Amorphous vanadium-based positive electrode material and preparation method and application thereof

Abstract

This invention provides an amorphous vanadium-based cathode material, its preparation method, and its applications. The amorphous vanadium-based cathode material comprises active material glass powder, wherein the active material glass powder uses vanadium pentoxide as the active precursor, manganese dioxide as the structural stabilizer, sodium tetraborate decahydrate as the glass network former, lithium carbonate as the lithium source and network modifier, and thiourea as the reducing agent and nitrogen and sulfur doping source. The process employs melt quenching combined with thermoelectric coupling field crystallization, which is simple, low-cost, and suitable for large-scale production. Lithium-ion batteries assembled with this amorphous cathode material have advantages such as high specific capacity, excellent rate performance, and long cycle life.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode material technology, and particularly relates to an amorphous vanadium-based cathode material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and low self-discharge rate, have become the core power source for portable electronic devices, electric vehicles, and large-scale energy storage systems. As a key component of lithium-ion batteries, the performance of the cathode material directly determines the battery's specific capacity, operating voltage, safety, and cost. Currently, commercially available cathode materials such as lithium cobalt oxide, ternary materials (NCM), and lithium iron phosphate have reached near-theoretical specific capacities, making it difficult to meet the ever-growing demands of future high-energy-density energy storage devices. Therefore, developing novel cathode materials with higher specific capacities has become a research hotspot in the field of lithium-ion batteries.

[0003] Vanadium (V) has multiple stable oxidation states (e.g., +5, +4, +3, +2). Its oxides (e.g., V₂O₅) can theoretically intercalate multiple lithium ions through multi-electron reactions, achieving a specific capacity of approximately 300 mAh / g, significantly higher than existing commercial cathode materials. In particular, amorphous vanadium oxides, with their unique long-range disordered and short-range ordered structure, can effectively alleviate the lattice stress generated during repeated lithium ion intercalation / extraction, suppress material pulverization and structural collapse, and exhibit excellent potential for cycle stability.

[0004] However, the development of amorphous vanadium-based cathode materials still faces two major bottlenecks: one is the extremely low intrinsic electronic conductivity of the material (typically only 10). -5 ~10 -6 The first limitation is that the capacity of the battery is 100 kW / cm, which severely restricts its rate performance; the second limitation is that the active material (vanadium ions) is easily dissolved in the electrolyte during charging and discharging, which leads to continuous capacity decay and deterioration of cycle stability.

[0005] Thiourea (CH4N2S), as a low-cost, low-toxicity solid small-molecule reducing agent, releases reducing gases such as NH3 and H2S when heated to high temperatures, thus enabling the reduction of V... 5+ The process allows for mild and controllable reduction, avoiding localized over-reduction. Simultaneously, the nitrogen (N) and sulfur (S) elements remaining after pyrolysis can be in-situ doped into the material network or the formed carbon framework, potentially reducing the band gap, improving electronic conductivity, and acting as a physical barrier to inhibit vanadium dissolution. Therefore, developing a novel process for the synergistic modification of amorphous vanadium-based materials using reduction-thermal treatment with thiourea is of great significance for overcoming the performance bottlenecks of amorphous vanadium-based cathode materials. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a low-cost preparation process for thiourea-modified amorphous vanadium-based materials. Lithium-ion batteries assembled from this amorphous vanadium-based material have advantages such as high specific capacity, excellent rate performance, and long cycle life.

[0007] This invention provides an amorphous vanadium-based cathode material, comprising active material glass powder;

[0008] The raw materials for preparing the active material glass powder include the active material precursor V2O5, the structural stabilizer MnO2, the glass network forming precursor Na2B4O7·10H2O, the glass network modifying precursor and lithium source Li2CO3, and the reducing agent and doping source CH4N2S.

[0009] In this invention, the molar ratio of V2O5, MnO2, Li2CO3, Na2B4O7·10H2O, and CH4N2S in the raw materials for preparing the active substance glass powder is 50:(10~30):10:10:(0~20), preferably 50:10:10:10:20.

[0010] In this invention, the active material glass powder is prepared by the following method:

[0011] S1) A glass block was prepared by melting and quenching a mixture of V2O5, MnO2, Li2CO3, Na2B4O7·10H2O, and CH4N2S under an inert atmosphere.

[0012] S2) Grind the amorphous glass block to obtain active material glass powder.

