Wadsley-roth structure composite oxide and preparation method and application thereof
By in-situ growing the PNb9O25 phase on the surface of TiNb2O7, a heterostructured composite oxide was constructed, which solved the problem of insufficient performance of TiNb2O7 and PNb9O25 materials in high-rate and long-cycle applications. This achieved a balance between high energy density and high power density, and improved the fast-charging performance and cycle life of lithium-ion batteries.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIHANG UNIV
- Filing Date
- 2026-04-01
- Publication Date
- 2026-07-31
AI Technical Summary
The performance of existing TiNb2O7 and PNb9O25 materials in high-rate and long-cycle applications still needs improvement. Simple physical mixing results in poor interfacial contact and discontinuous conductive network, making it difficult to achieve both high energy density and high power density.
By in-situ growing the PNb9O25 phase on the surface of TiNb2O7 particles, a heterostructured composite oxide is formed, and its microstructure is optimized. The preparation method includes solid-state reaction and heat treatment, and the content and morphology of PNb9O25 are controlled.
It significantly improves the high-rate discharge performance and fast-charge cycle life of lithium-ion battery anodes. The composite material maintains high capacity and extends cycle life at high rates, achieving a balance between high energy and high power.
Smart Images
Figure CN122494594A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium-ion battery electrode material technology, specifically relating to a composite oxide with a Wadsley-Roth structure, its preparation method, and its application in the negative electrode of a lithium-ion battery. Background Technology
[0002] With the development of electric vehicles and portable electronic devices, the demand for fast charging and high power output performance of lithium-ion batteries is becoming increasingly urgent. However, the widely used graphite anode material currently has a working potential close to that of metallic lithium (0.01-0.3V vs. Li). + Lithium titanate (Li₄Ti₅O₂) is prone to lithium dendrite precipitation during high-rate charging, posing a serious safety hazard. Furthermore, "zero-strain" lithium titanate (Li₄Ti₅O₂) 12 The negative electrode exhibits a high operating voltage (approximately 1.55 V) and excellent cycle stability, but its theoretical specific capacity is only about 175 mAh g⁻¹. -1 Its energy density is relatively low, and it requires nano-processing to meet the application requirements of high-rate charge and discharge.
[0003] Niobium-based oxides have attracted attention as a new generation of fast-charging anode materials. Among them, titanium niobium oxide (TiNb2O7) is a niobium titanium oxide with a Wadsley-Roth crystal shear structure and a theoretical specific capacity of approximately 388 mAh g⁻¹. -1 Furthermore, its operating potential is approximately 1.6 V. Compared to graphite, TiNb₂O₇'s higher lithium intercalation potential effectively avoids the risk of lithium plating and allows for multi-electron reactions, achieving higher performance than Li₄Ti₅O₇. 12 Higher capacity. The crystal structure of TiNb2O7 consists of an open framework of 3×3×∞ Ti / Nb-O octahedral blocks, which is conducive to the rapid migration of lithium ions. However, TiNb2O7 itself has low electronic conductivity, and the ion diffusion rate is limited by particle size and crystal defects, so its performance in high-rate and long-cycle applications still needs to be improved. To this end, some studies have attempted to improve its performance through carbon material composites, hollow structure construction, and cation doping (such as Sb). 5+ Mo 6+ Methods such as modification of TiNb2O7 can be used to improve its conductivity and structural stability, but the improvement is limited and cannot fully meet the requirements of extreme fast charging and long life.
[0004] PNb9O phosphate 25 It is a high-potential lithium-ion battery anode material that has emerged in recent years, and it also belongs to the Wadsley-Roth structure category. PNb9O 25It is constructed by crystal shearing of 3×3×∞ ReO3-type Nb-O octahedral blocks and PO4 tetrahedra, with a lithium intercalation plateau voltage of approximately 1.7 V. Compared to TiNb2O7, PNb9O... 25 It exhibits a higher operating potential, causing redox reactions to occur at higher potential ranges during charging. The additional charge carriers introduced during lithium-ion intercalation effectively modulate its band structure, thereby significantly improving electronic conductivity and gradually transforming the material from an intrinsic semiconductor to exhibiting metal-like conductive properties. Although PNb9O 25 While its theoretical capacity is slightly lower than TiNb2O7, its open three-dimensional framework and multi-electron redox mechanism give it excellent high-rate performance and cycling stability. Nanofiber-like PNb9O has been reported... 25 At 0.2C, the capacity is approximately 230 mAh g. -1 It can still reach approximately 180 mAh g at 6C rate. -1 After 1000 cycles, the capacity retention is approximately 70%. This indicates that PNb9O... 25 It can maintain high reversible capacity and good lifespan under high charge and discharge conditions, making it very suitable as a negative electrode material for fast-charging lithium batteries.
