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 of predicting performance of a secondary battery, the method including the steps of: manufacturing a cathode containing a cathode active material, the cathode active material containing a lithium-rich manganese oxide having a manganese content of 50 mol% or more and less than 100 mol% based on the total content of metals other than 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, and then measuring an average pore area ratio according to a range of ECD values of the cross section of the selected cathode active material particle; and predicting performance of a secondary battery containing the cathode from the average pore area ratio according to the range of ECD values of the cross section of the cathode active material particle, wherein ECD denotes the diameter of a circle having the same area as the cross-sectional area of the particle, and the pore area ratio denotes the pore area ratio with respect to the cross-sectional area of the cathode active material particle.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2024-0135855, filed on October 7, 2024, and Korean Patent Application No. 10-2025-0131694, filed on September 15, 2025, the disclosures of which are incorporated herein by reference in their entirety.

[0003] This invention relates to a method for predicting the performance of a secondary battery using 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 containing the positive electrode active material. Background Technology

[0004] In recent years, with the technological development and growing demand for mobile devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased rapidly.

[0005] Lithium-ion secondary batteries typically consist of a positive electrode, a negative electrode, a separator, and an electrolyte. In this case, the electrochemical performance of the secondary battery is affected by these components, with the positive electrode active material having a significant impact.

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

[0007] Therefore, research is underway to confirm the correlation between the porosity contained in the positive electrode active material and battery performance factors such as battery capacity and resistance. For example, although porosity is analyzed by SEM images of the positive electrode after cross-sectional treatment, this method has a problem: because the porosity on the surface and inside of the active material, which depends on the treatment location, is mixed and presented as a single value, the reliability of the results is reduced and large deviations occur.

[0008] To address these issues, the following method has been discussed: selecting only particles with a diameter close to D from SEM images. 50 Positive electrode active material particles (D 50 Filtration is used to analyze porosity, thus obtaining highly reliable and low-biased results. However, due to the limited overall parameters of the analyzed particles, this method has a high possibility of failing to represent the overall characteristics of the material.

[0009] Therefore, it is necessary to develop a predictive technique for the electrochemical performance of secondary batteries that can accurately analyze this correlation and represent the overall properties of the materials with high reliability. Summary of the Invention

[0010] Technical issues

[0011] The purpose of this invention is to provide a method for predicting the performance of a secondary battery by analyzing the pore area ratio based on the ECD (equivalent circle diameter) value range of the cross-section of the positive electrode particles using an electron microscope.

[0012] Another object of the present invention is to provide a positive electrode active material having optimal conditions confirmed in the process of deriving the prediction method, as well as a positive electrode and a secondary battery containing the material.

[0013] Technical solution

[0014] According to one aspect of the present invention, a method for predicting the performance of a secondary battery is provided, comprising the following steps: a) Manufacturing a positive electrode containing a positive electrode active material, wherein the positive electrode active material contains lithium-rich manganese oxide with a manganese content of more than 50 mol% and less than 100 mol% based on the total metal content excluding lithium; b) Milling the positive electrode to prepare a positive electrode sample; c) Obtain cross-sectional images of the cathode sample by scanning electron microscopy (SEM); d) Select a region of positive electrode active material particles from the cross-sectional image, and then measure the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​for the selected positive electrode active material particle cross-section; and e) Predict the performance of the secondary battery containing the positive electrode based on the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles. Wherein, ECD (Equivalent Circle Diameter) represents the diameter of a circle with the same area as the cross-sectional area of ​​the particle, and Wherein, the pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the positive electrode active material particles.

[0015] According to another aspect of the present invention, a positive electrode active material is provided, which contains lithium-rich manganese oxide with a manganese content of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium. Specifically, when analyzing the cross-section of the positive electrode active material, the average pore area ratio of particles with an ECD (equivalent circle diameter) greater than 2 μm and less than 4 μm was greater than 0.02, and ECD (Equivalent Circle Diameter) refers to the diameter of a circle with the same area as the cross-sectional area of ​​the particle.

[0016] According to another aspect of the present invention, a positive electrode comprising the above-described positive electrode active material is provided.

[0017] According to another aspect of the present invention, a secondary battery comprising the above-described positive electrode is provided.

[0018] Beneficial effects

[0019] This invention relates to a method for predicting the performance of secondary batteries using positive electrode active materials. The method utilizes the average pore area ratio of the ECD value range of positive electrode active material particles selected from SEM cross-sectional images to obtain highly reliable prediction results of secondary battery performance.

[0020] Furthermore, by utilizing positive electrode active materials with optimal conditions confirmed in the process of deriving the above prediction method, secondary batteries with excellent battery capacity and resistance performance can be manufactured. Attached Figure Description

[0021] Figure 1 The diagram shows a cross-sectional image taken in an experimental example of the present invention, and an SEM image of a region of positive electrode active material particles selected from the cross-sectional image.

[0022] Figure 2 A graph showing the ECD value of the particle cross section and the pore area ratio (PAR) calculated in the experimental example of the present invention.

