Amorphous na2tivi(po4)3 / c composite material, and preparation method and application thereof

Abstract

The application discloses an amorphous Na2TiV(PO4)3 / C composite material, a preparation method thereof and application of the composite material in a sodium ion battery. The material is obtained by adding a sodium source, a titanium source, a vanadium source, a phosphorus source and a carbon source into a volatile solvent, stirring and heating, and then grinding after sufficient drying; the precursor is sintered at 400-650 DEG C for 2-12 hours. The composite material can exert amorphous activity, break the limitation of the theoretical capacity of crystalline materials, and be isotropic to be beneficial to ion migration. The synthesis process of the composite material is simple, and energy consumption is low, thus breaking the limitation of traditional poly-anion high-temperature calcination; the composite material is used as a positive electrode material of the sodium ion battery, has high voltage and discharge specific capacity, and excellent cycle stability, the average working voltage is about 3.2 V, the capacity retention rate is as high as 93.4% after 150 cycles, and the composite material is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to an amorphous composite material, specifically to an amorphous Na2TiV(PO4)3 / C composite material, its preparation method, and its application, belonging to the field of sodium-ion battery technology. Background Technology

[0002] Compared to mechanical and electromagnetic energy storage, the electrochemical energy storage industry has ushered in a broader development space. Among them, lithium-ion batteries have developed rapidly due to their advantages such as flexible material systems, high energy density, long cycle life, and rapid technological updates, gaining a surge in market share in energy storage and power batteries. However, this has also led to a severe shortage of lithium resources and persistently high prices. Therefore, sodium-ion batteries have become a current research hotspot, and many technical challenges remain to be overcome in the field of sodium-ion batteries. For example, the radius of sodium ions is much larger than that of lithium ions, and sodium ions repeatedly intercalate and deintercalate during charging and discharging, which undoubtedly places higher demands on electrode materials.

[0003] Researchers have conducted extensive studies on cathode materials for sodium-ion batteries, with high specific capacity, long cycle life, high safety, and wide availability of raw materials remaining key objectives. Among existing cathode material systems, polyanionic compounds are considered the most promising electrode materials due to their high operating voltage and excellent structural stability. However, the preparation of these materials often involves high-temperature calcination, resulting in significant energy consumption, and the migration of sodium ions within the crystal structure of polyanionic compounds is constrained, limiting their theoretical capacity. Amorphous polyanionic cathodes represent a new area in sodium-ion battery cathode materials, with few reports and requiring in-depth understanding. Unlike traditional crystalline polyanionic cathodes, amorphous materials have significantly lower sintering temperatures and, due to their long-range disordered and short-range ordered network structure, allow for freer ion migration, thus exhibiting advantages in capacity, cycle life, and rate performance. Considering factors such as manufacturing cost, sodium storage performance, and environmental friendliness, developing novel amorphous polyanionic cathodes and their preparation methods is beneficial for promoting the industrial application of sodium-ion batteries. Summary of the Invention

[0004] To address the problems existing in the prior art, the first objective of this invention is to provide an amorphous Na₂TiV(PO₄)₃ / C composite material. This amorphous composite material exhibits amorphous activity, possessing a network structure with long-range disorder and short-range order, avoiding the lattice constraint of crystalline materials on sodium ions and breaking the theoretical capacity constraints of traditional crystalline systems. Simultaneously, the in-situ coating of a conductive carbon layer on the surface of the amorphous Na₂TiV(PO₄)₃ / C composite material accelerates the diffusion rate of sodium ions at the interface of the active material, inhibits the corrosion of the electrolytic material by the electrolyte, improves the thermal and chemical stability of the material, and expands the application scenarios of the composite material.

[0005] The second objective of this invention is to provide a method for preparing amorphous Na2TiV(PO4)3 / C composite materials. This method involves preparing a composite material precursor using a one-pot process and then calcining it under a specific atmosphere to form an in-situ coated conductive carbon layer, thereby obtaining uniform nanoparticles. Compared to the traditional preparation process of crystalline cathode materials, this method has advantages such as simple process, reduced energy consumption, and low cost, making it suitable for industrial production.

[0006] The third objective of this invention is to provide an application of an amorphous Na2TiV(PO4)3 / C composite material as a positive electrode active material for sodium-ion batteries, enabling the preparation of sodium-ion batteries. The sodium-ion battery positive electrode material prepared based on the amorphous composite material provided by this invention has a high voltage plateau. Because it lacks lattice confinement, there are no changes in crystal structure during charge and discharge, resulting in stability during charge and discharge over a wide electrochemical window of 1.5–4.3 V, exhibiting excellent cycle stability.

