Method for predicting secondary battery performance from positive electrode active material, positive electrode active material, positive electrode, and secondary battery

Abstract

The present invention relates to a method for predicting performance of a secondary battery, the method comprising the steps of: manufacturing a cathode comprising a cathode active material comprising an overlithiated manganese-rich oxide containing 50 mol% or more but less than 100 mol% of manganese on the basis of the total metal content excluding lithium; preparing a cathode sample by milling the cathode; obtaining a cross-sectional image by photographing the cathode sample and a cross-section with a scanning electron microscope; selecting a cathode active material particle region from the cross-sectional image, followed by measuring an average pore area ratio according to an ECD value range of the cross-section of the selected cathode active material particle; and predicting performance of a secondary battery comprising the cathode from the average pore area ratio according to the ECD value range of the cross-section of the cathode active material particle, wherein the ECD represents the diameter of a circle having the same area as the cross-sectional area of the particle, and the pore area ratio represents an area ratio of pores to the cross-sectional area of the cathode active material particle.

Description

Method for predicting secondary battery performance from positive electrode active material, positive electrode active material, positive electrode and secondary battery

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0135855 filed October 7, 2024 and Korean Patent Application No. 10-2025-0131694 filed September 15, 2025, and all contents disclosed in the documents of said Korean patent applications are incorporated herein as part of this specification.

[0003] The present invention relates to a method for predicting the performance of a secondary battery from a positive electrode active material, a positive electrode active material having excellent battery capacity and resistance performance, and a positive electrode and a secondary battery including the same.

[0004] Recently, with the increasing technological development and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source is rapidly increasing.

[0005] Such secondary batteries generally consist of a positive electrode, a negative electrode, a separator, and an electrolyte. In this case, the electrochemical performance of the secondary battery is influenced by these components, among which the positive active material included in the positive electrode has a significant influence.

[0006] Specifically, pores exist within the positive electrode active material particles, and it is known that the area, quantity, and distribution of the pores have a significant impact on the electrochemical performance of the secondary battery.

[0007] Accordingly, research is being conducted to verify the correlation between the pores contained within the cathode active material and battery performance, such as capacity and resistance. For example, porosity is analyzed using SEM images of cross-sectionally processed cathodes; however, this method suffers from low reliability of results and significant deviations because the porosity of the surface and interior of the active material is represented as a single value that is mixed depending on the processing location.

[0008] To solve this problem, the particle size in the SEM image is D 50 Select only positive active material particles close to (D 50 We discussed a method to obtain highly reliable and low-variance results by analyzing porosity through filtering; however, since the parameters of the particles analyzed are limited, this method is highly likely to fail to represent the characteristics of the entire material.

[0009] Therefore, there is a need to develop a technology that clearly analyzes these correlations to predict the electrochemical performance of secondary batteries with high reliability and capable of representing the overall characteristics of the material.

[0010] The present invention aims to provide a method for predicting the performance of a secondary battery by analyzing the pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the positive electrode active material particles through a cross-sectional image of the positive electrode taken with an electron microscope.

[0011] In addition, the purpose is to provide a positive electrode active material having optimal conditions identified in the process of deriving the above prediction method, and a positive electrode and a secondary battery containing the same.

[0012] One embodiment of the present invention comprises: a) a step of manufacturing a positive electrode comprising a positive electrode active material comprising a lithium manganese-rich oxide comprising 50 mol% or more and less than 100 mol% of manganese based on the total metal content excluding lithium;

[0013] b) a step of milling the anode to produce an anode sample;

[0014] c) a step of obtaining a cross-sectional image by photographing the cross-section of the anode sample using a scanning electron microscope (SEM);

[0015] d) a step of selecting a region of positive active material particles in the cross-sectional image above, and then measuring the average pore area ratio according to the range of ECD (equilibrium circle diameter) values ​​of the selected positive active material particle cross-section; and

[0016] e) a step of predicting the performance of a secondary battery including the anode from the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the anode active material particle; and

[0017] The above ECD (equilibrium circle diameter) represents the diameter of a circle having an area equal to the cross-sectional area of ​​the particle, and

[0018] The above pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the positive active material particles, thereby providing a method for predicting the performance of a secondary battery.

[0019] Another embodiment of the present invention is a positive electrode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium, wherein

[0020] When analyzing the cross-section of the above-mentioned cathode active material, the average pore area ratio of particle cross-sections with an ECD (equilibrium circle diameter) value greater than 2㎛ and less than or equal to 4㎛ is 0.02 or greater, and

[0021] The above ECD (equilibrium circle diameter) provides an anode active material representing the diameter of a circle having an area equal to the cross-sectional area of ​​the particle.

[0022] Another embodiment of the present invention provides a positive electrode comprising the positive electrode active material.

[0023] Another embodiment of the present invention provides a secondary battery comprising the anode.