[0023] Figure 3 A graph showing the evaluation of the resistance characteristics of the lithium secondary battery of the experimental example of the present invention.

[0024] Figure 4 A graph showing the evaluation of the discharge capacity of the lithium secondary battery in the experimental example of the present invention. Detailed Implementation

[0025] In the following sections, specific embodiments of the invention will be described in more detail to facilitate understanding of the invention.

[0026] The terms or words used in this specification and the claims should not be construed as limited to their ordinary or dictionary meanings, but should be interpreted based on the principle that the inventors can appropriately define the concepts of the terms in order to best describe their invention in a way that is consistent with the technical concept of the invention.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular form is intended to include the plural form as well, unless the context clearly indicates otherwise.

[0028] It should be understood that the terms “comprising,” “containing,” or “having,” as used herein, specify the presence of the stated features, figures, steps, ingredients, or combinations thereof, but do not exclude the presence or addition of one or more other features, figures, steps, ingredients, or combinations thereof.

[0029] The term "secondary particle" as used in this article refers to a particle formed by the aggregation of tens to hundreds of primary particles. More specifically, a secondary particle is an aggregate of more than 40 primary particles.

[0030] As used herein, the term "particle" may include any or all of a single particle, a quasi-single particle, a primary particle, a tuberculous particle, and a secondary particle.

[0031] The term "D" used in this article 50 "D" refers to the particle size corresponding to 50% of the cumulative volumetric particle size distribution. It can be measured using laser diffraction. 50 For example, the measurement can be performed by a method that includes the following steps: dispersing the positive electrode active material powder in a dispersion medium, introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasound at approximately 28 kHz with an output power of 60 W to obtain a volumetric cumulative particle size distribution map, and determining the particle size corresponding to 50% of the cumulative volume.

[0032] The term “pore area ratio (PAR)” used in this paper is defined as follows: a cross-sectional image of a cathode sample is obtained using a scanning electron microscope (SEM), a region of cathode active material particles is selected from the obtained cross-sectional image, and then the ratio of the pore area to the cross-sectional area of ​​the selected particles (pore area / particle cross-sectional area) is measured.

[0033] As used in this article, the term "ECD (Equivalent Circle Diameter)" refers to the diameter of a circle having the same area as the cross-sectional area of ​​the selected particle.

[0034] The specific embodiments of the present invention will be described in detail below.

[0035] Methods for predicting secondary battery performance

[0036] The inventors of this application investigated the correlation between porosity in positive electrode active materials and battery performance. They analyzed the cross-sectional area and pore area of ​​positive electrode active material particles obtained by scanning electron microscopy (SEM), confirming that secondary battery performance can be predicted by the pore area ratio (pore area / particle cross-sectional area) based on a range of ECD (equivalent circle diameter) values. The prediction method of this invention derives its results by dividing and analyzing the distribution of pores within positive electrode active material particles according to a range of ECD values. Compared to existing analytical methods that represent pores with a single value without considering their distribution, this method offers higher reliability. Furthermore, since no D... 50 The overall parameters of the filtered and analyzed particles are not limited, thus enabling the acquisition of results that are representative of the entire group of positive electrode active materials used in the analysis.

[0037] The method for predicting the performance of a secondary battery according to the present invention includes the following steps: a) Manufacturing a positive electrode containing a positive electrode active material, wherein the positive electrode active material contains lithium-rich manganese oxide with a manganese content of more than 50 mol% and less than 100 mol% based on the total metal content excluding lithium; b) Milling the positive electrode to prepare a positive electrode sample; c) Obtain cross-sectional images of the cathode sample by scanning electron microscopy (SEM); d) Select a region of positive electrode active material particles from the cross-sectional image, and then measure the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​for the selected positive electrode active material particle cross-section; and e) Predict the performance of the secondary battery containing the positive electrode based on the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles. Wherein, ECD (Equivalent Circle Diameter) represents the diameter of a circle with the same area as the cross-sectional area of ​​the particle, and Wherein, the pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the positive electrode active material particles.

[0038] The method for predicting the performance of secondary batteries according to the present invention will be described in detail below.

[0039] a) Steps for manufacturing the positive electrode

[0040] First, a slurry is obtained by dispersing the positive electrode active material and at least one of the optional binder, conductive material, and dispersant in a dispersion medium. The resulting slurry is then coated onto at least one surface of the positive electrode current collector and dried to form a layer of the positive electrode active material, thereby manufacturing the positive electrode. Specific details of the positive electrode current collector, positive electrode active material, binder, conductive material, dispersant, and dispersion medium used in the manufacture of the positive electrode are described below.

[0041] b) Steps for preparing the positive electrode sample

[0042] The cathode manufactured above was milled using an ion milling device (e.g., Hitachi IM5000) to prepare cathode samples for cross-sectional analysis.

[0043] c) Steps for obtaining the positive electrode cross-section image

[0044] Cross-sectional images of the milled cathode sample were obtained using a scanning electron microscope (SEM). The resulting cross-sectional images show the cross-section of the cathode sample cut along the thickness direction.

