Dumbbell-shaped sodium vanadium fluorophosphate oxyhydroxide positive electrode material
By preparing dumbbell-shaped sodium vanadium fluorophosphate cathode material, the problems of irregular morphology and low tap density of NVPOF material were solved, achieving high density, excellent kinetics and good structural stability, and improving the volumetric energy density and cycle stability of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- QINGDAO UNIV OF SCI & TECH
- Filing Date
- 2025-09-03
- Publication Date
- 2026-07-24
AI Technical Summary
Existing sodium vanadium fluorophosphate (NVPOF) cathode materials suffer from problems such as irregular morphology, wide particle size distribution, and low tap density, resulting in low electrode tap density, which affects the volumetric energy density of the battery. Furthermore, the low ionic conductivity, poor tap density of nanomaterials, and poor cycle stability are also issues.
The cathode material is a dumbbell-shaped sodium vanadium fluorophosphate with the chemical formula Na3V2(PO4)2O2F. The micron-sized particles have a dumbbell-shaped structure that is thin in the middle and large at both ends. They are assembled from nanoparticles, providing ion transport channels. The surface is uneven, resulting in high tap density and excellent reaction kinetics.
It achieves high tap density, improves battery volumetric energy density, enhances reaction kinetics, significantly improves structural stability, extends cycle life, and maintains a capacity retention rate of up to 80.3%.
Smart Images
Figure CN224554330U_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sodium-ion battery cathode materials, specifically to a dumbbell-shaped sodium vanadium fluorophosphate cathode material. Background Technology
[0002] Sodium-ion batteries have broad application prospects in large-scale energy storage due to their abundant resources and low cost. NVPOF, as a representative of polyanionic cathode materials, has attracted widespread attention due to its stable NASICON-type crystal structure, high operating voltage, and safety.
[0003] Currently, common NVPOF cathode materials can be mainly classified into the following categories according to their morphology:
[0004] Irregular blocks / particles: mainly synthesized via a high-temperature solid-state method. This method is simple, but the products are usually hard blocks or large particles with irregular morphology and wide particle size distribution, low tap density, and poor electrode processing performance.
[0005] Nanoparticles / nanowires: These materials are mainly synthesized via hydrothermal or solvothermal methods. They possess a large specific surface area, which is beneficial for ion transport and results in good rate performance. However, their low tap density leads to a lower volumetric energy density of the electrode, and the nanoparticles are prone to aggregation, posing challenges to cycle stability.
[0006] Spherical micron-sized particles: These are typically prepared by a combination of spray drying and calcination. Spherical particles have a high tap density, but their smooth surface and limited specific surface area may affect electrolyte wetting and ion transport rates. Utility Model Content
[0007] This invention discloses a dumbbell-shaped sodium vanadium fluorophosphate (NVPOF) cathode material, aiming to address the problems of irregular morphology, wide particle size distribution, and low tap density found in existing NVPOF cathode materials. Irregularly shaped particles are difficult to pack tightly during electrode fabrication, resulting in low electrode tap density and severely limiting the volumetric energy density of the battery. Simultaneously, the material inherently has low ionic conductivity, and while nanomaterials can improve kinetics, their tap density often worsens. This invention provides an NVPOF cathode material with a unique dumbbell-shaped micron-sized structure. This special morphology simultaneously achieves high tap density, good reaction kinetics, and excellent structural stability, effectively solving the aforementioned technical problems.
[0008] To achieve the above objectives, the technical solution of this invention is as follows:
[0009] A dumbbell-shaped sodium vanadium fluorophosphate cathode material, wherein the chemical formula of the cathode material is Na3V2(PO4)2O2F; the cathode material is micron-sized particles, wherein the micron-sized particles have a dumbbell-shaped structure that is thin in the middle and large at both ends, wherein the dumbbell-shaped structure is assembled from several primary nanoparticles, wherein ion transport channels are formed between the nanoparticles, and the surface of the micron-sized particles is uneven.
[0010] Preferably, the length of the micron-sized particles is 2 to 4 μm.
[0011] This novel dumbbell-shaped sodium vanadium fluorophosphate cathode material has the following beneficial effects:
[0012] 1. Higher tap density and volumetric energy density: Dumbbell-shaped particles can achieve a tighter interlocking and stacking during electrode fabrication. Their tap density is higher than that of nanomaterials and comparable to or even better than that of spherical micron particles. This allows for the fabrication of electrodes with higher compaction density, directly improving the volumetric energy density of the battery.