[0013] In this invention, the amorphous glass bulk material prepared by the melt-quenching method specifically includes:

[0014] The mixture was heated to 600-900℃ under an inert atmosphere and held for 20-35 minutes. The temperature was then further increased to 1200-1800℃ and held for 15-35 minutes. After cooling, a glass block was obtained. In a specific embodiment, a uniform heating rate of 10℃ / min was used.

[0015] In this invention, optionally, the amorphous glass block prepared in S1) is subjected to crystallization treatment to obtain a crystallized glass block; the crystallized glass block is ground to obtain active material glass powder.

[0016] In this invention, the crystallization treatment temperature is 200–400°C, and the crystallization treatment time is 200–2000 min; the electric field strength used in the crystallization treatment is 0.8–1.5 kV / cm, and the current density is 5–20 mA / cm². The crystallization treatment enables uniform nucleation and directional growth of microcrystalline phases within the glass, followed by slow cooling to room temperature to obtain a dense and uniform polycrystalline glass material. In a specific embodiment, the temperature is increased to 300°C at a heating rate of 10°C / min, and crystallization is carried out for 600 min under the action of a thermoelectric coupling field with an electric field strength of 0.9 kV / cm and a current density of 15 mA / cm², enabling uniform nucleation and directional growth of microcrystalline phases within the glass, followed by slow cooling to room temperature at a rate of 5°C / min.

[0017] In this invention, the average particle size of the active material glass powder is 200~400 nm.

[0018] In this invention, the amorphous vanadium-based cathode material further comprises a binder and a conductive filler; the mass ratio of the active material glass powder, the binder and the conductive filler is (6~10):(2~3):(1~2), preferably 7:2:1.

[0019] In this invention, the binder is selected from polyvinylidene fluoride; the conductive filler is selected from conductive carbon black.

[0020] In this invention, V₂O₅ serves as the main active precursor, providing vanadium centers for multi-electron reactions; MnO₂ acts as a structural stabilizer, helping to suppress the dissolution of vanadium ions during charging and discharging; Li₂CO₃ provides lithium ions, participating in the formation of the glass network; Na₂B₄O₇·10H₂O acts as the glass network former, promoting the stability of the amorphous structure; and CH₄N₂S acts as a reducing agent and nitrogen-sulfur doping source, reducing some pentavalent vanadium to V₂O₅ during high-temperature melting. 4 ⁺ and V³⁺, while simultaneously introducing N and S into the glass matrix.

[0021] This invention effectively improves the intrinsic conductivity of glass materials by introducing transition metal oxides, while alleviating the problems of large capacity loss in the first cycle and low capacity retention in the later stages of cycling. Thiourea is selected as a multifunctional additive; under high-temperature conditions, thiourea thermally decomposes to release reducing gases, which react with V₂O₅ in a redox reaction, partially reducing the V₂O₅ content. 5 ⁺ Restored to a low-price state V 4 ⁺ and V³⁺, thus significantly improving the electronic conductivity of the material.

[0022] The present invention also provides a method for preparing an amorphous cathode material, comprising mixing the active material glass powder, binder, conductive filler and solvent described in the present invention, ball milling and coating to obtain the amorphous cathode material.

[0023] The present invention also provides a lithium-ion battery comprising the amorphous vanadium-based cathode material described in the present invention.

[0024] The amorphous vanadium-based cathode material provided by this invention comprises active material glass powder. This active material glass powder is prepared from vanadium pentoxide, manganese dioxide, lithium carbonate, sodium tetraborate decahydrate, and thiourea as raw materials. The process involves melting and quenching to obtain an amorphous glass block, which is then ground. This method is simple, low-cost, and exhibits excellent specific capacity and cycle stability. Further improving the material's conductivity and cycle retention by subjecting the amorphous glass block to thermoelectric coupling field crystallization treatment followed by grinding further optimizes its overall performance. All raw materials used in this invention are conventional chemical materials, eliminating the need for rare materials and hazardous chemicals, thus improving production safety and reducing preparation costs. The amorphous vanadium-based cathode material prepared by this invention exhibits excellent electrochemical performance when applied to lithium-ion batteries. The electronic conductivity can reach 6 × 10⁻⁶. ⁻4 ~9×10 ⁻4 S / m; charge transfer impedance reduced to 450~600 Ω; coefficient of thermal expansion is 4×10⁻ 6 ~5×10⁻ 6 / K, open circuit voltage 3.5~4.0 V; initial discharge specific capacity can reach 330~380 mAh / g; after activation at 0.1C, after 200 cycles at 1C rate, the discharge capacity retention rate is as high as 90%~97%. Attached Figure Description

[0025] Figure 1 This is a SEM (Scanning Electron Microscopy) image of the active material glass powder prepared in Example 8 of the present invention.