[0005] In summary, TiNb2O7 and PNb9O 25 Each possesses the advantage of high capacity or high rate performance. However, how to effectively combine these two Wadsley-Roth structures to achieve both high energy density and high power density remains a pressing technical challenge. If only TiNb2O7 and PNb9O... 25 Simple physical mixing may result in problems such as poor interfacial contact and discontinuous conductive networks, making it difficult to fully utilize the synergistic effect of the two phases. Therefore, it is necessary to provide a novel composite material that integrates TiNb2O7 and PNb9O 25 The two phases are tightly bonded at the microscale to form a stable heterostructure, thereby simultaneously improving the high-rate discharge performance and fast-charge cycle life of the material to meet the application requirements of high-power lithium-ion batteries. Summary of the Invention
[0006] 1. Purpose of the invention
[0007] The purpose of this invention is to address the shortcomings of the prior art by providing a composite oxide with a Wadsley-Roth structure, its preparation method, and its application, which combines high specific capacity and high rate performance, significantly improving the fast charging performance and cycle life of lithium-ion battery anodes.
[0008] 2. Technical Solution
[0009] To achieve the above objectives, the present invention provides the following technical solution:
[0010] (1) Composite oxide material: A Wadsley-Roth structure composite oxide material, characterized by using titanium niobium oxide TiNb2O7 as a carrier, and growing phosphorus niobium oxide phase PNb9O in situ on the surface of its particles. 25 This forms a heterostructure (where TiNb2O7 is abbreviated as "TNO", PNb9O...). 25 (Abbreviated as "PNO"). This composite oxide contains both TNO and PNO crystalline phases, with the PNO phase tightly bonded to the surface of the TNO grains. Preferably, the composite oxide contains PNb9O. 25 The mass fraction of the PNO phase is 5%–50%, and the content and morphology of the PNO phase can be controlled by adjusting the precursor ratio and heat treatment conditions. The TNO phase has a monoclinic crystal structure, and the PNO phase has a tetragonal crystal structure; both belong to the Wadsley-Roth type crystal structure system.
[0011] (2) Preparation Method: The present invention also provides a method for preparing the above-mentioned composite oxide material, characterized by comprising the following steps: TNO preparation: TNO powder is synthesized by solid-state reaction method. TiO2 and Nb2O5 raw materials are mixed uniformly in stoichiometric ratio, calcined in air at 1000-1200℃ for 5-20 hours, and then cooled to obtain monoclinic TNO powder. In-situ generation of PNO phase: The obtained TNO powder is mixed with niobium-containing compounds and phosphorus-containing compounds and then heat-treated to form PNO phase in-situ on the TNO surface. Preferably, TNO powder is mixed uniformly with Nb2O5 and ammonium dihydrogen phosphate, sintered in air at 800-1200℃ for 2-20 hours, cooled and ground to obtain the TNO / PNO phase content. More preferably, the mixing process can be carried out by solid-state grinding methods such as ball milling to ensure that the precursor is uniformly dispersed and fully contacted with TNO particles. After sintering, the product can be lightly ground and pulverized to obtain the target composite oxide powder. The preferred addition ratio is: 5-50 parts by mass of Nb2O5 and 0.3-8 parts by mass of ammonium dihydrogen phosphate per 100 parts by mass of TNO powder. The proportion of PNO generated can be adjusted by controlling the amount of additives.
[0012] 3. Applications: The composite oxide of this invention can be used as a negative electrode material for lithium-ion batteries. Using the above-mentioned TNO / PNO composite oxide as the active material, combined with a conductive agent and binder to form a negative electrode sheet, can significantly improve the rate performance and cycle life of the battery. This invention also provides a lithium-ion battery in which the negative electrode active material comprises the above-mentioned composite oxide. The preferred negative electrode formulation is: 85% active material, 7% conductive carbon, and 8% binder (by mass). The negative electrode sheet is prepared using a conventional coating process and assembled with a lithium metal counter electrode, a separator, and an electrolyte to form a lithium-ion half-cell or with a positive electrode material to form a full cell. This composite material negative electrode is suitable for high-rate charge-discharge applications, such as electric vehicle power batteries and high-power energy storage devices.