[0024] The present invention relates to a method for predicting the performance of a secondary battery from a positive electrode active material, wherein reliable secondary battery performance prediction results can be obtained by utilizing the average pore area ratio according to the range of ECD values ​​of selected positive electrode active material particles in an SEM cross-sectional image.

[0025] In addition, a secondary battery with excellent battery capacity and resistance performance can be manufactured by using a positive electrode active material having optimal conditions identified in the process of deriving the above prediction method.

[0026] Figure 1 shows a cross-sectional image taken in an experimental example of the present invention and an SEM image showing a selected region of positive active material particles in the cross-sectional image.

[0027] Figure 2 is a graph showing the ECD values ​​and pore area ratio (PAR) of particle cross-sections calculated in the experimental example of the present invention.

[0028] Figure 3 is a graph showing the resistance characteristics of a lithium secondary battery evaluated according to an experimental example of the present invention.

[0029] Figure 4 is a graph showing the discharge capacity of a lithium secondary battery evaluated according to an experimental example of the present invention.

[0030] Hereinafter, the present invention will be described in more detail to aid in understanding the invention.

[0031] Terms and words used in this specification and claims shall not be interpreted as being limited to their ordinary or dictionary meanings, but shall be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0032] The terms used in this specification are used merely to describe exemplary embodiments and are not intended to make the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0033] In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should not be understood as precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0034] In the following specifications, “secondary particle” refers to a particle formed by the aggregation of tens to hundreds of multiple primary particles. More specifically, the secondary particle is an aggregate of 40 or more primary particles.

[0035] The term “particle” as used below may include any one or all of single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0036] Also, below, “D 50 " refers to the particle size at the 50% reference of the volume cumulative particle size distribution of the positive active material. The above D 50 It can be measured using the laser diffraction method. For example, after dispersing the positive active material powder in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), irradiated with ultrasound of about 28 kHz at an output of 60 W, obtained a volume cumulative particle size distribution graph, and then measured by determining the particle size corresponding to 50% of the volume cumulative amount.

[0037] In the following, the “Pore Area Ratio (PAR)” is obtained by acquiring a cross-sectional image of the anode sample using a scanning electron microscope (SEM), selecting a region of anode active material particles from the obtained cross-sectional image, and measuring the ratio of the pore area to the cross-sectional area of ​​the selected particles (pore area / particle cross-sectional area).

[0038] Additionally, “ECD (equilibrium circle diameter)” below refers to the diameter value of a circle having an area equal to the cross-sectional area of ​​the selected particle.

[0039] Specific embodiments of the invention will be described in detail below.

[0040]

[0041] Method for predicting the performance of secondary batteries

[0042] While conducting research on the correlation between the pores of a positive electrode active material and the performance of a battery, the inventors of this application analyzed the cross-sectional area of ​​the particle cross-section of the positive electrode active material and the pore area obtained through a scanning electron microscope (SEM), and confirmed that the performance of a secondary battery can be predicted from the pore area ratio (pore area / particle cross-sectional area) according to the range of the equilibrium circle diameter (ECD) value. The prediction method of the present invention is derived by analyzing the distribution locations of pores existing within the positive electrode active material particles according to the range of the equilibrium circle diameter (ECD) value; compared to existing analysis methods that represent a single value without considering the distribution locations of pores, it has higher reliability, and D 50 Since filtering is not performed, the parameters of the analyzed particles are not limited, allowing for results that represent the entire group of cathode active materials used in the analysis.

[0043] The method for predicting the performance of a secondary battery according to the present invention is,

[0044] a) a step of manufacturing a cathode comprising a cathode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium;

[0045] b) a step of milling the anode to produce an anode sample;

[0046] c) a step of obtaining a cross-sectional image by photographing the cross-section of the anode sample using a scanning electron microscope (SEM);

[0047] d) a step of selecting a region of positive active material particles in the cross-sectional image above, and then measuring the average pore area ratio according to the range of ECD (equilibrium circle diameter) values ​​of the selected positive active material particle cross-section; and

[0048] e) a step of predicting the performance of a secondary battery including the anode from the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the anode active material particle; and

[0049] The above ECD (equilibrium circle diameter) represents the diameter of a circle having an area equal to the cross-sectional area of ​​the particle, and

[0050] The above pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the anode active material particle.

[0051] The method for predicting the performance of a secondary battery according to the present invention will be explained in detail below.

[0052] a) Step of manufacturing the anode

[0053] First, a slurry obtained by dispersing a positive active material and, optionally, one or more of a binder, a conductive material, and a dispersant in a dispersion medium is applied to at least one surface of a positive current collector and dried to form a positive active material layer, thereby manufacturing a positive electrode. Specific descriptions of the positive current collector, positive active material, binder, conductive material, dispersant, and dispersion medium used in manufacturing the positive electrode will be provided later.

[0054] b) Step of preparing the anode sample

[0055] An anode sample for cross-sectional analysis is prepared by milling the anode prepared above using an ion milling device (e.g., Hitachi IM5000).