[0007] To achieve the above technical objectives, this invention provides a method for preparing an amorphous Na2TiV(PO4)3 / C composite material. The method involves uniformly mixing raw materials including sodium, titanium, vanadium, phosphorus, and carbon sources to obtain a precursor; then sintering the precursor under a protective atmosphere using a programmed temperature rise method to obtain the final product. The programmed temperature rise conditions are: increasing the temperature at 1–3 °C / min to 400–650 °C, holding at that temperature for 2–12 h, and then cooling the furnace to room temperature.

[0008] The amorphous Na2TiV(PO4)3 / C composite material provided by this invention not only possesses the advantages of phosphate cathode materials but also exhibits amorphous activity. It provides more sodium storage sites while allowing sodium ions to migrate freely without structural changes, thus exhibiting unique advantages in capacity, cycle life, and rate performance. The preparation process involves uniformly mixing the raw materials in a one-pot method, followed by drying and low-temperature calcination. This process is simple, energy-efficient, environmentally friendly, requires minimal equipment, and is easy to operate.

[0009] As a preferred embodiment, the raw material mixing process is as follows: the raw material is dispersed in a volatile solvent, heated and stirred until the solvent is completely evaporated, and then dried to obtain the final product.

[0010] As a preferred embodiment, the volatile solvent is at least one selected from deionized water, methanol, ethanol, propanol, acetone, and diethyl ether.

[0011] As a preferred embodiment, the heating and stirring conditions are: temperature of 60-150℃, stirring speed of 300-1000rpm, and time of 1-6h.

[0012] As a preferred option, the drying method is one of vacuum drying, forced air drying, and freeze drying.

[0013] As a preferred embodiment, the sodium source is at least one selected from sodium acetate, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium hydroxide, sodium metavanadate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate.

[0014] As a preferred embodiment, the titanium source is at least one selected from titanium nitrate, titanium oxalate, titanium monoxide, titanium dioxide, titanium acetylacetone, and tetrabutyl titanate.

[0015] As a preferred embodiment, the vanadium source is at least one of vanadium pentoxide, ammonium metavanadate, sodium metavanadate, vanadium oxalate, and vanadium acetylacetonate.

[0016] As a preferred embodiment, the phosphorus source is at least one selected from phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium pyrophosphate.

[0017] As a preferred embodiment, the carbon source is at least one of citric acid, glucose, sucrose, polyvinylpyrrolidone, dopamine hydrochloride, graphene, and carbon nanotubes.

[0018] As a preferred embodiment, the raw materials also include a reducing agent. When the transition metal elements in the vanadium and titanium sources exhibit high valences, a reducing agent needs to be added to prevent the formation of byproducts that could reduce the purity of the material and thus affect its electrochemical performance.

[0019] As a preferred embodiment, the reducing agent is at least one of citric acid, oxalic acid, ascorbic acid, glucose, and hydroxylamine hydrochloride.

[0020] As a preferred embodiment, the sodium source, titanium source, vanadium source and phosphorus source are provided in an elemental molar ratio of sodium:titanium:vanadium:phosphorus of 1.9-2.1:0.9-1.1:0.9-1.1:2.9-3.1.

[0021] As a preferred embodiment, the mass of the carbon source is 3 to 15% of the mass of Na2TiV(PO4)3.

[0022] As a preferred embodiment, the molar ratio of the reducing agent to the transition metal raw material is 0 to 5:1.

[0023] As a preferred embodiment, the protective atmosphere is an inert atmosphere and / or a reducing atmosphere.

[0024] As a preferred option, the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0025] As a preferred embodiment, the reducing atmosphere is a nitrogen-hydrogen mixture or an argon-hydrogen mixture, wherein the volume fraction of hydrogen in the mixture is 3-20%.

[0026] The present invention provides an amorphous Na2TiV(PO4)3 / C composite material, obtained by any of the above preparation methods; the composite material is composed of amorphous Na2TiV(PO4)3 and an in-situ encapsulated amorphous carbon layer.

[0027] As a preferred embodiment, the particle size of the composite material is 30–60 nm; the thickness of the carbon coating layer is 2–5 nm, and the mass percentage is 3–15%.

[0028] This invention also provides an application of an amorphous Na2TiV(PO4)3 / C composite material as a cathode material for sodium-ion batteries.

[0029] The amorphous composite material provided by this invention was tested within a potential window of 1.5–4.3 V. The average operating voltage of the amorphous Na₂TiV(PO₄)₃ / C composite material was approximately 3.2 V, and the operating voltage at 500 mA g / L was [not specified]. -1 The initial discharge specific capacity is 98 mAh g. -1 After 150 cycles, the capacity retention rate reached 93.4%. Furthermore, the amorphous Na₂TiV(PO₄)₃ / C composite exhibited excellent rate performance, even at 5A g. -1 It can also maintain 40mAh g -1 The capacity.

