Positive electrode active material and lithium secondary battery comprising same

Abstract

The present invention relates to a positive active material and a lithium secondary battery comprising same, the positive electrode active material being a high-nickel lithium transition metal composite oxide having a layered structure and having a lattice volume V satisfying [expression 1] and a Curie-Weiss temperature T satisfying [expression 2]. [Expression 1] 101.4 Å3 ≤ V ≤ 101.75 Å3 [Expression 2] 0K ≤ T ≤ 30K The present invention can easily check, at the material level, whether the battery capacity of a manufactured battery accurately conforms to the required capacity, and can control same, and enables the minimization of the deviation between the target design capacity and the actual capacity of the manufactured battery.

Description

Cathode active material and lithium secondary battery containing the same

[0001] This application claims the benefit of priority to Republic of Korea Patent Application No. 2024-0036442, dated March 15, 2024, Republic of Korea Patent Application No. 2024-0094617, dated July 17, 2024, and Republic of Korea Patent Application No. 2024-0179806, dated December 5, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material and a lithium secondary battery including the same.

[0003] As technological development and demand for various electronic devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries, which boast high energy density and voltage, long cycle life, and low self-discharge rates, are commercialized and widely used.

[0004] These lithium secondary batteries are being used in a variety of applications, including electric vehicles. There is a growing need to adjust specifications, such as the upper charge voltage and charge / discharge capacity, based on the type of application and customer needs.

[0005] The present invention relates to a layered structure high nickel lithium transition metal composite oxide cathode active material, in which the lattice volume and Curie-Weiss temperature are controlled within a predetermined range, thereby controlling the nickel occupancy (Ni) within the lithium layer. Li ), H2 / H3 structural transition and / or voltage plateau (V H2 / H3 ) by controlling a cathode active material and a lithium secondary battery including the same, which can easily check and control at the material level whether the design capacity of the manufactured secondary battery matches the required actual capacity.

[0006] The present invention relates to a cathode active material having a layered structure of a high nickel lithium transition metal composite oxide, characterized in that the lattice volume V of the cathode active material satisfies the following [Formula 1] and the Curie-Weiss temperature T satisfies the following [Formula 2]:

[0007] [Formula 1]

[0008] 101.4 Å 3 ≤ V ≤ 101.75 Å 3

[0009] [Formula 2]

[0010] 0K ≤ T ≤ 30K

[0011] The lattice volume V of the above positive electrode active material is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

[0012] In one embodiment, the positive electrode active material may be characterized by a lattice volume V satisfying the following [Equation 3]:

[0013] [Formula 3]

[0014] 101.5 Å 3 ≤ V ≤ 101.70 Å 3

[0015] In one embodiment, the positive electrode active material may be characterized by a Curie-Weiss temperature T satisfying the following [Equation 4]:

[0016] [Formula 4]

[0017] 10K ≤ T ≤ 25K

[0018] In one embodiment, the positive electrode active material may include a lithium layer and a transition metal layer, and the lithium layer may be characterized in that at least a portion of the lithium sites are occupied by nickel.

[0019] In one embodiment, the positive electrode active material has a nickel occupancy (Ni) of the lithium layer Li) can be characterized as being 0.003 to 0.015.

[0020] In one embodiment, the positive electrode active material has a nickel occupancy (Ni) of the lithium layer Li ) can be characterized as being 0.005 to 0.012.

[0021] In one embodiment, the positive electrode active material may be characterized by a crystal grain size of 100 nm to 300 nm.

[0022] In one embodiment, the positive electrode active material of the present invention may be characterized by being represented by the following chemical formula 1:

[0023] [Chemical Formula 1]

[0024] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0025] In the above formula, Q is at least one element selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B), and 0.96≤a≤1.04, 0≤b≤0.3, 0≤c≤0.3, 0≤d≤0.1, 0≤b+c+d≤0.3, -0.1≤δ≤0.1.

[0026] In one embodiment, the positive electrode active material of the present invention may be characterized in that 0≤b+c+d≤0.2 in the chemical formula 1.

[0027] The present invention also relates to a lithium secondary battery, characterized in that it includes a positive electrode, a negative electrode, and an electrolyte including the positive electrode active material according to the above.

[0028] The present invention also relates to a method for producing a layered high-nickel lithium transition metal composite oxide-based positive electrode active material, comprising the steps of: mixing a lithium precursor and a transition metal precursor so that the Li / M molar ratio becomes 0.96 to 1.04; performing a first firing at a temperature of 300°C to 500°C; and performing a second firing at a temperature of 600°C to 900°C, wherein the positive electrode active material has a lattice volume V that satisfies the above-described [Formula 1], and a Curie-Weiss temperature T that satisfies the above-described [Formula 2].

[0029] The present invention relates to a method for manufacturing a lithium secondary battery including a layered high-nickel lithium transition metal composite oxide-based cathode active material, wherein the voltage at which an H2 / H3 structural phase transition occurs is controlled by controlling the molar ratio of lithium to transition metal (Li / M molar ratio) included in the cathode active material, and the upper limit charge capacity during charging is controlled by controlling the voltage at which an H2 / H3 structural phase transition occurs.

[0030] In one embodiment, the step of controlling the molar ratio of lithium to transition metal (Li / M molar ratio) included in the positive electrode active material may include the steps of mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to transition metal (Li / M molar ratio) becomes a specific value; firing at a first firing temperature; and firing at a second firing temperature higher than the first firing temperature.

[0031] In one embodiment, the lattice volume V of the positive electrode active material is 101.4 Å 3 -101.75 Å 3The Curie-Weiss temperature T has a value between 0 K and 30 K, the lattice volume V is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

[0032] In one embodiment, the positive electrode active material may include a lithium layer and a transition metal layer, and the lithium layer may be characterized in that at least a portion of the lithium sites are occupied by nickel.

[0033] In one embodiment, the nickel occupancy (Ni) of the lithium layer Li ) can be characterized as being 0.003 to 0.015.

[0034] In one embodiment, the crystal grain size of the positive electrode active material may be 100 nm to 300 nm.

[0035] In one embodiment, the positive electrode active material may be characterized by being represented by the following chemical formula 1:

[0036] [Chemical Formula 1]

[0037] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0038] In the above formula, Q is at least one element selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B), and 0.96≤a≤ 1.04, 0≤b≤0.3, 0≤c≤0.3, 0≤d≤0.1, 0≤b+c+d≤0.3, -0.1≤δ≤0.1.

