Sodium-ion battery negative electrode material, preparation method thereof and sodium-ion battery

Abstract

The invention discloses a sodium-ion battery negative electrode material and a preparation method thereof, and belongs to the technical field of aqueous sodium-ion battery materials, the chemical general formula of the sodium-ion battery negative electrode material is NaBixV1-xO2-delta, 0.45 < = x < = 0.55, 0.05 < = delta < = 0.12, and the oxygen vacancy concentration is 1 * 10 < 18 > cm <-3 >-5 * 10 < 18 > cm <-3 >, so that the sodium-ion battery negative electrode material can be prepared by introducing oxygen vacancies with proper concentration. The electronic conductivity of the negative electrode material is greatly improved, and a sodium ion diffusion channel is widened; through local electronic structure change caused by oxygen vacancy, an oxidation-reduction potential platform of the negative electrode material is flatter and is at a relatively high potential, so that voltage platform fluctuation is effectively reduced, and the negative electrode potential of the battery is stably maintained at a hydrogen evolution potential; through lattice defects formed by oxygen vacancies, lattice stress is buffered, anisotropic expansion and contraction of lattices are effectively inhibited, and the stability of the negative electrode material is enhanced.

Description

Technical Field

[0001] This invention belongs to the technical field of aqueous sodium-ion battery materials, specifically relating to a sodium-ion battery anode material with controllable oxygen vacancy concentration and its preparation method. Background Technology

[0002] With the increasing global demand for large-scale energy storage systems, it is crucial to develop safe, low-cost, and environmentally friendly new electrochemical energy storage technologies. Aqueous sodium-ion batteries, due to their inherent advantages such as high safety, low raw material costs, environmental friendliness, and excellent ionic conductivity, have become one of the most promising energy storage technologies.

[0003] However, in aqueous environments, if the operating potential of the negative electrode material is too low, it can easily trigger a hydrogen evolution reaction at the interface, leading to electrolyte decomposition, battery failure, and safety issues. Therefore, the negative electrode of an aqueous sodium-ion battery needs to have a sufficiently high operating voltage (typically higher than 1.5 V vs. Na). + The anode material (Na) avoids the hydrogen evolution window thermodynamically, ensuring stable battery operation. On the other hand, to meet the long cycle life requirements of energy storage devices, the anode material must maintain excellent structural stability during repeated sodium ion insertion / extraction and has an extremely low volume expansion rate (less than 5%) to achieve long-term stable cycle performance and ensure battery cycle life.

[0004] Currently, research on anode materials for aqueous sodium-ion batteries still faces significant challenges. For example, while existing vanadium-based materials (such as Na3V2(PO4)3) possess stable framework structures, their main redox potential plateau is approximately 1.6V (vs. Na3V2(PO4)3). + The material is located near the Na group and is easily soluble in aqueous environments, resulting in a capacity loss exceeding 5% per 100 cycles, making it difficult to meet the stringent cycle life requirements of practical applications. Another example is sodium bismuth vanadate (such as NaBi). 0.5 V 0.5 Although O2 materials have high operating voltage potential, their intrinsic electronic conductivity is extremely low (typically below 10). -9 The oxygen vacancy concentration (S / cm) severely limits the charge transfer rate and rate performance; moreover, the material is mostly produced using traditional sintering processes, which makes it impossible to precisely control the oxygen vacancy concentration. Summary of the Invention

[0005] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a sodium-ion battery anode material, a method for preparing the same, and a sodium-ion battery, which has the characteristics of high voltage platform, high ion diffusion system and low cycle expansion rate.

[0006] To achieve the above objectives, one aspect of the present invention provides a sodium-ion battery anode material, wherein the general chemical formula of the sodium-ion battery anode material is NaBi. x V 1-x O 2-δ Where 0.45≤x≤0.55, 0.05≤δ≤0.12, and the oxygen vacancy concentration is 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0007] As a further improvement of the present invention, the crystal structure of the sodium-ion battery negative electrode material is a monoclinic phase.

[0008] As a further improvement of the present invention, the space group of the monoclinic phase crystal structure is C2 / m, and the cell parameter is c = 10.80~10.90 Å.