[0030] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0031] (1) The amorphous Na2TiV(PO4)3 / C composite material provided by this invention can exhibit amorphous activity. Due to its long-range disordered and short-range ordered network structure, sodium ions are not constrained by the lattice in crystalline materials, breaking the theoretical capacity constraint of traditional crystalline systems. At the same time, the surface of the amorphous Na2TiV(PO4)3 / C composite material is coated with a conductive carbon layer, which accelerates the diffusion rate of sodium ions at the interface of the active material, inhibits the corrosion of the electrolyte by the electrolytic material, improves the thermal and chemical stability of the material, and expands the application scenarios of the composite material.

[0032] (2) The preparation method provided by this invention involves preparing a composite material precursor in a one-pot process and calcining it under a specific atmosphere to form an in-situ coated conductive carbon layer, thereby obtaining uniform nanoparticles. Compared with the traditional crystalline cathode material preparation process, this method has the advantages of simple process, reduced energy consumption, and low cost, and is suitable for industrial production.

[0033] (3) In the technical solution provided by the present invention, the sodium-ion battery cathode material prepared based on the amorphous composite material provided by the present invention has a high voltage platform. Since there is no lattice limitation, there is no change in crystal structure, so the charge and discharge process is still stable in the wide electrochemical window of 1.5 to 4.3V, and it has excellent cycle stability. Attached Figure Description

[0034] Figure 1 XRD patterns of the Na2TiV(PO4)3 / C cathode materials prepared in Example 1 and Comparative Example 1;

[0035] Figure 2 TEM image of the amorphous Na2TiV(PO4)3 / C cathode material prepared in Example 1;

[0036] Figure 3 Elemental distribution diagram of the amorphous Na2TiV(PO4)3 / C cathode material prepared in Example 1;

[0037] Figure 4 XPS image of the amorphous Na2TiV(PO4)3 / C cathode material prepared in Example 1;

[0038] Figure 5 Charge-discharge curves of the Na2TiV(PO4)3 / C cathode materials prepared in Example 1 and Comparative Example 1;

[0039] Figure 6 Cyclic voltammetry curves of the Na2TiV(PO4)3 / C cathode materials prepared in Example 1 and Comparative Example 1;

[0040] Figure 7 Example 1: A sodium-ion battery assembled from the amorphous Na2TiV(PO4)3 / C cathode material was tested at 500 mA g. -1 The following is a graph showing the cyclic performance.

[0041] Figure 8 Rate performance of sodium-ion batteries assembled from Na2TiV(PO4)3 / C cathode materials prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0042] The present invention will be further illustrated by the following examples, but not by limiting the invention.

[0043] Example 1

[0044] In this embodiment, an amorphous composite material with the molecular formula Na2TiV(PO4)3 / C is provided. The preparation method of this battery cathode material includes the following steps:

[0045] Sodium acetate, vanadium acetylacetonate, tetrabutyl titanate, and phosphoric acid were added to an ethanol solution containing citric acid in stoichiometric ratios, with a molar ratio of metal elements (including V and Ti) to citric acid of 2:3. The mixture was then heated and stirred at 80°C until the ethanol was completely evaporated. The solution was then transferred to a vacuum oven and dried overnight at 100°C. The resulting precursor was ground and sintered at 600°C in a reducing atmosphere of Ar / H2 (containing 5% H2) for 5 hours. Natural cooling yielded an amorphous Na2TiV(PO4)3 / C cathode material.

[0046] This embodiment also provides the application of amorphous Na2TiV(PO4)3 / C composite material in sodium-ion batteries. The preparation of the electrode, the assembly of the battery, and the electrochemical performance testing are as follows:

[0047] Amorphous Na2TiV(PO4)3 / C cathode material was mixed with binder and conductive agent to form a slurry, which was then coated onto aluminum foil and cured to obtain the sodium-ion battery cathode. CR2016 coin cells were assembled in an argon glove box using a metallic sodium sheet anode, a glass fiber separator, and 1.0M NaClO4 in PC with 5% FEC electrolyte. The cells were tested at 500mA within a voltage range of 1.5–4.3V. -1 Its cycling performance was tested, and its rate performance was tested at different rates.

