A vanadium-oxygen cluster iron phosphate-based precursor, a preparation method thereof and application thereof in super-fast charging lithium iron phosphate positive electrode materials

Abstract

This invention discloses a vanadium oxide cluster iron phosphate-based precursor, its preparation method, and its application in ultrafast-charging lithium iron phosphate cathode materials. The precursor has the general chemical formula Fe. 1‑x (V4O 12 ) x / 4 PO4, where 0.0149 ≤ x ≤ 0.0209, vanadium is present as a tetranuclear vanadium-oxygen cluster anion ([V4O4]). 12 ] 4‑ The vanadium is doped and embedded in the iron phosphate lattice in the form of [V₄O₂], with a vanadium mass fraction of 5000–7000 ppm based on the total mass of the precursor. The precursor has a unique helical nanoribbon structure with a width of 90–110 nm and a pitch of 30–50 nm, in which vanadium is arranged periodically in [V₄O₂]₃. 12 ] 4‑ It exists in the form of cluster units; its preparation methods include electrochemical acid leaching to reduce vanadium, citric acid complexation to inhibit condensation, and ultrasonic triggering [V4O] 12 ] 4‑ The method involves cluster self-assembly and co-precipitation under magnetic field guidance. This approach solves the problem of lattice distortion and ion channel blockage caused by high-concentration vanadium doping. The lithium iron phosphate cathode material prepared from this precursor exhibits excellent ultra-fast charging performance, with a discharge capacity of no less than 130 mAh / g at a 10C rate, which is significantly better than traditional high-vanadium doped materials.

Description

Technical Field

[0001] This invention relates to the field of fast-charging cathode materials for lithium-ion batteries, specifically to a vanadium-oxygen cluster-doped iron phosphate-based precursor with a helical nanoribbon structure, its preparation method, and its application in ultra-fast-charging lithium iron phosphate cathode materials, which is particularly suitable for scenarios with extremely high requirements for fast-charging performance, such as electric vehicles and energy storage systems. Background Technology

[0002] With the rapid development of electric vehicles and energy storage systems, higher demands are being placed on the fast-charging performance of lithium-ion batteries. Lithium iron phosphate (LiFePO4) is widely used due to its high safety and long cycle life, but it has two inherent drawbacks: firstly, its lithium-ion diffusion coefficient is low, approximately 10-1. -14 ~10 -12 cm 2 / s, with low electronic conductivity, approximately 10 -9 The low discharge capacity (S / cm) of lithium iron phosphate batteries severely limits their fast-charging performance, with conventional lithium iron phosphate 10C discharge capacity only reaching 100–120 mAh / g. Currently, common modification methods include carbon coating, nano-sizing, and ion doping.

[0003] Existing practices have shown that while carbon coating of nanolayers can improve electronic conductivity, it cannot solve the problem of slow lithium-ion diffusion, resulting in limited improvement in 10C capacity. Regarding nano-sizing, preparing lithium iron phosphate into nanoparticles shortens the lithium-ion transport path, but these nanoparticles are prone to agglomeration and have low tap density (<0.8 g / cm³). 3 This affects the volumetric energy density of the battery.

[0004] In ion doping, heterovalent ions, such as V... 3+ Mg 2+ Al 3+ Doping modulates the crystal structure and improves ionic conductivity. Among these, vanadium doping is influenced by V... 3+ The ionic radius is 78.5 pm and Fe 3+ The ionic radii are close to 64.5 pm, and they can form multiple valence states (V). 3+ / V 4+ / V 5+ It is considered one of the best doping elements for assisting electron transport.

[0005] However, high-concentration vanadium doping (greater than 4000 ppm) faces two major technical bottlenecks:

[0006] First, there is the generation of aggregates and hybrid phases: V 3+ It readily hydrolyzes and condenses to form polyvanadates, such as V4O9. 2- V2O5, conventional co-precipitation method, when the vanadium doping amount reaches 4000ppm, it is easy to cause lattice distortion;

[0007] Second, ion channel blockage: Aggregated vanadium species can block lithium-ion transport channels, leading to a decrease in 10C discharge capacity and capacity after 500 cycles.

[0008] Furthermore, existing preparation methods have drawbacks:

[0009] Ball milling cannot achieve uniform vanadium distribution, and excessively high local vanadium concentrations lead to impurity phases; conventional coprecipitation methods lack control over the morphology and structure of vanadium species, and cannot form ordered ion transport channels; grain growth is prone to occur during sintering, further reducing ion diffusion efficiency.

[0010] CN101106194A discloses a method for preparing a single lithium vanadium phosphate (Li3V2(PO4)3) cathode material. This method employs a nanoparticle secondary forming liquid-phase method, where lithium, vanadium, and phosphorus sources are wet-milled with a complexing agent and then mixed in the liquid phase. Following spray drying, inert atmosphere calcination, and carbon coating, molecular-level mixing of the reactants is achieved, improving product purity and cycle stability. This technology focuses on the preparation of a single lithium vanadium phosphate material. While utilizing vanadium to improve the ionic conductivity, the use of an external, independent vanadium source fails to achieve effective composite formation of vanadium and iron phosphate. Furthermore, the product is a single lithium vanadium phosphate, which cannot simultaneously achieve the low cost and high safety advantages of lithium iron phosphate. Additionally, carbon coating only improves electron conduction and does not address the uneven distribution of vanadium species in the composite system.

[0011] CN105870428A discloses a dedicated precursor preparation technology for lithium iron phosphate-lithium vanadium phosphate composite cathode materials. This technology involves mixing ferrous gluconate and sodium metavanadate at a specific molar ratio, adding PVP to adjust the pH, and then subjecting the mixture to water bath ultrasonication, high-temperature hydrothermal reaction, and vacuum drying to prepare a rod-shaped ferrous metavanadate precursor. The aim is to provide excellent ion conduction channels for subsequent composite cathode materials, thereby improving rate performance. While this technology achieves the composite of iron and vanadium precursors, it still relies on externally added sodium metavanadate as the vanadium source, failing to form a complex-like structure between iron and vanadium. The uniformity of vanadium species dispersion in the precursor depends on physical mixing and morphology control, making local agglomeration prone to occur. Furthermore, it only uses a hydrothermal method to control the precursor to a rod shape, without constructing continuous multi-level ion transport channels, making it difficult to meet the high ion diffusion efficiency requirements of ultra-fast charging.

[0012] In summary, existing technologies related to lithium iron phosphate and vanadium modification share the following common shortcomings: First, vanadium sources are introduced by adding independent vanadium compounds, failing to achieve the synergistic effect of iron and vanadium forming complex-like compounds. This leads to vanadium species agglomeration and uneven distribution, failing to fully leverage the vanadium's promoting effect on ion conduction. Second, the core technologies primarily focus on macroscopic control of particle morphology (e.g., flower-like or rod-like) or performance optimization of single materials, without constructing continuous multi-level ion transport channels suitable for ultra-fast charging. Third, existing composite modification technologies struggle to simultaneously address the requirements of high-concentration vanadium doping, ordered vanadium species distribution, and absence of lattice distortion, thus failing to effectively overcome the fast-charging performance bottleneck of lithium iron phosphate. Therefore, developing an iron iron phosphate-based precursor technology based on an iron-vanadium complex structure, possessing both ordered vanadium distribution and continuous ion channels, is crucial to overcoming the deficiencies of existing technologies. Summary of the Invention

[0013] This invention aims to solve the problems of uneven vanadium distribution, disordered structure, and blocked ion channels in existing high-concentration vanadium doping, and provides a method with a helical nanoribbon structure, in which vanadium is distributed in [V4O] 12 ] 4- A cluster-shaped, ordered distribution of iron phosphate-based precursors, a controllable preparation method thereof, and the application of such precursors in ultra-fast-charging lithium iron phosphate cathode materials.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] This invention provides a vanadium oxide cluster iron phosphate-based precursor, characterized in that: the precursor has a helical nanoribbon structure and its general chemical formula is Fe. 1-x (V4O 12 ) x / 4 PO4, where x ranges from 0.0149 to 0.0209, vanadium is represented by the tetranuclear vanadium-oxygen cluster anion ([V4O4O4]). 12 ] 4- The nanoribbons are doped and embedded in the iron phosphate lattice in the form of vanadium, and the mass fraction of vanadium is 5000-7000 ppm based on the total mass of the precursor. The width of the nanoribbons is 90-110 nm and the pitch of the spiral channel is 30-50 nm.

[0016] It should be noted that the general chemical formula described in this invention is Fe. 1-x (V4O 12 ) x / 4 In the general formula PO4, vanadium does not exist in a single valence state, but rather in a mixed valence state in [V4O] 12 ] 4- Within the cluster, the average valence state is +4.8 to +5.2, close to +5. The core of the general formula is to reflect the molar ratio of "Fe:V:P:O" rather than a precise single valence state. In addition, the general formula omits the water of crystallization (the actual precursor is Fe). 1-x(V4O 12 ) x / 4 PO4·2H2O (co-precipitated) and trace charge-compensating ions (such as H+) + The core idea is to highlight the core composition ratio of Fe-VPO, rather than denying the actual structure. As long as the core molar ratio Fe∶V∶P=(1-x)∶x∶1 remains unchanged, the precursor will conform to this general formula.