[0045] d) Measure the average pore area based on the ECD (equivalent circle diameter) value range of the cross-section of the positive electrode active material particles. Steps of comparison

[0046] The cross-sectional image captured in step c) is digitally processed. The region containing the positive electrode active material particles is selected and analyzed pixel by pixel (image processing) to measure the average pore area ratio based on the ECD (equivalent circle diameter) value range of the cross-section of the positive electrode active material particles. A pixel is the smallest unit of a digital image, representing the actual area; each pixel represents the same area.

[0047] The digital cross-sectional image is proportionally corrected based on the resolution of the SEM to convert the number of pixels into actual area. Then, the pore area ratio is calculated by dividing the total area of ​​pixels identified as pores by the total area of ​​all pixels (particle area). At this point, each pixel of the pore can be binarized, classifying it as black (pore) or white (particle) with a value of 0 or 1.

[0048] Such a measurement process can be performed using software or program code capable of image processing and analysis. In one implementation, the process can be performed using Python programming.

[0049] In addition, the ECD (equivalent circle diameter) value of each particle can be calculated from the area of ​​each particle calculated above, and the average pore area ratio can be calculated based on the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles.

[0050] Figure 1 Cross-sectional images obtained in the experimental examples of the present invention described later are shown, along with SEM images of selected positive electrode active material particle regions from the cross-sectional images. (Refer to...) Figure 1 In the image, the circular gray area represents the positive electrode active material, the black area inside the gray area represents the pores, and the outer area of ​​the positive electrode active material corresponds to the binder, conductive material and dispersant. Figure 1 The area shown in red represents the selected positive electrode active material particle region.

[0051] The positive electrode active material particle region refers to the cross-section of the positive electrode active material particles within the selected positive electrode active material layer in the cross-sectional image, while the cross-section of the positive electrode active material particles refers to the cross-section of the positive electrode active material particles cut along the thickness direction. The size of the cross-section of the positive electrode active material particles shown in the captured cross-sectional image varies depending on the position where the particles are processed. Specifically, the cross-sectional size is largest when the processing position is near the particle center, and decreases as the position approaches the particle edge. Within the following ECD (equivalent circle diameter) value range, it can be understood that the cross-sectional processing position gets closer and closer to the particle edge in the order of greater than 8 μm and less than 10 μm, greater than 6 μm and less than 8 μm, and greater than 2 μm and less than 4 μm.

[0052] Figure 2A graph showing the ECD value of the particle cross section and the pore area ratio (PAR) calculated using the above method in the experimental examples of the present invention described later.

[0053] Since the positive electrode active material particles are not perfectly spherical, the cross-section cut along the thickness direction is not perfectly circular, making it difficult to determine the diameter of the particle cross-section. Therefore, in this invention, the cross-sectional area of ​​the selected positive electrode active material particles is measured and converted into an ECD (equivalent circle diameter) value, which represents the diameter of a circle with the same area.

[0054] As described above, the obtained ECD (equivalent circle diameter) values ​​are divided into multiple ranges, and the average pore area ratio of the cross-section of the positive electrode active material particles corresponding to each range is calculated. Even in this case, the calculation is still performed using the image processing procedure described above. The capacity and resistance performance of the secondary battery are predicted using the average pore area ratio based on the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles.

[0055] According to one embodiment of the present invention, step d) includes measuring the average pore area ratio of the cross-section of the positive electrode active material particles with an ECD (equivalent circle diameter) value greater than 2 μm and less than 4 μm.

[0056] According to one embodiment of the present invention, step d) may include one or more of the following steps: measuring the average pore area ratio of the cross-section of the positive electrode active material particles with an ECD (equivalent circle diameter) value greater than 6 μm and less than 8 μm, and measuring the average pore area ratio of the cross-section of the positive electrode active material particles with an ECD (equivalent circle diameter) value greater than 8 μm and less than 10 μm.

[0057] e) Steps for predicting secondary battery performance

[0058] The inventors manufactured a secondary battery comprising the positive electrode manufactured in the experimental example below, measured the capacity and resistance performance of the battery, and analyzed the measurement results and the average pore area ratio obtained in step d) based on the ECD (equivalent circle diameter) value range of the cross section of the positive electrode active material particles to confirm the correlation, thereby enabling the prediction of the secondary battery performance.

[0059] Specifically, according to one embodiment of the present invention, when the average pore area ratio of the cross-section of the positive electrode active material particles with an ECD (equivalent circle diameter) value greater than 2 μm and less than 4 μm is 0.02 or higher, excellent battery capacity and resistance performance can be predicted. Since the electrochemical reaction occurs on the particle surface, the amount of porosity distributed on the outside of the particle has a more significant impact on the reaction than on the center. Therefore, when the average pore area ratio of the cross-section of the positive electrode active material particles with an ECD (equivalent circle diameter) value greater than 2 μm and less than 4 μm meets the above-mentioned range, the electrochemical reaction occurs rapidly, enabling the manufacture of a battery with excellent capacity and resistance performance.