[0009] In another aspect, the present invention provides a sodium-ion battery comprising the above-described sodium-ion battery negative electrode material.

[0010] In another aspect, the present invention provides a method for preparing a sodium-ion battery anode material, for use in the preparation of the aforementioned sodium-ion battery anode material, comprising the following steps: S1: Weigh Na2CO3, Bi2O3, and V2O5 according to the set stoichiometric ratio, ball mill them together, and then dry them to obtain the precursor; S2: The precursor is sintered under an argon-hydrogen mixture to obtain the sodium-ion battery anode material.

[0011] As a further improvement of the present invention, in step S1, the ball milling is carried out in a zirconium oxide ball milling jar under anhydrous ethanol medium, the ball-to-material ratio is (15~5):1, the ball milling speed is 200~600 rpm, and the time is 4~10h.

[0012] As a further improvement of the present invention, in step S1, the drying is performed in a vacuum environment at 60~100°C for 6~15 hours.

[0013] As a further improvement of the present invention, in step S2, the flow rate of the argon-hydrogen mixture is 40~60 mL / min, and the volume fraction of hydrogen in the argon-hydrogen mixture is 2.5%~3.5%.

[0014] As a further improvement of the present invention, step S2 involves heating the mixture to 450-550°C at a rate of 3-8°C / min under an argon-hydrogen mixture and holding it at that temperature for 6-12 hours.

[0015] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0016] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include: (1) The sodium-ion battery anode material NaBi of the present invention x V 1-x O 2-δ By introducing an appropriate concentration of oxygen vacancies, the electronic conductivity of the anode material is significantly improved, and the sodium ion diffusion channels are broadened. The local electronic structure changes caused by oxygen vacancies make the redox potential plateau of the anode material flatter and at a higher potential, effectively reducing voltage plateau fluctuations and ensuring that the anode potential of the battery is stably maintained at the hydrogen evolution potential. The lattice defects formed by oxygen vacancies buffer lattice stress, effectively suppressing anisotropic expansion and contraction of the lattice and enhancing the stability of the anode material.

[0017] (2) The method for preparing the sodium-ion battery negative electrode material of the present invention involves sintering the precursor under an argon-hydrogen atmosphere. Under the protective atmosphere formed by argon, hydrogen is used as a reducing agent to react with the lattice oxygen on the surface of the precursor, thereby precisely creating oxygen vacancies in the bulk phase of the negative electrode material and forming a stable defect structure. The concentration of the negative electrode material is controlled at 1×10⁻⁶ by controlling the volume of hydrogen introduced and the sintering temperature. 18 cm -3 ~5×10 18 cm -3 This is to avoid insufficient electronic conductivity due to excessively low hydrogen content, and to avoid excessively high hydrogen content, which would lead to oversaturation of oxygen vacancies and consequently cause the structure of the negative electrode material to collapse easily. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the electron paramagnetic resonance (EPR) image of the sodium-ion battery anode material in the embodiments of the present invention; Figure 2 This is a half-cell long-term cycle curve of the sodium-ion battery anode material and conventional materials in the embodiments of the present invention. Figure 3 This is the XRD pattern of the sodium-ion battery anode material in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0021] In the description of this invention, it should be understood that, unless otherwise expressly specified and limited, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0022] Furthermore, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically limited.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] Example: The preferred embodiment of the sodium-ion battery anode material of the present invention has the general chemical formula NaBi. x V 1-x O 2-δ Where x is the Bi / V molar ratio, and 0.45≤x≤0.55, δ is the corresponding value of oxygen vacancy concentration, and 0.05≤δ≤0.12, and the oxygen vacancy concentration of the sodium-ion battery anode material is 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

[0026] This invention introduces an appropriate concentration of oxygen vacancies into the negative electrode material. It is understood that the generation of oxygen vacancies is accompanied by the release of electrons. These additional electrons are injected into the conduction band of the material and can even reduce transition metal ions to form more charge carriers, thereby significantly improving electronic conductivity. Simultaneously, the local distortion and charge rearrangement of the surrounding lattice caused by oxygen vacancies widens the sodium ion diffusion channels. Furthermore, as a controllable lattice defect, oxygen vacancies can accommodate local stress during sodium ion insertion / extraction, acting as a buffer and effectively suppressing anisotropic expansion and contraction of the lattice. The pre-introduced oxygen vacancies put the lattice in a "pre-relaxed" state, allowing the negative electrode material to better adapt to volume changes during cycling, thereby effectively reducing volume expansion during battery charging and discharging and ensuring battery cycle life.