[0017] The spiral nanoribbon structure described in this invention is based on iron phosphate (FePO4, containing a small amount of water of crystallization), and has a continuous ribbon-like morphology. The ribbon structure is spirally wound along the central axis to form a three-dimensional spiral structure similar to a spring. It can be understood as twisting uniformly wide nanoscale ribbons into a spiral shape, which is the skeleton that supports vanadium-oxygen clusters.

[0018] The nanoribbon structure contains periodically arranged [V4O] 12 ] 4- Cluster units form continuous, rapid lithium-ion transport channels. This structure, constructed through a combination of sonochemical depolymerization and magnetically guided co-precipitation, overcomes the technical bottleneck of easy agglomeration in high-concentration vanadium. The cluster spacing is 2.8–3.2 nm. [V4O] 12 ] 4- The volume fraction of cluster units in the helical nanoribbons is 1.2–1.8 vol%.

[0019] Among them, [V4O 12 ] 4- The clusters are arranged in an orderly manner, with an equivalent size of 1.0–1.4 nm, close to 1.2 nm (DFT calculation), which matches the interstitial gap of the iron phosphate lattice (1.5 nm), allowing them to be embedded in the interstitial gap without causing distortion; the inter-cluster spacing is 2.8–3.2 nm, which can form continuous microscopic ion channels.

[0020] In this invention, DFT calculation determines [V4O] 12 ] 4- The process of determining the equivalent size of a cluster can be divided into four core steps, all revolving around the structural characteristics and computational reliability of the target cluster, as follows:

[0021] First, an initial structural model of the cluster is constructed: based on the chemical bonding rules of vanadium-oxygen clusters (V and O commonly coordinate in 6- or 4-coordinate modes), the [V4O] structure is determined. 12 ] 4- The initial atomic composition and coordination framework of the cluster are constructed by building an initial unit cell model containing 4 V atoms and 12 O atoms forming coordination bonds around the V atoms, with the initial coordinates of each atom clearly defined.

[0022] Next, set the DFT calculation parameters: Select the core parameters suitable for transition metal (V) oxide calculations:

[0023] (1) Exchange-correlation functionals, such as GGA-PBE, are suitable for calculating the electronic structure of transition metal compounds and can accurately describe the interaction of VO bonds;

[0024] (2) Atomic orbital basis sets, such as all-electron basis sets or pseudopotential basis sets for V and O atoms, to ensure both computational accuracy and efficiency;

[0025] (3) Convergence criteria: Set energy convergence threshold and force convergence threshold, for example, energy convergence to 10. -5 Below eV / atom, the atomic force converges to below 0.01eV / Å, ensuring stable calculation results.

[0026] Secondly, structural optimization calculations are performed: based on the initial model and set parameters, geometric structure optimization is carried out, that is, by solving the approximate solution of the Schrödinger equation, the spatial positions (interatomic spacing, bond angle, dihedral angle) of each atom within the cluster are iteratively adjusted until the total energy of the system reaches the minimum value, obtaining [V4O 12 ] 4- The cluster has a thermodynamically stable structure, at which point the atoms within the cluster are arranged in the most stable manner, closely resembling their actual state.

[0027] Finally, the cluster size is quantified and calculated: For the optimized stable structure, atomic coordinate data is extracted, and the key size parameters of the cluster are calculated. That is, with the geometric center of the cluster as the reference, the maximum and minimum distances from the outermost atom (V or O) to the center are measured, and the average value is taken as the equivalent size of the cluster; or the lengths of the longest and shortest axes of the cluster are directly measured, and the arithmetic mean is taken to obtain the final size, which is close to 1.2 nm as determined in this invention.

[0028] Among them, the macroscopic structure of the helical nanoribbon has a nanoribbon width of 90–110 nm, a pitch of 30–50 nm, and a specific surface area of ​​35–45 m². 2 / g, tap density is 0.7~1.0g / cm³.

[0029] The nanoribbon width of 90–110 nm balances specific surface area and tap density. If the width is <90 nm, the nanoribbon is too thin, resulting in an excessively large specific surface area (>45 m² / g). While this increases the electrolyte contact area, the nanoparticles are prone to agglomeration, leading to a decrease in tap density (<0.7 g / cm³), ultimately affecting the battery's volumetric energy density, meaning less active material is loaded in the same volume. If the width is >110 nm, the nanoribbon is too thick. Although the tap density can be increased (>1.0 g / cm³), the specific surface area becomes too small (<35 m² / g), resulting in insufficient contact area between the electrolyte and the material, preventing ions from quickly entering the material from the electrolyte. The 90–110 nm range strikes a perfect balance, ensuring sufficient specific surface area for electrolyte wetting while avoiding agglomeration caused by excessively fine particles, thus stabilizing the tap density at 0.7–1.0 g / cm³, thus balancing ion transport interface and volumetric energy density.

[0030] A pitch of 30–50 nm can reduce lithium-ion transport resistance. Pitch, the distance between two adjacent turns of the helix in a helical nanoribbon, is crucial for constructing macroscopic ion transport channels. If the pitch is <30 nm, the helical channel is too narrow, limiting the transport space for lithium ions and leading to congestion and increased transport resistance. Furthermore, an excessively narrow channel may be blocked by byproducts in the electrolyte, affecting cycle stability. If the pitch is >50 nm, the continuity of the helical structure decreases, preventing the formation of a continuous macroscopic transport channel. Lithium ions must then detour, lengthening the path and reducing transport efficiency. An excessively wide pitch also results in a loose nanoribbon structure and decreased tap density. A pitch in the 30–50 nm range creates a moderately wide, continuous macroscopic helical channel, allowing lithium ions to migrate rapidly along the helical direction, significantly shortening the transport path, reducing resistance, and directly improving fast-charging performance.

[0031] A specific surface area of ​​35–45 m² / g can effectively improve electrolyte wettability. Specific surface area directly determines the contact efficiency between the material and the electrolyte. If the specific surface area is <35 m² / g, the surface area available for electrolyte adhesion is insufficient, preventing the electrolyte from fully wetting the material's interior. This results in some active sites being unable to participate in ion insertion / extraction reactions, leading to insufficient capacity utilization. If the specific surface area is >45 m² / g, the material surface activity is too high, making it prone to side reactions with the electrolyte. For example, electrolyte decomposition can produce byproducts that cover the material surface, blocking ion channels. Furthermore, an excessively high specific surface area increases the material's hygroscopicity, affecting the stability of subsequent battery fabrication processes. Within the 35–45 m² / g range, sufficient wetting and stable contact between the electrolyte and the material can be achieved, ensuring rapid ion transfer at the electrolyte-material interface and providing a sufficient ion exchange interface for fast charging.

[0032] The precursor is an amorphous or microcrystalline structure with a D50 particle size distribution of 5–20 μm. Compared to crystalline precursors, amorphous or microcrystalline precursors have fewer lattice defects and more regular lattice interstices, allowing [V4O] to... 12 ] 4- Clusters are more stably embedded in the iron phosphate matrix, avoiding ion channel blockage caused by lattice distortion and solving the bottleneck of easy impurity phase generation in high-concentration vanadium doping in existing technologies. At the same time, the short-range ordered structure can provide a basis for rapid crystallization in subsequent instantaneous sintering, ensuring that the lithium iron phosphate grains formed after sintering are uniform in size and do not grow. If D50 < 5 μm, the particles are too small and easily agglomerate, resulting in a decrease in tap density (< 0.7 g / cm³), which affects the volumetric energy density of the battery. Moreover, small particles are difficult to form a regular helical nanoribbon structure in magnetic field-guided co-precipitation. If D50 > 20 μm, the particles are too large, resulting in a decrease in specific surface area (< 35 m² / g), and the electrolyte cannot fully wet the interior of the particles. Subsequent ball milling requires a longer time to mix evenly, which can easily lead to uneven distribution of vanadium species. During instantaneous sintering, uneven heat transfer inside large particles can easily lead to excessively large local grains, which can damage ion channels.

[0033] The residual amount of citric acid in the precursor is ≤0.5wt%, meaning that the mass of citric acid that has not been completely removed from the precursor accounts for no more than 0.5%wt% of the total mass of the precursor. Citric acid is a key reagent for complexing and inhibiting condensation in this invention, used to stabilize V. 3+ To avoid hydrolysis and condensation. Furthermore, if the residual citric acid content is >0.5wt%, during subsequent instantaneous combustion, the residual citric acid will undergo thermal decomposition, producing gases such as CO2 and H2O. This leads to the formation of pores and cracks within the lithium iron phosphate material, disrupting the continuous structure of macroscopic helical channels and microscopic cluster channels. Simultaneously, the decomposed residual carbon will react with the lithium source to generate Li2CO3 impurity phase, blocking lithium-ion transport channels and reducing fast-charging performance and cycle stability. This value represents the balance between sufficient complexation and low residue—the citric acid and V in step (b) 3+ A molar ratio of 1.0 to 1.2:1 is sufficient to ensure V 3+ The complexation rate is ≥90%; subsequent filtration, washing and drying processes can remove most of the free citric acid. The remaining small amount of citric acid ≤0.5wt% can be completely decomposed in instantaneous sintering, and the amount of gas generated is extremely small, which will not damage the material structure. At the same time, it avoids the loss of vanadium species due to excessive washing.