[0056] c) Step of acquiring a cross-sectional image of the anode

[0057] A cross-sectional image is obtained by photographing the cross-section of the anode sample milled as described above using a scanning electron microscope (SEM). The obtained cross-sectional image represents a cross-section of the anode sample cut in the thickness direction.

[0058] d) A step of measuring the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the positive active material particles.

[0059] By digitizing the cross-sectional image captured in step c) above, selecting the region of the positive active material particles, and analyzing it at the pixel level (image processing), the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the positive active material particles can be measured. The pixel is the smallest unit of a digital image and represents the actual area, and each pixel represents the same area.

[0060] The digitized cross-sectional image is scaled based on the resolution of the SEM to convert the number of pixels into an actual area. Subsequently, the pore area ratio is calculated by dividing the total area of ​​pixels recognized as pores by the total area of ​​all pixels (particle area). At this time, each pixel of the pore can be binary processed to distinguish between black (pore) and white (particle) with a value of 0 or 1.

[0061] This measurement process can be performed through software or program code capable of image processing and analysis. According to an embodiment, it can be performed using Python programming.

[0062] In addition, the ECD (equilibrium circle diameter) value of each particle can be calculated from the particle area calculated above, and based on this, the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cathode active material particle cross-section can be calculated.

[0063] Figure 1 shows a cross-sectional image obtained in an experimental example of the present invention described below, and an SEM image of a selected region of positive electrode active material particles in the cross-sectional image. Referring to the image in Figure 1, the round gray region represents the positive electrode active material, the black region located inside the gray region represents the pore area, and the region outside the positive electrode active material corresponds to the binder, conductive material, and dispersant. Additionally, the part marked in red in Figure 1 represents the selected region of positive electrode active material particles.

[0064] The above-mentioned positive active material particle region refers to the cross-section of a positive active material particle existing within the positive active material layer selected in the cross-sectional image, and the cross-section of the positive active material particle refers to the cross-section of the positive active material particle cut in the thickness direction. The size of the cross-section of the positive active material particle shown in the captured cross-sectional image varies depending on the location where the particle is processed. Specifically, the size of the cross-section is largest when the processed location passes through the center of the particle, and the size of the cross-section decreases as it moves from the center of the particle closer to the edge of the particle. In the range of ECD (equilibrium circle diameter) values ​​to be described later, it can be interpreted that the cross-sectional processing location approaches the edge of the particle in the order of greater than 8㎛ and less than or equal to 10㎛, greater than 6㎛ and less than or equal to 8㎛, and greater than 2㎛ and less than or equal to 4㎛.

[0065] FIG. 2 is a graph showing the ECD values ​​and pore area ratio (PAR) of particle cross-sections calculated through the method described above in one experimental example of the present invention described below.

[0066] Since the above-mentioned positive active material particles are not in the shape of a perfect sphere, the cross-section cut in the thickness direction does not exhibit the shape of a perfect circle, which presents a problem in determining the diameter of the particle cross-section. For this reason, in the present invention, the cross-sectional area of ​​the selected positive active material particle is measured and converted into an ECD (equilibrium circle diameter) value representing the diameter of a circle having the same area, and used.

[0067] As described above, the equilibrium circle diameter (ECD) values ​​obtained above are divided into ranges to calculate the average pore area ratio of the cathode active material particle cross-sections corresponding to each range. This calculation is also performed using the program used in the image processing described above. The average pore area ratio according to the range of the ECD values ​​of the cathode active material particle cross-sections is used to predict the capacity and resistance performance of the secondary battery.

[0068] According to one embodiment of the present invention, step d) includes measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the anode active material particle cross-section is greater than 2㎛ and less than or equal to 4㎛.

[0069] In addition, according to one embodiment of the present invention, step d) may further include at least one of the following steps: measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the positive active material particle cross-section is greater than 6 μm and less than or equal to 8 μm; and measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the positive active material particle cross-section is greater than 8 μm and less than or equal to 10 μm.

[0070] e) Step of predicting the performance of the secondary battery

[0071] The inventors manufactured a secondary battery containing a positive electrode prepared in the experimental example described below and measured the capacity and resistance performance of the battery. By analyzing the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the positive electrode active material particle cross-section obtained in step d) and the measured results, they confirmed the correlation and were able to predict the performance of the secondary battery.

[0072] Specifically, looking at one embodiment of the present invention, it can be predicted that the battery will have excellent capacity and resistance performance when the average pore area ratio of particle cross-sections with an ECD (equilibrium circle diameter) value of 2㎛ or more and 4㎛ or less is 0.02 or more. Since the electrochemical reaction occurs on the surface of the particle, it is more significantly affected by the amount of pores distributed on the outer edge of the particle than by the center of the particle. Therefore, when the average pore area ratio of particle cross-sections with an ECD value of 2㎛ or more and 4㎛ or less satisfies the above range, the electrochemical reaction occurs rapidly, and a battery with excellent capacity and resistance performance can be manufactured.