[0039] The cathode active material having the same lattice volume and Curie-Weiss temperature as the present invention can be manufactured by controlling the synthesis conditions of the cathode active material (e.g., Li / M molar ratio, sintering temperature, sintering time, etc.). Through this control, the crystal grain size and nickel occupancy in the lithium layer (Ni Li ), and the resulting H2 / H3 phase transition behavior can be effectively controlled.

[0040] As a result, by the present invention, in the layered structure high-nickel positive electrode active material, it was confirmed that the lattice volume and the Curie-Weiss temperature were within a predetermined range, and thus the crystal grain size and nickel occupancy (Ni) in the lithium layer Li ), H2 / H3 phase transition and / or voltage plateau (V H2 / H3 ) and other effective control is possible. Accordingly, it is possible to easily check and control at the material level whether the design capacity of the manufactured secondary battery matches the required actual capacity, and to minimize the deviation between the intended design capacity and the actual manufactured secondary battery capacity.

[0041] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description of the invention described below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0042] Figure 1 is a flow chart illustrating a method for manufacturing a positive electrode active material according to one embodiment of the present invention.

[0043] Figure 2 shows the nickel occupancy (Ni) of the lithium layer of the positive electrode active material. 2+ at Li site, Ni Li ) is a graph showing the grid volume V according to the

[0044] Figure 3 shows the nickel occupancy (Ni) of the lithium layer of the positive electrode active material. 2+ at Li site, Ni Li) is a graph showing the Curie-Weiss temperature (T).

[0045] Figure 4 is a graph showing the crystal size of the positive electrode active material.

[0046] Figure 5 is a graph showing the microstrain of the positive electrode active material.

[0047] The Ref. data in FIGS. 2 and 3 above are referenced from the following literature: Philipp Kurzhals, Felix Riewald, Matteo Bianchini, Heino Sommer, Hubert A. Gasteiger, and Jurgen Janek, The LiNiO2 cathode active material: a comprehensive study of calcination conditions and their correlation with physicochemical properties. Part I. Structural Chemistry. J. Electrochem. Soc. 168, 110518 (2021).

[0048] Terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0049] Therefore, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention. Therefore, it should be understood that various equivalents and modified examples may exist that can replace them at the time of filing this application. In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0050] When a part in this specification is said to “comprise” a certain component, this does not exclude other components unless specifically stated to the contrary, but rather means that other components may be included. Thus, for example, a composition comprising compound A may include compounds other than A. However, the term “comprise” also encompasses, as a specific embodiment thereof, the more restrictive meanings of “consisting essentially / essentially of” and “consisting of,” so that, for example, “a composition comprising compound A” may also consist (essentially / essentially) of compound A.

[0051] In this connection, it should be understood that terms such as “have” or “have” as used herein are intended to specify the presence of a feature, number, step, component, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0052] Where a quantity, concentration, or other value or parameter is given herein as a range, a range, or an enumeration of upper and lower values, it should be understood that this specifically discloses all ranges that can be formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values ​​is recited herein, unless otherwise stated, e.g., there is no qualifying term such as greater than, less than, etc., the range is intended to include the endpoint values ​​and all integers and fractions within the range. The scope of the present invention is not intended to be limited to the specific values ​​recited when defining a range. Furthermore, as used herein, "about," "approximately," and "substantially" are used to mean a range of or near the numerical value or degree, taking into account inherent manufacturing and material tolerances.

[0053] Among the properties mentioned in this specification, if the measurement temperature affects the property, the property is measured at room temperature unless otherwise specified. The term "room temperature" refers to the natural temperature without heating or cooling, and may mean, for example, any temperature within the range of about 10°C to 30°C, or about 23°C or about 25°C. In addition, unless otherwise specified, the unit of temperature in this specification is ℃.

[0054] In addition, among the properties mentioned in this specification, if the measurement pressure affects the property, the property is measured at normal pressure, i.e., atmospheric pressure (approximately 1 atm), unless otherwise specified.

[0055] Satisfying the diverse applications and needs of various customers for lithium secondary batteries requires not only material composition but also the exploration and combination of various cell components. Consideration also needs to be given to factors such as development time, effort, and cost. For example, customers often require specific battery design specifications, and the upper voltage limit may vary depending on the purpose and application.

[0056] The present invention provides an efficient technology capable of finely adjusting charge / discharge capacity according to changes in the upper limit voltage of a charge, taking into account various uses and needs, while maintaining cell components at a level as similar as possible to existing ones.

[0057] The first aspect of the present invention relates to a positive electrode active material.

[0058] The present invention may relate to a cathode active material, for example, a high nickel lithium transition metal composite oxide cathode active material having a layered structure, characterized in that the lattice volume V of the cathode active material satisfies the following [Formula 1] and the Curie-Weiss temperature T satisfies the following [Formula 2]:

[0059] [Formula 1]

[0060] 101.4 Å 3 ≤ V ≤ 101.75 Å 3

[0061] [Formula 2]

[0062] 0K ≤ T ≤ 30K

[0063] The above lattice volume V may be a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature may be a value measured by a superconducting quantum interference device (SQUID). The XRD and SQUID may each be performed according to the evaluation examples described below.

[0064] In this specification, "layered structure" may mean that the positive electrode active material has a structure including a lithium layer and a transition metal layer. In this specification, "high-nickel" may mean that in a lithium-transition metal composite oxide, Ni is included in an amount of, for example, 70 mol% or more with respect to the total transition metal, and in other examples, it may mean that it is included in an amount of 75 mol% or more or 80 mol% or more.

[0065] The present invention can provide a positive electrode active material having a lattice volume V and a Curie-Weiss temperature T within the above ranges by controlling the configurations described below.

[0066] As battery performance becomes a key specification for final products, consumers have increasingly stringent, specific, and sophisticated requirements and standards. Consequently, meeting customer requirements necessitates appropriate modifications to battery design conditions, such as the utilization and optimization of materials, including active materials. However, battery development without a clear direction and design blueprint can involve numerous trial-and-error iterations, leading to inefficiencies. Therefore, identifying and controlling the most efficient process variables from the materials stage to the final battery stage and designing batteries accordingly is crucial for optimizing battery performance and enhancing safety within cost constraints.

[0067] The present invention provides a positive electrode active material in which the lattice volume V and the Curie-Weiss temperature T of the positive electrode active material are controlled within a predetermined range as a means for solving such problems. The positive electrode active material in which the lattice volume V and the Curie-Weiss temperature T are controlled as described above has nickel occupancy characteristics of a lithium layer at an appropriate level as described below, and thus the phase transition during the charge / discharge process of the battery, particularly the H2 / H3 phase transition, can be controlled to have a desired level of charge / discharge capacity. According to the present invention, by controlling the lattice volume V and the Curie-Weiss temperature T of the positive electrode active material, which can be measured relatively easily in a method according to an evaluation example described below, within a predetermined range, the electrochemical properties, including the charge / discharge capacity of the final manufactured battery, can be controlled at the material level as required.

