KR-20260065120-A - positive electrode active material for sodium secondary battery, method for preparing the same and sodium secondary battery including the same

KR20260065120AKR 20260065120 AKR20260065120 AKR 20260065120AKR-20260065120-A

Abstract

One embodiment of the present invention provides a positive electrode active material for a sodium secondary battery comprising: a composite transition metal oxide comprising at least one transition metal selected from nickel, iron, manganese, and cobalt, sodium, and a doping metal, wherein a plurality of primary particles are aggregated into secondary particles; and a coating layer comprising an oxide of the doping metal covering at least a portion of the surface of the primary particles and at least a portion of the pores formed between the plurality of primary particles, wherein the doping metal is provided throughout including the center of the secondary particles, and exhibits a higher concentration in the center than in the surface portion of the secondary particles.

Inventors

전예진
김다모아
이동욱
박아람
곽환욱
조민수

Assignees

주식회사 에코프로비엠

Dates

Publication Date: 20260508
Application Date: 20241031

Claims (15)

A composite transition metal oxide comprising at least one transition metal selected from nickel, iron, manganese, and cobalt, sodium, and a doping metal, wherein a plurality of primary particles are aggregated into secondary particles; and A coating layer comprising an oxide of the doping metal, covering at least a portion of the surface of the primary particle and at least a portion of the pores formed between the plurality of primary particles; A positive electrode active material for a sodium secondary battery, wherein the doping metal is provided throughout the entire secondary particle including the center, and exhibits a higher concentration in the center than in the surface portion of the secondary particle.
In paragraph 1, A positive electrode active material for a sodium secondary battery, wherein the ratio (C2/C1) of the doping metal concentration (C1, atomic mol%) in the center of the secondary particle to the doping metal concentration (C2, atomic mol%) in the surface portion of the secondary particle is 1.1 to 3.5.
In paragraph 1, A positive electrode active material for a sodium secondary battery, wherein the doping metal is provided in the entire body including the center of the primary particle and in the coating layer, and exhibits a maximum concentration in the coating layer.
In paragraph 1, The above coating layer is a positive electrode active material for a sodium secondary battery, wherein the thickness of the coating layer formed on at least a portion of the surface of the primary particle is 2 to 30 nm.
In paragraph 1, A positive electrode active material for a sodium secondary battery, wherein the molar ratio (M1:M2) of the doping metal (M1) included in the composite transition metal oxide and the doping metal (M2) included in the doping metal oxide is 70:30 to 95:5.
In paragraph 1, The above doping metal comprises calcium and is substituted into the sodium layer of the above complex transition metal oxide, a positive electrode active material for a sodium secondary battery.
In paragraph 1, A positive electrode active material for a sodium secondary battery , wherein in the coating layer, the oxide of the doping metal comprises at least one selected from sodium calcium oxide ( Na₂CaO₂ ) and calcium oxide (CaO).
In paragraph 1, The above-mentioned 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-2x Ca x [(M y TM 1-y )]O 2 In the above chemical formula 1, TM is at least one selected from Ni, Fe, Mn and Co, and M is at least one selected from P, Sr, Ba, Ti, Zr, Al, W, Ce, Hf, Ta, Cr, F, Mg, Cr, V, Fe, Zn, Si, Y, Ga, Sn, Mo, Ge, Nd, B, Nb, Gd and Cu, and 0.80<a<1.20, 0.001≤x≤0.1, 0≤y≤0.1, 0.9≤1-y≤1.
In paragraph 1, The above secondary particle has an O3 crystal structure in X-ray diffraction analysis, and A positive electrode active material for a sodium secondary battery, having a full width at half maximum (FWHM) of the peak corresponding to the NiO (003) plane of 0.15 to 0.2°.
In paragraph 1, A positive electrode active material for a sodium secondary battery, comprising a secondary particle center density that is higher than the secondary particle surface density.
In paragraph 1, The above secondary particles are positive electrode active materials for sodium secondary batteries, having a particle strength of 14 to 16 kgf/ mm² .
A method for manufacturing a positive electrode active material comprising mixing a positive electrode active material precursor, a doping metal compound, and a sodium compound, and calcining the mixture, wherein The above-described positive electrode active material comprises: secondary particles formed by the aggregation of a plurality of primary particles; and a coating layer covering at least a portion of the surface of the primary particles and at least a portion of the pores formed between the plurality of primary particles, the coating layer comprising an oxide of the doping metal. A method for manufacturing a positive electrode active material for a sodium secondary battery, wherein the above calcination is performed such that the doping metal is provided throughout the entire secondary particle including the center, and exhibits a higher concentration in the center than in the surface portion of the secondary particle.
In Paragraph 12, A method for manufacturing an anode active material, wherein the above calcination is performed by calcining the above mixture at 875 to 975°C for 5 to 40 hours.
A cathode for a sodium secondary battery comprising a positive active material according to any one of claims 1 to 11.
Sodium secondary battery using a positive electrode according to Paragraph 14.