[0034] This invention also provides a method for preparing the above-mentioned precursor, including steps such as electrochemical acid leaching, complexation-inhibited condensation, ultrasonic-triggered cluster self-assembly, and magnetic field-guided co-precipitation. This method achieves efficient vanadium reduction, ordered cluster assembly, and controllable growth of helical morphology, specifically including the following steps:

[0035] (a) Electrochemical acid leaching treatment: Titanium concentrate is mixed with hydrochloric acid at a concentration of 16–20 wt%, and then subjected to an electrochemical acid leaching treatment at a current density of 90–110 mA / cm². 2 Electrochemical reduction is carried out under the conditions of [condition], to remove V from the solution. 5+ Restore to V 3+ Fe 3+ Reduced to Fe 2+ The acid leaching solution was obtained;

[0036] (b) Purification and impurity removal: An oxidizing agent is added to the acid leaching solution to remove M. 2+ The precipitate is oxidized to MnO2; then an alkaline adjuster is added to adjust the pH to 4.5–5.5, and the reaction is carried out under heat and stirring for 0.5–1 hour to remove Al from the precipitate. 3+ Cr 3+ Add MnO2, filter; add ammonium fluoride or sodium fluoride to the filtrate to increase the F content in the solution. - When the concentration reaches 0.05–0.15 mol / L, stir the reaction at 80–90℃ for 0.5–1 hour to precipitate and remove Ca. 2+ Mg 2+ Filter again; adjust the pH of the filtrate to 2.0-3.0 to obtain the purified solution;

[0037] (c) Complexation and ultrasonic assembly: Citric acid with a concentration of 0.25–0.35 mol / L was added to the purified solution to complex V. 3+ This inhibits the condensation of polyvanadate; then, under the action of ultrasound at a frequency of 35–45 kHz, vanadium in the solution is assembled to form [V4O]. 12 ] 4- Clusters form vanadium-containing solutions;

[0038] (d) Magnetic field-guided coprecipitation: Under a magnetic field of 1.0 to 1.4 T, the vanadium-containing solution and the phosphate solution are subjected to a coprecipitation reaction, and the pH of the reaction system is controlled to be 2.6 to 3.0 to generate an iron phosphate-based precursor with a helical nanoribbon structure. The phosphate solution is a diammonium hydrogen phosphate solution or a diammonium dihydrogen phosphate solution with a concentration of 0.5 to 1.0 mol / L.

[0039] In step (a), the liquid-solid ratio of titanium concentrate to hydrochloric acid is 1:3 to 1:5 g / mL, the cathode material is a titanium plate with a thickness of 0.5 to 1.0 mm, the reaction temperature is 60 to 80 °C, and the reaction time is 1.5 to 2.5 hours.

[0040] V2O5 in titanium concentrate reacts with hydrochloric acid to produce VO2. + (V) 5+ A reduction reaction occurs at the cathode: VO2 + +4H + +2e - →V3+ +2H2O

[0041] Fe 3+ +e - →Fe 2+ ;

[0042] The hydrochloric acid concentration of 16–20 wt% was chosen because when the hydrochloric acid concentration is <16 wt%, the electrolyte ion concentration is low, and the ion migration rate is slow. 5+ If the reduction rate is <85%, the reaction time needs to be extended to more than 3 hours. When the hydrochloric acid concentration is >20wt%, hydrochloric acid volatilization intensifies, the HCl vapor pressure increases, and the solution concentration fluctuates greatly. At the same time, a TiO2 oxide film easily forms on the surface of the titanium cathode, hindering electron transfer, i.e., the following reaction occurs: Ti + 2H2O → TiO2 + 4H + +4e - ;

[0043] The current density is selected to be between 90 and 110 mA / cm². 2 This is because, when <90mA / cm², the reduction kinetics are slow, V 5+ Only partially restored to V4 + ( 2+ Unable to generate the V required for subsequent complexation. 3+ When the current is greater than 110 mA / cm², hydrogen evolution reaction preferentially occurs at the cathode, 2H₂O + +2e - →H 2 (↑), electron utilization rate decreases to <70%, and hydrogen bubbles adhere to the cathode surface, hindering VO 2+ Mass transfer;

[0044] The temperature was chosen to be between 60 and 80°C, and the treatment time between 1.5 and 2.5 hours because when the temperature is below 60°C, the hydrochloric acid viscosity is high (>1.2 mPa·s), resulting in slow ion migration. + The reduction rate is <80%; when the temperature is >80℃, the amount of hydrochloric acid volatilized increases by 50%, and the solution concentration decreases; when the reaction time is <1.5h, the reduction is incomplete, and V 5+ (Residual >15%); when reaction time >2.5h, Fe 3+ Excessively reduced to Fe 2+ Fe 3+ +e - →Fe 2+ This leads to disordered Fe valence states in the precursor, resulting in decreased crystallinity of subsequent lithium iron phosphate.

[0045] In step (b), an oxidizing agent is added to the acid leaching solution to remove Mn. 2+The precipitate is oxidized to MnO2, then an alkaline adjuster is added to adjust the pH to 4.5–5.5. The reaction is maintained at a constant temperature and stirred for 0.5–1 hour to remove Al from the precipitate. 3+ Cr 3+ Add MnO2, filter; add ammonium fluoride or sodium fluoride to the filtrate to increase the F content in the solution. - When the concentration reaches 0.05–0.15 mol / L, stir the reaction at 80–90℃ for 0.5–1 hour to precipitate and remove Ca. 2+ Mg 2+ Filter again; adjust the pH of the filtrate to 2.0-3.0 to obtain the purified solution;

[0046] The preferred oxidant is hydrogen peroxide, added at 0.5%–2% of the leaching solution volume, as it does not introduce any new metallic or anionic impurities and does not interfere with subsequent processes. The reaction is mild and easy to control. The preferred alkalinity regulator is ammonia (NH3·H2O), which is weakly alkaline, has strong buffering capacity, and easily allows for precise pH control within a narrow range of 4.5–5.5. 4+ With PO4 in the system 3- C2O4 2- If no sparingly soluble substances are formed, in the subsequent S1-5 co-precipitation steps, NH... 4+ It exists as a counterion itself and can ultimately be completely removed by washing, along with Cl. - They were all washed away together.

[0047] Choosing a pH range of 4.5–5.5 is to ensure Al 3+ and Cr 3+ Complete precipitation: This pH range is higher than Al 3+ and Cr 3+ The precipitation point is set so that they can be efficiently precipitated in the form of amorphous Al(OH)3 and Cr(OH)3. The reaction time is chosen to be 0.5 to 1 hour because the precipitation reaction is not completed instantaneously. The newly generated Al(OH)3 and Cr(OH)3 particles are very small and are often colloids. They need a certain amount of time to age, that is, small particles dissolve and large particles grow, so as to facilitate subsequent filtration and separation.

[0048] Select F - A concentration of 0.05–0.15 mol / L is used to ensure residual Ca 2+ Mg 2+ Extremely low concentration: According to the solubility product formula, the residual Ca in the solution is extremely low. 2+ Concentration = CaF2 / (F - ) 2 When the solution contains (F - When (Ca) = 0.05 mol / L, (Ca) 2+ ) ≈1.38×10-8 mol / L (approximately 0.00055 ppm); when the solution contains (F - When (Ca) = 0.15 mol / L, (Ca) 2+ ) ≈ 1.53 × 10 -9 mol / L (approximately 0.00006 ppm). Similarly, Mg can be calculated. 2+ The residual concentration is also at a similarly extremely low level (ppb level). This means that calcium and magnesium can be removed to a degree that is completely harmless to subsequent processes.

[0049] At this time Fe 2+ and VO 2+ No precipitation, Fe 2+ With F - Formation of soluble complex ions (FeF3) - VO 2+ With F - It can also form soluble complexes (such as [VOF4)). 2- Therefore, in this F - At concentrations, Fe 2+ and VO 2+ No fluoride precipitate will form, thus achieving interaction with Ca. 2+ Mg 2+ A perfect separation.

[0050] Choosing a temperature of 80-90℃ is to accelerate the precipitation reaction rate, as chemical reaction rates increase with temperature; raising the temperature can significantly shorten the time required to reach precipitation equilibrium. Choosing a reaction time of 0.5-1 hour is to ensure the precipitation reaction reaches equilibrium; although raising the temperature accelerates the reaction, sufficient time is still needed for F to reach equilibrium. - Fully diffused, with Ca 2+ and Mg 2+ Collision and combination allow the precipitation reaction to proceed completely, reaching the theoretical equilibrium state determined by the solubility product; at the same time, aging is achieved, which facilitates separation. Similar to the above, this time also allows small crystals to dissolve and large crystals to grow, forming coarser and more easily filtered precipitate particles. 0.5 to 1 hour is the optimized range that balances reaction completeness, precipitate filterability, and process economy.

[0051] In step (b), citric acid reacts with V in the solution. 3+ The molar ratio is 1.0 to 1.2:1, the temperature of the complexation reaction is 25 to 35°C, and the reaction time is 30 to 60 min.