[0068] The positive electrode active material of the present invention may be characterized, for example, by a lattice volume V satisfying the following [Formula 3]:

[0069] [Formula 3]

[0070] 101.5 Å 3 ≤ V ≤ 101.70 Å 3

[0071] The positive electrode active material of the present invention may be characterized, for example, by having a Curie-Weiss temperature T satisfying the following [Equation 4]:

[0072] [Formula 4]

[0073] 10K ≤ T ≤ 25K

[0074] The cathode active material of the present invention may include, for example, a lithium layer and a transition metal layer, and the lithium layer may be characterized in that at least a portion of the lithium sites are occupied by nickel.

[0075] The positive electrode active material of the present invention has, for example, a nickel occupancy (Ni) of the lithium layer Li) can be characterized as being 0.003 to 0.015. In this specification, the nickel occupancy of the lithium layer (Ni Li )" may mean the molar fraction of nickel in the lithium layer. The nickel occupancy can be measured according to the evaluation example described below. In this specification, "lithium" or "nickel" means including ions. In another example, the positive electrode active material of the present invention may be measured by measuring the nickel occupancy (Ni) of the lithium layer. Li ) may be characterized by being 0.004 to 0.014 or 0.04 to 0.013, for example, being characterized by being 0.005 to 0.012. By allowing the positive electrode active material to include nickel occupying the lithium layer as described above in a predetermined range, a positive electrode active material that simultaneously satisfies the conditions of the lattice volume V and the Curie-Weiss temperature T of the positive electrode active material can be provided, which allows for easy confirmation and control at the material level of the control of the H2 / H3 phase transition behavior and the securing of the battery capacity according to the design purpose accordingly.

[0076] In a layered structure high-nickel lithium transition metal composite oxide cathode active material, Ni 2+ The ionic radius (0.69 Å) of Li in an octahedral environment + Since it is similar to the ionic radius of Ni (0.76 Å), 3+ A small amount of Ni reduced in 2+ can easily occupy lithium sites and replace lithium in the lithium layer. Accordingly, at least a part of the lithium layer is occupied by nickel, and the nickel occupancy of the lithium layer (Ni Li ) can affect the phase transition occurring during the charge / discharge process, for example, the H2 / H3 phase transition behavior. Nickel contained in the lithium layer has a pillar effect that controls the collapse of the lithium layer during the phase transition process, so it is necessary to ensure that nickel is appropriately occupied within the lithium layer. For example, nickel occupancy in the lithium layer (NiLi ) increases, the H2 / H3 transition peak appears at a higher voltage, and the voltage plateau (V H2 / H3 ) may increase, and conversely, the nickel occupancy (Ni) of the lithium layer Li ) becomes smaller, the H2 / H3 transition peak appears at a lower voltage, and the voltage plateau (V H2 / H3 ) can be reduced. Based on this tendency, the voltage value at which the H2 / H3 structural phase transition occurs can be adjusted according to the required upper limit voltage of the charge / discharge of the lithium secondary battery to optimize the charge / discharge capacity of the battery. The H2 / H3 phase transition refers to the phase transition from the second hexagonal phase to the third hexagonal phase, and can cause crack formation and gas generation. Therefore, the nickel occupancy (Ni) of the lithium layer Li ) and the resulting H2 / H3 phase transition must be properly controlled to achieve the desired electrochemical properties, including the charge / discharge capacity, of the battery.

[0077] Nickel occupancy of the above lithium layer (Ni Li ) can be controlled, for example, by adjusting the synthesis conditions of the positive electrode active material (including but not limited to Li / M molar ratio, sintering temperature, sintering time, etc.). In one example, the Li / M molar ratio can be controlled within the range of 0.96 to 1.04. As the Li / M molar ratio increases, the nickel occupancy (Ni) of the lithium layer Li ) may decrease, and conversely, as the Li / M molar ratio decreases, the nickel occupancy (Ni) of the lithium layer Li ) may increase.

[0078] In one example, a second firing process may be performed during the manufacture of the positive electrode active material. The firing temperature during the first firing process may be within a range of 300°C to 500°C, and the firing time may be within a range of 3 to 5 hours. Additionally, the firing temperature during the second firing process may be within a range of 600°C to 900°C, and the firing time may be within a range of 5 to 7 hours. At least one of the first and / or second firing processes may be performed, for example, under an oxygen atmosphere.

[0079] The cathode active material of the present invention may or may not include lithium in the transition metal layer, for example. That is, in one example, the cathode active material of the present invention may have a structure in which only the lithium sites of the lithium layer are replaced with nickel or added thereto, and in another example, it may further include a structure in which some of the transition metals of the transition metal layer are replaced with lithium or added thereto.

[0080] The positive electrode active material of the present invention may be characterized by, for example, a crystal grain size of 100 nm to 300 nm. By ensuring that the positive electrode active material of the present invention has a crystal grain size within the above range, the contact surface between the positive electrode active material and the electrolyte can be prevented or suppressed from becoming excessively wide, and the volume expansion of the positive electrode active material or the battery due to charge and discharge can be prevented from becoming excessive, and the phenomenon of the lithium charge and discharge path becoming longer due to an enlarged crystal grain size, thereby reducing the overall capacity of the battery, can be suppressed.

[0081] The positive electrode active material of the present invention may be characterized by, for example, being represented by the following chemical formula 1:

[0082] [Chemical Formula 1]

[0083] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0084] In the above formula, Q may be one or more elements selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B), and may satisfy 0.96≤a≤1.04, 0≤b≤0.3, 0≤c≤0.3, 0≤d≤0.1, 0≤b+c+d≤0.3, -0.1≤δ≤0.1.

[0085] The positive electrode active material of the present invention may be characterized, for example, by the fact that the value of “b+c+d” in the chemical formula 1 is 0≤b+c+d≤0.2.

