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WO-2026091148-A1 - POSITIVE ELECTRODE MATERIAL, PREPARATION METHOD THEREFOR, POSITIVE ELECTRODE SHEET, AND SODIUM ION BATTERY

WO2026091148A1WO 2026091148 A1WO2026091148 A1WO 2026091148A1WO-2026091148-A1

Abstract

The present application provides a positive electrode material, a preparation method therefor, a positive electrode sheet, and a sodium ion battery. The positive electrode material comprises composite particles, the molecular formula of the composite particles being: Na x Fe y (PO 4 ) n (P 2 O 7 ) m , wherein x is 4.2-4.5, y is 3.2-3.5, n is 2.2-2.5, and m is 0.9-1.1. The composite particles comprise an olivine-type phosphate and a polyanionic phosphate coated on the surface of the olivine-type phosphate, and the molar ratio of the olivine-type phosphate to the polyanionic phosphate is (0.2-0.5):1. By optimizing the molar ratio of the olivine-type phosphate to the polyanionic phosphate in an iron-based composite phosphate material and designing the microstructure of the composite particles formed by the olivine-type phosphate and the polyanionic phosphate, the present application achieves nanocrystallization at the crystal structure level and interfacial permeation between the two phases, thereby significantly increasing the capacity of the positive electrode material.

Inventors

  • PENG, Tangping
  • LV, Fei
  • LV, Huihui

Assignees

  • 湖北万润新能源科技股份有限公司

Dates

Publication Date
20260507
Application Date
20241104
Priority Date
20241031

Claims (10)

  1. A positive electrode material, characterized in that the positive electrode material comprises composite particles, the molecular formula of which is: NaxFey ( PO4 ) n ( P2O7 ) m , wherein x is 4.2-4.5, y is 3.2-3.5, n is 2.2-2.5, and m is 0.9-1.1; The composite particles include olivine phosphate and polyanionic phosphate coated on the surface of the olivine phosphate, and the molar ratio of the olivine phosphate to the polyanionic phosphate is (0.2-0.5):1.
  2. According to claim 1, the positive electrode material is characterized in that the molar ratio of the olivine phosphate to the polyanionic phosphate is (0.2-0.4):1.
  3. The cathode material according to claim 1 or 2 is characterized in that the cathode material further includes a carbon layer coated on the surface of the composite particles, and the mass fraction of the carbon layer is 1.5% to 3.0% based on the total weight of the cathode material as 100%. Preferably, the carbon layer is an amorphous carbon portion formed by an organic carbon source and/or an inorganic carbon portion formed by an inorganic carbon source; More preferably, the carbon layer is a combination of the amorphous carbon portion and the inorganic carbon portion, and the inorganic carbon portion accounts for 2.5% to 5.0% of the total weight of the carbon layer (100%).
  4. The positive electrode material according to any one of claims 1 to 3 is characterized in that the powder resistivity of the positive electrode material is 12000 Ω·cm to 93000 Ω·cm.
  5. A method for preparing a positive electrode material, characterized in that the method comprises: Sodium source, iron source and phosphorus source are formulated into the first slurry; The first slurry is subjected to a first drying and a first calcination to obtain a precursor; The precursor and carbon source are formulated into a second slurry; The second slurry is subjected to a second drying and a second calcination to obtain the positive electrode material.
  6. According to the method for preparing the cathode material according to claim 5, the molar ratio of sodium, iron and phosphorus in the first slurry is (4.2-4.86):(3.2-3.5):(4.2-4.5). Preferably, the first calcination includes a first calcination and a second calcination performed sequentially, and, The first calcination is carried out at a temperature of 400℃ to 500℃ for 1.5h to 2.5h; the second calcination is carried out at a temperature of 550℃ to 650℃ for 10h to 14h. More preferably, the first calcination is carried out under a protective atmosphere.
  7. According to the method for preparing the cathode material according to claim 6, the sodium source is selected from one or more of sodium bicarbonate, sodium phosphate, sodium monohydrogen phosphate, and sodium dihydrogen phosphate; the iron source is selected from one or more of anhydrous ferric phosphate, polyhydrate ferric phosphate, monohydrogen phosphate, and ferrous oxalate; and the phosphorus source is selected from one or more of anhydrous ferric phosphate, ammonium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, polyhydrate ferric phosphate, and monohydrogen phosphate. Preferably, the carbon source includes an organic carbon source and/or an inorganic carbon source; Preferably, the organic carbon source is selected from one or more of citric acid, glucose, sucrose, soluble starch and polyethylene glycol; and/or, the inorganic carbon source is selected from one or more of graphite, carbon nanotubes and graphene. Preferably, the carbon source includes the soluble starch, the polyethylene glycol, and the graphene; More preferably, the polyethylene glycol is PEG-2000.
  8. The method for preparing the cathode material according to any one of claims 5 to 7, characterized in that the second calcination comprises the following sequential steps: The first stage of calcination is carried out at a temperature of 40℃～60℃ and a holding time of 1h～2h. The second stage of calcination is carried out at a temperature of 100℃～130℃, and the holding time is 0.5h～1.5h. The third stage of calcination is carried out at a temperature of 180℃～210℃, and the holding time is 2h～4h. The fourth stage of calcination is carried out at a temperature of 500℃～600℃ and a holding time of 2h～6h. Preferably, the heating rates of the first calcination stage, the second calcination stage, the third calcination stage, and the fourth calcination stage are each independently 3℃/min to 10℃/min.
  9. A positive electrode sheet, characterized in that the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 4, or the positive electrode material prepared by the preparation method of the positive electrode material according to any one of claims 5 to 8.
  10. A sodium-ion battery, characterized in that the sodium-ion battery includes the positive electrode sheet as described in claim 9.