[0073] According to another embodiment of the present invention, when the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value greater than 6㎛ and less than or equal to 8㎛ is 0.03 or higher, it can be predicted that the battery will have excellent capacity and resistance performance.

[0074] In addition, in one embodiment, when the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value greater than 8㎛ and less than or equal to 10㎛ of the positive active material particle cross-section is 0.04 or higher, it can be predicted that the battery will have excellent capacity and resistance performance.

[0075]

[0076] positive electrode active material

[0077] In the process of deriving the performance prediction method for the above secondary battery, a positive electrode active material having excellent battery performance was identified.

[0078] A positive electrode active material according to one embodiment of the present invention is a positive electrode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium, wherein when the positive electrode active material is analyzed cross-sectionally, the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value greater than 2 μm and less than or equal to 4 μm is 0.02 or more, preferably 0.03 or more, and more preferably 0.05 or more, wherein the ECD (equilibrium circle diameter) represents the diameter of a circle having an area equal to the cross-sectional area of ​​the particle. When the average pore area ratio of particle cross-sections having an ECD value greater than 2 μm and less than or equal to 4 μm satisfies the above range, an electrochemical reaction occurs rapidly, and a battery with excellent capacity and resistance performance can be manufactured.

[0079] The cross-sectional analysis of the above positive active material is performed through steps a) to d).

[0080] According to another embodiment, when analyzing the cross-section of the positive active material, the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value of 6㎛ or more and 8㎛ or less may be 0.03 or more, preferably 0.05 or more, and more preferably 0.07 or more.

[0081] In one embodiment of the present invention, when analyzing the cross-section of the positive active material, the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value of 8㎛ or more and 10㎛ or less may be 0.04 or more, preferably 0.07 or more, and more preferably 0.10 or more.

[0082] In one embodiment of the present invention, the positive electrode active material comprises the lithium-rich manganese oxide. The lithium-rich manganese oxide has a structure in which a layered lithium metal oxide and a lithium manganese oxide (Li2MnO3) having a rock salt structure are mixed, and the lithium manganese oxide is additionally activated during the activation process and / or charge / discharge process, and the resulting manganese redox reaction can contribute to capacity development.

[0083] In a specific embodiment, the lithium-rich manganese oxide may be represented by the following chemical formula 1.

[0084] [Chemical Formula 1]

[0085] Li a [Mn 1-b-c Ni b M c ] 2-a O2

[0086] In the above chemical formula 1,

[0087] M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr, and

[0088] a, b, and c are the atomic fractions of independent elements, 1 <a, 0≤b≤0.5, 0≤c≤0.5, 0<b+c≤0.5이다.

[0089] Specifically, the above a is 1 as the molar ratio of Li in the lithium-over-manganese-rich oxide. <a, 1.1≤a≤1.5, 또는 1.1≤a≤1.3일 수 있다. a가 상기 범위를 만족할 때, 고용량을 구현할 수 있다.

[0090] The above b is the molar ratio of Ni in the lithium manganese-rich oxide, and may be 0≤b≤0.5, 0.1≤b≤0.4, or 0.2≤b≤0.4.

[0091] The above c is the molar ratio of doping element M in the lithium-rich manganese oxide, and may be 0≤c≤0.5, 0≤c≤0.3, or 0≤c≤0.1. The above doping element M may be, for example, Co, and if the content of the doping element is too high, it may not only adversely affect the capacity of the active material but also increase the oxygen oxidation / reduction reaction, which may lead to gas generation and intensify the degradation of the cathode active material, thereby potentially degrading the lifespan characteristics.

[0092] The above 1-bc is the molar ratio of Mn in the lithium manganese-rich oxide, and may be 0.5≤1-bc<1, 0.5≤1-bc≤0.8, or 0.5≤1-bc≤0.7. When 1-bc is less than 0.5, that is, when b+c is greater than 0.5, the proportion of the rock salt phase becomes too small, and the cathode irreversible compensation and capacity improvement effects are negligible.

[0093] Meanwhile, in the lithium-rich manganese oxide represented by the above chemical formula 1, the ratio of the moles of Li to the moles of all metal elements (Me) excluding Li (Li / Me) may be 1.2 to 1.5, or 1.25 to 1.5, or 1.30 to 1.45. When the Li / Me ratio satisfies the above range, excellent rate characteristics and capacity characteristics are exhibited. If the Li / Me ratio is too high, electrical conductivity decreases and the rock salt phase (Li2MnO3) increases, which may accelerate the degradation rate, and if it is too low, the effect of improving energy density is negligible.

[0094] Meanwhile, the composition of the above-mentioned lithium manganese-rich oxide may also be represented by the following chemical formula 2.

[0095] [Chemical Formula 2]

[0096] X*Li2MnO3· (1-X)*Li[Ni 1-y-z Mn y M z ]O2

[0097] In the above chemical formula 2,

[0098] M is one or more selected from the group consisting of Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, B, W, Ga, In, Ru, Nb, Sn, Sr and Zr, and

[0099] 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.5.