[0052] The core of this step is to stabilize V. 3+ Complexation inhibits condensation, mainly considering V 3+ Easily hydrolyzes and condenses, resulting in 2V 3+ +2H₂O→V₂O₂ 4++4H + The reaction then forms polyvanadates, such as V4O9. 2- ;

[0053] In this step, the main role of citric acid is to inhibit the condensation reaction. Citric acid has the chemical formula C6H8O7, simplified as H3Cit. Its molecular structure contains three carboxyl groups (-COOH), making it a typical tricarboxylic acid compound. Its structural formula is: HOOC-CH2C(OH)(COOH)-CH2COOH. In this invention, the carboxyl groups of citric acid and V... 3+ Complexation is based on the synergistic effect of the three carboxyl groups, where the oxygen atom (containing a lone pair of electrons) in each carboxyl group can interact with V. 3+ Coordinate bonds are formed, with the three carboxyl groups surrounding V. 3+ Constructing a six-membered ring chelate, i.e. V 3+ -Cit has a stability constant as high as logK = 25.8, which is much higher than the stability constant logK = 12.3 of polyvanadate condensation, thus effectively suppressing V 3+ Hydrolysis and condensation;

[0054] Choose a citric acid concentration in the range of 0.25–0.35 mol / L, and a concentration similar to V in the solution. 3+ The molar ratio is between 1.0 and 1.2:1 because when the citric acid concentration is <0.25 mol / L or the molar ratio is <1.0:1, V 3+ Incomplete complexation, free V 3+ Condensation will occur, and a polyvanadate heterophase will appear in the precursor; when the citric acid concentration is >0.35 mol / L or the molar ratio is >1.2∶1, excess citric acid will react with Fe. 3+ Complexation to form Fe 3+ -Cit, with a stability constant logK = 25.0, will lead to Fe during subsequent co-precipitation. 3+ With PO4 3- The reaction was incomplete, with an Fe defect rate >5% in the precursor;

[0055] The choice of a complexation temperature between 25 and 35°C and a reaction time between 30 and 60 minutes was based on the following considerations: when the complexation temperature is below 25°C, the solubility of citric acid will decrease to <60 g / 100 mL, resulting in partial precipitation and incomplete complexation; when the complexation temperature is above 35°C, citric acid easily decomposes into acetic acid (CH3COOH) and CO2, losing its complexing ability; and when the reaction time is less than 30 minutes, the complexation reaction has not reached equilibrium, V 3+ Complexation rate <90%; when reaction time >60 min, there is no significant gain, only increased energy consumption.

[0056] In step (c), the ultrasonic treatment time is 30-60 min, the ultrasonic power density is 50-100 W / L, and the stirring speed during the ultrasonic treatment is 100-150 rpm.

[0057] Step (c) is the ultrasonic-triggered cluster self-assembly to generate [V4O] 12 ] 4- The core step of the cluster, its ultrasonic mechanism, is that the cavitation effect of mid-frequency ultrasound at 35–45 kHz forms bubbles with a diameter of 1–10 μm. When these bubbles oscillate and burst, they generate local high temperatures of 5000 K and high pressures of 100 MPa, triggering the following reactions:

[0058] (1) First step: The generation of hydroxyl radicals (·OH) and V 3+ Preliminary oxidation

[0059] At the moment the cavitation bubble breaks, H2O molecules in the solution undergo homolytic cleavage under extreme conditions, generating highly oxidizing hydroxyl radicals (·OH, standard oxidation potential approximately 2.8V); ·OH preferentially reacts with V in the solution. 3+ An oxidation reaction occurs, reducing some of the V 3+ Oxidized to V 4+ The reaction equation is as follows: V 3+ +·OH→V 4+ +OH - The V generated in this step 4+ It provides a key intermediate for subsequent cluster recombination, and the oxidation intensity of ·OH can be precisely controlled (only oxidizing V). 3+ (Without disrupting the complexation skeleton of citric acid and vitamin V).

[0060] (2) Second step: V 4+ deep oxidation

[0061] Due to the strong oxidizing properties of ·OH (its oxidizing power is higher than that of V), 4+ →V 5+ The oxidation requirement, V 4+ →V 5+ The standard oxidation potential is approximately 1.0 V), and some V 4+ It will be further oxidized to V by ·OH. 5+ The reaction formula is: V 4+ +·OH→V 5+ +OH - This step is crucial for the subsequent formation of a stable [V4O] 12 ] 4- The core prerequisite for a cluster is the generation of V. 5+ Only through valence state coordination can the charge balance requirements of the cluster be met.

[0062] (3) Third step: V 3+ -Cit chelate with V4+ / V 5+ Coordination and recombination (cluster unit generation)

[0063] Driven by localized high temperature and high pressure due to cavitation effect, unoxidized V 3+ -Cit chelates will react with the generated V 4+ V 5+ Coordinate bond breaking and recombination occur: the carboxyl group (-COOH) of citric acid dissociates, V 3+ V 4+ V 5+ Based on a ratio of "4 V atoms as the core", it forms a coordination structure with the O atoms provided by the H2O molecules in the solution, and finally recombines into [V4O]. 12 ] 4- Anionic clusters; simultaneously, the reaction releases free electrons (e - The electrons are captured by excess ·OH to generate H2O, thus avoiding electron interference with cluster stability. The overall reaction process can be represented as (including V) 5+ (Complete response of the participants)

[0064] 3V 3+ +1V 4+ +0V 5+ +12H2O→[V4O 12 ] 4- +24H + +2e -

[0065] ·OH+e - +H + →H2O

[0066] The final generated [V4O 12 ] 4- The cluster size is approximately 1.2 nm (verified by DFT calculations), and V in the cluster is V 5+ The dominant element (≥95%) has an average valence state of +4.8 to +5.2, close to +5. Calculations based on charge balance show: 4 V atoms have a total positive charge of +20, 12 O atoms have a total negative charge of -24, resulting in a total charge of -4. This matches [V4O]. 12 ] 4- .

[0067] Simultaneously, the ultrasonic cavitation effect in step (c) generates ·OH radicals with sufficient oxidizing power to oxidize Fe. 2+ , (Fe 2+ →Fe 3+ The standard oxidation potential is approximately 0.77V, but only partial oxidation occurs. The core reason for this is the synergistic control of process parameters and reaction activity.

[0068] ·OH preferentially oxidizes V 3+In step (c), V 3+ With “V” 3+ It exists in the form of "-Cit chelate", where the carboxyl group of citric acid interacts with V. 3+ The formed coordinate bonds weaken V 3+ The electron cloud density makes V 3+ More prone to losing electrons (higher reactivity than free Fe) 2+ Meanwhile, V 3+ →V 4+ Although its oxidation potential (≈1.0V) is higher than that of Fe, 2+ →Fe 3+ But chelated V 3+ The actual reaction energy barrier is lower, causing ·OH to preferentially react with V. 3+ The reaction resulted in only a small amount of ·OH remaining to oxidize Fe. 2+ In actual processes, Fe 2+ The oxidation rate is controlled at 30%–50%, and the generated Fe 3+ The precipitation requirement of step (d) is just met, and the remaining Fe... 2+ It can be reduced by an inert atmosphere during the subsequent sintering process without affecting the final product.

[0069] The reason for choosing an ultrasonic frequency in the range of 35–45 kHz is that when the ultrasonic frequency is <35 kHz, the cavitation effect is insufficient and V cannot be oxidized. 3+ It can only disperse particles and cannot form clusters; when the ultrasonic frequency is >45kHz, the cavitation effect is too strong and will destroy the already formed [V4O] 12 ] 4- Cluster structure, generating amorphous vanadium oxides;

[0070] The power density was chosen to be in the range of 50–100 W / L, and the treatment time was in the range of 30–60 min. This was because when the power density is <50 W / L, the number of cavitation bubbles is low, and the cluster formation rate will be <70%, leading to uneven vanadium distribution in the precursor; when the power density is >100 W / L, the solution may overheat locally (>80℃), causing citric acid to decompose and leading to cluster aggregation; a treatment time <30 min may result in incomplete cluster formation; and a treatment time >60 min may lead to secondary cluster aggregation, resulting in a cluster spacing >4.0 nm. The Fe content was controlled by adjusting the ultrasonic power density (50–100 W / L). 2+ For every 10 W / L increase in power density, the oxidation rate of Fe²⁺ increases by 4% to 6%, which can be monitored and adjusted in real time by titration.

[0071] In step (d), the stirring speed during co-precipitation is 200–300 rpm, the reaction temperature is 50–70℃, and the reaction time is 2–3 h.

[0072] The main purpose of step (d) is to construct helical nanoribbons through magnetic field-guided co-precipitation. The core mechanism is that [V4O 12 ] 4- Clusters carrying a negative charge (-4 valence) align along the direction of the magnetic field due to the magnetic dipole moment, [V4O 12 ] 4- The clusters exhibit an orderliness ≥90% along the magnetic field direction, determined by SEM-EDS mapping to statistically analyze the uniformity of V element distribution; simultaneously, PO4 3- with Fe 3+ A coprecipitation reaction occurs, specifically the following reaction:

[0073] Fe 3+ +PO4 3- +2H2O→FePO4·2H2O↓, the orderly arranged clusters are embedded in the iron phosphate matrix, guiding the formation of helical nanoribbons;

[0074] The magnetic field strength was chosen to be in the range of 1.0–1.4 T because when the magnetic field strength is <1.0 T, the magnetic guiding force is insufficient, the clusters are randomly arranged and cannot form a helical structure, and may only generate disordered nanosheets; when the magnetic field strength is >1.4 T, the clusters are strongly adsorbed on the surface of the magnetic field device, the cluster concentration in the solution decreases, and the vanadium content deviation will be >10%.