[0013] 2. Superior reaction kinetics: Unlike smooth spherical particles, dumbbell-shaped structures have greater surface roughness and specific surface area, providing more channels for electrolyte wetting, more active interfaces and shorter diffusion paths for sodium ion insertion / extraction, thus exhibiting superior rate performance compared to spherical micron-sized particles.
[0014] 3. Significantly enhanced structural and cycling stability: Due to its unique geometry, the dumbbell-shaped structure possesses superior mechanical strength, effectively absorbing and buffering the lattice stress generated during sodium ion insertion / extraction, reducing particle breakage and active material shedding during cycling. For example... Figure 3 As shown in (c), its capacity retention rate is as high as 80.3% after 400 cycles at 1C rate, and its cycle stability is far superior to most reported NVPOF materials.
[0015] 4. The dumbbell-shaped sodium fluorophosphate cathode material described above has the characteristics of regular morphology, uniform particle size distribution, high tap density, excellent rate performance, and stable cycle performance. Attached Figure Description
[0016] Figure 1 Scanning electron microscope (SEM) image of this novel NVPOF.
[0017] Figure 2 XRD spectrum of this novel NVPOF.
[0018] Figure 3 Figure (a) Charge-discharge curve of NVPOF at 1C; Figure (b) Rate performance of NVPOF; Figure (c) Cycling performance of NVPOF. Detailed Implementation
[0019] The following is a detailed description of the embodiments of the present invention in a step-by-step manner. This description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
[0020] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or a specific orientational structure and operation. Therefore, they should not be construed as limitations on this invention.
[0021] Example 1
[0022] A dumbbell-shaped sodium vanadium fluorophosphate cathode material, with the chemical formula Na3V2(PO4)2O2F; the core of this material lies in its unique microstructure. (See attached image.) Figure 1 As shown in the scanning electron microscope (SEM) images, the material consists of single, regularly shaped dumbbell-shaped microparticles (a large number of microparticles constitute the material powder). The overall size (length) distribution of the dumbbell-shaped particles is uniform, mainly concentrated in the range of 2–4 μm. Each dumbbell-shaped particle is assembled from even smaller primary nanoparticles.
[0023] like Figure 1 As shown, the dumbbell-shaped structure exhibits a geometric shape with a relatively slender middle section and significantly enlarged ends, resembling a dumbbell. This unique morphology combines the advantages of both micron- and nano-materials.
[0024] The micron scale ensures that the particles have a high tap density, which is beneficial for the close packing of electrodes.
[0025] In addition, the nanoparticles assembled with an uneven surface provide a large specific surface area and abundant ion transport channels.
[0026] As mentioned above, the material's unique mechanical structure allows it to better withstand and buffer volume changes during charging and discharging.
[0027] Appendix Figure 2 The X-ray diffraction (XRD) pattern of the material is provided. The pattern shows that it has a standard NASICON-type crystal structure, with sharp diffraction peaks and no impurity peaks, indicating that the material has high crystallinity and high phase purity.
[0028] Example 2
[0029] Based on Example 1, this example discloses the preparation method of this novel invention, as follows:
[0030] S1: Place the sodium source (e.g., sodium fluoride), phosphorus source (e.g., sodium dihydrogen phosphate), and fluorine source in beaker A according to their stoichiometric ratio. Add deionized water and stir at 300 rpm for 60 minutes at room temperature until completely dissolved. Use ammonia solution as a pH adjuster and slowly add it dropwise to beaker A while stirring. Monitor the pH with a precision pH meter and accurately adjust the solution to 8.0 ± 0.05, maintaining stirring for 30 minutes to ensure uniformity and stability.
[0031] Alternatively, a vanadium source (such as vanadium oxysulfate) is dissolved in deionized water in beaker B according to a stoichiometric ratio to form a homogeneous solution under the same stirring conditions. Then, while continuously stirring (300 rpm), the solution in beaker A is slowly added dropwise to beaker B through a constant-pressure dropping funnel, and a gray flocculent precipitate is immediately observed to form. After the addition is complete, the reaction is continued with stirring for 2 hours.
[0032] The reaction system was allowed to stand at room temperature for 36 hours to complete the directional self-assembly process of the NVPOF precursor. After standing, the supernatant was clear and the precipitate was bluish-green.
[0033] S2: The obtained precipitate is centrifuged and washed three times alternately with deionized water and anhydrous ethanol. It is then vacuum dried at 80°C for 12 hours. The resulting powder is placed in an agate grinding medium and lightly ground to obtain dumbbell-shaped NVPOF material.