[0100] The above X represents the ratio of the Li2MnO3 phase (rock salt structure compound phase) in the lithium-over-manganese-rich oxide, and may be 0.2≤X≤0.5, 0.25≤X≤0.5, or 0.25≤X≤0.4. When the ratio of the Li2MnO3 phase in the lithium-over-manganese-rich oxide satisfies the above range, high capacity characteristics can be achieved.

[0101] The above y is LiM'O2(M'= [Ni 1-y-z Mn y M z ]; in the layered structure compound phase), the molar ratio of Mn can be 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0102] The above z is LiM'O2(M'= [Ni 1-y-z Mn y M z ]; in the layered structure compound phase), the molar ratio of doping element M can be 0≤z≤0.5, 0≤z≤0.3, or 0≤z≤0.1.

[0103] According to one embodiment of the present invention, the positive electrode active material may be in the form of secondary particles in which a plurality of primary particles are aggregated, and the average particle size (D) of the secondary particles 50 ) can be 6㎛ to 10㎛, preferably 8㎛ to 10㎛.

[0104] Meanwhile, the size of the primary particle may be 100 nm to 300 nm, preferably 100 nm to 250 nm, and more preferably 100 nm to 200 nm.

[0105] Meanwhile, the above-mentioned lithium manganese-rich oxide can be prepared by mixing a transition metal precursor and a lithium raw material and then calcining. However, this manufacturing method may follow the general manufacturing process and conditions of lithium manganese-rich oxide known previously. In this case, to prepare a lithium manganese-rich oxide that satisfies the average pore area ratio of particle cross-sections according to the range of the ECD value, the concentration of the base included in the mixture for the synthesis of the lithium manganese-rich oxide precursor, the synthesis time, stirring speed and temperature, and calcination temperature can be controlled.

[0106] The mixture for synthesizing the above precursor includes a metal solution, a complexing agent such as ammonium ions, and a base such as NaOH. At this time, the initial base concentration during synthesis and changes in the base concentration over time may affect the distribution of pores inside the particles. To prepare the lithium-rich manganese oxide of the present invention, the initial base concentration during synthesis can be controlled to a pH of 10 or higher and less than 12, specifically to a pH of 11 or higher and less than 12, and more specifically to a pH of 11 or higher and less than 11.5. Additionally, the distribution location of pores within the particles can be controlled by adjusting the base concentration over time. For example, if the base concentration decreases as time passes, particles with more pores distributed at the edges than at the center of the particles can be synthesized.

[0107] In addition, the calcination temperature may be in the range of 800°C to 1,000°C, specifically 800°C to 950°C. Since a higher calcination temperature induces the growth of primary particles and forms dense cathode active material particles, the calcination temperature can be controlled to the above range to obtain the lithium-rich manganese oxide of the present invention.

[0108]

[0109] anode

[0110] A positive electrode comprising the aforementioned positive electrode active material is described. The positive electrode may be manufactured by applying a positive electrode slurry, in which the positive electrode active material is dispersed in a dispersion medium, onto a positive electrode current collector and then drying it.

[0111] In addition to the cathode active material containing the lithium-rich manganese oxide, the above-mentioned anode slurry may optionally further include a binder, a conductive material, a dispersant, etc., as needed.

[0112] The above positive current collector may include a highly conductive metal, and is not particularly limited as long as it facilitates the adhesion of the positive active material layer and is non-reactive within the voltage range of the battery. The above positive current collector may be, for example, stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc. Additionally, the above positive current collector may typically have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive active material. It may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

[0113] The above-mentioned cathode active material may further include conventional cathode active materials in addition to the aforementioned lithium-rich manganese oxide, for example, LCO (LiCoO2), LNO (LiNiO2), LFP (LiFePO4), and NCM (Li[Ni p Co q Mn r1 It may further include one or more positive electrode active materials selected from the group consisting of ]O2, 0<p<1, 0<q<1, 0<r1<1, p+q+r1=1), but preferably may include at least 70 weight% of lithium-rich manganese oxide based on the weight of the total positive electrode active material, and may be composed only of lithium-rich manganese oxide.

[0114] At this time, the positive active material may be included in an amount of 80% to 99% by weight, more specifically 90% to 98% by weight, based on the total weight of the positive active material layer.

[0115] The above conductive material is used to impart conductivity to the electrode, and in the battery being constructed, it may be used without special limitations as long as it possesses electronic conductivity without causing chemical changes. 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, thermal black, and carbon fibers; metal powder or metal fibers such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and one of these alone or a mixture of two or more may be used. The above conductive material may be included in an amount of 0.01% to 10% by weight, preferably 0.1% to 9% by weight, and more preferably 0.1% to 5% by weight, based on the total weight of the positive electrode active material layer.