[0075] The pH value was chosen to be in the range of 2.6 to 3.0 because the solubility product of FePO4, Ksp, is 1.3 × 10⁻⁶. −22 When pH < 2.6, H + With PO4 3- Combined to form HPO4 2- H2PO4 - PO4 3- At low concentrations, precipitation is impossible; when pH > 3.0, Fe... 3+ Hydrolysis produces Fe(OH)3, with a Ksp = 2.7 × 10⁻⁶. −39 It will co-precipitate with FePO4 to form an impurity phase;

[0076] The stirring speed was chosen to be in the range of 200–300 rpm and the reaction temperature to be in the range of 50–70 °C because, when the stirring speed is less than 200 rpm, the precipitated particles grow larger, the width of the nanoribbons will be greater than 110 nm, and the pitch will be irregular; when the stirring speed is greater than 300 rpm, the shear force is too large, the helical structure breaks, and short rod-shaped particles are easily generated; when the reaction temperature is less than 50 °C, the precipitation rate is slow (>4 h); when the reaction temperature is greater than 70 °C, the precipitation is too fast, the clusters cannot be embedded in an orderly manner, and the vanadium is unevenly distributed.

[0077] Furthermore, this invention provides the application of this precursor in the preparation of ultrafast-charging lithium iron phosphate cathode materials. By mixing with a precursor, a lithium source, and a conductive carbon material, and then subjecting it to fluidized bed instantaneous sintering, a lithium iron phosphate material with excellent fast-charging performance and a 10C discharge capacity ≥130mAh / g is obtained, comprising the following steps:

[0078] (1) Ingredient mixing: The precursor, lithium source and conductive carbon material are mixed at a mass ratio of 100:(30-35):(8-12) to obtain a mixture.

[0079] (2) Ball milling: The mixture obtained in step (1) is ball milled to obtain a uniform powder;

[0080] (3) Instantaneous sintering: The powder obtained in step (2) is instantaneously sintered in a fluidized bed reactor under an inert atmosphere to obtain an ultra-fast charging lithium iron phosphate cathode material; the inert atmosphere is one of nitrogen, argon or helium, the gas inlet rate of the fluidized bed reactor is 5 to 10 L / min; the instantaneous sintering temperature is 900 to 1000℃, and the residence time of the powder in the reactor is 0.3 to 1.0 s.

[0081] In step (1), the lithium source is one or more of lithium carbonate, lithium hydroxide or lithium oxalate; the conductive carbon material is one or more of carbon nanotubes, graphene or carbon nanofibers, and the amount of conductive material added is 8 to 12 wt% of the theoretical mass of lithium iron phosphate.

[0082] In step (2), the ball milling speed is 300-500 rpm and the ball milling time is 2-4 hours.

[0083] In step (3), the instantaneous sintering is carried out in the temperature range of 900 to 1000°C and the sintering time is 0.3 to 1.0 seconds. In contrast, traditional sintering, such as holding at 800°C for 8 hours, will cause the lithium iron phosphate grains to grow (>500 nm) and the lithium ion transport path to be prolonged.

[0084] In fluidized bed instantaneous sintering, the powder residence time in the high-temperature zone is short. A pneumatic conveying and precise temperature control design in the high-temperature zone is employed. By adjusting the air inlet rate (5–10 L / min) and the length of the high-temperature zone (5–10 cm), the powder residence time is controlled to be 0.3–1.0 s; the grain size is controlled between 100–200 nm. Simultaneously, [V4O 12 ] 4- Clusters are stably embedded in the lattice to form LiFe 1-x ·V x In PO4 solid solutions, the lithium-ion diffusion coefficient is increased to 1.0–1.2 × 10⁻⁶. −10 cm 2 / s, which is 10 to 100 times that of conventional lithium iron phosphate.

[0085] Beneficial effects

[0086] This invention is because it designs [V4O] 12 ] 4- The core structure of cluster-ordered doping and helical nanoribbon bilevel channels, coupled with a synergistic electrochemical acid leaching-complexation-ultrasound-magnetic field preparation process, addresses existing technological bottlenecks from three dimensions: structural innovation, performance breakthrough, and process adaptation. Its specific beneficial effects are as follows:

[0087] First, high-concentration vanadium orderly doping:

[0088] Overcoming the bottleneck of inevitable agglomeration in high-doped materials, and avoiding lattice distortion and channel blockage. [V4O] 12 ] 4- The cluster size design (approximately 1.2 nm, matching the 1.5 nm lattice gap of iron phosphate); the combination of citric acid complexation inhibiting condensation and ultrasonic-triggered cluster self-assembly process ensures that V exists in cluster form rather than as free ions;

[0089] Cluster structure adapted lattice: [V4O 12 ] 4- The geometric dimensions of the cluster are precisely matched with the interstitial space of the iron phosphate matrix, allowing it to be embedded in the interstitial space without destroying the original lattice structure. X-ray diffraction (XRD) tests show that there are no impurity peaks in the precursor and the final lithium iron phosphate, and the lattice integrity is over 99%.

[0090] Orderly distribution controls concentration: Ultrasonic cavitation effect triggers V 3+ -Cit chelate recombines to [V4O] 12 ] 4- Clusters are then guided by a magnetic field to achieve periodic arrangement of clusters in helical nanoribbons (cluster spacing 2.8–3.2 nm). Even if the vanadium doping concentration is increased to 5000–7000 ppm, the uniform distribution of vanadium species can still be maintained (SEM-EDS Mappings show that the uniformity of V element distribution is ≥95%), completely avoiding agglomeration and channel blockage caused by excessively high local vanadium concentration.

[0091] Second, the construction of dual-level ion channels significantly improves lithium-ion transport dynamics, laying the structural foundation for ultra-fast charging.

[0092] Existing technologies (such as carbon coating and single-unit nano-sizing) can only improve electron conduction or shorten local ion pathways, but cannot construct a continuous macroscopic and microscopic dual-level ion channel, resulting in a lithium-ion diffusion coefficient of only 10. -11 ~10 -10 cm² / s is insufficient to support ultra-fast charging demands. This invention achieves a leap in transmission dynamics through dual-stage channel collaboration:

[0093] Macroscopic helical channel reduces resistance: The pitch (30-50nm) of the helical nanoribbon forms a continuous macroscopic transport channel, allowing lithium ions to migrate rapidly along the helical direction, avoiding detours and shortening the transport path by more than 60%; the width of the nanoribbon (90-110nm) can balance the specific surface area (35-45m² / g) and the tap density (0.7-1.0g / cm³), ensuring sufficient electrolyte wetting (wetting efficiency ≥98%) while avoiding channel narrowing caused by nanoparticle agglomeration;

[0094] Microscopic cluster channels accelerate diffusion: [V4O 12 ] 4- V in the cluster 5+ The d-orbital electron cloud can form a weak interaction with lithium ions, lowering the lithium ion migration barrier. Simultaneously, the periodic arrangement of the clusters forms continuous microscopic ion channels. GITT testing shows that the lithium iron phosphate of this invention has a lithium-ion diffusion coefficient of 1.2 × 10⁻⁶. -10 cm² / s, which is higher than that of traditional lithium iron phosphate (10 -14 ~10 -12 It is 100 to 1000 times faster than the current (cm² / s), significantly improving the ion transport rate.

[0095] Third, the preparation process is highly controllable: it enables precise control of key parameters and is suitable for stable industrial production.

[0096] Existing technologies (such as mechanical mixing and conventional co-precipitation) suffer from high parameter sensitivity and poor batch stability, with vanadium content deviations often exceeding 10%, insufficient reproducibility of nanostructures, and difficulty in industrial-scale mass production. This invention achieves high controllability and stability of the process through the synergistic control of multi-step parameters:

[0097] The parameters of each step can be quantified: the current density control of electrochemical acid leaching V 5+ →V 3+ The reduction rate (≥90%) and citric acid concentration (0.25~0.35mol / L) ensure V 3+ Complexation rate (≥95%), cluster formation rate controlled by ultrasonic power density (≥85%), and pitch deviation of helical nanoribbon controlled by magnetic field strength (≤10%). All key parameters are quantitatively controlled without ambiguity.

[0098] Fourth, it boasts both ultra-fast charging and excellent cycle performance: it balances high-rate capacity with long-cycle stability, making it suitable for energy storage and power battery scenarios.

[0099] In existing technologies, even if vanadium doping is achieved, fast charging performance often decays rapidly due to channel blockage or grain growth (capacity retention rate ≤80% after 500 cycles at 10C), making it impossible to balance high rate and long cycle life. However, this invention achieves a performance breakthrough through synergistic improvements in structure and process.

[0100] High capacity for ultra-fast charging: The dual-level ion channel shortens the lithium-ion transport path, and instantaneous sintering controls the lithium iron phosphate grain size to 100-200nm (without grain growth), resulting in a discharge capacity of ≥130mAh / g at 10C rate (138.2mAh / g in Example 1) and ≥110mAh / g at 20C rate, which is far superior to the prior art (10C capacity ≤120mAh / g).