[0013] 4. Beneficial effects
[0014] Compared with the prior art, the composite oxide anode material of the present invention has the following significant advantages:
[0015] (1) High-rate capacity enhancement: Thanks to the high-speed lithium-ion transport channels of the PNO phase in the heterostructure, the composite material of this invention can still maintain a high capacity under high-rate discharge. Experimental results show that at 20 A g -1 At ultra-high current densities, the specific capacity of the composite material of this invention is consistently superior to that of pure TNO material. Figure 5 It can be seen that in 0.1-2 Ag -1 Within the rate range, the discharge capacity of the composite material electrode is higher than that of the pure TNO electrode, especially in the high-rate region where the advantage is significant.
[0016] (2) Extended cycle life: The composite material of this invention exhibits excellent stability under fast-charge cycling conditions. (Using 4A g) -1 After repeated charging and discharging at the current density for 1000 cycles, the composite material electrode can still retain more than 90% of its initial capacity, while the capacity retention rate of the pure TNO electrode under the same conditions is only 80%. Figure 6 The cycling performance curves shown demonstrate that the capacity decay of the material of the present invention is greatly reduced under long-term cycling, effectively suppressing stress concentration and pulverization of the electrode material during lithium insertion / extraction, and significantly improving cycle life.
[0017] (3) Synergistic Electrochemical Performance: The two Wadsley-Roth phases of this invention form a robust interface through in-situ growth, achieving a synergistic effect: TNO provides high capacity, and PNO provides high rate kinetics. Under the combined effect of the two phases, the overall performance of the electrode is far superior to that of a single-phase material. For example, the composite oxide of this invention simultaneously possesses the high capacity of TNO and the high rate characteristics of PNO, achieving a capacity of 250 mAh g at conventional current densities. -1Furthermore, it can provide significantly higher capacity output even under fast charging conditions. This balance and improvement in performance is difficult to achieve with existing single-phase anode materials.
[0018] In summary, this invention achieves in-situ growth of PNb9O on the surface of TiNb2O7. 25 The phase constructs a heterogeneous composite oxide, which effectively overcomes the contradiction between high capacity and high rate of operation in the existing technology, and greatly improves the fast charging performance and service life of lithium-ion battery anodes, which has important practical value and application prospects. Attached Figure Description
[0019] Figure 1 The TiNb2O7 / PNb9O obtained in Example 1 25 X-ray diffraction (XRD) pattern of composite material.
[0020] Figure 2 The images are scanning electron microscope (SEM) images of pure-phase TNO and the composite material obtained in Example 1, with scale bars of 2 μm and 1 μm.
[0021] Figure 3 The image shows the energy dispersive spectroscopy (EDS) elemental distribution of the composite material in Example 1.
[0022] Figure 4 The differential capacity curves of pure-phase TNO and the composite material obtained in Example 1 as negative electrode materials in a half-cell with metallic lithium as the counter electrode are shown.
[0023] Figure 5 Comparison of rate performance of pure-phase TNO and the composite materials obtained in Examples 1-3 as negative electrode materials for lithium-ion batteries in half-cells with metallic lithium as the counter electrode.
[0024] Figure 6 Comparison of cycle performance of pure-phase TNO and the composite material obtained in Example 2 as negative electrode materials in a half-cell with metallic lithium as the counter electrode. Detailed Implementation
[0025] The present invention will be further illustrated below with specific embodiments, but the present invention is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents used in the embodiments are all conventional industrial products or analytical grade reagents, and the percentages used in the experiments are all mass percentages.
[0026] Comparative Example 1: Preparation and Properties of Pure TiNb2O7 Material
[0027] (1) Preparation of TiNb2O7: TiO2 and Nb2O5 powders were mixed and ground evenly at a Ti:Nb atomic ratio of 1:2. The mixture was calcined at 1100℃ for 10 h in air atmosphere, and then furnace cooled to room temperature. The resulting sintered block was ground into powder using a mortar and pestle to obtain white TiNb2O7 precursor powder. The TiNb2O7 grains were polycrystalline and dense, as observed by SEM. Figure 2 As shown in (a) and (b), the particle size is approximately 1-3 μm.