[0116] The above binder serves to improve the adhesion between positive active material particles and the adhesion between the positive active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which hydrogens thereof are substituted with Li, Na, or Ca, or various copolymers thereof, and one of these alone or a mixture of two or more may be used. The above binder may be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0117] The dispersion medium may be a solvent commonly used in the relevant technical field, and may use NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto. The dispersion medium may be included in an amount such that the anode slurry composition has an appropriate viscosity and solid content. Specifically, the dispersion medium may be included in an amount such that the solid content in the slurry is 40% to 75% by weight, more specifically 40% to 65% by weight.

[0118]

[0119] secondary battery

[0120] Next, a secondary battery according to the present invention will be described. Specifically, a lithium secondary battery, which is a representative example of a secondary battery, comprises the aforementioned positive electrode, a negative electrode positioned opposite to the positive electrode, and a separator and an electrolyte interposed between the positive electrode and the negative electrode.

[0121] The above cathode can be manufactured by applying a cathode slurry, in which a cathode active material is dispersed in a dispersion medium, onto a cathode current collector and then drying it.

[0122] In addition to the cathode active material, the above cathode slurry may optionally include a binder, conductive material, dispersant, etc., as needed.

[0123] The above-mentioned negative current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. In addition, the above-mentioned negative current collector may typically have a thickness of 3 μm to 500 μm, and, similar to the positive current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding strength of the negative active material. For example, it may be used in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0124] In one embodiment of the present invention, the negative electrode active material may be a compound capable of reversible intercalation and deintercalation of lithium. Specific examples include 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 alloys, Sn alloys, or Al alloys; and SiO₂ βExamples include metal oxides capable of doping and dedoping lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites comprising the metal compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more of these may be used.

[0125] In addition, a metallic lithium thin film may be used as the above-mentioned negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon may be used as carbon materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include amorphous, plate-like, flake-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature heat-treated carbons such as petroleum or coal tar pitch-derived cokes.

[0126] The above-mentioned negative electrode active material may be included in an amount of 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight based on the total weight of the negative electrode active material layer.

[0127] The above binder is a component that assists in the bonding between the conductive material, the active material, and the current collector, and can typically be added in an amount of 0.1% to 10% by weight based on the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0128] The above conductive material is a component for further improving the conductivity of the negative electrode active material and may be included in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight based on the total weight of the negative electrode active material layer. Such conductive material is not particularly limited as long as it is conductive without causing chemical changes in the battery, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powders such as aluminum or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; conductive materials such as polyphenylene derivatives may be used.

[0129] The dispersion medium may be a solvent commonly used in the relevant technical field, and may use NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto. The dispersion medium may be included in an amount such that the cathode slurry composition has an appropriate viscosity and solid content. Specifically, the dispersion medium may be included in an amount such that the solid content in the slurry is 40% to 75% by weight, more specifically 40% to 65% by weight.

[0130] Meanwhile, the separator in the above-mentioned lithium secondary battery separates the negative electrode and the positive electrode and provides a pathway for the movement of lithium ions. Any separator typically used in lithium secondary batteries can be used without special restrictions, and it is particularly desirable that it has low resistance to the movement of electrolyte ions and excellent electrolyte moisture retention capacity. Specifically, a porous polymer film, such as a porous polymer film made from a polyolefin-based polymer like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber, may be used. Furthermore, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and it may optionally be used in a single-layer or multi-layer structure.

[0131] In addition, examples of electrolytes that can be used in the manufacture of lithium secondary batteries include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, molten inorganic electrolytes, etc., but are not limited to these.

[0132] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0133] The above organic solvent may be used without special restrictions as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the above organic solvent may include ester-based solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; and aromatic hydrocarbon-based solvents such as benzene and fluorobenzene. Carbonate-based solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double bond, a directional ring, or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes may be used. Among these, a carbonate-based solvent is preferred, 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 low-viscosity linear carbonate-based compound (e.g., ethylmethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) is more preferred.

[0134] The above lithium salt may be used without special restrictions as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, as the anion of the above lithium salt, F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may be at least one selected from the group consisting of, and the lithium salt is, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2) 2. LiCl, LiI, or LiB(C2O4)2, etc., may be used. It is preferable to use the lithium salt in a concentration range of 0.1M to 4.0M, preferably 0.5M to 3.0M, and more preferably 1.0M to 2.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, so it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0135] In addition to the above electrolyte components, the above electrolyte may further include one or more additives for the purpose of improving the lifespan characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery, such as, for example, a haloalkylene carbonate-based compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, triamide hexaphosphate, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, the additive may be included in an amount of 0.1 to 10 weight% based on the total weight of the electrolyte.

[0136] The above secondary battery may follow the configuration of a general secondary battery, except that the aforementioned lithium-rich manganese oxide is used as the positive electrode active material. For example, the above secondary battery may be manufactured by sequentially stacking and drying an electrode assembly by placing a separator between a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, inserting the assembly into a case, and then optionally injecting an electrolyte to seal it. The lithium secondary battery may be a cylindrical, prismatic, coin-type, or pouch-type battery.