[0027] Preferably, the sodium-ion battery anode material has a monoclinic crystal structure with a space group of C2 / m and a cell parameter of c = 10.80~10.90 Å.

[0028] Furthermore, based on the sodium-ion battery anode material of the present invention, the present invention also includes a sodium-ion battery comprising the above-mentioned sodium-ion battery anode material.

[0029] Furthermore, the present invention also includes a method for preparing a sodium-ion battery anode material, which specifically includes the following steps: S1: Weigh Na2CO3, Bi2O3, and V2O5 according to the set stoichiometric ratio, ball mill them together, and then dry them to obtain the precursor.

[0030] Preferably, in the preferred embodiment of the present invention, the ball milling is carried out in a zirconium oxide ball milling jar under anhydrous ethanol medium, the ball-to-material ratio is (15~5):1, the ball milling speed is 200~600 rpm, the time is 4~10 h, and then it is dried in a vacuum environment at 60~100℃ for 6~15 h.

[0031] S2: The precursor is sintered under an argon-hydrogen mixture to obtain the sodium-ion battery anode material.

[0032] It is understandable that during the sintering of the precursor, an argon-hydrogen mixture is introduced to form an inert atmosphere using argon as a protective gas and hydrogen as a reducing agent to react with the lattice oxygen on the precursor surface. This precisely creates oxygen vacancies in the bulk material phase, and under high-temperature thermal drive, the generated oxygen vacancies diffuse into the bulk material phase. At the same time, the metal ions and remaining oxygen ions in the lattice relax and rearrange to form a stable defect structure.

[0033] Preferably, the volume fraction of hydrogen in the argon-hydrogen mixture is 2.5% to 3.5%, and the flow rate of the argon-hydrogen mixture during sintering is 50 mL / min, so as to avoid insufficient electronic conductivity due to too low hydrogen content, and to avoid excessive oxygen vacancy oversaturation due to too high hydrogen content, which would cause the structure of the prepared anode material to collapse easily.

[0034] Preferably, the precursor is sintered by heating to 450-550°C at a rate of 3-8°C / min, holding at that temperature for 6-12 hours, and then cooling to room temperature to obtain a black blocky product, which is NaBi. x V 1-x O 2-δ Sodium-ion battery anode material.

[0035] This invention regulates the concentration and depth distribution of oxygen vacancies by controlling the sintering temperature, hydrogen concentration, and holding time, so that the oxygen vacancy concentration of the obtained sodium-ion battery anode material meets the set requirements.

[0036] Example 1: Na2CO3, Bi2O3, and V2O5 were weighed according to the stoichiometric ratio and ball-milled in anhydrous ethanol using a zirconium oxide ball mill jar with a ball-to-material ratio of 10:1, a rotation speed of 400 rpm, and a time of 8 hours. After ball milling, the mixture was dried in a vacuum environment at 80°C for 12 hours to obtain the precursor. The precursor was placed in an alumina crucible and then placed in a tube furnace. The precursor was sintered under an argon-hydrogen mixture. The flow rate of the argon-hydrogen mixture was 50 mL / min, and the volume fraction of hydrogen in the argon-hydrogen mixture was 3%. The sintering method was to heat the product to 500°C at a rate of 5°C / min and hold it at that temperature for 8 hours. Then, the product was cooled to room temperature in the tube furnace to obtain a black blocky product, which is the sodium-ion battery anode material.