[0101] Good cycle stability: [V4O 12 ] 4- The cluster embedding suppresses the volume expansion rate of lithium iron phosphate (LFP) during charge and discharge by ≤3%, compared to 5%–8% for conventional LFP, reducing structural damage. Simultaneously, the coating with conductive carbon materials (such as carbon nanotubes) further enhances electronic conductivity stability. Testing shows that this LFP retains ≥90% of its capacity after 1000 cycles at 10C, and its cycle life is more than 1.5 times that of conventional LFP, fully meeting the application requirements of electric vehicles (requiring more than 2000 cycles) and energy storage systems (requiring more than 1000 cycles). Attached Figure Description

[0102] Figure 1 The charging (a) and discharging (b) curves of lithium iron phosphate 10C prepared for the example are shown in Figures a and b. Figures a and b are a comparison of charging and discharging of Example 1 and Comparative Example 1 at different currents. The results show that under the same current, Example 1 has a shorter charging time, a longer discharging time, and better pulse discharge power. Detailed Implementation

[0103] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0104] This invention pertains to a key technological link in the integrated green circular economy industrial chain of "chlorine-titanium-lithium battery". Under this industrial model, the byproduct hydrochloric acid and vanadium-containing chloride tailings generated during the chloride process of titanium dioxide production are recycled. Vanadium and iron elements are extracted from these by acid leaching to prepare precursors for lithium iron phosphate cathode materials. Titanium concentrate, as the core raw material for chloride-process titanium dioxide, contains ferrous chloride and vanadium in its acid leaching solution, making it a natural intermediate product in this industrial chain.

[0105] Because this industry chain has formed a relatively mature industrial layout in China, the separation and purification technologies for various impurity elements in titanium concentrate acid leaching solutions, such as the separation of iron from titanium, aluminum, and chromium, are already widely disclosed in existing technologies and patent documents. Different titanium concentrates have different compositions and contents, resulting in slight differences in separation and purification techniques, but these do not affect the scope of protection of this invention. Therefore, the following embodiments only provide a brief description of this part; those skilled in the art can refer to relevant existing technologies for implementation.

[0106] The titanium concentrates used in the various embodiments and comparative examples of the present invention below have the same chemical composition and content for comparison purposes. The composition and content of the titanium concentrates are shown in Table 1:

[0107] Table 1: Typical chemical composition and mass content (%) of titanium concentrate

[0108]

[0109] The following describes the implementation process of the present invention in detail with reference to four embodiments, and verifies the technical effect through performance testing. All embodiments and comparative examples use the same raw materials and equipment models:

[0110] Titanium concentrate: containing 52.8wt% V2O and 35.0wt% Fe, particle size: ≤3% of material on a 325-mesh sieve, 300-mesh sieve;

[0111] Hydrochloric acid: Industrial grade (concentration: HCl≥31%)

[0112] Citric acid: analytical grade (purity 99.8%);

[0113] Phosphate: Diammonium hydrogen phosphate (analytical grade, purity 99.5%);

[0114] Lithium source: Lithium carbonate (battery grade, 99.9% purity);

[0115] Conductive carbon: carbon nanotubes (5-10 nm in diameter, 1-5 μm in length);

[0116] Equipment: Vertical sand mill (0.3mm zirconia beads), planetary ball mill (QM-1SP4), tube furnace (99.999% argon in inert atmosphere), fluidized bed reactor (adjustable gas inlet rate), laser particle size analyzer (Malvin 3000), battery tester (Newwell BTS-5V10mA).

[0117] It should be noted in advance that in Examples 1-4, the general formula Fe 1-x (V4O 12 ) x / 4 The theoretical value of x in PO4 is derived based on the linear correspondence between x and vanadium content in the claims. The measured error originates from fluctuations in raw material purity during industrial production, trace vanadium loss during the washing process, and ±2% accuracy deviation of the testing instrument. This error (0.29% to 3.7%) is far lower than the ±5% normal deviation allowed in the lithium-ion battery material industry, and does not deviate from the core technical range of x∈[0.0149,0.0209] and vanadium content∈[5000,7000ppm], so it can be ignored.

[0118] Test method:

[0119] Lithium-ion diffusion coefficient (GITT): calculated based on Fick's second law with a current density of 0.05C and an interval of 30min.

[0120] Complexation rate: ICP-OES measurement of free V 3+ Content, complexation rate = (total V) 3+ -Free V 3+ ) / total V 3+ ×100%;

[0121] Fe 2+ Oxidation rate: o-phenanthroline titration method, oxidation rate = (total Fe - free Fe) 2+ ) / total Fe×100%;

[0122] Cluster volume percentage: TEM image statistics (10 fields of view were randomly selected, and the [V4O] were statistically analyzed). 12 ] 4- (The number and size of clusters are calculated in conjunction with the total volume of the precursor).

[0123] Specific surface area (BET): according to GB / T 19587-2004, degassing conditions 120℃ / 2h; tapped density: according to GB / T23651-2009, vibration frequency 200 times / min.

[0124] Example 1: Vanadium doping limit 5020 ppm, corresponding to x = 0.0149

[0125] Step (a) Electrochemical acid leaching treatment: Titanium concentrate was mixed with 16wt% hydrochloric acid at a liquid-to-solid ratio of 1:3 g / mL. A 0.5 mm thick titanium plate was used as the cathode. The current density was 90 mA / cm², and the reaction was carried out at 60 °C for 1.5 h. After reduction, the V in the solution was... 5+ →V 3+ Vanadium reduction rate 90%, Fe 3+ →Fe 2+ The iron reduction rate was 88%, resulting in an acid leaching solution.

[0126] Step (b) Purification and impurity removal: Hydrogen peroxide is added to the acid leaching solution at a volume of 0.5% to 2% of the solution volume. Mn 2+ The precipitate is oxidized to MnO2, then ammonia is added to adjust the pH to 4.5–5.5. The mixture is then kept at a constant temperature and stirred for 0.5–1 hour to remove Al from the precipitate. 3+ Cr 3+ Add MnO2, filter; add ammonium fluoride or sodium fluoride to the filtrate to increase the F content in the solution. - When the concentration reaches 0.05–0.15 mol / L, stir the reaction at 80–90℃ for 0.5–1 hour to precipitate and remove Ca. 2+ Mg 2+Filter again; adjust the pH of the filtrate to 2.0–3.0 to obtain Ca. 2+ Content <0.5ppm, Mg 2+ Purification solution with a concentration of <0.5 ppm;

[0127] Step (c) Complexation and ultrasonic assembly: Add 0.25 mol / L citric acid to the purification solution. Citric acid reacts with V... 3+ Molar ratio 1.0:1, stirred at 25℃ for 30 min, after complexation V 3+ Complexation rate 92%; under 35kHz ultrasound, power density 50W / L, treatment for 30 min, stirring speed 100rpm, [V4O] was formed. 12 ] 4- Clusters, cluster formation rate 85%, Fe 2+ The oxidation rate is about 30%, forming a vanadium-containing solution;

[0128] Step (d) Magnetic field guided coprecipitation: Under a magnetic field of 1.0T, 0.5mol / L diammonium hydrogen phosphate solution was added dropwise to the vanadium-containing solution, the pH was controlled at 2.6, the mixture was stirred at 50℃ for 2h at a stirring speed of 200rpm, filtered, and vacuum dried at 80℃ for 8h to obtain the precursor;

[0129] Step (e) Preparation of lithium iron phosphate:

[0130] Ingredient mixing: Precursor, lithium carbonate, and carbon nanotubes are mixed in a mass ratio of 100:30:8;

[0131] Ball milling: 300 rpm for 2 hours, ball-to-material ratio 5:1;

[0132] Instantaneous sintering: The reaction was carried out in a fluidized bed reactor with an argon gas inlet rate of 5 L / min and sintering at 900℃ for 0.3 s to obtain lithium iron phosphate cathode material.

[0133] Example 2: Vanadium doping intermediate value 5780ppm, corresponding to x=0.0170

[0134] Step (a) Electrochemical acid leaching treatment: Titanium concentrate was mixed with 18wt% hydrochloric acid at a liquid-to-solid ratio of 1:4 g / mL. A 0.8 mm thick titanium plate was used as the cathode. The current density was 100 mA / cm², and the reaction was carried out at 70 °C for 2 h. 5+ →V 3+ Vanadium reduction rate 95%, Fe 3+ →Fe 2+ The iron reduction rate was 92%, resulting in an acid leaching solution.

[0135] Step (b) is the same as in Example 1;

[0136] Step (c) Complexation Inhibition of Condensation: Add 0.3 mol / L citric acid, citric acid reacts with V 3+Molar ratio 1.1:1, stirred at 30℃ for 45 min, V 3+ Complexation rate 96%;

[0137] Step (c) Ultrasonic triggering cluster self-assembly: Treatment with 40kHz ultrasound at a power density of 75W / L for 45 min, with a stirring speed of 120rpm, to form [V4O 12 ] 4- Clusters, cluster formation rate 90%, Fe 2+ The oxidation rate is approximately 40%.

[0138] Step (d) Magnetic field guided coprecipitation: Under a magnetic field of 1.2T, 0.8 mol / L ammonium dihydrogen phosphate solution was added dropwise, pH=2.8, stirred at 60℃ for 2.5h at a stirring speed of 250 rpm, filtered, and vacuum dried at 90℃ for 8h to obtain the precursor.

[0139] Step (e) Preparation of lithium iron phosphate

[0140] Ingredient mixing ratio: 100:32:10 (by weight);

[0141] Ball milling: 400 rpm for 3 hours, ball-to-material ratio 6:1;

[0142] Instantaneous sintering: The reaction was carried out in a fluidized bed reactor with an argon gas inlet rate of 8 L / min and sintering at 950℃ for 0.6 s to obtain lithium iron phosphate cathode material.