[0034] S3: The prepared NVPOF material, Super P conductive agent, and PVDF binder were mixed in a mass ratio of 8:1:1 to form a slurry, which was then uniformly coated onto an aluminum foil current collector. After drying and rolling, a positive electrode sheet was formed. Using a sodium metal sheet as the negative electrode, glass fiber as the separator, and 1M NaPF6 in EC:DEC (1:1) as the electrolyte, CR2032 coin cells were assembled in an argon-protected glove box.
[0035] The working principle of this new type:
[0036] like Figure 1 The image shows a SEM image of the dumbbell-shaped NVPOF sample prepared according to this novel method. It is clearly visible that the obtained material exhibits a highly uniform dumbbell-shaped micron structure with an overall size distribution between 2 and 4 μm. It is composed of ordered primary nanoparticles with regular morphology and good dispersion. This dumbbell-shaped structure effectively increases the tap density of the material, facilitating close packing during electrode fabrication. Simultaneously, its unique geometry provides a suitable specific surface area, which is beneficial for electrolyte wetting and provides more active interfaces and shorter diffusion paths for sodium ion insertion / extraction.
[0037] like Figure 2The image shows the XRD pattern of the dumbbell-shaped NVPOF material prepared in this novel manner. The absence of impurity peaks indicates that a high-purity, well-crystallized NVPOF material was successfully synthesized under room temperature and pH-controlled conditions.
[0038] like Figure 3 As shown in (a), the first charge-discharge curves of the dumbbell-shaped NVPOF material at a 1C rate and a voltage window of 2–4.3V are displayed. Two distinct voltage plateaus are observed, located approximately at 3.6 / 3.7V and 4.0 / 4.1V, respectively, corresponding to the sodium ion insertion / extraction processes at the Na2 and Na1 sites. The first-cycle discharge specific capacity reaches approximately 113.4 mAh / g, demonstrating excellent electrochemical reversibility.
[0039] like Figure 3 (b) shows the rate performance of the material at different current densities from 0.1C to 20C. It exhibits good capacity retention at all rates, demonstrating excellent reaction kinetics and structural stability.
[0040] like Figure 3 (c) shows the long-term cycling performance of the material at 1C current. The initial discharge specific capacity is 113.4 mAh / g, and after 400 cycles, the capacity retention rate is still as high as 80.3%, exhibiting extremely excellent cycling stability. This is mainly attributed to the effective buffering effect of the dumbbell-shaped structure on volumetric strain during cycling.
[0041] As mentioned above, the existing technology has the following problems:
[0042] 1. The contradiction between morphology and performance: Micron-sized materials with high tap density (such as spherical particles and irregular blocks) often have low specific surface area and long ion diffusion paths, resulting in poor reaction kinetics; while nanomaterials with good kinetic properties (such as nanoparticles and nanowires) have problems such as low tap density, poor electrode processing performance and poor cycle stability.
[0043] 2. Insufficient structural stability: Sodium ions cause repeated changes in the volume of the material during the insertion and extraction process. Traditional spherical or irregular particles are prone to breakage and pulverization after long-term cycling, resulting in the separation of the active material from the conductive network and rapid capacity decay.
[0044] To address the aforementioned shortcomings, this novel invention achieves the following breakthroughs:
[0045] 1. High tap density is ensured through a micron-level dumbbell-shaped structure, thereby improving the volumetric energy density of the battery.
[0046] 2. Its unique "large at both ends and thin in the middle" morphology provides a moderate specific surface area and abundant surface active sites, which promotes electrolyte wetting, shortens the ion diffusion path, and improves reaction kinetics.
[0047] 3. By utilizing the excellent mechanical strength of the dumbbell-shaped structure, the volumetric strain during the cycling process is buffered, reducing particle breakage and thus significantly improving the cycle life of the material.
Claims
1. A dumbbell-shaped sodium vanadium fluorophosphate cathode material, characterized in that, The chemical formula of the positive electrode material is Na3V2(PO4)2O2F; the positive electrode material is a micron-sized particle, which is a dumbbell-shaped structure that is thin in the middle and large at both ends. The dumbbell-shaped structure is assembled from several primary nanoparticles, and ion transport channels are formed between the nanoparticles. The surface of the micron-sized particle is uneven.
2. The dumbbell-shaped sodium vanadium fluorophosphate cathode material as described in claim 1, characterized in that, The length of the micron-sized particles is 2–4 μm.