2O4, in which a portion of Li in the formula is replaced by an alkaline earth metal ion; a disulfide compound; Fe2(MoO4)3, etc.

[0115] In addition, the positive electrode mixture layer may include 0.001 to 5.0 parts by weight of the sacrificial positive electrode material prepared by the preparation method according to the present invention based on 100 parts by weight of the positive electrode active material. More specifically, the content of the sacrificial positive electrode material may be 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 based on 100 parts by weight of the positive electrode active material.

[0116] In addition, the conductive material may be included in an amount of 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, based on 100 parts by weight of the positive active material.

[0117] Furthermore, the conductive material is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; 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 can be used.

[0118] In addition, the organic binder polymer is a component that helps to bond the active material to the conductive material and to the current collector, and the content of the organic binder polymer 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 based on 100 parts by weight of the positive electrode active material.

[0119] In addition, examples of the organic binder polymer include polyvinylidene fluoride (PVdF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, various copolymers, etc.

[0120] In addition to the positive electrode active material, conductive material, and organic binder polymer, the positive electrode mixture layer may also contain a filler for suppressing positive electrode expansion. This filler is not particularly limited if it is a fibrous material that does not cause chemical changes in the battery. Specifically, fillers such as olefin polymers, such as polyethylene or polypropylene, and fibrous materials, such as glass fiber or carbon fiber, can be used.

[0121] In addition, the positive electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used, and in the case of aluminum or stainless steel, carbon, nickel, titanium, silver, etc. can be used for surface treatment. In addition, fine concavoconvexity 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, nets, porous bodies, foams, and non-woven fabrics are possible. In addition, considering the conductivity and total thickness of the positive electrode to be manufactured, the average thickness of the positive electrode current collector can be appropriately applied within the range of 3 μm to 500 μm.

[0122] Electrode assembly

[0123] Furthermore, in one embodiment, the present invention provides an electrode assembly including the above-mentioned positive electrode.

[0124] The electrode assembly according to the present invention may have a structure including the above-described positive electrode, negative electrode, and a separator interposed between the positive electrode and the negative electrode, and may not include a separator in some cases.

[0125] Here, the negative electrode is manufactured by coating a negative electrode active material on a negative electrode current collector, drying and pressing, and may optionally further contain the conductive material, organic binder polymer, filler, etc. as described above, if necessary.

[0126] In addition, as the negative electrode active material, for example, graphite having a completely layered crystal structure (such as natural graphite) and soft carbon having a layered crystal structure with low crystallinity (graphene structure; a structure in which hexagonal honeycomb planes of carbon are arranged in layers), as well as graphite-based materials such as hard carbon, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerenes, activated carbon, etc., in which carbon and these structures are mixed with an amorphous portion; metal composite oxides such as Lix 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, elements of Group 1, Group 2 and Group 3 of the periodic table, and halogens; 0 <x≤1;1≤y≤3;1≤z≤8);锂金属;锂合金;硅类合金;锡类合金;金属氧化物,如SnO、SnO2、PbO、PbO2、Pb2O3、Pb3O4、Sb2O3、Sb2O4、Sb2O5、GeO、GeO2、Bi2O3、Bi2O4和Bi2O5;导电聚合物,如聚乙炔;Li-Co-Ni类材料;氧化钛;锂钛氧化物等。

[0127] In addition, the negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause chemical changes in the battery, and for example, copper, stainless steel, nickel, titanium, calcined carbon, etc. can be used, and in the case of copper or stainless steel, carbon, nickel, titanium, silver, etc. can be used for surface treatment. In addition, similar to the positive electrode current collector, fine concavoconvexity can be formed on the surface of the negative electrode current collector to enhance adhesion with the negative electrode active material, and various forms such as films, sheets, foils, nets, porous materials, foams, non-woven fabric materials, etc. are possible. In addition, 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 within the range of 3 μm to 500 μm.

[0128] In addition, the diaphragm is between the negative electrode and the positive electrode, and an insulating film with high ion permeability and mechanical strength is used. There is no particular limitation on the diaphragm as long as it is commonly used in the art, but specifically, a sheet or non-woven fabric made of chemically resistant and hydrophobic polypropylene, glass fiber, polyethylene, etc. can be used, and in some cases, inorganic particles / organic particles can be used to be coated on a porous polymer substrate (such as a sheet or non-woven fabric) through an organic binder polymer. When a solid electrolyte such as a polymer is used as an electrolyte, the solid electrolyte can also serve as a diaphragm. In addition, the average pore size of the diaphragm can be 0.01 μm to 10 μm, and the average thickness can be 5 μm to 300 μm.

