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KR-20260065117-A - positive electrode active material for sodium secondary battery, method for preparing the same and sodium secondary battery including the same

KR20260065117AKR 20260065117 AKR20260065117 AKR 20260065117AKR-20260065117-A

Abstract

One embodiment of the present invention provides a positive electrode active material for a sodium secondary battery, comprising: a sodium transition metal fluoride (Na-M-F); and a coating layer surrounding at least a portion of the sodium transition metal fluoride particles, wherein the coating layer comprises a sacrificial positive electrode material.

Inventors

  • 김다모아
  • 이동욱
  • 김종순

Assignees

  • 주식회사 에코프로비엠
  • 성균관대학교산학협력단

Dates

Publication Date
20260508
Application Date
20241031

Claims (14)

  1. Sodium transition metal fluoride (Na-MF); and It includes a coating layer surrounding at least a portion of the above sodium transition metal fluoride particles, and The above coating layer is a positive active material for a sodium secondary battery, comprising a sacrificial positive material.
  2. In paragraph 1, The above coating layer is a positive active material for a sodium secondary battery, comprising sodium phosphate as a sacrificial positive material.
  3. In paragraph 1, The above coating layer comprises Na₃PO₄ as a sacrificial anode material, and The above coating layer is a positive electrode active material for a sodium secondary battery comprising at least one selected from MPO4, MP2O7, MPO4F, M3(PO4)2 ( P2O7 ) and Na x MPO4F ( 1≤x≤2 ), which is a compound synthesized by the Na3PO4 releasing a sodium ion source and reacting with the sodium transition metal fluoride.
  4. In paragraph 3, The above coating layer is a positive electrode active material for a sodium secondary battery comprising at least one selected from FePO4 , FeP2O7 , FePO4F , Fe3 ( PO4 ) 2 ( P2O7 ) and Na x FePO4F ( 1≤x≤2 ) , which is a compound synthesized by the Na3PO4 releasing a sodium ion source and reacting with the sodium transition metal fluoride.
  5. In paragraph 1, The sodium transition metal fluoride (Na-MF) having the above-mentioned coating layer has a decreasing concentration gradient of the transition metal (M) within the sodium transition metal fluoride from the center of the particle toward the coating layer on the surface portion of the particle. A positive electrode active material for a sodium secondary battery, characterized in that the surface portion of the above particle has an increasing concentration gradient of the remaining metal after releasing the sodium ion source within the sacrificial positive electrode material from the center of the particle toward the coating layer.
  6. In paragraph 1, A positive electrode active material for a sodium secondary battery, comprising 1 to 20 weight% based on the total weight of the sodium transition metal fluoride on which the coating layer is formed.
  7. In paragraph 1, The above sodium transition metal fluoride 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 x M y F 7 In the above chemical formula 1, M is at least one transition metal selected from the group consisting of Fe, Mn, Ti and Co, and 1≤x≤3, 1≤y≤3.
  8. In paragraph 1, The above sodium transition metal fluoride is a positive electrode active material for a sodium secondary battery comprising Na₂Fe₂F₆ .
  9. In paragraph 1, For a sodium secondary battery comprising a positive electrode using the above-mentioned positive electrode active material and a sodium metal plate counter electrode, when performing high-voltage initial charging and initial discharging at 25℃, a voltage range of 1.5V to 4.6V, and a discharge rate of 0.1C, A positive electrode active material for a sodium secondary battery having a (003) plane peak intensity ratio (CH/DCH) of the positive electrode after initial charging (CH)/after initial discharging (DCH) as determined by X-ray diffraction analysis (XRD) of 0.95 to 1.2.
  10. In paragraph 1, For a sodium secondary battery comprising a positive electrode using the above-mentioned positive electrode active material and a sodium metal plate counter electrode, after performing high-voltage initial charging and initial discharging at 25℃, a voltage range of 1.5V to 4.6V, and a discharge rate of 0.1C, A positive electrode active material for a sodium secondary battery, wherein in the Fe 2p region by X-ray photoelectron spectroscopy (XPS), the ratio of the peak area [F3/(F2+F3)] of the (Fe 3+ ) peak area originating from a binding energy of 705–725 eV and the (Fe 2+ ) peak area originating from a binding energy of 705–730 eV is 0.65 to 0.70.
  11. A step of preparing a mixture by mixing sodium transition metal fluoride and sacrificial anode material; and A method for manufacturing a positive electrode active material for a sodium secondary battery, comprising a heat treatment step of heat-treating the above mixture to produce the positive electrode active material of claim 1.
  12. In Paragraph 11, A method for manufacturing an anode active material, wherein the heat treatment step involves heat-treating the mixture at 200 to 400°C in an inert gas atmosphere for 2 to 6 hours.
  13. A cathode for a sodium secondary battery comprising a cathode active material according to any one of claims 1 to 10.
  14. Sodium secondary battery using a positive electrode according to Paragraph 13.