[0028] (2) Electrode Preparation and Electrochemical Testing: The pure TiNb2O7 powder was used as the negative electrode active material and mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) at a mass ratio of 85:7:8. N-methylpyrrolidone (NMP) was used to prepare a slurry. The slurry was uniformly coated onto a copper foil current collector, dried under vacuum at 110℃ for 12 hours, and then punched into circular electrode sheets with a diameter of 12 mm to obtain the TiNb2O7 negative electrode sheet. In an argon-atmosphere glove box, using the above negative electrode sheet as the working electrode and a lithium metal sheet as the counter electrode, with a glass fiber membrane (GF / D) as the separator, 1 mol L... -1 Electrochemical tests were performed on CR2032 coin cells assembled with LiPF6 electrolyte (solvent: ethylene carbonate EC – dimethyl carbonate DMC – ethyl methyl carbonate EMC = 1:1:1, volume ratio). All cells were allowed to stand at room temperature for 12 hours before testing. Electrochemical tests were conducted at 1–2.5 V (vs. LiPF6). + Within the / Li) voltage window, charge-discharge cycles were performed at different constant current rates, and the cyclic voltammetry (CV) and differential capacity (dQ / dV) curves were periodically tested to analyze the reaction mechanism.
[0029] (3) Performance test results: The initial discharge specific capacity of the pure TiNb2O7 anode is 0.1 A g. -1 Approximately 250 mAh g at current density -1 As the multiplier increases, its capacity decreases significantly, reaching 8 A g. -1 Only about 126 mAh g -1 Approximately 0.1 Ag -1 50% of the capacity. Differential capacity curves show that pure TiNb2O7 has a distinct lithium insertion / extraction potential at approximately 1.6 V, with no other reaction peaks in the higher potential region (see [link to relevant documentation]). Figure 4 (The gray curve in the figure). Regarding cycle stability, with 4 A g... -1 After 1000 consecutive charge-discharge cycles at a high rate, the capacity of the pure TiNb2O7 electrode decayed to about 83% of its initial value, demonstrating the shortcomings of rapid capacity decay and limited fast-charging life.
[0030] Example 1: TiNb2O7 / PNb9O 25 Core-shell composite materials (low PNb9O) 25 Preparation of (content)
[0031] (1) Precursor mixing: Take 5.0 g of TiNb2O7 powder obtained in Comparative Example 1, add 0.50 g of Nb2O5 powder and 0.05 g of (NH4)2HPO4. Grind thoroughly in an alumina mortar for 30 minutes to make the precursor mixture containing Nb and P uniformly adhere to the surface of TiNb2O7 powder.
[0032] (2) Heat treatment reaction: The uniformly mixed powder is placed in an alumina crucible, transferred to a muffle furnace, and heated at 5°C for 1 minute in an air atmosphere. -1 The heating rate was increased to 1000℃, and sintering was carried out at this temperature for 5 hours, followed by furnace cooling to room temperature. During sintering, (NH4)2HPO4 decomposed and reacted with the surrounding Nb2O5 and TiNb2O7 surfaces, forming a phosphorus niobium oxide phase in situ on the surface of the TiNb2O7 particles. After cooling, the sintered block was gently ground and passed through a 200-mesh sieve to obtain white TiNb2O7 / PNb9O. 25 Composite oxide powder sample A.
[0033] (3) Phase and morphology analysis: XRD showed that TiNb2O7 and PNb9O coexisted in sample A. 25 Two crystalline phases, their diffraction patterns are as follows Figure 1 As shown. In the black curve (sample A), in addition to retaining the main diffraction peaks of TiNb2O7 (characteristic peaks such as monoclinic phase (110)), a series of PNb9O peaks appeared at positions such as 2θ≈23° and 28°. 25 The characteristic diffraction peaks of the phase indicate that PNb9O has been grown in situ on the TiNb2O7 surface under heat treatment at 1000℃. 25 Crystal. SEM morphology observation (see...) Figure 2 (c) and (d) show that, compared to the smooth surface of the pure TNO sample, the TiNb2O7 particles in sample A have fine particles with a size of approximately 500 nm attached to their surface. Energy dispersive spectroscopy (EDS) elemental analysis is as follows: Figure 3 As shown, the P element signal appears on the surface of TiNb2O7 particles.
[0034] (4) Electrochemical performance testing: Coin cells of sample A were prepared using the same method as in Comparative Example 1, and rate performance and cycle performance were tested. Differential capacity curves ( Figure 4The black curve shows that sample A has a redox peak pair corresponding to TiNb2O7 at approximately 1.6 V, and a new peak not found in pure TiNb2O7 appears at approximately 2.2 V (see [reference]). Figure 4 (gray shaded area), this is PNb9O 25 Li of phase + Characteristic peaks of intercalation / deintercalation reactions. This indicates that PNb9O 25 The phase not only exists in sample A but also participates in the electrode reaction, contributing additional capacity to the material. Electrochemical charge-discharge test results show that, compared with the pure TiNb2O7 electrode, sample A exhibits higher capacity at high rates: for example, at 8 A g... -1 The specific capacity of sample A at the current density is approximately 140 mAh g. -1 It is significantly higher than the approximately 126 mAh g of pure TNO. -1 This indicates a small amount of PNb9O. 25 The introduction of [a specific ingredient] has significantly improved the rate performance of TiNb2O7.