[0060] According to another embodiment of the present invention, when the ECD (equivalent circle diameter) value of the cross section of the positive electrode active material particles is greater than 6 μm and the average pore area ratio of the particle cross section is greater than 0.03, it can be predicted that it has excellent battery capacity and resistance performance.

[0061] According to another embodiment of the present invention, when the ECD (equivalent circle diameter) value of the cross section of the positive electrode active material particles is greater than 8 μm and the average pore area ratio of the particle cross section is greater than 0.04, it can be predicted that it has excellent battery capacity and resistance performance.

[0062] Positive electrode active material

[0063] In the process of deriving a method for predicting the performance of secondary batteries, a positive electrode active material with excellent battery performance was identified.

[0064] The positive electrode active material of the present invention is a lithium-rich manganese oxide containing a manganese content of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium. When analyzing the cross-section of the positive electrode active material, the average pore area ratio of the particle cross-section with an ECD (equivalent circle diameter) value greater than 2 μm and less than 4 μm is 0.02 or more, preferably 0.03 or more, and more preferably 0.05 or more. Here, ECD (equivalent 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 the particle cross-section with an ECD value greater than 2 μm and less than 4 μm satisfies the above range, the electrochemical reaction occurs rapidly, enabling the manufacture of a battery with excellent capacity and resistance performance.

[0065] Cross-sectional analysis of the positive electrode active material was performed through steps a) to d).

[0066] According to one embodiment, when analyzing the cross-section of the positive electrode active material, the average pore area ratio of the cross-section of particles with an ECD (equivalent circular diameter) value greater than 6 μm and 8 μm or less can be 0.03 or more, preferably 0.05 or more, and more preferably 0.07 or more.

[0067] According to one embodiment, when analyzing the cross-section of the positive electrode active material, the average pore area ratio of the cross-section of particles with an ECD (equivalent circular diameter) value greater than 8 μm and 10 μm or less can be 0.04 or more, preferably 0.07 or more, and more preferably 0.10 or more.

[0068] In one embodiment of the present invention, the positive electrode active material contains the lithium-rich manganese oxide. The lithium-rich manganese oxide has a structure in which a layered lithium metal oxide is mixed with a lithium manganese oxide (Li2MnO3) having a rock salt structure. Therefore, during the activation process and / or charge-discharge cycle, the lithium manganese oxide is further activated, enabling the redox reaction of manganese to contribute to the achievement of capacity.

[0069] In a specific embodiment, the lithium-rich manganese oxide can be represented by the following Chemical Formula 1.

[0070] [Chemical Formula 1]

[0071] Li a [Mn 1-b-c Ni b M c 2-a O2

[0072] Wherein, in Formula 1, M is at least one 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, a, b, and c are atomic fractions of each independent element, where 1 < a, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, and 0 < b + c ≤ 0.5.

[0073] Specifically, a is the molar ratio of Li in the lithium-rich manganese oxide, which can be 1 < a, 1.1 ≤ a ≤ 1.5, or 1.1 ≤ a ≤ 1.3. When a satisfies the above range, high capacity can be achieved.

[0074] b is the molar ratio of Ni in the lithium-rich manganese oxide, which can be 0 ≤ b ≤ 0.5, 0.1 ≤ b ≤ 0.4, or 0.2 ≤ b ≤ 0.4.

[0075] ​c represents the molar ratio of dopant element M in lithium-rich manganese oxide, which can be 0 ≤ c ≤ 0.5, 0 ≤ c ≤ 0.3, or 0 ≤ c ≤ 0.1. Dopant element M can be, for example, Co. If the content of dopant element is too high, it may not only adversely affect the capacity of the active material, but also exacerbate gas generation and degradation of the positive electrode active material due to the increased oxidation / reduction reaction of oxygen, potentially leading to a decrease in lifetime characteristics.

[0076] 1-bc represents the molar ratio of Mn in lithium-rich manganese oxide, which can 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 rock salt phase becomes too small, so the effect of irreversible compensation and capacity improvement of the negative electrode is negligible.

[0077] On the other hand, in lithium-rich manganese oxides represented by Equation 1, the ratio of the molar number of Li to the molar number of all metal elements other than Li (Li / Me) can be 1.2 to 1.5, or 1.25 to 1.5, or 1.30 to 1.45. When the Li / Me ratio meets the above range, excellent rate performance and capacity characteristics can be exhibited. If the Li / Me ratio is too high, the conductivity may decrease, and the rock salt phase (Li₂MnO₃) may increase, which may accelerate the degradation rate. If the Li / Me ratio is too low, the effect on improving energy density is minimal.

[0078] On the other hand, the composition of the lithium-rich manganese oxide can be represented by the following chemical formula 2.

[0079] [Chemical Formula 2]

[0080] X Li2MnO3·(1-X) Li[Ni 1-y-z Mn y M z O2

[0081] In Equation 2, M can be at least one 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 0.2≤X≤0.5, 0.4≤y<1, 0≤z≤0.5.

[0082] X refers to the ratio of the Li2MnO3 phase (rock salt structure compound phase) in lithium-rich manganese oxide, which can 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 lithium-rich manganese oxide meets the above range, high capacity characteristics can be achieved.