[0143] Example 3: Vanadium doping intermediate value 6490ppm, corresponding to x=0.0190

[0144] Step (a) Electrochemical acid leaching treatment: Titanium concentrate was mixed with 18wt% hydrochloric acid at a liquid-to-solid ratio of 1:4 g / mL, cathode was a 0.8 mm titanium plate, current density was 100 mA / cm², reaction was carried out at 70℃ for 2 h, V 5+ →V 3+ Vanadium reduction rate 96%, Fe 3+ →Fe 2+ Iron reduction rate was 93%, resulting in an acid leaching solution;

[0145] Step (b) is the same as in Example 1;

[0146] Step (c) Complexation Inhibition of Condensation: Add 0.3 mol / L citric acid, citric acid reacts with V 3+ Molar ratio 1.1:1, stirred at 30℃ for 45 min, V 3+ Complexation rate: 97%.

[0147] Step (c) Ultrasonic triggering cluster self-assembly: Treatment with 40kHz ultrasound at a power density of 75W / L for 45 min, stirring at 120rpm, to form [V4O 12 ] 4-Clusters, cluster formation rate 91%, Fe 2+ The oxidation rate is approximately 50%.

[0148] Step (d) Magnetic field guided coprecipitation: Under a magnetic field of 1.2T, 0.8 mol / L diammonium hydrogen phosphate was added dropwise, pH=2.8, stirred at 60℃ for 2.5h at a stirring speed of 250 rpm, filtered, and vacuum dried at 90℃ for 8h to obtain the precursor.

[0149] Step (e) Preparation of lithium iron phosphate

[0150] Ingredient mixing ratio: 100:33:11 (by weight);

[0151] Ball milling: 400 rpm for 3 hours, ball-to-material ratio 7:1;

[0152] Instantaneous sintering: The reaction was carried out in a fluidized bed reactor with an argon gas inlet rate of 8 L / min and sintering at 950℃ for 0.6 s to obtain lithium iron phosphate cathode material.

[0153] Example 4: Vanadium doping limit: 6980 ppm, corresponding to x = 0.0209

[0154] Step (a) Electrochemical acid leaching treatment: Titanium concentrate was mixed with 20wt% hydrochloric acid at a liquid-to-solid ratio of 1:5 g / mL, with a 1.0 mm titanium plate as the cathode, a current density of 110 mA / cm², and a reaction time of 2.5 h at 80 °C. 5+ →V 3+ Vanadium reduction rate 96%, Fe 3+ →Fe 2+ Iron reduction rate of 95% yielded acid leaching solution;

[0155] Step (b) is the same as in Example 1;

[0156] Step (c) Complexation Inhibition of Condensation: Add 0.35 mol / L citric acid, citric acid reacts with V 3+ (Molar ratio 1.2:1), stir at 35℃ for 60 min, V 3+ Complexation rate: 98%.

[0157] Step (c) Ultrasonic trigger cluster self-assembly: Under 45kHz ultrasound and a power density of 100W / L, the mixture was treated for 60 min with stirring at 150 rpm to form [V4O] 12 ] 4- Clusters, with a cluster formation rate of 93%.

[0158] Step (d) Magnetic field guided coprecipitation: Under a magnetic field of 1.4T, 1.0 mol / L ammonium dihydrogen phosphate was added dropwise, pH=3.0, stirred at 70℃ for 3h at a stirring speed of 300rpm, filtered, and vacuum dried at 100℃ for 8h to obtain the precursor.

[0159] Step (e) Preparation of lithium iron phosphate

[0160] Ingredient mixing ratio: 100:35:12 (by weight);

[0161] Ball milling: 500 rpm for 4 hours, ball-to-material ratio 8:1;

[0162] Instantaneous sintering: The reaction was carried out in a fluidized bed reactor with an argon gas inlet rate of 10 L / min and sintering at 1000 °C for 1.0 s to obtain lithium iron phosphate cathode material.

[0163] Comparative Example 1: Added vanadium source, vanadium doping 4980ppm, conventional co-precipitation

[0164] Raw material preparation: Ferric phosphate precursor (prepared by conventional coprecipitation method, D50=10μm) was used, and ammonium metavanadate (analytical grade) was added to adjust the vanadium content to 5000ppm (without electrochemical acid leaching and complexation steps).

[0165] Coprecipitation: The ferric phosphate precursor was mixed with ammonium metavanadate solution, and 0.8 mol / L diammonium hydrogen phosphate was added. The mixture was at pH 2.8 and stirred at 60°C for 2.5 h (250 rpm) without ultrasound or magnetic field. The mixture was then filtered and dried to obtain the precursor.

[0166] Preparation of lithium iron phosphate: Same as step (e) in Example 2.

[0167] Comparative Example 2: Vanadium source added, vanadium doping 6950ppm, conventional co-precipitation.

[0168] Raw material preparation: ferric phosphate precursor (same as comparative example 1), with ammonium metavanadate added to adjust the vanadium content to 7000 ppm.

[0169] Coprecipitation: Same as comparative example 1.

[0170] Preparation of lithium iron phosphate: Same as step (e) in Example 4.

[0171] The performance of the precursor and cathode materials of Examples 1-4 and Comparative Examples 1-2 was tested using the following methods.

[0172] I. Precursor Performance Testing

[0173] Vanadium content: Inductively coupled plasma atomic emission spectrometry (ICP-OES, PEOptima8000);

[0174] Nanoribbon size / pitch: Transmission electron microscope (TEM, FEITalosF200X);

[0175] Specific surface area (BET): Liquid nitrogen adsorption method (Micromeritics ASAP2460);

[0176] Tap density: Quantachrome Autotap tap density meter;

[0177] Citric acid residue: High performance liquid chromatography (HPLC, Agilent 1260).

[0178] D50 particle size: Laser particle size analyzer (Malvin 3000);

[0179] Phase: X-ray diffraction (XRD, Bruker D8 Advance).

[0180] II. Lithium Iron Phosphate Performance Testing

[0181] Button cell assembly: positive electrode (lithium iron phosphate:PVDF:acetylene black prepared from precursor = 8:1:1), negative electrode is lithium metal, separator is Celgard2400, electrolyte is 1mol / L LiPF6 / EC+DMC (volume ratio 1:1), assembled in an argon glove box.

[0182] Charge and discharge performance: coin cell (CR2016), voltage range 2.0~3.75V, tested at 10C and 20C rates;

[0183] Cyclic stability: Calculate capacity retention after 1000 cycles at 10C rate;

[0184] Lithium-ion diffusion coefficient: Intermittent titration technique (GITT).

[0185] Table 1 shows a comparison of the core indicators of the precursors from Examples 1-4 and Comparative Examples 1-2, and Table 2 shows a comparison of the electrochemical performance of Examples 1-4 and Comparative Examples 1-2.

[0186] Table 1: Comparison of core indicators of precursors from Examples 1-4 and Comparative Examples 1-2

[0187]

[0188] As can be seen from Table 1, regarding the precursor structure and purity: the present invention achieves an ordered structure, low residue, and no impurities, while the comparative example has inherent defects.

[0189] From the perspective of structural integrity, Examples 1-4 all form regular helical nanoribbon structures (width 90-110 nm, pitch 30-50 nm), [V4O 12 ] 4- The clusters are arranged periodically with a spacing of 2.8–3.2 nm and account for 1.2–1.8 vol% of the volume, which perfectly matches the design goal; while comparative examples 1-2 have no nanoribbons or cluster structures, and are only blocky / agglomerated particles, which cannot be used to construct ion transport channels.

[0190] In terms of purity and residue control, the citric acid residue in the examples was ≤0.4wt% (far below the upper limit of ≤0.5wt%), and no impurity peaks were observed in the XRD, proving that vanadium is present in [V4O] 12 ] 4- The clusters are stably embedded in the iron phosphate matrix, without any polyvanadate impurities; the comparative example has 0.6–0.7 wt% residual citric acid (too high), and due to the lack of complexation-ultrasonic regulation, V 3+ Hydrolysis and condensation generate V4O9 (Comparative Example 1) and V4O9+V2O5 (Comparative Example 2) impurity phases, which directly destroy the matrix structure.

[0191] From a macroscopic performance perspective, the specific surface area of ​​the example sample (35–45 m² / g) ensures effective electrolyte wetting, the tap density (0.7–1.0 g / cm³) balances volumetric energy density, and the D50 particle size (5–20 μm) is suitable for subsequent ball milling and sintering, with these three indicators being synergistically optimized. In contrast, the specific surface area of ​​the comparative sample is only 18–22 m² / g, which clearly suffers from insufficient electrolyte wetting, and the tap density (0.55–0.6 g / cm³) results in low volumetric energy density, failing to meet the requirements of power batteries.

[0192] Table 2: Comparison of Electrochemical Performance between Examples 1-4 and Comparative Examples 1-2

[0193]

[0194] As can be seen from Table 2, the present invention has high fast charging capacity, stable cycling, and fast diffusion, while the comparative model is completely unsuitable for ultra-fast charging.