[0026] Figure 2 This is a SEM (Scanning Electron Microscopy) image of the active material glass powder prepared in Example 8 of the present invention.

[0027] Figure 3 This is a TEM transmission electron microscope image of the active material glass powder prepared in Example 8 of the present invention.

[0028] Figure 4 This is a TEM transmission electron microscope image of the active material glass powder prepared in Example 8 of the present invention.

[0029] Figure 5 The above are the electrochemical impedance spectroscopy (EIS, Nyquist plots) of Comparative Example 2, Examples 1-4 and Example 8 of the present invention, where VA-1 is the test result of Comparative Example 2, VA-3 is the test result of Example 2, VA-4 is the test result of Example 3, VA-5 is the test result of Example 4 and VA-8 is the test result of Example 8.

[0030] Figure 6The above are X-ray photoelectron spectroscopy (XPS) valence state analysis diagrams of Comparative Example 2, Examples 1-4 and Example 8 of the present invention, wherein VA-1 is the XPS analysis diagram of Comparative Example 2, VA-3 is the XPS analysis diagram of Example 2, VA-4 is the XPS analysis diagram of Example 3, VA-5 is the XPS analysis diagram of Example 4 and VA-8 is the XPS analysis diagram of Example 8.

[0031] Figure 7 The X-ray diffraction (XRD) patterns of Comparative Examples 2, Examples 1-4 and Example 8 of the present invention are shown, wherein VA-1 is the XRD pattern of Comparative Example 2, VA-3 is the XRD pattern of Example 2, VA-4 is the XRD pattern of Example 3, VA-5 is the XRD pattern of Example 4 and VA-8 is the XRD pattern of Example 8.

[0032] Figure 8 These are long-cycle analysis diagrams for Comparative Examples 2, 4, and 8 of the present invention, where VA-1 is the long-cycle analysis diagram for Comparative Example 2, VA-5 is the long-cycle analysis diagram for Example 4, and VA-8 is the long-cycle analysis diagram for Example 8.

[0033] Figure 9 These are the magnification analysis charts for Comparative Example 2, Examples 1-4 and Example 8 of the present invention, where VA-1 is the magnification analysis chart for Comparative Example 2, VA-3 is the magnification analysis chart for Example 2, VA-4 is the magnification analysis chart for Example 3, VA-5 is the magnification analysis chart for Example 4 and VA-8 is the magnification analysis chart for Example 8.

[0034] Figure 10 These are cyclic voltammetry characteristic analysis diagrams for Comparative Example 2, Example 4, and Example 8 of the present invention, wherein VA-1 is the cyclic voltammetry characteristic analysis diagram for Comparative Example 2, VA-5 is the cyclic voltammetry characteristic analysis diagram for Example 4, and VA-8 is the cyclic voltammetry characteristic analysis diagram for Example 8. Detailed Implementation

[0035] To further illustrate the present invention, the following detailed description of the amorphous vanadium-based cathode material, its preparation method, and its application are provided in conjunction with embodiments, but this application is not limited to these embodiments.

[0036] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially. Unless otherwise specified, all testing methods employed are conventional methods.

[0037] Example 1

[0038] A mixture of V₂O₅, MnO₂, Li₂CO₃, Na₂B₄O₇·10H₂O, and CH₄N₂S in a molar ratio of 50:25:10:10:5 was stirred and ground until homogeneous. The resulting mixture was transferred to an alumina crucible and melted in a tubular furnace under argon protection. The temperature was increased to 700°C at a rate of 10°C / min and held for 30 min. Then, the temperature was increased to 1200°C at a rate of 10°C / min and held for 25 min. The mixture was then quickly poured onto a smooth, clean copper plate and rapidly pressed with another copper plate to cool it to room temperature, yielding an amorphous glass block. The glass block was ground thoroughly using a ball mill and passed through a 400-mesh sieve to obtain a positive electrode active material glass powder.

