KR-20260065115-A - positive electrode active material for sodium secondary battery, method for preparing the same and sodium secondary battery including the same

KR20260065115AKR 20260065115 AKR20260065115 AKR 20260065115AKR-20260065115-A

Abstract

One embodiment of the present invention provides a positive electrode active material for a sodium secondary battery comprising a single-crystal sodium complex transition metal oxide comprising at least sodium; two or more major elements selected from transition metals; and two or more doping elements selected from transition metals, satisfying Equation 1 which indicates the uniformity of the doping elements.

Inventors

박아람
정구현
허승우
이동욱

Assignees

주식회사 에코프로비엠

Dates

Publication Date: 20260508
Application Date: 20241031

Claims (12)

A sodium complex transition metal oxide in the form of a single crystal, comprising at least sodium; two or more major elements selected from transition metals; and two or more doping elements selected from transition metals. A positive electrode active material for a sodium secondary battery satisfying the following relationship 1, which indicates the compositional uniformity of the first doping element. [Relationship 1] B/A ≤ 0.15 (In Equation 1, A and B are measured at at least 30 arbitrary points along a cross-section passing through the center of the positive electrode active material, and represent the average value (A) and standard deviation (B) of the content (wt%) of the first doping element for all metals excluding sodium.)
In paragraph 1, The above positive active material is a positive active material for a sodium secondary battery satisfying the following relationship 2, which indicates the uniformity of distribution of a first doping element among a plurality of sodium composite transition metal oxide single crystal particles. [Relationship 2] D/C ≤ 0.10 (In Equation 2, C and D are measured among at least 10 randomly selected single-crystal grains and represent the average value (C) and standard deviation (D) of the content (wt%) of the first doping element in the total metal excluding sodium.)
In paragraph 1, The above positive active material is a positive active material for a sodium secondary battery containing less than 3 weight% of an oxide of a first doping element.
In paragraph 1, The above sodium complex transition metal oxide single crystal has an O3-type crystal structure, and The above transition metal comprises Ni; Mn; and at least one of Fe and Co; and A positive electrode active material for a sodium secondary battery, wherein among two or more doping elements selected from the above transition metals, the first doping metal is Cu and the second doping metal is Zn or Zr.
In paragraph 1, The above sodium complex transition metal oxide is a positive electrode active material for a sodium secondary battery comprising a compound represented by the following chemical formula 1. [Chemical Formula 1] Na a [(Ni x Mn y Fe z Cu b M1 c )]O 2 (In Chemical Formula 1, M1 is Zn or Zr, 0.8<a<1.2, 0.1≤x≤0.9, 0.1≤y≤0.9, 0.1≤z≤0.9, 0.05≤b≤0.13, 0.005≤c≤0.02, x+y+z+b+c=1)
In paragraph 1, The above sodium complex transition metal oxide is a positive electrode active material for a sodium secondary battery comprising a compound represented by Chemical Formula 2. [Chemical Formula 2] Na a [(Ni x Mn y Fe z Cu b M1 c )]O 2 (In Chemical Formula 2, M1 is Zn, 0.9<a<1.1, 0.16≤x≤0.26, 0.27≤y≤0.37, 0.27≤z≤0.37, 0.05≤b≤0.13, 0.005≤c≤0.02, 0.27≤x+b≤0.37, x+y+z+b+c=1)
In paragraph 1, The above sodium composite transition metal oxide is characterized by a molar ratio of the content of the first doping element to the content of the second doping element of 10 to 25, and is a positive electrode active material for a sodium secondary battery.
A precursor preparation step comprising a first doping element and at least two transition metals; and A step of manufacturing an anode active material by mixing the above precursor and sodium compound and heat-treating to uniformly dope the surface and interior of the anode active material particles with a first doping element; A method for manufacturing a positive electrode active material for a sodium secondary battery, wherein the above-mentioned precursor manufacturing step or positive electrode active material manufacturing step involves further mixing a compound of a second doping element.
In paragraph 8, The above precursor manufacturing step is, A method for manufacturing a positive electrode active material for a sodium secondary battery, comprising mixing at least two transition metal compounds and a compound of the first doping element, and then manufacturing a transition metal hydroxide precursor through a co-precipitation reaction.
In paragraph 8, The above precursor manufacturing step is, A method for manufacturing a positive electrode active material for a sodium secondary battery, wherein a compound of a transition metal hydroxide precursor and a first doping element is mixed and heat-treated to coat at least a portion of the surface of the transition metal hydroxide precursor with the first doping element.
A cathode for a sodium secondary battery comprising a cathode active material according to any one of claims 1 to 7.
Sodium secondary battery comprising a positive electrode according to paragraph 11.