[0137]

[0138] Preferred embodiments are presented below to aid in understanding the invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such changes and modifications fall within the scope of the appended claims.

[0139]

[0140] [Experimental Example]

[0141] Preparation of anode samples and measurement of average pore area ratio according to the range of ECD values

[0142] Example 1.

[0143] The precursor for the synthesis of lithium-over-manganese-rich oxide was prepared by maintaining the base concentration of the mixture constant at pH 11.5, and the prepared precursor was used to Li 1.130 Mn 0.561 Ni 0.304 Co 0.004 An O2-composition lithium manganese-rich oxide was prepared.

[0144] A cathode slurry was prepared by adding the lithium-rich manganese oxide prepared above as a cathode active material, Li435 (DENKA) as a conductive material, KF9700 (KUREHA) as a binder, and BM-740H (ZEON) as a dispersant to NMP, a solvent, in a weight ratio of 96.25:1.5:2.1:0.15. The cathode slurry was coated onto an Al thin film with a thickness of 20 μm and dried to produce a cathode.

[0145] An anode sample for cross-sectional analysis was prepared by ion milling the manufactured anode using an ion milling device (Hitachi, IM5000) and Ar ion milling (Voltage: 6kV, Ion beam current: 150µA).

[0146] Subsequently, a cross-sectional image of the anode sample was captured using an SEM (JEOL, IT-800), and the region of the anode active material particles was selected from the obtained cross-sectional image. The captured cross-sectional image is shown in Fig. 1 as described above.

[0147] Next, image processing was performed to obtain information regarding the pores. Specifically, the cross-sectional area of ​​the selected cathode active material particle was calculated by determining the number of pixels included in the cross-section, and the diameter of a circle with the same area (ECD) was calculated. Additionally, the pore area was calculated by determining the number of pixels corresponding to the pores within the particle cross-section. Furthermore, the pore area ratio (pore area / particle cross-sectional area) was calculated from the particle cross-sectional area and the pore area.

[0148]

[0149] Example 2.

[0150] The initial base concentration of the mixture for the synthesis of the precursor of lithium-over-manganese-rich oxide was adjusted to pH 11.5, and the precursor was prepared by gradually decreasing the base concentration over time; and using the prepared precursor, Li 1.130 Mn 0.561 Ni 0.304 Co 0.004 An O2-composition lithium manganese-rich oxide was prepared.

[0151] A cathode was prepared in the same manner as in Example 1, except that the lithium-rich manganese oxide prepared above was used as the cathode active material, and the ECD value and pore area ratio were calculated in the same manner.

[0152]

[0153] Comparative Example 1.

[0154] A precursor was prepared by maintaining the base concentration of the mixture for the synthesis of lithium-over-manganese-rich oxide precursors at a constant pH of 12, and the prepared precursor was used to Li 1.130 Mn 0.561 Ni 0.304 Co 0.004 An O2-composition lithium manganese-rich oxide was prepared.

[0155] The ECD value and pore area ratio were calculated using the same method, except that the lithium-rich manganese oxide prepared above was used as the positive electrode active material.

[0156]

[0157] Based on the ECD values ​​and pore area ratios obtained in Example 1, Example 2 and Comparative Example 1 above, the ECD values ​​were divided into ranges of greater than 2㎛ and less than or equal to 4㎛, greater than 6㎛ and less than or equal to 8㎛, and greater than 8㎛ and less than or equal to 10㎛. The average pore area ratio of the cross-sections of the cathode active material particles corresponding to each range was calculated, and the results are shown in Table 1 below.

[0158] ECD Value Range Average Pore Area Ratio Example 1 Comparative Example 1 Example 22㎛ > 4㎛ ≤ 0.05 0.01 0.066㎛ > 8㎛ ≤ 0.07 0.02 0.138㎛ > 10㎛ ≤ 0.10 0.03 0.12

[0159] Battery Manufacturing and Performance Evaluation

[0160] A coin cell was prepared by mixing the anode prepared in Example 1, Example 2, or Comparative Example 1, a Li cathode, polyethylene (PE) as a separator, EC and EMC as an electrolyte in a volume ratio of 3:7 (EC:EMC), and adding 1M LiPF6, FEC (fluoroethylene carbonate) and LiBF4 (Lithium tetrafluoroborate) as additives at 3 wt% and 0.5 wt% of the total weight of the electrolyte, respectively.

[0161] A coin cell prepared including the anode prepared in Example 1, Example 2, or Comparative Example 1 was activated at 45°C under conditions of 0.1C and 2.0V-4.65V, and then a charge / discharge cycle was performed at 25°C under conditions of 0.33C and 2.5V-4.4V. Subsequently, the resistance characteristics of the lithium secondary battery were evaluated and are shown in Fig. 3, and the discharge capacity was evaluated and is shown in Fig. 4. In addition, the resistance value and discharge capacity at SOC 50% were measured and are shown in Table 2 below.