[0039] A mixture of positive electrode active material glass powder, binder (polyvinylidene fluoride), and conductive carbon black (particle size distribution 1~10 μm) powder in a mass ratio of 7:2:1 was mixed, and then ball-milled with an appropriate amount of solvent N-methylpyrrolidone (20% of the powder). The resulting slurry was coated onto aluminum foil and dried. After vacuum drying at 60 °C for 12 hours, it was cut into discs with a diameter of 14 mm and used as the positive electrode. A CR2016 button cell was prepared by using lithium sheet as the reference electrode and 1 M LiPF6 in a mixture of ethylene carbonate, dimethyl carbonate, and diethyl carbonate (1:1:1 v / v / v) as the electrolyte in an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). The cycle performance of the battery was tested using a LAND CT3001A battery testing system, and electrochemical impedance spectroscopy (EIS) was performed using a CHI660E, recording frequencies from 10⁻² to 10⁻¹⁰. 5 Hz, amplitude is 5mV.

[0040] Examples 2-4

[0041] According to the process flow of Example 1, the different amounts of V2O5, MnO2, Li2CO3, Na2B4O7·10H2O and CH4N2S added are shown in Table 1.

[0042] Table 1. Types and amounts of raw materials used in the preparation of amorphous cathode materials in Examples 1-4.

[0043]

[0044] Examples 5-8

[0045] Amorphous glass blocks obtained in Examples 1-4 were placed in a thermoelectric coupling field device; the temperature was increased to 300°C at 10°C / min, and crystallization was carried out for 600 min under an electric field strength of 0.9 kV / cm and a current density of 15 mA / cm², allowing uniform nucleation and directional growth of microcrystalline phases within the glass; subsequently, the glass blocks were slowly cooled to room temperature at 5°C / min to obtain crystallized glass blocks. The crystallized glass blocks were then thoroughly ground in a ball mill and passed through a 400-mesh sieve to obtain positive electrode active material glass powder. Subsequent electrode preparation, battery assembly, and performance testing were the same as in Example 1.

[0046] Example 5: The same raw material ratio as Example 1, and is the crystallized sample of Example 1;

[0047] Example 6: The same raw material ratio as Example 2, this is the sample from Example 2 after crystallization treatment;

[0048] Example 7: The same raw material ratio as Example 3, this is the sample from Example 3 after crystallization treatment;

[0049] Example 8: Same raw material ratio as Example 4, this is the sample from Example 4 after crystallization treatment. Table 2: Types and amounts of raw materials used in the heat treatment preparation of mixed-crystalline cathode materials in Examples 5-8.

[0050]

[0051] Comparative Example 1

[0052] Dry V₂O₅ powder and Co₂O₃ powder were mixed in a stoichiometric ratio and melted in a hydrogen atmosphere to prepare an 80V₂O₅·20Co₂O₃ glass sample. The mixture was stirred and homogenized before being placed in a quartz crucible. Glass melting was performed in a tube furnace. The sample was heated to 800℃ for 5 min to obtain a vanadium-cobalt glass melt. The molten glass was poured onto an iron plate and then annealed in a muffle furnace at 250℃ for 2 h, followed by furnace cooling. The pre-prepared glass was ground into powder with a particle size <20 μm using an agate mortar.

[0053] The electrode was prepared by mixing active material (vanadium cobalt glass powder), carbon black, and polytetrafluoroethylene (PTFE) binder in a mass ratio of 8:1.5:0.5. Weighed vanadium cobalt glass powder and carbon black were ground in an agate mortar for 30 minutes to obtain a homogeneous mixture. Then, PTFE was added to the prepared mixture and vigorously mixed to obtain a uniform film (80 μm thick). The prepared cathode film was punched into a disc using an 8 mm diameter circular cutter and then evenly adhered to an aluminum mesh. A CR2032 type coin cell (316L stainless steel, polypropylene gasket) was then assembled in a glove box using a CR2016 type coin cell as the cathode, 1 mol / L LiPF6 as the ethylene carbonate / dimethyl carbonate (volume ratio 1:1) electrolyte, Celgard 2025 as the separator, and a lithium sheet as the counter electrode. The charge-discharge performance of this control lithium-ion battery at different current densities within the voltage range of 2.0–3.2 V was tested on an electrochemical workstation. Test data shows that it has a specific capacity of 256 mAh·g⁻¹ for the first time, and the capacity retention is about 90% after 100 cycles.

[0054] Comparative Example 2

[0055] Based on Example 1, the difference is that the raw materials used are 50 parts V2O5, 30 parts MnO2, 10 parts Li2CO3 and 10 parts Na2B4O7·10H2O, and no CH4N2S is added. Other processes and parameters are exactly the same as in Example 1.