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, so the development of high-performance cathode active materials is required for commercialization. Currently, carbon-based and silicon (Si)-based anode active materials, such as graphite, and layered transition metal oxide-based cathode active materials are being used to improve the energy density of sodium-ion secondary batteries. However, while these cathode and anode materials exhibit high reversible capacity, they suffer from a problem where the limited sodium ions in the cathode material are consumed due to irreversible phase transitions, such as the formation of solid electrolyte interface (SEI, CEI) films on the electrode surface during the initial charging process, thereby degrading the energy density and cycle stability of the secondary battery. Accordingly, research is underway to commercialize a material called a sacrificial cathode, which replenishes sodium ions instead of the cathode active material during the initial charging reaction. This sacrificial cathode material is expected to solve the problem of sodium ion consumption, thereby preventing performance degradation in sodium-ion secondary batteries and improving charge imbalance issues. Sodium replenishment technologies currently under development are classified into positive electrode sodium replenishment and negative electrode sodium replenishment methods. Among these, the positive electrode sodium replenishment method involves forming a sacrificial anode layer by applying a sodium replenishment slurry onto a positive electrode active material layer formed on a positive electrode plate; however, this method has problems in that it increases process complexity and makes quality control difficult during the manufacture of the positive electrode plate. Another method involves manufacturing a composite cathode active material by mixing or coating the cathode active material with a sodium supplement, and sodium carbonate, sodium oxalate, sodium azide, sodium oxide, etc., are generally used as sodium supplements. The characteristics required for such sodium supplementation materials include the ability to achieve high capacity during the initial charging process by containing an excess amount of sodium ions compared to the positive electrode active material, and irreversibility characteristics that prevent participation in the electrochemical reactions of the positive and negative electrode materials of the sodium-ion secondary battery during subsequent charging and discharging processes. Prior art document 1 (Chinese Published Patent No. 112928252) aims to improve rate characteristics and lifespan characteristics by removing residual sodium through a reaction between residual sodium on the surface of the positive electrode active material and an acidic solution, while simultaneously forming a sodium salt with high ion conductivity. Specifically, it presents a P2-type Na x MO 2 (0.66 < x ≤ 1, M can be a combination of Ni, Co, and Mn) sodium ion battery positive electrode active material coated with sodium borate or sodium phosphate. However, as described in the literature above, when sodium borate, sodium phosphate, etc. are coated on the surface of an oxide-based cathode material and initial charging is performed, sodium is released and remains as boric acid or phosphoric acid. Since the boric acid or phosphoric acid is difficult to structurally react with the oxide-based cathode material, it is difficult to form a coating layer. Even if a coating layer is formed after the reaction, Na delamination and O delamination occur simultaneously, making it difficult for the reaction between the surface of the cathode material and the coating layer to occur, and there is a problem of reduced structural stability of the cathode material. Prior art document 2 (Korean Registered Patent No. 10-2170280) provides a cathode material with improved stability, such as thermal stability, through surface treatment, and presents a P2-type Na x [Mn 1 -yz M1 y M2 z ]O 2-α Z α (x is 0.5 to 1, y i