[0086] The positive electrode active material of the present invention may be doped with, for example, a doping element, and the doping element may be characterized by being at least one selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B). The doping metal may be included in a molar fraction of 10.0% or less, 9.0% or less, 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.0% or less, 3.0% or less, 2.5% or less, 2.0% or less, 1.5% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, or 0.5% or less, or 0.01% or more, 0.1% or more, 0.3% or more, 0.5% or more, 1.0% or more, 2.0% or more, or 2.5% or more in the lithium transition metal composite oxide, but is not limited thereto. Although some modifications may occur in the synthesis conditions of the positive electrode active material depending on the doping, within the aforementioned range, the crystal grain size or nickel occupancy (Ni) of the lithium layer Li ) can be controlled within an appropriate range, and as a result, it is possible to secure accurate battery capacity according to the design purpose.

[0087] The shape of the positive electrode active material may be, for example, a particle shape such as a sphere, an ellipse, or a spherical particle. The particle size of the positive electrode active material is not particularly limited and may be within a range applicable to positive electrode active materials of conventional lithium secondary batteries.

[0088] The second aspect of the present invention relates to a lithium secondary battery.

[0089] Matters relating to the first aspect of the present invention may be equally applied to matters relating to the second aspect unless specifically stated otherwise.

[0090] The lithium secondary battery of the present invention may be characterized by including, for example, a positive electrode, a negative electrode, and an electrolyte including the positive electrode active material according to the first aspect. The lithium secondary battery of the present invention may also optionally further include, for example, a separator.

[0091] The above positive electrode may include a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer may include a positive electrode active material, a conductive material, a binder and / or an additive according to the first aspect.

[0092] The conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used. The conductive material may typically be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0093] The above binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof. The binder may be included in an amount of 1 wt% to 30 wt% based on the total weight of the positive electrode active material layer.

[0094] The additive may be a plastic additive or an irreversible additive. The plastic additive may be characterized by including at least one of zirconium, yttrium, and strontium, for example. The irreversible additive may be a lithium peroxide, such as, but not limited to, Li2NiO2, Li6CoO4, etc.

[0095] The above-mentioned positive electrode can be manufactured according to a conventional positive electrode manufacturing method, except that the above-mentioned positive electrode active material is used. For example, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, which includes the above-mentioned positive electrode active material and optionally a binder, a conductive agent, and / or an additive, onto a positive electrode current collector, followed by drying and rolling. At this time, the composition for forming a positive electrode active material layer may further include a solvent, and the types and contents of the positive electrode active material, binder, conductive agent, and additive are as described above.

[0096] The solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, etc., taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0097] The above positive electrode can also be manufactured by casting the composition for forming the positive electrode active material layer on a separate support, and then laminating the film obtained by peeling it from the support onto a positive electrode current collector.

[0098] The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and may be made of, for example, copper (Cu), nickel (Ni), aluminum (Al), vanadium (V), gold (Au), platinum (Pt), chromium (Cr), iron (Fe), zinc (Zn), indium (In), germanium (Ge), lithium (Li), magnesium (Mg), stainless steel, titanium (Ti), cobalt (Co), or an alloy thereof. In addition, the positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric. The positive electrode current collector may be omitted in some cases.

[0099] In addition to the aforementioned configuration, the above-mentioned positive electrode may further include known configurations that can be included in a positive electrode in a lithium secondary battery.

[0100] In the lithium secondary battery, the negative electrode may, in one example, include a negative electrode current collector and a negative electrode active material layer positioned on the negative electrode current collector. In another example, the negative electrode may be an anode-less battery negative electrode that does not include a negative electrode active material layer immediately after battery manufacturing, but in which a negative electrode active material layer, such as a lithium metal layer, is formed through battery charging.

[0101] The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0102] The above-described negative electrode active material layer optionally includes a binder, a conductive agent, an additive, etc., together with the negative electrode active material. The above-described negative electrode active material layer may be manufactured, for example, by applying a negative electrode forming composition including a negative electrode active material onto a negative electrode current collector and drying the same, or by casting the negative electrode forming composition onto a separate support and then laminating the resulting film onto a negative electrode current collector by peeling the same from the support. The negative electrode forming composition may further include a solvent, and the solvent may be selected from among the examples of solvents included in the positive electrode forming composition described above.

[0103] As the negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium may be used. For example, carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; SiO β (0<βSnO2, vanadium oxide, lithium vanadium oxide, and the like; or a composite including the above metallic compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, etc., and any one or a mixture of two or more of these may be used. In addition, a metallic lithium thin film may be used as the negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon may be used as the carbon material. Representative examples of low-crystalline carbon include soft carbon and hard carbon, and examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived High-temperature calcined carbon such as cokes is representative. In addition, the binder and conductive material may be the same as those described above for the positive electrode.

[0104] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without special restrictions. For example, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity can be used. According to one embodiment, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., can also be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength can be used, and can optionally be used in a single-layer or multi-layer structure. The separator may be omitted in some cases.

[0105] In addition, examples of the electrolyte used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0106] The electrolyte may include, for example, an organic solvent and a lithium salt.

[0107] The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) can be used.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0108] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. For example, the lithium salt may include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is preferable that the concentration of the lithium salt be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0109] In addition to the electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.

[0110] The lithium secondary battery may also optionally further include, for example, a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0111] The third aspect of the present invention relates to a method for manufacturing a positive electrode active material.

[0112] Matters relating to the first and / or second aspects of the present invention may be equally applied to matters relating to the third aspect unless specifically stated otherwise.

[0113] Referring to FIG. 1, the present invention relates to a method for manufacturing a layered high-nickel lithium transition metal composite oxide-based positive electrode active material, for example, comprising the steps of: (S1) mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to the transition metal (Li / M molar ratio) becomes 0.96 to 1.04; (S2) performing a first firing at a temperature of 300°C to 500°C; and (S3) performing a second firing at a temperature of 600°C to 900°C, and characterized in that the lattice volume V of the positive electrode active material satisfies the following [Formula 1], and the Curie-Weiss temperature T satisfies the following [Formula 2]:

[0114] [Formula 1]

[0115] 101.4 Å 3 ≤ V ≤ 101.75 Å 3

[0116] [Formula 2]

[0117] 0K ≤ T ≤30K

[0118] The above lattice volume V is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

[0119] The above first firing step may be performed at a temperature of 350°C to 450°C or a temperature of 380°C to 420°C in other examples. The above first firing step may be performed for, for example, 1 hour to 7 hours, and in other examples, may be performed for 3 hours to 5 hours.

[0120] The secondary firing step may be performed at a temperature of 650 to 850°C or a temperature of 690 to 730°C in other examples. The secondary firing step may be performed for, for example, 2 to 10 hours, and in other examples, may be performed for 3 to 9 hours, 4 to 8 hours, or 5 to 7 hours.