[0035] Example 2: TiNb2O7 / PNb9O 25 Core-shell composite materials (high PNb9O) 25 Preparation of (content)
[0036] (1) TiNb2O7 precursor was prepared according to the method in Example 1, and the amounts of added Nb2O5 and (NH4)2HPO4 were changed to increase the amount of PNb9O generated. 25 Content. Specifically, 5.0 g of TiNb2O7 powder, 1.0 g of Nb2O5, and 0.10 g of (NH4)2HPO4 were ground and mixed evenly, then sintered in air at 1000℃ for 5 hours. After cooling and grinding, the composite oxide powder sample B was obtained. The amount of phosphorus and niobium sources added during the preparation of this sample was increased compared to Example 1, theoretically allowing for the formation of a higher proportion of PNb9O. 25 Mutually.
[0037] (2) XRD analysis revealed that TiNb2O7 and PNb9O in sample B were... 25 The diffraction peaks of both phases are clearly visible, and PNb9O 25 The diffraction peak intensity is significantly enhanced compared to sample A, indicating that its PNb9O 25 Higher content. SEM showed that the TiNb2O7 particles in sample B were covered with more nanoparticles. EDS elemental distribution and Figure 3 Similarly, the signal from P element is stronger on the particle surface. These results indicate that by increasing the amount of precursor, PNb9O 25 The adhesion of TiNb2O7 to the surface is significantly improved.
[0038] (3) The electrochemical performance of sample B is further improved compared to sample A. Notably, at lower rates (e.g., 0.1C), the capacity of sample B is essentially the same as that of sample A, and does not decrease significantly with the increase in PNO content. This indicates that PNb9O 25 The phases themselves also possess high reversible capacity, and the total capacity after the two phases are combined remains at a high level. Sample B exhibits excellent rate performance at 8 A g. -1 Specific capacity at current density is approximately 161 mAh g -1 It is 1.3 times that of pure TNO. Sample B also showed outstanding performance in terms of cycle stability, at 4 A g -1 After 1000 cycles at high rate, the capacity retention is approximately 90%, which is better than the approximately 83% retention of the pure TNO electrode, indicating that the introduction of PNb9O 25 This phase can improve the cycling stability of the electrode. Considering both rate capability and cycling performance, this embodiment demonstrates that appropriately increasing the PNb9O phase can improve the cycling stability of the electrode. 25 The ratio is an effective means to improve the overall performance of TiNb2O7-based anodes.
[0039] Example 3: Effect of sintering temperature on TiNb2O7 / PNb9O 25 Influence of composite material properties
[0040] (1) This embodiment investigates the effect of heat treatment temperature on the formation and properties of the composite structure. The proportions of each material were the same as in Example 2, but the sintering temperature was changed to 1200℃ (other conditions remained unchanged, and the sintering time was 5 hours). The composite oxide obtained by sintering was denoted as sample C.
[0041] (2) XRD analysis showed that TiNb2O7 and PNb9O were present in sample C. 25 The two phases still coexist. SEM showed that the microstructure of sample C was similar to that of sample B, but the particles were slightly larger, and some areas of nanoparticles underwent sintering and agglomeration. Electrochemical tests showed that the performance of sample C at high magnification was basically equivalent to that of sample B, with a slight decrease. It can be considered that an appropriate sintering temperature is beneficial to PNb9O 25 Phase formation and interfacial bonding are important, but excessively high temperatures may lead to increased particle size and decreased specific surface area, which is detrimental to low-rate capacity utilization. Therefore, the method of this invention can prepare composite materials with excellent performance within the range of 900-1100℃. Taking all factors into consideration, the preferred sintering temperature of this invention is about 1000℃, at which a more ideal composite structure and comprehensive electrochemical performance can be obtained.