[0083] y represents the LiM'O2 phase (M' = [Ni 1-y-z Mn y M z The molar ratio of Mn in the layered compound phase can be 0.4≤y<1, 0.4≤y≤0.8, or 0.4≤y≤0.7.

[0084] z represents the LiM'O2 phase (M' = [Ni]). 1-y-z Mn y M z The molar ratio of dopant element M in the layered compound phase can be 0≤z≤0.5, 0≤z≤0.3, or 0≤z≤0.1.

[0085] According to one embodiment of the present invention, the positive electrode active material may be in the form of secondary particles formed by the aggregation of multiple primary particles. The average particle size (D) of the secondary particles... 50 The size can be 6 to 10 μm, preferably 8 to 10 μm.

[0086] Meanwhile, the size of the primary particles can be 100 to 300 nm, preferably 100 to 250 nm, and more preferably 100 to 200 nm.

[0087] Meanwhile, the lithium-rich manganese oxide can be prepared by mixing a transition metal precursor and a lithium source material, followed by calcination. However, this preparation method follows typical preparation processes and conditions previously known for lithium-rich manganese oxides. In this case, to prepare lithium-rich manganese oxides that meet the average pore area ratio of particle cross-sections according to the ECD value range, factors such as the concentration of alkali in the precursor mixture used for synthesizing the lithium-rich manganese oxide, the synthesis time, the stirring speed and temperature, and the calcination temperature can be adjusted.

[0088] The mixture used for precursor synthesis includes a metal solution, a complexing agent (such as ammonium ions), and a base (such as NaOH). In this case, the initial base concentration during the synthesis process and the change of base concentration over time can affect the pore distribution inside the particles. To prepare the lithium-rich manganese oxide of the present invention, the initial base concentration during the synthesis process can be adjusted to a pH of 10 or higher and lower than 12, specifically 11 or higher and lower than 12, or more specifically 11 or higher and lower than 11.5. Furthermore, by adjusting the base concentration according to the synthesis time, the distribution position of pores inside the particles can be adjusted. For example, when the base concentration decreases with the passage of synthesis time, particles with a more densely distributed pore distribution at the edges than at the center can be synthesized.

[0089] Furthermore, the firing temperature can be from 800°C to 1000°C, specifically from 800°C to 950°C. Since a higher firing temperature induces the growth of primary particles to form dense positive electrode active material particles, the firing temperature can be adjusted within the above range to obtain the lithium-rich manganese oxide of the present invention.

[0090] positive electrode

[0091] The positive electrode containing the above-mentioned positive electrode active material will be described. This positive electrode can be manufactured by coating a positive electrode slurry formed by dispersing the positive electrode active material in a dispersion medium onto a positive electrode current collector, followed by drying.

[0092] In addition to positive electrode active materials containing lithium-rich manganese oxides, the positive electrode slurry may optionally contain binders, conductive materials, dispersants, etc., if necessary.

[0093] The positive electrode current collector can contain a highly conductive metal, and there are no particular limitations, as long as the positive electrode active material layer can easily adhere to it and it is non-reactive within the battery's voltage range. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel treated with one of carbon, nickel, titanium, or silver can be used as the positive electrode current collector. Furthermore, the thickness of the positive electrode current collector is typically from 3 μm to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0094] In addition to the aforementioned lithium-rich manganese-based oxides, the positive electrode active material may also include conventional positive electrode active materials. For example, the positive electrode active material may also include LCO (LiCoO2), LNO (LiNiO2), LFP (LiFePO4), and NCM (Li[Ni]O2). p Co q Mn r1 The positive electrode active material is one or more of the group consisting of O2, 0 < p < 1, 0 < q < 1, 0 < r1 < 1, p + q + r1 = 1. However, based on the total weight of the positive electrode active material, the positive electrode active material preferably contains at least 70% by weight of lithium-rich manganese oxide, and may consist only of lithium-rich manganese oxide.

[0095] At this point, based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by weight, more specifically from 90% to 98% by weight.

[0096] Conductive materials are used to provide conductivity to the electrodes. Any conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause any chemical changes in the battery. Specific examples of conductive materials can be: graphite such as natural or artificial graphite; carbonaceous materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, and carbon fibers; powders or fibers of metals such as copper, nickel, aluminum, and silver; conductive tubes such as carbon nanotubes; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. Any one or a mixture of two or more of these can be used. Based on the total weight of the positive electrode active material layer, the content of the conductive material can be from 0.01% by weight to 10% by weight, preferably from 0.1% by weight to 9% by weight, and more preferably from 0.1% by weight to 5% by weight.

[0097] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of adhesives may be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers with hydrogen substituted by Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. Based on the total weight of the positive electrode active material layer, the adhesive content may be from 1% to 30% by weight, preferably from 1% to 20% by weight, more preferably from 1% to 10% by weight.

[0098] The dispersion medium can be a solvent commonly used in the art, such as NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited thereto. The dispersion medium can be included in an amount that gives the cathode slurry composition a suitable viscosity and solids content. Specifically, the content of the dispersion medium can be such that the solids content in the slurry is from 40% to 75% by weight, more specifically from 40% to 65% by weight.