[0121] The present invention may relate to a method for manufacturing a lithium secondary battery, for example, by controlling the molar ratio of lithium to a transition metal (Li / M molar ratio) included in the positive electrode active material to control the voltage at which an H2 / H3 structural phase transition occurs, and by controlling the voltage at which an H2 / H3 structural phase transition occurs to control the upper limit charge capacity during charging.

[0122] The step of controlling the molar ratio of lithium to transition metal (Li / M molar ratio) included in the positive electrode active material may include, for example, a step of mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to transition metal (Li / M molar ratio) becomes a specific value; a step of firing at a first firing temperature; and a step of firing at a second firing temperature higher than the first firing temperature. The specific value may be, for example, 0.96 to 1.04, but is not limited thereto. The second firing temperature may be, for example, higher than the first firing temperature by within a range of 100°C to 1000°C. In another example, the second firing temperature may be higher than the first firing temperature by within a range of 200°C to 800°C, 300°C to 400°C, or 300°C to 350°C.

[0123] Hereinafter, the present invention will be described in detail by way of examples to specifically illustrate the disclosure of the present invention and the intended functions and effects thereof. However, these examples may be modified in various ways, and the scope of this specification is not construed as being limited to these examples. It should be emphasized that these examples are provided to illustrate the present invention to those skilled in the art.

[0124] Design of the experiment

[0125] After preparing a cathode active material (Example 1) having a specific precursor Li / M molar ratio, the nickel occupancy within the lithium layer was measured. Thereafter, based on Example 1, cathode active materials (Examples 2 to 5) having various nickel occupancies within the lithium layer were prepared while maintaining the crystal grain size as similar as possible. The trend between the lattice volume of the layered structure and the Curie-Weiss temperature for the nickel occupancy within the lithium layer of Examples 1 to 5 was confirmed.

[0126] Example.

[0127] Examples 1-5 are examples of synthesizing positive electrode active materials by performing primary and secondary firing while changing the input Li / M. For example, as shown in the table below, the Li / M ratios of Examples 1, 2, 3, 4, and 5 increase by a certain amount and are 1, 1.01, 1.02, 1.03, and 1.04, respectively.

[0128] Example 1.

[0129] Ni, a precursor of positive electrode active material 0.87 Co 0.08 Mn 0.05Lithium source LiOH·H2O was added to (OH)2 so that the Li / M molar ratio was 1 and mixed. The mixed powder was placed in an alumina crucible. Afterwards, it was first calcined for 4 hours in an oxygen atmosphere at 400°C. Afterwards, the powder that went through the crushing, water washing, and drying processes was mixed with 30.1 wt% of H3BO and secondarily calcined for 6 hours in an air atmosphere at 710°C to obtain a lithium transition metal composite oxide cathode active material.

[0130] Examples 2 to 5

[0131] A positive electrode active material was manufactured in the same manner as in Example 1, except that the synthesis conditions were changed as shown in Table 1 below. As a result, parameters such as grain size and capacity characteristics were shown as shown in Table 1 below.

[0132] At the same sintering temperature, when the Li / M molar ratio decreases, the grain size tends to decrease, and when the Li / M molar ratio increases, the grain size tends to increase. In order to control the grain size as similarly as possible, the second sintering temperature was finely adjusted (-2ΔT, -1ΔT, 0, ΔT, 2ΔT) as in the examples. Since the grain size change pattern according to the Li / M molar ratio varies depending on the reference sintering temperature, the ΔT value may vary depending on the sintering temperature. At this time, as the nickel occupancy of the lithium layer decreased, the microstrain tended to decrease, and a cathode active material showing trends such as a decrease in the layered structure lattice volume and a decrease in the Curie-Weiss temperature could be obtained.

[0133]

[0134] Referring to Table 1, when making LiMO2 (M = Ni, Co, Mn, Al, etc.) layered structure cathode active material, five types of examples according to the synthesis conditions, parameters representing the characteristics of such cathode active materials (e.g., XRD and SQUID measurement results), and Spec-In (suitable) and Spec-Out (unsuitable) according to the charge capacity measurement of a cylindrical battery are shown. The reason for distinguishing between the case where the charge capacity upper limit voltage is 4.1 V (lower than the voltage at which the H2 / H3 structural phase transition occurs (e.g., 4.15 V - 4.175 V)) and the case where the upper limit voltage is 4.2 V (higher than the voltage at which the H2 / H3 structural phase transition occurs) is because the influence according to the Li / M input ratio differs before and after the H2 / H3 structural phase transition voltage.

[0135] First, when synthesizing high-nickel NCM(A), Ni 2+ The atomic radius of Li + Because it is similar to the ideal Ni 3+ It does not exist in the transition metal position of the layered structure, and some Ni 2+ The lithium layer is naturally occupied. When the input ratio of the Li source precursor and the M transition metal source precursor is changed during synthesis to increase the input Li / M molar ratio, a relative oxidation atmosphere is created based on the transition metal during synthesis, so that the Ni of the lithium layer 2+ It can lower the occupancy rate. As a result, Ni 2+ By controlling the occupancy of the LiMO2, the H2 / H3 structural transition voltage near the upper limit of the charge voltage can be controlled, and when drawing a charge / discharge curve (capacity vs. voltage), the capacity increases rapidly at the H2 / H3 structural transition voltage, so by finely controlling the H2 / H3 structural transition voltage, the capacity can be controlled to suit the purpose.

[0136] Evaluation Example 1. Lattice volume V

[0137] XRD measurements were performed using a Bruker D8 Endeavor instrument (Cu target 40 kV, 40 mA; Lynxeye-XE-T 1D detector). The measurement conditions were fixed divergence slit 0.5°, 2θ°, Δθ°, and time per step 0.4 s. Depending on the micro-deformation or crystallinity of the powder sample, the slit gap adjustment, 2θ measurement range, Δθ gap, and time per step can be adjusted to suit the sample. The same powder sample was sampled three times, and the average and deviation values ​​were obtained. Then, the TOPAS program was used to obtain the lattice constants a, c, and lattice volume V for the XRD measurement data.

[0138] Rietveld structural analysis was performed using the fundamental parameter approach to take into account the measurement equipment information, and the lattice constants a and c, lattice volume V, grain size, and microstrain were calculated for the R-3m crystal group.