Description

Positive electrode materials, their preparation methods, positive electrode sheets and sodium-ion batteries Technical Field This invention relates to the field of sodium-ion battery technology, and more specifically, to a positive electrode material, its preparation method, a positive electrode sheet, and a sodium-ion battery. Background Technology In recent years, significant efforts have been devoted to developing cost-effective and high-performance cathode materials for commercially viable sodium-ion batteries, such as those used in new energy vehicles. In a related field, lithium-ion batteries, the LiFePO4 cathode has achieved tremendous commercial success. This type of iron-based phosphate material offers superior performance and is inexpensive, making it considered one of the best choices for cathode active materials in rechargeable batteries. However , olivine-type NaFePO4 (NFP) exhibits poor thermodynamic properties and is considered electrochemically inert. In contrast, pyrophosphate Na2FeP2O7 materials, due to their open three-dimensional Na + channels in their microstructure and the strong inductive effect of P2O74- in their crystals , allow for higher operating voltages (~3.0V). However, the low reversible capacity (< 100mAh · g⁻¹ ) of Na2FeP2O7 severely hinders its practical applications. Both olivine-type phosphates and polyanionic phosphates have certain shortcomings when used as positive electrode active materials in sodium-ion batteries, resulting in inferior battery performance. Current technology provides a polyanionic positive electrode material comprising phosphates and a carbon layer coating the phosphate surface. The phosphates include NFPP, NFP, and NNFPO, and the ratio of NFP to NNFPO content is controlled through multiple short-time sintering processes. However, this technology only reduces impurity phases in the positive electrode material and does not achieve synergistic effects between different crystalline phases; therefore, the performance of the resulting positive electrode material still needs improvement. Therefore, how to design the positive electrode active material of sodium-ion batteries at the crystalline phase level to give it superior electrochemical performance is one of the important technical problems that need to be solved in this field. Summary of the Invention The main objective of this invention is to provide a cathode material, its preparation method, a cathode sheet, and a sodium-ion battery, so as to solve the problem of poor electrical performance of cathode materials in existing sodium-ion batteries. To achieve the above objectives, the first aspect of the present invention provides a positive electrode material comprising composite particles with the molecular formula NaxFey ( PO4 ) n ( P2O7 ) m , where x is 4.2–4.5, y is 3.2–3.5, n is 2.2–2.5, and m is 0.9–1.1. The composite particles comprise olivine phosphate ( NaFePO4 , NFP) and polyanionic phosphate ( Na4Fe3 ( PO4 ) 2P2O7 , i.e., NFPP) coated on the surface of the olivine phosphate, and the molar ratio of the olivine phosphate to the polyanionic phosphate is (0.2–0.5):1. This invention optimizes the cathode material, specifically the molar ratio of olivine phosphate to polyanionic phosphate in the iron-based composite phosphate material, to be (0.2–0.5):1. Simultaneously, it designs the microstructure of the composite particles formed by these two components, allowing the polyanionic phosphate phase to encapsulate the olivine phosphate crystals. This achieves nanocrystallization at the crystal structure level and interfacial penetration between the two phases, inducing Na + to pass through the olivine phosphate phase, thereby realizing the electrochemical activation of the olivine phosphate phase and significantly improving the capacity of the iron-based composite phosphate (NxFPP). Furthermore, the molar ratio of olivine phosphate to polyanionic phosphate is (0.2–0.4):1. When the proportion of olivine phosphate in the material structure is too high, the polyanionic phosphate crystal phase cannot completely encapsulate the olivine phosphate crystal, resulting in the presence of olivine phosphate crystals forming independently on the outside of the polyanionic phosphate crystal, becoming an impurity phase within the polyanionic phosphate crystal, leading to a lower capacity of the composite material. When the proportion of olivine phosphate is too low, there are correspondingly fewer olivine phosphate crystals inside the polyanionic phosphate crystal, making it difficult to fully penetrate the two-phase interface, resulting in fewer electrochemically activated olivine phosphate phases, thus making it difficult to significantly improve the capacity of the composite material. Furthermore, in order to improve the conductivity of the obtained cathode material and its structural stability during the charge-discharge process, the cathode material also includes a carbon layer coated on the surface of the co