[0099] Secondary batteries

[0100] Next, a secondary battery according to another embodiment of the present invention will be described. Specifically, a lithium secondary battery, as a representative example of a secondary battery, includes the above-described positive electrode, a negative electrode located opposite the positive electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte.

[0101] The negative electrode can be manufactured by coating a positive electrode slurry containing a positive electrode active material dispersed in a dispersion medium onto a negative electrode current collector, followed by drying.

[0102] In addition to the negative electrode active material, the negative electrode slurry may optionally include binders, conductive materials, dispersants, etc., if necessary.

[0103] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel treated with carbon, nickel, titanium, or silver, or aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm. Similar to the positive electrode current collector, the negative electrode current collector can also have fine irregularities formed on its surface to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0104] In one embodiment of the present invention, a compound capable of reversibly inserting and de-intercalating lithium can be used as the negative electrode active material. Specific examples of negative electrode active materials may include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal 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 metal oxides capable of doping and de-doping lithium, such as SiO2. β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a complex containing a metal compound and a carbonaceous material, such as a Si-C complex or a Sn-C complex, may be used alone or in mixtures of two or more of them.

[0105] Additionally, lithium metal films can be used as anode active materials. Furthermore, both low-crystallinity and high-crystallinity carbon can be used as carbon materials. Typical examples of low-crystallinity carbon include soft carbon and hard carbon. Typical examples of high-crystallinity carbon include amorphous, plate-like, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, and high-temperature sintered carbons such as mesophase pitch and coke derived from petroleum or coal tar pitch.

[0106] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be 80% to 99% by weight, 82% to 99% by weight, or 84% to 99% by weight.

[0107] Adhesives are components that facilitate the bonding between conductive agents, active materials, and current collectors. Typically, the amount of adhesive added is from 0.1% to 10% by weight, based on the total weight of the negative electrode active material layer. Examples of adhesives include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0108] Conductive materials are components used to further improve the conductivity of the negative electrode active material. The content of the conductive material can be 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. There are no particular limitations on the conductive material, as long as it is conductive and does not cause chemical changes in the battery. Examples include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; conductive fibers, such as carbon fibers or metal fibers; fluorinated carbon; metal powders such as aluminum powder or nickel powder; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0109] The dispersion medium can be a solvent commonly used in the art, such as NMP (N-methyl-2-pyrrolidone), DMF (dimethylformamide), DMSO (dimethyl sulfoxide), ethanol, isopropanol, water, or mixtures thereof, but is not necessarily limited thereto. The dispersion medium can be included in an amount that gives the negative electrode slurry composition a suitable viscosity and solids content. Specifically, the content of the dispersion medium can be such that the solids content in the slurry is from 40% to 75% by weight, more specifically from 40% to 65% by weight.

[0110] On the other hand, in lithium secondary batteries, the separator is used to separate the negative and positive electrodes and provide a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is commonly used as a separator in lithium secondary batteries. In particular, separators with high electrolyte retention capacity and low impedance to the movement of electrolyte ions are preferred. Specifically, porous polymer membranes can be used, for example, porous polymer membranes prepared using polyolefin polymers (such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or laminated structures of two or more layers can be used. Additionally, typical porous nonwoven fabrics can be used, for example, nonwoven fabrics formed from glass fibers or polyethylene terephthalate fibers with high melting points. Furthermore, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0111] In addition, the electrolyte used in lithium secondary batteries can be any of the following types that can be used in the manufacture of lithium secondary batteries: organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte, and molten inorganic electrolyte, but it is not limited to these.

[0112] Specifically, electrolytes may include organic solvents and lithium salts.

[0113] Organic solvents can be used without particular restrictions, as long as they can serve as a medium through which ions participating in the electrochemical reactions of the battery can move. Specifically, the following solvents can be used as organic solvents: 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 solvents, such as benzene and fluorobenzene; carbonate 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 solvents, such as ethanol and isopropanol; nitriles, such as R-CN (wherein R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are suitable, and more preferably are mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery and linear carbonate compounds (e.g., methyl ethyl carbonate, dimethyl carbonate or diethyl carbonate) with low viscosity.

[0114] Lithium salts can be used without particular restrictions, as long as they can provide lithium ions for lithium-ion secondary batteries. Specifically, the anions of the lithium salt can include those selected from 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 - At least one of the group consisting of [list of components]. Specifically, as lithium salts, 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., can be used. The concentration range of the lithium salt can be from 0.1M to 4.0M, preferably from 0.5M to 3.0M, and more preferably from 1.0M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0115] In addition to the electrolyte components, to improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, the electrolyte may also contain one or more additives selected from the following: haloalkylene carbonate compounds (such as ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the content of the additives may be from 0.1% by weight to 10% by weight.