[0129] On the other hand, the electrode assembly may be wound in the form of a roll and stored in a cylindrical battery, a prismatic battery, or a pouch-type battery, or may be stored in a pouch-type battery in a folded or stacked and folded form, but is not limited thereto.

[0130] lithium secondary batteries

[0131] Furthermore, in one embodiment, the present invention provides a lithium secondary battery including the above-described electrode assembly.

[0132] The lithium secondary battery according to the present invention may have a structure in which an electrode assembly is impregnated with an electrolyte containing a lithium salt.

[0133] In this case, the lithium salt-containing electrolyte may be composed of an electrolyte and a lithium salt, and as the electrolyte, a nonaqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like may be used.

[0134] As the nonaqueous organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene 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, triester phosphate, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate or ethyl propionate can be used.

[0135] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polyalginate-lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, polymer materials containing ion dissociative groups, and the like can be used.

[0136] As an inorganic solid electrolyte, Li nitrides, halides, sulfates, etc. can be used, such as Li3N, LiI, Li5Ni2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2.

[0137] Lithium salts are materials that are easily soluble in non-aqueous electrolytes, such as LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, lithium imide, etc.

[0138] In addition, in order to improve the charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (condensed) glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted Oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, in order to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride and trifluoroethylene may be further contained, and carbon dioxide gas may be further contained to improve high-temperature storage characteristics, and fluoroethylene carbonate (FEC), propene sultone (PRS), etc. may be further contained.

[0139] Furthermore, in one embodiment, the present invention provides a battery module including the above-described secondary battery as a unit battery, and provides a battery pack including the battery module.

[0140] The battery pack can be used as a power source for medium and large-sized devices that require high-temperature stability, long cycle characteristics and high-rate characteristics, and specific examples of the medium and large-sized devices include: electric 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-bikes) and electric scooters (E-scooters); electric golf carts; and systems for storing electricity. More specifically, specific examples of the medium and large-sized devices include hybrid electric vehicles (HEVs), but are not limited thereto.

[0141] Preferred Implementation

[0142] Hereinafter, the present invention will be described in detail through examples.

[0143] However, the following examples and experimental examples are only for illustrating the present invention, and the contents of the present invention are not limited to the following examples and experimental examples.

[0144] Examples 1 to 6 and Comparative Examples 1 to 2. Preparation of Sacrificial Positive Electrode Materials

[0145] Lithium oxide (Li2O, unimodal distribution, D 50 =10 to 30 μm) and cobalt oxide (CoO) were placed in a reactor at a molar ratio of 3.0 to 3.03:1 and uniformly dry-mixed using a mixer for approximately 30 minutes. The prepared raw material mixture was then placed in an electric furnace and calcined at approximately 700°C for 10 hours under argon (Ar) to obtain lithium cobalt oxide (Li6CoO4). The relative humidity (RH) in the electric furnace and the partial pressure of oxygen (O2) contained in the argon gas during the calcination are shown in Table 1 below.

[0146] [Table 1]

[0147] RH[%] <![CDATA[O2分压[%]]]> Example 1 1 0.1 to 1.0 Example 2 5 0.1 to 1.0 Example 3 10 0.1 to 1.0 Example 4 15 0.1 to 1.0 Example 5 0 0.1 to 1.0 Example 6 10 ≤0.08 Comparative Example 1 25 0.1 to 1.0 Comparative Example 2 10 1.01 to 1.5

[0148] Experimental Example 1.

[0149] The sacrificial positive electrode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were subjected to X-ray diffraction measurement to confirm the change in the oxygen partial pressure in the inert gas when the raw material mixture was calcined, and the ratio of the components contained in each sacrificial positive electrode material was calculated from the measured X-ray diffraction. At this time, X-ray diffraction was performed using an X-ray diffraction analyzer from Rigaku (Japan Rigaku Co., Ltd.). The X-ray diffraction pattern was obtained at a scanning speed of 5° / second with a 2θ range of 15° to 64°. The ratios of the components contained in the prepared sacrificial positive electrode material were calculated from the obtained X-ray diffraction pattern, and the results are shown in Table 2 and Table 3. Figure 1 and 2 middle.

[0150] [Table 2]

[0151]

[0152] As shown in Table 2, in the sacrificial positive electrode material prepared according to the present invention, the relative humidity and the oxygen partial pressure in the inert gas are controlled within a certain range when the raw material mixture is calcined. From this, it can be seen that the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1 increases to more than 90%, specifically more than 97%.