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. With the surging demand for lithium-ion rechargeable batteries, which are widely used as energy storage devices in various electronic technology fields, 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 required for commercialization. Layered transition metal oxides are typically used as cathode active materials for sodium-ion secondary batteries because they have a simple structure, excellent electrochemical performance, and are easy to synthesize. Layered transition metal oxides are generally classified into O3-type and P2-type based on their crystal structure; cathode active materials based on the O3-type structure exhibit a composition such as Na x (TM) O2 (2/3 < x < 1.2), while cathode active materials based on the P2-type structure have a composition of Na x (TM) O2 (x ≤ 2/3). Although O3-type layered oxides have a higher energy density compared to P2-type layered oxide particles, they have disadvantages such as reduced cycle stability due to larger structural changes during the charge-discharge process, which makes commercial application difficult. Research on methods for doping and coating metals onto cathode active materials is actively underway for the purpose of improving the aforementioned problems. Prior art document 1 (Registered Patent KR 2466222 B1) presents a calcium-doped cathode active material to achieve improved cycle characteristics by improving the cathode active material used in sodium secondary batteries. However, the prior art document has the disadvantage that when manufacturing the cathode active material, it is calcined at a relatively low temperature (600~850℃ or lower), so the calcium remains on the surface of the secondary particles of the cathode active material or is only doped into the interior of some primary particles, resulting in insufficient improvement in structural stability and difficulty in suppressing side reactions of the electrolyte at grain boundaries and improving particle compressive strength. Prior art document 2 (Published Patent CN 118039868 A) presents an anode active material in which a coating layer is formed on the surface of secondary particles and on the grain boundaries of primary particles. However, in the prior art, since the coating (doping) concentration on the surface is higher than the coating (doping) concentration on the center of the secondary particles, it is difficult to improve particle density and particle compressive strength. Furthermore, there are problems such as increased crack occurrence and deterioration of cycle life due to an increased reaction surface area with the electrolyte during the course of cycle life. Additionally, in the prior art, an anode active material is manufactured by synthesizing a transition metal (NFM) precursor, selectively mixing NaCO3 and a doping element, performing a first sintering, and then mixing a coating source and performing a second sintering. However, since both the first sintering (doping process) and the second sintering (coating process) are carried out at high temperatures, there is a problem in that the doping element migrates excessively to the surface of the secondary particles, increasing the coating/doping concentration on the surface. Therefore, it is necessary to develop Ca coating technology to manufacture stable and high-performance O3-type layered cathode active materials. Figures 1a to 1d are the results of cross-sectional TEM-EDS (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy) analysis of the cathode active materials according to Comparative Examples 1 and 2 and Examples 1 and 2. Figure 2 shows the results of analyzing the thickness of the Ca coating layer through cross-sectional TEM-EDS (Transmission Electron Microscopy-Energy Dispersive X-ray Spectroscopy) of the cathode active materials according to Comparative Examples 1 and 2 and Examples 1 and 2. Figures 3a and 3b are X-ray Diffraction (XRD) analysis results of the cathode active materials according to Comparative Examples 1 and 2 and Examples 1 and 2, and a graph of the FWHM (full width half mean) analysis of the NiO (