[0116] Besides using the aforementioned lithium-rich manganese oxide as the positive electrode active material, this secondary battery can follow the conventional configuration of a secondary battery. For example, it can be manufactured by sequentially placing a separator between a positive electrode containing the positive electrode active material and a negative electrode containing the negative electrode active material, stacking and drying them sequentially to form an electrode assembly, inserting this assembly into a casing, optionally injecting electrolyte and sealing it. The lithium secondary battery can be cylindrical, prismatic, button-shaped, or pouch-shaped.

[0117] Preferred embodiments are provided below to aid in understanding the invention; however, these embodiments are merely illustrative and will be readily apparent to those skilled in the art that various changes and modifications can be made within the scope and concept of the invention, and such changes and modifications are also within the scope of the appended claims.

[0118] [Experimental Example]

[0119] Cathode sample preparation and measurement of average pore area ratio based on ECD value range

[0120] Example 1

[0121] The alkali concentration of the mixture used to synthesize the lithium-rich manganese oxide precursor was maintained at a constant pH of 11.5 to prepare the precursor, and the prepared precursor was used to prepare a product with the composition Li. 1.130 Mn 0.561 Ni 0.304 Co 0.004 Lithium-rich manganese oxides containing O2.

[0122] The lithium-rich manganese oxide prepared above as the positive electrode active material, Li435 (DENKA) as the conductive material, KF9700 (KUREHA) as the binder, and BM-740H (ZEON) as the dispersant were added to NMP as the solvent in a weight ratio of 96.25:1.5:2.1:0.15 to prepare a positive electrode slurry. The positive electrode slurry was coated on an Al film with a thickness of 20 μm and dried to prepare the positive electrode.

[0123] Ar ion milling (voltage: 6 kV, ion beam current: 150 μA) was used to prepare cathode samples for cross-sectional analysis by using an ion milling device (e.g., Hitachi IM5000).

[0124] Subsequently, cross-sectional images of the cathode sample were captured using a SEM (JEOL, IT-800). The active material particle regions of the cathode were selected from the obtained cross-sectional images. As described above, the captured cross-sectional images are shown below. Figure 1 .

[0125] Next, image processing is performed to obtain information about the pores. Specifically, the number of pixels within the cross-section of the selected positive electrode active material particle is identified, the cross-sectional area of ​​the particle is calculated, and the equivalent circle diameter (ECD) of a circle with the same area is calculated. The number of pixels in the particle cross-section corresponding to the pore region is identified, and the pore area is calculated. The pore area ratio (pore area / particle cross-sectional area) is also calculated based on the particle cross-sectional area and the pore area.

[0126] Example 2

[0127] The initial alkali concentration of the mixture used to synthesize the lithium-rich manganese oxide precursor was adjusted to pH 11.5, and then the alkali concentration was gradually decreased over time to prepare the precursor. Using the prepared precursor, a lithium oxide precursor with the following composition was prepared: Li 1.130 Mn 0.561 Ni 0.304 Co 0.004 Lithium-rich manganese oxides containing O2.

[0128] Except for using the lithium-rich manganese oxide prepared above as the positive electrode active material, the positive electrode was manufactured in the same manner as in Example 1, and the ECD value and pore area ratio were calculated using the same method.

[0129] Comparative Example 1

[0130] The alkali concentration of the mixture used to synthesize the lithium-rich manganese oxide precursor was maintained at a constant pH of 12 to prepare the precursor, and the prepared precursor was used to prepare a product with the composition Li. 1.130 Mn 0.561 Ni 0.304 Co 0.004 Lithium-rich manganese oxides containing O2.

[0131] In addition to using the lithium-rich manganese oxide prepared above as the positive electrode active material, the ECD value and pore area ratio were calculated using the same method.

[0132] Based on the ECD values ​​and pore area ratios obtained in Examples 1, 2 and Comparative Example 1, the ECD values ​​were divided into the following ranges: greater than 2 μm and less than 4 μm, greater than 6 μm and less than 8 μm, and greater than 8 μm and less than 10 μm. The average pore area ratio of the cross-section of the positive electrode active material particles corresponding to each range was calculated, and the results are shown in Table 1 below.

[0133] [Table 1]

[0134] Battery manufacturing and performance evaluation

[0135] A coin battery was manufactured using the positive electrode, lithium negative electrode, polyethylene (PE) separator, and electrolyte prepared in Example 1, Example 2, or Comparative Example 1, which consisted of a mixture of EC and EMC in a volume ratio of 3:7 (EC:EMC) and contained 1M LiPF6 and FEC (ethylene fluorocarbonate) and LiBF4 (lithium tetrafluoroborate) additives added at 3 wt% and 0.5 wt% respectively based on the total weight of the electrolyte.

[0136] A coin cell containing the positive electrode prepared in Example 1, Example 2, or Comparative Example 1 was activated at 45°C, 0.1C, and 2.0 V–4.65 V, followed by charge-discharge cycling at 25°C, 0.33C, and 2.5 V–4.4 V. The resistivity characteristics of the lithium secondary battery were then evaluated and are shown below. Figure 3 Evaluation of discharge capacity and its presentation Figure 4 In addition, the resistance and discharge capacity at 50% SOC are shown in Table 2 below.