[0153] In addition, reference Figure 1 and Figure 2When a raw material mixture of lithium oxide (Li20) and cobalt oxide (CoO) is calcined at about 700°C under a non-reactive gas atmosphere, lithium cobalt metal oxide (Li6Co04) represented by Chemical Formula 1 is produced as a product. In addition, when the relative humidity (RH) during calcination of the raw material mixture is 15% or less and the oxygen partial pressure is 0.1 to 1.0%, the proportion of the lithium cobalt metal oxide represented by Chemical Formula 1 increases, no impurity peaks (A≒0) are identified in the range of θ=18.9±0.1°, and it is identified that the peaks (C≒0) present in the range of θ=38.5±0.3° have no significant intensity. On the other hand, when the oxygen partial pressure during calcination is 0.2% or more, the intensity of these peaks (A and C) is high because of a high proportion of impurities, and thus it is identified that the proportion (A / B and C / D) of the intensity (B and D) of the peaks representing the lithium cobalt metal oxide represented by Chemical Formula 1 is 0.174 or more and 0.37 or more, respectively. This means that an increase in moisture and oxygen in the non-reactive gas inhibits the synthesis of the lithium cobalt metal oxide represented by Chemical Formula 1, thereby reducing the yield.

[0154] From these results, it can be seen that, during calcination, the relative humidity and the oxygen partial pressure in the non-reactive gas affect the proportion of the metal oxide contained in the sacrificial cathode material.

[0155] Experimental Example 2.

[0156] In order to evaluate the performance of the sacrificial cathode material prepared in the present application, the following experiment was performed.

[0157] A) Measurement of gas emissions

[0158] The N-methylpyrrolidone solvent was put into a homomixer, and each of the sacrificial cathode materials prepared in Examples 1 to 6 and Comparative Examples 1 to 2, acetylene black conductive material, modified silanol binder, and dispersant were added in a weight ratio of 95:3:1.7:0.3, and then mixed at 3000 rpm for 60 minutes to prepare a pre-dispersion.

[0159] The prepared pre-dispersion was mixed with a cathode active material so that the content of the sacrificial cathode material was 2 parts by weight based on 100 parts by weight of the cathode active material (LiNi 0.6 Co 0.2 Mn 0.2 O2), the content of the sacrificial cathode material was 2 parts by weight, and the cathode active material, PVdF as a binder, and carbon black as a conductive material mixed in the N-methylpyrrolidone solvent were put into a homomixer in a weight ratio of 96:1:3, and then dispersed at 3000 rpm for 80 minutes to prepare a cathode slurry. The prepared cathode slurry was coated on one surface of an aluminum current collector, dried at 100°C, and roll-pressed to manufacture a cathode.

[0160] A 2032-type battery was fabricated using the positive electrode and a lithium metal counter electrode. A separator (thickness: about 16 μm) made of a porous polyethylene (PE) film was interposed between the positive electrode and the lithium metal counter electrode, and an electrolyte was injected to fabricate a half-cell type battery.

[0161] At this time, as the electrolyte, a mixed solution of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 (volume ratio), lithium hexafluorophosphate (LiPF6, 0.7M), lithium bis(fluorosulfonyl)imide (LiFSI, 0.5M), lithium tetrafluoroborate (LiBF4, 0.2 wt%), ethylene carbonate (VC, 2 wt%), 1,3-propane sultone (PS, 0.5 wt%) and ethylene sulfate (Esa, 1 wt%) was used.

[0162] The fabricated battery was charged / discharged once under 4.5C / 0.3C conditions for formation. The amount and composition of the gas generated during each of 50 repetitions of charging and discharging at 45°C under 0.3C conditions and during storage at 60°C for 4 weeks were analyzed. The results are shown in Table 3 and Table 4. Figure 3 and 4 middle.

[0163] [Table 3]

[0164]

[0165] As shown in Table 3 and Figure 3 and 4 As shown, in the case of the sacrificial positive electrode material prepared according to the present invention, the amount of gas generated during charge / discharge was found to be reduced. It can be confirmed that this trend occurs when the relative humidity (RH) in the electric furnace and the oxygen (O2) in the inert gas during the calcination of the raw material mixture meet the specific ranges of the present invention.

[0166] B) Initial charge / discharge evaluation

[0167] A half-cell type battery was manufactured in the same manner as in the measurement of gas emission, except that a mixed solution of ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 1:2:1 (volume ratio), lithium hexafluorophosphate (LiPF6, 1.0 M) and ethylene carbonate (VC, 2 wt %) was used as the electrolyte.

[0168] The initial charge capacity and irreversible capacity were measured by charging / discharging (forming) each of the manufactured batteries. At this time, charging / discharging (forming) was performed under the conditions of 70 mAh / 3 mAh, and the results are shown in Table 4 and Table 5 below. Figure 5 and 6 middle.