[0195] In terms of 10C charge / discharge capacity and efficiency, Examples 1-4 have a 10C discharge capacity of 130.5–138.2 mAh / g (all ≥ 130 mAh / g design target), a 10C charge capacity of 133.2–141.5 mAh / g, and an initial coulombic efficiency of 97.7%–98.0% (energy loss of only 2%–2.3%). Comparative Examples 1-2 have a 10C discharge capacity of only 95.3–102.4 mAh / g (20%–31% lower than the Examples), a charge capacity of 103.5–108.6 mAh / g, and an initial coulombic efficiency of 92.1%–94.3% (energy loss of 5.7%–7.9%). The core reason is that the comparative examples lack bilevel ion channels, resulting in obstructed lithium-ion transport, and the impurity phase consumes active sites.

[0196] In terms of cycle stability, Examples 1-4, after 1000 cycles at a 10C rate, maintained a capacity retention of 90.1%–93.5%, significantly higher than the comparative examples' 75.1%–78.3%. The essential difference lies in: Example [V4O] 12 ] 4-Clusters can suppress volume expansion during the charging and discharging process of lithium iron phosphate (volume expansion rate ≤3%), and the helical nanoribbon structure is not easily damaged; while the vanadium impurity phase in the comparison ratio is easy to fall off during cycling, resulting in loss of active material and continuous blockage of channels.

[0197] From the perspective of lithium-ion diffusion kinetics, the lithium-ion diffusion coefficient in the examples is 1.0 to 1.2 × 10⁻⁶. -10 cm² / s, which is the comparative example (2.2~2.8×10 -11 The speed is 4 to 5 times that of cm² / s; the key lies in the fact that the embodiment constructs a macroscopic spiral channel (shortening the transmission path by more than 60%) and a microscopic cluster channel V. 5+ The d-orbital reduces the migration barrier in a bipolar network, while the comparative network lacks ordered channels, requiring lithium ions to detour through aggregated particles and impurity phases, significantly increasing diffusion resistance.

[0198] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A vanadium oxide cluster phosphate-based precursor, characterized in that: The precursor has a helical nanoribbon structure and its general chemical formula is Fe. 1-x (V4O 12 ) x / 4 PO4, where x ranges from 0.0149 to 0.0209, vanadium is represented by the tetranuclear vanadium-oxygen cluster anion ([V4O4O4]). 12 ] 4- The nanoribbons are doped and embedded in the iron phosphate lattice in the form of vanadium, and the mass fraction of vanadium is 5000-7000 ppm based on the total mass of the precursor. The width of the nanoribbons is 90-110 nm and the pitch of the spiral channel is 30-50 nm.

2. The vanadium oxide cluster phosphate-based precursor as described in claim 1, characterized in that: The nanoribbon structure contains periodically arranged [V4O] 12 ] 4- Cluster units with a cluster spacing of 2.8–3.2 nm.

3. The vanadium oxide cluster phosphate-based precursor as described in claim 1, characterized in that: The precursor has a specific surface area of ​​35–45 m² / g and a tap density of 0.7–1.0 g / cm³.

4. The vanadium oxide cluster phosphate-based precursor as described in claim 1, characterized in that: The precursor has an amorphous or microcrystalline structure with a D50 particle size distribution of 5–20 μm.

5. The vanadium oxide cluster phosphate-based precursor as described in claim 1, characterized in that: The residual amount of citric acid in the precursor is ≤0.5wt%.

6. The vanadium oxide cluster phosphate-based precursor as described in claim 2, characterized in that: The [V4O] 12 ] 4- The volume fraction of cluster units in the helical nanoribbons is 1.2–1.8 vol.

7. A method for preparing a vanadium oxide cluster phosphate-based precursor as described in any one of claims 1 to 6, characterized in that, Includes the following steps: (a) Electrochemical acid leaching treatment: Titanium concentrate is mixed with hydrochloric acid at a concentration of 16–20 wt%, and then subjected to an electrochemical acid leaching treatment at a current density of 90–110 mA / cm². 2 Electrochemical reduction is carried out under the conditions of [condition], to remove V from the solution. 5+ Restore to V 3+ Fe 3+ Reduced to Fe 2+ The acid leaching solution was obtained; (b) Purification and impurity removal: An oxidizing agent is added to the acid leaching solution to remove M. 2+ The precipitate is oxidized to MnO2; then an alkaline adjuster is added to adjust the pH to 4.5–5.5, and the reaction is carried out under heat and stirring for 0.5–1 hour to remove Al from the precipitate. 3+ Cr 3+ Add MnO2, filter; add ammonium fluoride or sodium fluoride to the filtrate to increase the F content in the solution. - When the concentration reaches 0.05–0.15 mol / L, stir the reaction at 80–90℃ for 0.5–1 hour to precipitate and remove Ca. 2+ Mg 2+ Filter again; adjust the pH of the filtrate to 2.0-3.0 to obtain the purified solution; (c) Complexation and ultrasonic assembly: Citric acid at a concentration of 0.25–0.35 mol / L is added to the purified solution to complex V³⁺ and inhibit polyvanadate condensation; then, under the action of ultrasound at a frequency of 35–45 kHz, the vanadium in the solution is assembled to form [V₄O₂]. 12 ] 4- Clusters form vanadium-containing solutions; (d) Magnetic field-guided coprecipitation: Under a magnetic field of 1.0 to 1.4 T, the vanadium-containing solution and the phosphate solution are subjected to a coprecipitation reaction, and the pH of the reaction system is controlled to be 2.6 to 3.0 to generate an iron phosphate-based precursor with a helical nanoribbon structure.

8. The preparation method according to claim 7, characterized in that: In step (a), the liquid-solid ratio of titanium concentrate to hydrochloric acid is 1:3 to 1:5 g / mL, the cathode material is a titanium plate with a thickness of 0.5 to 1.0 mm, the reaction temperature is 60 to 80 °C, and the reaction time is 1.5 to 2.5 hours.

9. The preparation method according to claim 7, characterized in that: In step (c), citric acid reacts with V in the acid leaching solution. 3+ The molar ratio is 1.0 to 1.2:1, the temperature of the complexation reaction is 25 to 35°C, and the reaction time is 30 to 60 min.

10. The preparation method according to claim 7, characterized in that: In step (c), the ultrasonic treatment time is 30-60 min, the ultrasonic power density is 50-100 W / L, and the stirring speed during the ultrasonic treatment is 100-150 rpm.

11. The preparation method according to claim 7, characterized in that: The phosphate solution is a diammonium hydrogen phosphate solution or a diammonium dihydrogen phosphate solution, with a concentration of 0.5–1.0 mol / L.

12. The preparation method according to claim 7, characterized in that: In step (d), the stirring speed during co-precipitation is 200-300 rpm, the reaction temperature is 50-70℃, and the reaction time is 2-3 h.

13. The application of the vanadium oxide cluster iron phosphate-based precursor as described in any one of claims 1 to 6 in the preparation of ultrafast-charging lithium iron phosphate cathode materials, characterized in that... Includes the following steps: (1) Mixing of ingredients: The precursor, lithium source and conductive carbon material are mixed at a mass ratio of 100:(30-35):(8-12) to obtain a mixture. (2) Ball milling: The mixture obtained in step (1) is ball milled to obtain a uniform powder; (3) Instantaneous sintering: The powder obtained in step (2) is instantaneously sintered in a fluidized bed reactor under an inert atmosphere to obtain ultra-fast charging lithium iron phosphate cathode material.

14. The application as described in claim 13, characterized in that: In step (1), the lithium source is one or more of lithium carbonate, lithium hydroxide or lithium oxalate; the conductive carbon material is one or more of carbon nanotubes, graphene or carbon nanofibers, and the amount of conductive material added is 8 to 12 wt% of the theoretical mass of lithium iron phosphate.

15. The application as described in claim 13, characterized in that: In step (2), the ball milling speed is 300-500 rpm and the ball milling time is 2-4 hours.

16. The application as described in claim 13, characterized in that: In step (3), the inert atmosphere is one of nitrogen, argon or helium, the gas inlet rate of the fluidized bed reactor is 5 to 10 L / min, the instantaneous sintering temperature is 900 to 1000 °C, and the residence time of the powder in the reactor is 0.3 to 1.0 s.

17. The application as described in claim 13, characterized in that: The obtained lithium iron phosphate cathode material has a discharge capacity of ≥130mAh / g at a 10C rate.

18. The vanadium oxide cluster phosphate-based precursor as described in claim 2, characterized in that: The [V4O] 12 ] 4- The average valence state of vanadium in the cluster is +4.8 to +5.2, and the equivalent size of the cluster is 1.0 to 1.4 nm.

19. The vanadium oxide cluster phosphate-based precursor according to claim 1, characterized in that: The volume expansion rate of the spiral nanoribbon is ≤3%, and XRD testing shows no V4O9 or V2O5 impurity phase diffraction peaks.

20. The preparation method according to claim 7, characterized in that: In step (c), Fe 2+ The oxidation rate is 30%–50%, and for every 10 W / L increase in ultrasonic power density, Fe… 2+ The oxidation rate increases by 4% to 6%.

21. The preparation method according to claim 7, characterized in that: In step (d), [V4O 12 ] 4- The clusters are arranged with an orderliness of ≥90% along the magnetic field direction. The orderliness is determined by SEM-EDS Mapping to statistically analyze the uniformity of V element distribution.

22. The application as described in claim 13, characterized in that: The obtained lithium iron phosphate cathode material retains ≥90% of its capacity after 1000 cycles at 10C rate.

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