[0137] [Table 2]

[0138] Referring to Tables 1 and 2, it can be confirmed that compared with the battery of Comparative Example 1 (when the ECD value of the cross-section of the positive electrode active material particles is greater than 2 μm and less than 4 μm, the average pore area ratio is less than 0.02), the batteries of Examples 1 and 2 (when the ECD value of the cross-section of the positive electrode active material particles is greater than 2 μm and less than 4 μm, the average pore area ratio is greater than 0.02) exhibit superior battery capacity and resistance performance.

[0139] Furthermore, the above experimental examples confirm that battery performance can be predicted by dividing the ECD value range of the cross-section of the positive electrode active material particles and analyzing the average pore area ratio of each range.

Claims

1. A method for predicting the performance of a secondary battery, comprising the following steps: a) Manufacturing a positive electrode containing a positive electrode active material, wherein the positive electrode active material contains lithium-rich manganese oxide with a manganese content of more than 50 mol% and less than 100 mol% based on the total metal content excluding lithium; b) Milling the positive electrode to prepare a positive electrode sample; c) Obtain cross-sectional images of the cathode sample by scanning electron microscopy (SEM); d) Select a region of positive electrode active material particles from the cross-sectional image, and then measure the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​for the selected positive electrode active material particle cross-section; and e) Predict the performance of the secondary battery containing the positive electrode based on the average pore area ratio within the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles. Wherein, ECD (Equivalent Circle Diameter) represents the diameter of a circle with the same area as the cross-sectional area of ​​the particle, and Wherein, the pore area ratio represents the ratio of the pore area to the cross-sectional area of ​​the positive electrode active material particles.

2. The method for predicting the performance of a secondary battery as described in claim 1, in, The cross-section of the positive electrode active material particle refers to the cross-section obtained by cutting the positive electrode active material particle along the thickness direction.

3. The method for predicting the performance of a secondary battery as described in claim 1, in, Step d) includes measuring the ECD (equivalent circle diameter) of the cross-section of the positive electrode active material particles for particles with an ECD greater than 2 μm and less than 4 μm, and the average pore area ratio of the particle cross-section. The capacity and resistance performance of the battery are predicted by using the average pore area ratio based on the range of ECD (equivalent circle diameter) values ​​of the cross-section of the positive electrode active material particles.

4. The method for predicting the performance of a secondary battery as described in claim 3, in, When the ECD (equivalent circle diameter) value of the cross-section of the positive electrode active material particles is greater than 2 μm and the average pore area ratio of the particle cross-section is greater than 0.02, it is predicted that it has excellent battery capacity and resistance performance.

5. The method for predicting the performance of a secondary battery as described in claim 3, in, Step d) further includes measuring the ECD (equivalent circle diameter) of the cross-section of the positive electrode active material particles, specifically the average pore area ratio of particle cross-sections with ECD values ​​greater than 6 μm and less than 8 μm. When the ECD (equivalent circle diameter) value of the cross-section of the positive electrode active material particles is greater than 6 μm and the average pore area ratio of the particle cross-section is greater than 0.03 for particles smaller than 8 μm, it is predicted that it will have excellent battery capacity and resistance performance.

6. The method for predicting the performance of a secondary battery as described in claim 3, in, Step d) further includes measuring the average pore area ratio of particle cross-sections with ECD (equivalent circle diameter) values ​​greater than 8 μm and less than 10 μm for positive electrode active material particles, and... When the ECD (equivalent circle diameter) value of the cross-section of the positive electrode active material particles is greater than 8 μm and the average pore area ratio of the cross-section of particles less than 10 μm is greater than 0.04, it is predicted that it has excellent battery capacity and resistance performance.

7. The method for predicting the performance of a secondary battery as described in claim 1, in, The average particle size (D) of the positive electrode active material 50 The thickness ranges from 6 μm to 10 μm.

8. A positive electrode active material, comprising lithium-rich manganese oxide with a manganese content of 50 mol% or more and less than 100 mol% based on the total metal content excluding lithium. in, When analyzing the cross-section of the positive electrode active material, the average pore area ratio of particles with an ECD (equivalent circle diameter) greater than 2 μm and less than 4 μm was greater than 0.02, and ECD (Equivalent Circle Diameter) refers to the diameter of a circle with the same area as the cross-sectional area of ​​the particle.

9. The positive electrode active material as described in claim 8, in, The average particle size (D) of the positive electrode active material 50 The thickness ranges from 6 μm to 10 μm.

10. The positive electrode active material as described in claim 8, in, When analyzing the cross-section of the positive electrode active material, the average pore area ratio of particles with an ECD (equivalent circle diameter) value greater than 6 μm and less than 8 μm is greater than 0.

03.

11. The positive electrode active material as described in claim 8, in, When analyzing the cross-section of the positive electrode active material, the average pore area ratio of particles with an ECD (equivalent circle diameter) value greater than 8 μm and less than 10 μm is greater than 0.

04.

12. A positive electrode comprising the positive electrode active material according to any one of claims 8 to 11.

13. A secondary battery comprising the positive electrode as described in claim 12.

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