[0048] Example 2

[0049] Compared to Example 1, the difference lies in lowering the sintering temperature, as detailed below:

[0050] Sodium acetate, vanadium acetylacetonate, tetrabutyl titanate, and phosphoric acid were added to an ethanol solution containing citric acid in stoichiometric ratios, with the molar ratio of metal elements (including V and Ti) to citric acid being 2:3. The mixture was then heated and stirred at 80°C until the ethanol was completely evaporated. The solution was then transferred to a vacuum oven and dried overnight at 100°C. The resulting precursor was ground and sintered at 500°C in a reducing atmosphere of Ar / H2 (containing 5% H2) for 5 hours. Natural cooling yielded an amorphous Na2TiV(PO4)3 / C cathode material.

[0051] Example 3

[0052] Compared to Example 1, the difference lies in increasing the sintering time, as detailed below:

[0053] Sodium acetate, vanadium acetylacetonate, tetrabutyl titanate, and phosphoric acid were added to an ethanol solution containing citric acid in stoichiometric ratios, with a molar ratio of metal elements (including V and Ti) to citric acid of 2:3. The mixture was then heated and stirred at 80°C until the ethanol was completely evaporated. The solution was then transferred to a vacuum oven and dried overnight at 100°C. The resulting precursor was ground and sintered at 600°C in a reducing atmosphere of Ar / H2 (containing 5% H2) for 10 hours. Natural cooling yielded an amorphous Na2TiV(PO4)3 / C cathode material.

[0054] Comparative Example 1

[0055] This comparative example provides a highly crystallinity Na2TiV(PO4)3 / C composite material and its preparation method.

[0056] The preparation method of the highly crystalline Na2TiV(PO4)3 / C composite material in this comparative example is similar to that in the examples, except for the calcination conditions:

[0057] Sodium acetate, vanadium acetylacetonate, tetrabutyl titanate, and phosphoric acid were added to an ethanol solution containing citric acid in stoichiometric ratios, with the molar ratio of metal elements (including V and Ti) to citric acid being 2:3. The mixture was then heated and stirred at 80°C until the ethanol was completely evaporated. The solution was then transferred to a vacuum oven and dried overnight at 100°C. The resulting precursor was ground and sintered at 800°C in a reducing atmosphere of Ar / H2 (containing 5% H2) for 5 hours. Natural cooling yielded a highly crystalline Na2TiV(PO4)3 / C cathode material.

[0058] The electrode preparation, battery assembly, and performance testing steps are the same as in Example 1.

[0059] Comparative Example 2

[0060] This comparative example provides an amorphous Na2TiV(PO4)3 / C composite material and its preparation method.

[0061] The preparation method of the amorphous Na2TiV(PO4)3 / C composite material in this comparative example is similar to that in the examples, except for the calcination conditions:

[0062] Sodium acetate, vanadium acetylacetonate, tetrabutyl titanate, and phosphoric acid were added to an ethanol solution containing citric acid in stoichiometric ratios, with the molar ratio of metal elements (including V and Ti) to citric acid being 2:3. The mixture was then heated and stirred at 80°C until the ethanol was completely evaporated. The solution was then transferred to a vacuum oven and dried overnight at 100°C. The resulting precursor was ground and sintered at 300°C in a reducing atmosphere of Ar / H2 (containing 5% H2) for 5 hours. Natural cooling yielded a highly crystalline Na2TiV(PO4)3 / C cathode material.

[0063] The electrode preparation, battery assembly, and performance testing steps are the same as in Example 1.

[0064] This embodiment describes an amorphous Na2TiV(PO4)3 / C composite material, its preparation method, and its application in sodium-ion batteries. Figure 1 and Figure 2 As shown, the calcination temperature plays a decisive role in the crystallinity of the material. The Na2TiV(PO4)3 / C composite material prepared in Example 1 has insignificant diffraction peak intensities, indicating a typical amorphous structure, consistent with the TEM diffraction results. Furthermore, this composite material exhibits uniformly sized nanoparticles. In contrast, the Na2TiV(PO4)3 / C composite material provided in Comparative Example 1, calcined at 800℃, exhibits high crystallinity. Moreover, through… Figure 3 and Figure 4 Elemental analysis confirmed that the material prepared in Example 1 was a Na₂TiV(PO₄)₃ / C composite material. Figures 5 to 8 It can be seen that the amorphous Na₂TiV(PO₄)₃ / C has a higher average operating voltage than the crystalline Na₂TiV(PO₄)₃ / C. Furthermore, the amorphous Na₂TiV(PO₄)₃ / C has no lattice confinement and does not exhibit any changes in its crystal structure. Tests conducted over a wide electrochemical window of 1.5–4.3 V showed an initial discharge specific capacity as high as 98 mAh g⁻¹. -1 After 150 cycles, the capacity retention was 93.4%, demonstrating excellent cycling stability. The amorphous Na₂TiV(PO₄)₃ / C structure is characterized by long-range disorder and short-range order, providing more sodium storage sites and facilitating electrochemical reactions of sodium ions on the material surface. Furthermore, the isotropic nature of the amorphous state promotes sodium ion migration. At 5A g… -1 It can also reach close to 40mAh g -1 The amorphous material prepared in Comparative Example 2 exhibits extremely high capacity. Therefore, it significantly outperforms the crystalline Na2TiV(PO4)3 / C material provided in the comparative example in terms of output voltage, discharge specific capacity, and stability. However, the amorphous material prepared in Comparative Example 2 turned brown due to its excessively low sintering temperature, indicating that the carbon coating layer on the surface was not carbonized, preventing the composite material from exhibiting electrochemical activity. Therefore, only by calcining within a suitable temperature range can an amorphous composite material with electrochemical activity be obtained; otherwise, it is difficult to achieve the desired control effect.