[0162] Example 1 Comparative Example 1 Example 2 Discharge Capacity [mAh / g] 207.5 203.9 206.9 SOC 50% Resistance [Ω] 12.6 9 17.0 112.7

[0163] Referring to Tables 1 and 2 above, it was confirmed that the batteries of Example 1 and Example 2, which have an average pore area ratio of 0.02 or higher when the ECD value range of the cross-section of the positive active material particles is greater than 2㎛ and less than 4㎛, have superior capacity and resistance performance compared to the battery of Comparative Example 1, which has an average pore area ratio of less than 0.02 when the ECD value range of the cross-section of the positive active material particles is greater than 2㎛ and less than 4㎛.

[0164] In addition, through the above experimental example, it was confirmed that it is possible to predict the performance of a battery by dividing the range of ECD values ​​of the cross-section of the positive active material particles and analyzing the average pore area ratio of each range.

Claims

1. As a method for predicting the performance of a secondary battery, a) a step of manufacturing a cathode comprising a cathode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium; b) a step of milling the anode to produce an anode sample; c) a step of obtaining a cross-sectional image by photographing the cross-section of the anode sample using a scanning electron microscope (SEM); d) a step of selecting a region of positive active material particles in the cross-sectional image above, and then measuring the average pore area ratio according to the range of ECD (equilibrium circle diameter) values ​​of the selected positive active material particle cross-section; and e) a step of predicting the performance of a secondary battery including the anode from the average pore area ratio according to the range of the ECD (equilibrium circle diameter) values ​​of the cross-section of the anode active material particle; and The above ECD (equilibrium circle diameter) represents the diameter of a circle having an area equal to the cross-sectional area of ​​the particle, and A method for predicting the performance of a secondary battery, wherein the above pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the positive active material particle.

2. In Paragraph 1, A method for predicting the performance of a secondary battery, wherein the above-mentioned cross-section of the positive active material particle refers to a cross-section obtained by cutting the positive active material particle in the thickness direction.

3. In Paragraph 1, The above step d) includes the step of measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the cathode active material particle cross-section is greater than 2㎛ and less than or equal to 4㎛, and A method for predicting the performance of a secondary battery, wherein the average pore area ratio according to the range of ECD (equilibrium circle diameter) values ​​of the cross-section of the positive active material particles is used to predict the capacity and resistance performance of the battery.

4. In Paragraph 3, A method for predicting the performance of a secondary battery, wherein the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value of 2㎛ or more and 4㎛ or less of the above positive active material particle cross-section is 0.02 or higher.

5. In Paragraph 3, The above step d) further includes the step of measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the cathode active material particle cross-section is greater than 6㎛ and less than or equal to 8㎛, and A method for predicting the performance of a secondary battery, wherein the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value greater than 6㎛ and less than or equal to 8㎛ of the above positive active material particle cross-section is 0.03 or higher.

6. In Paragraph 3, The above step d) further includes the step of measuring the average pore area ratio of particle cross-sections in which the ECD (equilibrium circle diameter) value of the cathode active material particle cross-section is greater than 8㎛ and less than or equal to 10㎛, and A method for predicting the performance of a secondary battery, wherein the average pore area ratio of particle cross-sections having an ECD (equilibrium circle diameter) value greater than 8㎛ and less than or equal to 10㎛ of the above positive active material particle cross-section is 0.04 or higher.

7. In Paragraph 1, The above positive active material has an average particle size (D 50 A method for predicting the performance of a secondary battery in which ) is 6㎛ to 10㎛.

8. A positive electrode active material comprising a lithium manganese-rich oxide containing manganese in an amount of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium, wherein When analyzing the cross-section of the above-mentioned cathode active material, the average pore area ratio of particle cross-sections with an ECD (equilibrium circle diameter) value greater than 2㎛ and less than or equal to 4㎛ is 0.02 or greater, and The above ECD (equilibrium circle diameter) represents the diameter of a circle having an area equal to the cross-sectional area of ​​a particle, in a positive active material.

9. In Paragraph 8, The above positive active material has an average particle size (D 50 A positive electrode active material having a thickness of 6㎛ to 10㎛.

10. In Paragraph 8, A positive active material having an average pore area ratio of particle cross-sections with an ECD (equilibrium circle diameter) value greater than 6㎛ and less than or equal to 8㎛ when analyzing the cross-section of the above positive active material, wherein the ratio is 0.03 or higher.

11. In Paragraph 8, A positive active material having an average pore area ratio of particle cross-sections with an ECD (equilibrium circle diameter) value greater than 8㎛ and less than or equal to 10㎛ when analyzing the cross-section of the above positive active material, wherein the ratio is 0.04 or higher.

12. A positive electrode comprising a positive electrode active material according to any one of paragraphs 8 to 11.

13. A secondary battery comprising a positive electrode according to paragraph 12.