[0042] Overall performance comparison: Figure 5This paper summarizes the electrochemical performance comparison between the composite materials obtained in Comparative Example 1 (pure TiNb2O7) and Examples 1–3, providing a direct comparison of the discharge capacity of each sample at different rates. The data in the figures show that the capacity of the pure TiNb2O7 sample decreases significantly with increasing rate, exhibiting severe capacity decay during cycling; while the composite materials of this invention show higher capacity and slower capacity decay across the entire rate range. Specifically, the initial capacities of samples A, B, and C at 0.1C are all close to 250-260 mAh g⁻¹. -1 The capacity was comparable to that of pure TNO, indicating that the composite structure did not sacrifice low-rate capacity. With increasing rate, the capacity of pure TNO rapidly decreased to a lower value, while the composite sample maintained a significantly higher capacity: at 8 A g... -1 At the given current density, samples A, B, and C have approximately 140, 161, and 151 mAh g⁻¹, respectively. -1 This is significantly higher than the approximately 126 mAh g of pure TNO. -1 . Figure 6 The results show that sample B and pure TNO were mixed at 4 A g. -1 The capacity decay curve under fast charging cycling is shown. After 1000 cycles, pure TNO only retains about 83% of its capacity, while sample A retains about 90% of its initial capacity. This verifies that with the increase of PNb9O... 25 Through the introduction and optimization of the phase, the high-rate charge-discharge capability and fast-charge durability of the composite oxide of this invention are significantly superior to those of traditional TiNb2O7 materials. These results from the embodiments are consistent with the analysis in the foregoing figures (…). Figure 1-6 This is consistent with the above, which fully demonstrates the effectiveness and superiority of the technical solution of the present invention.
[0043] In summary, through the specific description of the above embodiments, it can be seen that the "Wadsley-Roth structured composite oxide and its preparation method and application" provided by the present invention can achieve the expected technical effects. Without departing from the spirit of the present invention, those skilled in the art can make certain changes or equivalent substitutions to the material ratios, process parameters, etc., and these changes should all be considered to fall within the protection scope of the present invention. The above embodiments are only used to further illustrate the technical solution of the present invention and should not be construed as limiting the protection scope of the present invention. All equivalent substitutions or improvements made without departing from the concept of the present invention should be included within the scope of the claims of the present invention.
Claims
1. A composite oxide, characterized in that: It contains two oxide phases with Wadsley-Roth crystal structures, one of which is titanium niobium oxide TiNb2O7 phase (A), and the other is phosphorus niobium oxide PNb9O. 25 Phase (B); Phase (B) grows in situ on the surface of phase (A) particles to form a composite oxide material with a heterogeneous structure.
2. A method for preparing the composite oxide of claim 1, characterized in that, Includes the following steps: 1) Provide titanium niobium oxide (TiNb2O7) precursor powder; 2) Mix TiNb2O7 powder with niobium-containing and phosphorus-containing compounds uniformly, and heat-treat at 800-1200℃ for 2-20 hours to generate niobium niobium oxide (PNb9O) phase in situ on the surface of TiNb2O7 particles. 25 The composite oxide is obtained after cooling.
3. The composite oxide according to claim 1, characterized in that: The PNb9O 25 The content of the phase accounts for 5-50% of the total mass of the composite oxide.
4. The composite oxide according to claim 1, characterized in that: The PNb9O 25 The phase is formed by nanoparticles attached to the surface of TiNb2O7 core particles.
5. The composite oxide according to claim 1, characterized in that: The TiNb2O7 phase and PNb9O 25 Both phases belong to the Wadsley-Roth crystal shear structure type.
6. The composite oxide according to claim 1, characterized in that: It is used as the negative electrode active material in lithium-ion batteries.
7. A lithium-ion battery negative electrode, characterized in that: It includes an active material, a conductive agent, and a binder, wherein the active material is the composite oxide as described in claim 1.
8. A lithium-ion battery, characterized in that: Its negative electrode active material comprises the composite oxide material as described in claim 1.
9. The method according to claim 2, characterized in that: The niobium-containing compound is Nb₂O₅, and the phosphorus-containing compound is ammonium dihydrogen phosphate (NH₄)₂HPO₄.
10. The method according to claim 9, characterized in that: The mass ratio of TiNb2O7 powder, Nb2O5 and (NH4)2HPO4 is 100:5-50:0.3-8.
11. The method according to claim 2, characterized in that: The heat treatment step is carried out in an air atmosphere, with a heating rate of 1–15 °C / min, and is cooled with the furnace after the heat treatment is completed.
12. The method according to claim 2, characterized in that: The TiNb2O7 powder in step 1) is obtained by mixing TiO2 and Nb2O5 precursors in a Ti:Nb stoichiometric ratio and calcining at 1000-1200℃ for 5-20 hours.