[0065] In summary, the amorphous composite material provided by this invention, prepared by a combination of one-pot method and low-temperature calcination, exhibits excellent electrochemical performance as a cathode for sodium-ion batteries.

Claims

1. A method for preparing an amorphous Na₂TiV(PO₄)₃ / C composite material, characterized in that: Mixing raw materials including sodium source, titanium source, vanadium source, phosphorus source and carbon source uniformly, then the precursor is obtained; the precursor is sintered by programmed temperature rising in a protective atmosphere, then the non-crystalline Na2TiV(PO4)3 / C composite material is obtained; the programmed temperature rising conditions are as follows: rising to 400-600 ℃ at 1-3 ℃ / min, keeping temperature for 2-12 h, and cooling to room temperature with the furnace; The raw materials further include a reducing agent; the reducing agent is at least one of citric acid, oxalic acid, ascorbic acid, glucose and hydroxylamine hydrochloride; The mass of the carbon source is 3-15% of the mass of Na2TiV(PO4)3. The molar ratio of the reducing agent to the transition metal raw material is 0-5:

1.

2. The preparation method of the amorphous Na2TiV(PO4)3 / C composite material according to claim 1, characterized in that: The mixing process of the raw materials is as follows: the raw materials are dispersed in a volatile solvent, then the solvent is completely volatilized by heating and stirring, and then the mixture is dried, then the mixture is obtained.

3. The amorphous Na2TiV(PO4)3 / C composite material according to claim 2, characterized by the preparation method thereof. The volatile solvent is at least one of deionized water, methanol, ethanol, propanol, acetone and diethyl ether; the heating and stirring conditions are as follows: the temperature is 60-150 ℃, the stirring speed is 300-1000 rpm, and the time is 1 h-6 h; and the drying mode is one of vacuum drying, air drying and freeze drying.

4. The non-crystalline Na2TiV(PO4)3 / C composite material and the preparation method thereof according to claim 1, characterized in that: The sodium source is at least one of sodium acetate, sodium carbonate, sodium bicarbonate, sodium oxalate, sodium hydroxide, sodium metavanadate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate; The titanium source is at least one of titanium nitrate, titanium oxalate, titanium monoxide, titanium dioxide, titanium acetylacetonate and tetrabutyl titanate; The vanadium source is at least one of vanadic oxide, ammonium metavanadate, sodium metavanadate, oxovanadium oxalate and oxovanadium acetylacetonate; The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate and sodium pyrophosphate; The carbon source is at least one of citric acid, glucose, sucrose, polyvinylpyrrolidone, dopamine hydrochloride, graphene and carbon nanotube.

5. The amorphous Na2TiV(PO4)3 / C composite material according to claim 1, characterized by a preparation method thereof. The element molar ratio of the sodium source, the titanium source, the vanadium source and the phosphorus source is 1.9-2.1:0.9-1.1:0.9-1.1:2.9-3.1 of sodium:titanium:vanadium:phosphorus.

6. An amorphous Na2TiV(PO4)3 / C composite material, characterized in that: The composite material is obtained by the preparation method in any one of claims 1-5; the composite material is composed of non-crystalline Na2TiV(PO4)3 and in-situ wrapped amorphous carbon layer.

7. The amorphous Na2TiV(PO4)3 / C composite material according to claim 6, characterized in that: The particle size of the composite material is 30-60 nm; the thickness of the carbon coating layer is 2-5 nm, and the mass percentage is 3-15%.

8. Use of an amorphous Na2TiV(PO4)3 / C composite material according to claim 6 or 7, characterized in that: The composite material is used as a positive electrode material of a sodium ion battery.

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