[0037] The oxygen vacancy concentration, electrochemical performance, and structural stability of the prepared sodium-ion battery anode material were tested: (1) Electron paramagnetic resonance (EPR) test was performed, and the oxygen vacancy concentration corresponding to the signal intensity of g=2.003 was 3.2×10. 18 cm -3 ,like Figure 1 As shown in the figure; (2) Half-cell testing was conducted, and its voltage plateau was found to be 1.62V, the first-cycle capacity at 0.2C was 182mAh / g, and the capacity remained at 97.5% after 1000 cycles, as shown in the figure. Figure 2 As shown in the figure; (3) in-situ XRD (charge-discharge process) was performed, and the cell volume change rate was found to be 1.7%, as shown in the figure. Figure 3 As shown in the image.

[0038] Based on the above test results, compared with conventional samples sintered in air atmosphere (no oxygen vacancies, voltage plateau fluctuation ±0.15V, capacity decay to 75% after 100 cycles) and conventional Na3V2(PO4)3 anode material (volume change rate of 8.2%), the sodium-ion battery anode material prepared in this invention has better electrochemical performance and structural stability.

[0039] The sodium-ion battery anode material of this invention effectively broadens the sodium-ion diffusion channel through oxygen vacancies, resulting in a voltage plateau fluctuation of <0.03V (0.1-5C).

[0040] The sodium-ion battery anode material of this invention buffers lattice stress through oxygen vacancies, ensuring that the volume expansion rate does not exceed 1.8% after 1000 cycles, thus effectively guaranteeing the cycle life of the sodium-ion battery.

[0041] The sodium-ion battery anode material of this invention exhibits a metal dissolution rate of <0.01wt% in an electrolyte with pH=9, effectively improving the water resistance of the anode material.

[0042] The sodium-ion battery anode material of this invention can increase the electronic conductivity to >10. -7While maintaining a voltage of 1.60~1.70V and a volume expansion rate of <2% after 1000 cycles, it can meet the application requirements of high working voltage and low volume expansion of sodium-ion battery anode materials. It is suitable for neutral / alkaline aqueous electrolytes and has good application prospects and promotion value.

[0043] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit 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.

Claims

1. A sodium-ion battery anode material, characterized in that, The general chemical formula of the sodium-ion battery anode material is NaBi. x V 1-x O 2-δ Where 0.45≤x≤0.55, 0.05≤δ≤0.12, and the oxygen vacancy concentration is 1×10⁻⁶. 18 cm -3 ~5×10 18 cm -3 .

2. The sodium-ion battery anode material and its preparation method according to claim 1, characterized in that, The crystal structure of the sodium-ion battery anode material is monoclinic.

3. The sodium-ion battery anode material and its preparation method according to claim 2, characterized in that, The space group of the monoclinic crystal structure is C2 / m, and the cell parameter is c = 10.80~10.90 Å.

4. A sodium-ion battery, characterized in that, The sodium-ion battery anode material includes any one of claims 1 to 3.

5. A method for preparing a sodium-ion battery anode material, used for preparing the sodium-ion battery anode material according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Weigh Na2CO3, Bi2O3, and V2O5 according to the set stoichiometric ratio, ball mill them together, and then dry them to obtain the precursor; S2: The precursor is sintered under an argon-hydrogen mixture to obtain the sodium-ion battery anode material.

6. The sodium-ion battery anode material and its preparation method according to claim 5, characterized in that, In step S1, the ball milling is carried out in a zirconia ball mill jar under anhydrous ethanol medium, with a ball-to-material ratio of (15~5):1, a ball milling speed of 200~600 rpm, and a time of 4~10 h.

7. The sodium-ion battery anode material and its preparation method according to claim 5, characterized in that, In step S1, the drying process involves drying in a vacuum environment at 60-100°C for 6-15 hours.

8. The sodium-ion battery anode material and its preparation method according to claim 5, characterized in that, In step S2, the flow rate of the argon-hydrogen mixture is 40~60 mL / min, and the volume fraction of hydrogen in the argon-hydrogen mixture is 2.5%~3.5%.

9. The sodium-ion battery anode material and its preparation method according to claim 5, characterized in that, Step S2 involves heating the gas to 450-550°C at a rate of 3-8°C / min under an argon-hydrogen mixture and holding it at that temperature for 6-12 hours.

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