[0139] Evaluation Example 2. Nickel occupancy within the lithium layer

[0140] Assuming an ideal simple crystal structure model, lithium in the LiMO2 unit cell is located at Wyckoff position 3a (0 0 0), M such as transition metal and Al is located at position 3b (0 0 0.5), and oxygen is located at position 6c (0 0 z). In the actual synthesis of high-nickel cathode active materials, Ni 2+ Ga Li + have a similar radius, some Ni 3+ Go Ni 2+ When reduced to Ni 2+ Ga Li +can occupy the position. At this time, the lithium that is substituted may exist in a different form outside the LiMO2 unit cell or may occupy the transition metal layer, so the crystal structure model (Li) in which Wyckoff position 3a is mainly occupied by lithium and some nickel, and 3b is mainly occupied by nickel and some lithium 1-x Ni 2+ x ) 3a (Ni 3+ 1-y Li y ) 3b Rietveld analysis was performed using O2 as the initial model. At this time, the nickel occupancy x at the 3a position and the lithium occupancy y at the 3b position do not need to be the same in the crystal structure model. In this evaluation example, the lithium occupancy y at the 3b position was fitted as 0, and the crystal structure model was simplified (Li 1-x Ni 2+ x ) 3a (M) 3b The O2(M=Ni, Co, Mn, Al, etc.) model was used. With this XRD measurement and analysis method, the changes in lattice constants and lattice volume can be precisely measured with a deviation of lattice constants a=0.0002Å, c=0.001Å, and lattice volume V=0.01Å, and this subtle change in lattice constants means that the Nigel occupancy within the lithium layer is well controlled.

[0141] Evaluation Example 3. Grain Size

[0142] The grain size can be evaluated using the LVol-IB value or LVol-FWHM value obtained by the Rietveld analysis method of the TOPAS program. In this evaluation example, the LVol-IB value when k = 1 of the TOPAS program was used for the Rietveld grain size. However, in the case of a sample with a large microstrain or when the microstrain increases due to the pressurization of the rolling electrode process, the microstrain affects the FWHM of the diffraction peak along with the grain size, so the grain size cannot be properly obtained. Since the increase in the FWHM of the diffraction peak due to the microstrain increases as the measurement angle of XRD increases, in such cases, the grain size in the (003) direction can be obtained by applying Scherrer's equation for the (003) diffraction peak.

[0143] The TOPAS program uses a fundamental parameter approach that takes into account the equipment resolution to perform single-peak fitting for the (003) diffraction peak. The grain size in the (003) direction can be obtained using the following formula:

[0144] crystalline size (003) =κλ / {FWHM (003),sample cos(θ)}, κ=0.89, λ:x-ray wavelength

[0145] At this time, the FWHM by the equipment resolution is deconvoluted for the FWHM of the (003) diffraction peak measured, and the FWHM by the crystal grain size of the sample is deconvoluted. (003),sample can be obtained.

[0146] Grain size (nm) (003) Grain size (nm) Example 1 1 3 3 1 4 5 Example 2 1 2 7 1 4 9 Example 3 1 3 1 1 4 8 Example 4 1 2 7 1 5 3 Example 5 1 2 4 1 5 1

[0147]

[0148] Referring to Table 2, the grain size can also be obtained using only the (003) diffraction peak and Rietveld structural analysis. Obtaining the grain size using the (hkl) diffraction peak measured from the entire XRD pattern by Rietveld analysis is a method of measuring the grain size in the average (hkl) crystal plane direction. However, unlike powder samples, it is sometimes difficult to obtain the grain size in the case of rolled electrode samples due to high-angle peak broadening caused by microdeformation. Therefore, Table 2 shows the grain size obtained using only the low-angle (003) diffraction peak.

[0149] Evaluation Example 4. Curie-Weiss Temperature

[0150] Using MPMS equipment from Quantum Design, the magnetic susceptibility was measured in the range of 5 to 300 K. The magnetic field and measurement temperature step can be changed depending on the sample measurement conditions. In this evaluation example, a magnetic field of 1 Tesla was applied, and the measurement temperature step was measured at 5 K intervals. In Examples 1 to 5, a rapid increase in the magnetic susceptibility due to ferromagnetic impurities was not observed.

[0151] On the other hand, if there are other magnetic impurities, the magnetic susceptibility can be described by the general equation including the impurities as follows (see Stephen Blundell, Magnetism in Condensed Matter).

[0152] χ m cgs [emu / mol / Oe]=M / H=χ sample +(χ T +χ0) impurity = C / (T-θ CW ) + C T / T+χ0

[0153] The magnetic susceptibility of the sample of interest and the magnetic susceptibility of the impurity may be mixed, and the magnetic susceptibility of the impurity is a temperature-dependent magnetic susceptibility C that follows the Curie-Weiss law. T / T can be distinguished by χ0, which has little temperature dependence.

[0154] If we take the inverse of this magnetic susceptibility and plot it against temperature, we can draw a line with a constant slope and y-intercept in the temperature range above the magnetic phase transition temperature. By removing the influence of the magnetic susceptibility due to impurities and finding the slope a and y-intercept b of the inverse magnetic susceptibility for the magnetic susceptibility of the sample, we can obtain the effective magnetic moment Curie-Weiss temperature.

[0155] 1 / χ=(T-θ CW ) / C=1 / C*T-θ CW / C=aT+b

[0156] Effective magnetic moment μ eff =2.827sqrt(χ m cgs T) 2.827sqrt(C)=2.827sqrt(1 / a)

[0157] Curie-Weiss temperature

[0158] θ CW =-b*C

[0159] The Curie-Weiss temperature represents the average strength of the magnetic interaction in a magnetic material. In high-nickel layered active materials, the Curie-Weiss temperature has a positive value (ferromagnetic interaction dominance) when the nickel occupancy in the lithium layer is high. At this time, as the nickel occupancy decreases, the positive Curie-Weiss temperature tends to decrease. The change in the Curie-Weiss temperature according to the nickel occupancy in the lithium layer is more sensitive than the change in the effective magnetic moment, and unlike the case of Rietveld structural analysis, it is less dependent on the crystal structure model. Therefore, observing the lattice constant and Curie-Weiss temperature change of XRD can complementarily synthesize a sample with controlled nickel occupancy in the lithium layer.

[0160] Evaluation Example 5. Charging Capacity

[0161] (Manufacturing of coin half cells)

[0162] All coin half cells were manufactured in the same manner except for the cathode active material and measured in the same manner and under the same conditions.

[0163] First, the synthesized NCM active material, conductive agent (Super C), and binder (PVDF) are mixed in an N-methylpyrrolidone (NMP) solvent to prepare a slurry. The slurry is coated on one side of an aluminum current collector, then dried and roll-pressed at 130°C to produce an electrode. At this time, the thickness of the positive electrode layer excluding the current collector is less than 100 μm. Next, a lithium metal electrode is used as the counter electrode (cathode), and a porous polyethylene (PE) separator is placed between the positive and negative electrodes. Finally, the electrolyte is added to complete the coin half cell.