Description

Positive electrode active material for sodium secondary battery, method for preparing the same and sodium secondary battery including the same The present invention relates to a positive electrode active material for a sodium secondary battery, a method for manufacturing the same, and a sodium secondary battery comprising the same. Rechargeable batteries have been widely used as energy storage devices in various fields of electronic technology. Recently, with the surge in demand for lithium-ion rechargeable batteries, sodium-ion rechargeable batteries are attracting attention as a replacement for lithium, an expensive metal. Sodium-ion secondary batteries are one of the next-generation materials with high potential for application as secondary batteries because they have an insertion/extraction reaction operating principle similar to that of lithium-ion secondary batteries. However, they show lower performance in terms of capacity, lifespan, and rate characteristics compared to lithium-ion secondary batteries, making commercialization difficult. Therefore, the development of high-performance cathode active materials is essential for the commercialization of sodium-ion secondary batteries. Layered transition metal oxides, which have a simple structure, excellent electrochemical performance, and are easy to synthesize, are typically used as positive electrode active materials for sodium-ion secondary batteries. Layered transition metal oxides are typically classified into O3-type and P2-type depending on their crystal structure. Positive electrode active materials based on the O3-type structure exhibit a composition such as Na x (TM) O2 (2/3 < x ≤ 1), while positive electrode active materials based on the P2-type structure have a composition such as Na x (TM) O2 (x ≤ 2/3). P2-type layered oxides have relatively excellent cycle stability, but their commercial application is difficult due to disadvantages such as relatively degraded capacity characteristics resulting from a low sodium content. O3-type layered oxides have a higher energy density than P2-type layered oxide particles, but they have the disadvantage of reduced cycle stability due to greater structural changes during the charge-discharge process. Specifically, they have poor air and water stability, and during storage and processing, they react with surrounding H₂O and CO₂ to form sodium byproducts on the particle surface in the form of Na₂CO₃ and NaOH , causing structural degradation. As one of the various methods for doping cathode active materials to enhance properties, the introduction of mono- and multi-valence cations as doping elements is being studied. Since the doping elements are positioned within the lattice of the cathode active material, they can provide an effect that improves the physical and electrochemical properties of the cathode active material according to the unique characteristics of each doping element, such as binding energy and oxidation state. These doping elements can be selected from a variety of elements and adjusted to optimal concentrations depending on the desired effect. However, since the doping effect can vary depending on various internal and external factors such as size, diffusivity, and the manufacturing environment of the cathode active material, complex doping combining multiple elements may be more advantageous for improving the characteristics of the cathode active material than mono-doping substituting a single element, taking these variables into account. Specifically, complex doping has the advantage of selectively and combinedly providing various effects available for each doping element, such as structural stability, thermal stability, changes in cation mixing, and capacity changes of the cathode active material. However, even in the case of such complex doping, the potential effects of the doping elements must be considered, along with the characteristics of the sodium and transition metal elements in the cathode active material into which the doping elements are introduced, and the correlations between the doping elements. If complex doping elements are formulated without such consideration, problems may arise where doping efficiency decreases or, conversely, the characteristics of the cathode active material are degraded. Therefore, there is a high need for technology capable of optimizing the composition and content of doping elements to more efficiently improve the characteristics of the cathode active material. Figures 1 and 2 are cross-sectional SEM-EDS (Scanning electron microscope-energy dispersive x-ray spectroscopy) Cu analysis images of the transition metal hydroxide precursors prepared in Comparative Example 1 and Examples 1 and 2 (Figure 1), and cross-sectional SEM-EDS Cu, Zn analysis images of the prepared cathode active material particles (Figure 2). Figure 3 is an analysis result showing the average value (A) and standard deviation (B) of the total metal content (atomic mol%) excludin