[0169] [Table 4]

[0170] RH[%] <![CDATA[O2分压[%]]]> Initial charging capacity [mAh] Example 1 1 0.1 to 1.0 810.8 Example 2 5 0.1 to 1.0 802.7 Example 3 10 0.1 to 1.0 792.4 Example 4 15 0.1 to 1.0 749.5 Example 5 0 0.1 to 1.0 788.1 Example 6 10 ～0.08 817 Comparative Example 1 25 0.1 to 1.0 723.5 Comparative Example 2 10 1.01 to 1.5 682

[0171] As shown in Table 4 and Figure 5 and Figure 6 As shown, it can be seen that the sacrificial positive electrode material prepared according to the present invention has the effect of improving battery performance. Specifically, when the relative humidity (RH) in the electric furnace is high when the raw material mixture is calcined and the oxygen (O2) in the inert gas has a low partial pressure, it is found that the sacrificial positive electrode material of the embodiment has a higher initial charge capacity. This means that when the relative humidity (RH) in the electric furnace is high when the raw material mixture is calcined, the initial charge capacity increases, but the gas generation during charge / discharge increases.

[0172] From these results, it can be seen that by adjusting the relative humidity (RH) during the calcination of the raw material mixture and the oxygen (O2) gas partial pressure in the inactive gas to a specific range, the sacrificial positive electrode material prepared according to the present invention has an excellent effect of improving battery performance, and can reduce the gas generated in the electrode assembly during battery charging, especially the generation of oxygen (O2) gas, thereby improving the stability and life of the battery containing the sacrificial positive electrode material.

[0173] While the foregoing has been described with reference to the preferred embodiments of the present invention, those skilled in the art or ordinary skill in the art will appreciate 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.

[0174] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A method for preparing a sacrificial positive electrode material, the method comprising the following steps: A raw material mixture of lithium oxide (Li2O) and cobalt oxide (CoO) is calcined in an inert gas atmosphere containing oxygen at a partial pressure of 0.1% to 1% to prepare a lithium cobalt metal oxide represented by the following chemical formula (1), in, The relative humidity (RH) during calcination is a relative humidity in the range of 0.1% to 15%, [Chemical Formula 1] Li x Co (1-y) M y O 4-z A z in, M is at least one selected from the group consisting of Ti, Al, Zn, Zr, Mn, and Ni, A is a halogen that replaces oxygen, x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.

001.

2. The method according to claim 1, wherein The calcination is performed at a temperature of 500°C to 800°C.

3. The method according to claim 1, wherein The raw material mixture of lithium oxide (Li2O) and cobalt oxide (CoO) is a mixture in which lithium oxide (Li2O) and cobalt oxide (CoO) are mixed in a molar ratio of 2 to 4:

1.

4. The method according to claim 1, wherein Average particle size D of lithium oxide (Li2O) 50 In the range of 10μm to 30μm.

5. The method according to claim 1, wherein When measured by X-ray diffraction analysis, the sacrificial positive electrode material satisfies one or more of the following formulas 1 and 2: [Formula 1] A / B≤0.1 [Formula 2] C / D≤0.35 in, A represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 18.9 ± 0.1°, B represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 19.2 ± 0.1°, C represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 38.5 ± 0.1°, D represents the intensity of the strongest peak among peaks appearing in the range of 2θ=47.9±0.1°.

6. A positive electrode, comprising: a positive electrode current collector; and a positive electrode mixture layer on the positive electrode current collector, the positive electrode mixture layer comprising a positive electrode active material, a conductive material, an organic binder polymer, and a sacrificial positive electrode material prepared by the method of claim 1; The sacrificial positive electrode material includes a lithium cobalt metal oxide represented by the following Chemical Formula 1, and satisfies one or more of Formulas 1 and 2 when measured by X-ray diffraction analysis: [Chemical Formula 1] Li x Co (1-y) M y O 4-z A z in, M is at least one selected from the group consisting of Ti, Al, Zn, Zr, Mn, and Ni, A is a halogen that replaces oxygen, x, y and z are 5≤x≤7, 0≤y≤0.4 and 0≤z≤0.001, [Formula 1] A / B≤0.1 [Formula 2] C / D≤0.35 in, A represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 18.9 ± 0.1°, B represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 19.2 ± 0.1°, C represents the intensity of the strongest peak among the peaks appearing in the range of 2θ = 38.5 ± 0.1°, D represents the intensity of the strongest peak among peaks appearing in the range of 2θ=47.9±0.1°.

7. 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 group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), zinc (Zn), titanium (Ti), magnesium (Mg), chromium (Cr), and zirconium (Zr).

8. The positive electrode according to claim 6, wherein The sacrificial positive electrode material may be present in an amount of 0.001 to 5.0 parts by weight based on 100 parts by weight of the positive electrode active material. 9 . An electrode assembly comprising the positive electrode according to claim 6 . 10 . A lithium secondary battery comprising the electrode assembly according to claim 9 .

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