[0164] (Evaluation of charging capacity)

[0165] The manufactured coin cells are charged (0.2 C) to 4.25 or 4.175 V using the CC-CV method at 25°C, and the terminal voltage is maintained until the termination current becomes 0.05 C to measure the final charge capacity.

[0166] Evaluation Example 6. Spec-In / Out Determination

[0167] For a specific cathode active material used as a reference, the voltage plateau of the H2 / H3 structural phase transition can be determined through measurement. Since the Spec In / Out range of charge capacity varies depending on whether the target upper charge limit voltage during battery design is above or below the voltage plateau, it is possible to determine whether to increase or decrease the input Li / M molar ratio within a specific range.

[0168] As a method for determining Spec-In / Out, the percentage of the expressed capacity relative to the theoretical capacity when the Li / M molar ratio is 1 can be used as a reference value. At this time, since the 4.175 V and 4.25 V of the coin battery standard have anode potentials (electrochemical potentials) similar to those of the cylindrical cell at 4.1 V and 4.2 V, the suitability of the cylindrical cell can also be determined based on the coin battery.

[0169] For example, when a coin cell is assembled with each positive electrode active material and lithium metal and the charge capacity value is measured four times when the cut-off voltage is 4.175 V, if it exceeds 70.5% of the theoretical capacity all four times, it is determined to be a Spec-In for a 4.1 V cylindrical cell. If the charge capacity is measured at a 4.25 V cut-off and is 78.5% or more of the theoretical capacity all four times, it can be determined to be a Spec-In for a 4.2 V cylindrical cell. If the standard capacity value is not achieved even once out of four times, it can be determined to be Spec-Out.

[0170] Referring to Table 1, when the upper charge limit voltage is 4.1 V, which is lower than the H2 / H3 structural transition voltage (e.g., 4.15 V - 4.175 V), increasing the Li / M input ratio reduces the nickel occupancy within the lithium layer, relatively lowers the H2 / H3 structural transition voltage, and increases the charge capacity. In this case, Example 1 with a small Li / M input ratio becomes the Spec-Out based on the charge capacity, and Example 2-5 with an increased Li / M input ratio becomes the Spec-In.

[0171] On the other hand, when the upper limit voltage of the charge is 4.2 V, which is higher than the H2 / H3 structural transition voltage (e.g., 4.15 V - 4.175 V), the charge capacity cannot be increased by lowering the structural transition voltage because the upper limit voltage is already higher than the H2 / H3 structural transition voltage. Rather, the charge capacity is reduced by reducing the number of transition metals contributing to the Redox reaction, and as a result, Example 5 with a large Li / M input ratio becomes the Spec-Out.

[0172] Figure 2 shows the nickel occupancy (Ni) of the lithium layer of the positive electrode active material according to one embodiment of the present invention. 2+ at Li site, Ni Li ) is a graph showing the grid volume V according to the equation.

[0173] Referring to Figure 2, Ni of the lithium layer 2+ is decreasing and Li + When the direction changes so that it completely enters the lithium layer (arrow direction in Fig. 2), the lattice volume V decreases, so that the transition metal is relatively Ni 3-x In Ni 3+ It can be seen that as the oxidation number increases, the unit cell volume changes in the direction of decreasing.

[0174] Figure 3 shows the nickel occupancy (Ni) of the lithium layer of the positive electrode active material according to one embodiment of the present invention. 2+ at Li site, Ni Li ) is a graph showing the Curie-Weiss temperature (T).

[0175] Referring to Figure 3, Ni of the lithium layer 2+ As the Curie-Weiss temperature decreases, the Curie-Weiss temperature tends to decrease. The Curie-Weiss temperature indicates the average strength of the magnetic interaction, and the Ni in the lithium layer 2+ The strength of the magnetic interaction between the magnetic atoms tends to change very sensitively depending on the nickel occupancy of the lithium layer. Therefore, the nickel occupancy of the lithium layer (Ni 2+ at Li site, Ni Li) according to the Curie-Weiss temperature of the lithium layer 2+ The cathode active material with controlled occupancy can be characterized.

[0176] FIG. 4 is a graph showing the crystalline size of the positive electrode active material for Example 1-5 (Sample No. 1-5) of the present invention.

[0177] Referring to Fig. 4, it is shown that as the input Li / M ratio increases across Examples 1-5 (corresponding to Sample No. 1-5), the grain size tends to increase based on the same sintering temperature. Therefore, it can be seen that the influence of process variables can be minimized by appropriately lowering the sintering temperature or adjusting the holding time to maintain a constant grain size.

[0178] FIG. 5 is a graph showing the microstrain of the positive electrode active material for Example 1-5 of the present invention (corresponding to Sample No. 1-5).

[0179] Referring to Figure 5, Ni of the lithium layer 2+ As the occupancy decreases, the microstrain tends to decrease. For example, in the case of an ideal perfect crystal, the microstrain has a value of 0. Therefore, based on this tendency, the Ni of the lithium layer 2+ Micro-deformation can be controlled by adjusting the occupancy rate.

[0180] As seen above, the present invention enables the production of battery cells that meet customer needs while maintaining the existing process parameters as similar as possible, thereby shortening the development period and reducing costs.

[0181] For example, the high nickel (High Nickel) NCM(A) layered cathode active material is synthesized using Ni 2+ It spontaneously occupies the Li layer (Ni 2+ Wow Li +) have similar atomic radii). Consequently, the Ni of the Li layer 2+ Occupancy affects the voltage at which the H2 / H3 structural transition at the terminal of the charge occurs. For example, Ni 2+ As the occupancy decreases, the H2 / H3 structural transition voltage decreases, and Ni 2+ As the occupancy increases, the H2 / H3 structural transition voltage tends to increase.

[0182] Based on these results, if the charging limit voltage required by the customer is lower than the H2 / H3 structural transition voltage (in the case of Table 1, 4.1 V as an example for a cylindrical battery), the input Li / M ratio is increased, and Ni 2+ The charging capacity can be increased by reducing the occupancy and lowering the H2 / H3 structural transition voltage. In the above embodiments, embodiment 1 is a Spec-Out case, and embodiments 2 to 5 are Spec-In cases.