[0056] The performance test results of lithium-ion batteries assembled with glass cathode materials prepared in Examples 1-8 and Comparative Examples 1 and 2 are shown in Table 3.

[0057] Table 3 Performance test results of batteries prepared in the embodiments and comparative examples of the present invention

[0058]

[0059] As can be seen from the above embodiments, the present invention provides an amorphous cathode material, comprising active material glass powder; the raw materials for preparing the active material glass powder include vanadium pentoxide, manganese dioxide, lithium carbonate, sodium tetraborate decahydrate, and thiourea; wherein the molar ratio of vanadium pentoxide, manganese dioxide, lithium carbonate, sodium tetraborate decahydrate, and thiourea is 50:(10~30):10:10:(0~20), preferably 50:10:10:10:20. The above raw materials are used to prepare a glass block by melt quenching, which is then placed in a thermoelectric coupling field device for crystallization treatment to obtain a crystallized glass block. This block is then ground to obtain the active material glass powder. Lithium-ion batteries assembled with this amorphous cathode material have advantages such as high specific capacity, excellent rate performance, and long cycle life. Experimental results show that the active material glass powder has an amorphous structure with an average particle size of 200~400 nm; when applied in lithium-ion batteries, the electronic conductivity can reach 6×10⁻⁶. ⁻4 ~9×10 ⁻4 S / m; charge transfer impedance reduced to 450~600 Ω; coefficient of thermal expansion is 4×10⁻ 6 ~5×10⁻ 6 / K, open circuit voltage 3.5~4.0 V; initial discharge specific capacity can reach 330~380 mAh / g; after activation at 0.1C, after 200 cycles at 1C rate, the discharge capacity retention rate is as high as 90%~97%.

[0060] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An amorphous vanadium-based cathode material, characterized in that, Including active material glass powder; The raw materials for preparing the active material glass powder include the active material precursor V2O5, the structural stabilizer MnO2, the glass network forming precursor Na2B4O7·10H2O, the glass network modifying precursor and lithium source Li2CO3, and the reducing agent and doping source CH4N2S.

2. The amorphous vanadium-based cathode material according to claim 1, characterized in that, In the raw materials for preparing the active substance glass powder, the molar ratio of V2O5, MnO2, Li2CO3, Na2B4O7·10H2O, and CH4N2S is 50:(10~30):10:10:(0~20).

3. The amorphous vanadium-based cathode material according to claim 1, characterized in that, The active material glass powder is prepared by the following method: S1) An amorphous glass bulk was prepared by melting and quenching a mixture of the active material precursor V2O5, the structural stabilizer MnO2, the glass network forming precursor Na2B4O7·10H2O, the glass network modifier precursor and lithium source Li2CO3, and the reducing agent and doping source CH4N2S under an inert atmosphere. S2) Grind the amorphous glass block to obtain active material glass powder.

4. The amorphous vanadium-based cathode material according to claim 3, characterized in that, The amorphous glass bulk material prepared by the melt-quenching method specifically includes: The mixture is heated to 600-900℃ under an inert atmosphere and held for 20-35 minutes. Then, the temperature is further increased to 1200-1800℃ and held for 15-35 minutes. After cooling, the mixture is solidified to obtain a glass block.

5. The amorphous vanadium-based cathode material according to claim 3, characterized in that, Optionally, the amorphous glass block prepared in S1) is subjected to crystallization treatment to obtain a crystallized glass block; the crystallized glass block is ground to obtain active material glass powder.

6. The amorphous vanadium-based cathode material according to claim 5, characterized in that, The crystallization treatment temperature is 200–400 °C, and the crystallization treatment time is 200–2000 min; The electric field strength used in the crystallization process is 0.8~1.5kV / cm, and the current density is 5~20mA / cm².

7. The amorphous vanadium-based cathode material according to claim 1, characterized in that, The average particle size of the active material glass powder is 200~400 nm.

8. The amorphous vanadium-based cathode material according to claim 1, characterized in that, It also includes a binder and a conductive filler; the mass ratio of the active material glass powder, the binder and the conductive filler is (6~10):(2~3):(1~2).

9. A method for preparing an amorphous cathode material, characterized in that, An amorphous cathode material is obtained by ball milling and coating an active material glass powder, binder, conductive filler and solvent, as described in any one of claims 1 to 8.

10. A lithium-ion battery comprising the amorphous vanadium-based cathode material according to any one of claims 1 to 8 or claim 9.

Images