[0183] In addition, when the charging upper limit voltage required by the customer is higher than the H2 / H3 structural transition voltage (in the case of Table 1, 4.2 V as an example for a cylindrical battery), there is no advantage in the charging capacity obtained by lowering the H2 / H3 structural transition voltage by increasing the input Li / M ratio, and rather, the charging capacity may be reduced by lowering the ratio of transition metals that undergo redox reaction. In the above examples, examples 1 to 4 are Spec-In cases, and example 5 is Spec-Out cases.

[0184] In summary, when manufacturing a lithium secondary battery including a layered high-nickel lithium transition metal composite oxide cathode active material, the voltage at which the H2 / H3 structural phase transition occurs can be controlled by controlling the molar ratio of lithium to the transition metal included in the cathode active material (Li / M molar ratio), and the charge capacity can be controlled by controlling the voltage at which the H2 / H3 structural phase transition occurs. In addition, the step of controlling the molar ratio of lithium to the transition metal included in the cathode active material (Li / M molar ratio) may include the steps of mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to the transition metal (Li / M molar ratio) becomes a specific value, the step of firing at a first firing temperature, and the step of firing at a second firing temperature higher than the first firing temperature.

[0185] Although the present disclosure has been described above with reference to embodiments thereof, it will be understood by those skilled in the art or having ordinary knowledge in the art that various modifications and changes to the various embodiments of the present disclosure may be made without departing from the technical scope of the various embodiments of the present disclosure as set forth in the claims below. Accordingly, the technical scope of the various embodiments of the present disclosure should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. As a layered structure high nickel lithium transition metal composite oxide cathode active material, The lattice volume V of the above positive electrode active material satisfies the following [Equation 1], A cathode active material characterized by a Curie-Weiss temperature T satisfying the following [Equation 2]: [Formula 1] 101.4 Å 3 ≤ V ≤ 101.75 Å 3 [Formula 2] 0K ≤ T ≤ 30K The lattice volume V of the above positive electrode active material is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

2. In paragraph 1, A cathode active material characterized in that the lattice volume V of the cathode active material satisfies the following [Formula 3]: [Formula 3] 101.5 Å 3 ≤ V ≤ 101.70 Å 3 3. In paragraph 1, A cathode active material characterized in that the Curie-Weiss temperature T of the cathode active material satisfies the following [Equation 4]: [Formula 4] 10K ≤ T ≤ 25K 4. In paragraph 1, A cathode active material comprising a lithium layer and a transition metal layer, wherein at least a portion of the lithium site of the lithium layer is occupied by nickel.

5. In paragraph 4, Nickel occupancy of the above lithium layer (Ni Li ) is 0.003 to 0.015, characterized in that the positive electrode active material.

6. In paragraph 4, Nickel occupancy of the above lithium layer (Ni Li ) is 0.005 to 0.012, characterized in that the positive electrode active material.

7. In paragraph 1, A cathode active material, characterized in that the crystal grain size of the cathode active material is 100 nm to 300 nm.

8. In paragraph 1, The above positive electrode active material is characterized by being represented by the following chemical formula 1: [Chemical Formula 1] Li a Ni 1-b-c-d Co b Mr c Q d O 2+δ In the above formula, Q is at least one element selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B), and 0.96≤a≤ 1.04, 0≤b≤0.3, 0≤c≤0.3, 0≤d≤0.1, 0≤b+c+d≤0.3, -0.1≤δ≤0.

1.

9. In paragraph 8, A positive electrode active material characterized in that 0≤b+c+d≤0.2 in the above chemical formula 1.

10. A lithium secondary battery characterized by comprising a positive electrode, a negative electrode, and an electrolyte including a positive electrode active material according to Article 1.

11. A method for manufacturing a layered high-nickel lithium transition metal composite oxide cathode active material, A step of mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to transition metal (Li / M molar ratio) is 0.96 to 1.04; A first firing step at a temperature of 300℃ to 500℃; and Secondary firing step at a temperature of 600℃ to 900℃; Including, The lattice volume V of the above positive electrode active material satisfies the following [Equation 1], A method for manufacturing a positive electrode active material, characterized in that the Curie-Weiss temperature T satisfies the following [Equation 2]: [Formula 1] 101.4 Å 3 ≤ V ≤ 101.75 Å 3 [Formula 2] 0K ≤ T ≤30K The above lattice volume V is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

12. A method for manufacturing a lithium secondary battery including a layered structure high nickel lithium transition metal composite oxide cathode active material, By controlling the molar ratio of lithium to transition metal (Li / M molar ratio) included in the above positive electrode active material, the voltage at which the H2 / H3 structural phase transition occurs is controlled, A method for manufacturing a lithium secondary battery, which controls the upper limit charge capacity during charging by controlling the voltage at which the H2 / H3 structural phase transition occurs.

13. In paragraph 12, The step of controlling the molar ratio of lithium to transition metal (Li / M molar ratio) included in the above positive electrode active material is: A step of mixing a lithium precursor and a transition metal precursor so that the molar ratio of lithium to transition metal (Li / M molar ratio) becomes a specific value; A step of firing at the first firing temperature; and A method for manufacturing a lithium secondary battery, comprising a step of firing at a secondary firing temperature higher than a primary firing temperature.

14. In paragraph 13, The lattice volume V of the above positive electrode active material is 101.4 Å 3 -101.75 Å 3 With values ​​between, The Curie-Weiss temperature T has a value between 0K and 30K, A method for manufacturing a lithium secondary battery, wherein the above lattice volume V is a value measured by X-ray powder diffraction (XRD), and the Curie-Weiss temperature is a value measured by a superconducting quantum interference device (SQUID).

15. In paragraph 12, A method for manufacturing a lithium secondary battery, wherein the positive electrode active material includes a lithium layer and a transition metal layer, and at least a portion of the lithium site of the lithium layer is occupied by nickel.

16. In paragraph 15, Nickel occupancy of the above lithium layer (Ni Li ) is 0.003 to 0.015, a method for manufacturing a lithium secondary battery.

17. In paragraph 12, A method for manufacturing a lithium secondary battery, wherein the crystal grain size of the positive electrode active material is 100 nm to 300 nm.

18. In paragraph 12, The above positive electrode active material is represented by the following chemical formula 1, and is a method for manufacturing a lithium secondary battery: [Chemical Formula 1] Li a Ni 1-b-c-d Co b Mr c Q d O 2+δ In the above formula, Q is at least one element selected from zirconium (Zr), titanium (Ti), tungsten (W), aluminum (Al), and boron (B), and 0.96≤a≤ 1.04, 0≤b≤0.3, 0≤c≤0.3, 0≤d≤0.1, 0≤b+c+d≤0.3, -0.1≤δ≤0.1.

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