A porous aculeiform vanadium-doped iron phosphate precursor, a preparation method thereof, and application of the precursor in a lithium iron phosphate positive electrode material

Abstract

The application discloses a porous thorn ball-shaped vanadium-doped iron phosphate precursor, wherein the doping content of vanadium element is 3000-5000 ppm based on the total mass of the iron phosphate, the iron phosphate is secondary particles, presents a thorn ball-shaped morphology, the ball diameter is 2-4 microns, and the secondary particles are composed of flaky primary particles which grow radially from the surface, the thorn length of the flaky primary particles is 400-600 nm, and the vanadium mass content of the particle surface is 2±0.1 times of the vanadium mass content of the particle body. ‑2 ~10 ‑1 S / cm (2-3 times of conventional 3000 ppm doping), the porous thorn ball-shaped structure formed by the application improves the electrolyte infiltration efficiency by 50%, the lithium ion diffusion coefficient is improved to 10 ‑11 ~10 ‑10 cm² / s, and lays a foundation for high-rate performance; the application realizes the double leap of low temperature and high-rate performance, the obtained lithium iron phosphate has a 5C discharge capacity of >140 mAh / g, a cycle retention rate of ≥75% at -10 DEG C after 8000 cycles, and can meet the severe requirements of fast-charging power batteries and low-temperature energy storage systems.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology. Specifically, it relates to a porous spiky spherical vanadium-doped iron phosphate precursor with a specific microstructure and high concentration of vanadium doping, its precise preparation method, and the application of the precursor in high-performance lithium iron phosphate (LiFePO4) cathode materials. It is particularly suitable for power batteries and energy storage batteries with stringent requirements for high-rate discharge performance and low-temperature cycle stability. Background Technology

[0002] Lithium iron phosphate (LiFePO4) has become the mainstream cathode material in the fields of power batteries and energy storage due to its high safety, long cycle life, environmental friendliness, and cost advantages. However, its intrinsic electronic conductivity (≈10) -10 ~10 -8 S / cm) and lithium-ion diffusion coefficient (≈10) -14 The low speed (cm² / s) is a significant drawback, especially under high-rate charging and discharging (e.g., 5C and above) and low-temperature conditions (e.g., -10℃), which severely restricts its application in fast-charging power batteries and low-temperature energy storage systems.

[0003] To improve the above performance, existing technologies mainly enhance electronic conductivity through vanadium doping: vanadium (especially V) 4+ Vanadium can reduce the electron transport energy barrier by forming defect sites through lattice substitution. However, existing vanadium doping technologies have significant bottlenecks:

[0004] First, the doping concentration is limited: existing solutions mostly concentrate vanadium doping concentration at low levels. When the concentration is increased to above 3000ppm, vanadium agglomeration can easily lead to lattice distortion, which in turn damages the stability of the material structure, hinders lithium-ion migration, and triggers phase transition stress during charging and discharging, resulting in accelerated capacity decay.

[0005] Secondly, the doping uniformity is poor: solid-phase mixing methods are often used, such as sintering after physically mixing vanadium source with iron phosphate and lithium source. It is impossible to achieve a uniform molecular-level distribution of vanadium element. If the local concentration is too high, impurity phases such as V2O5 will easily form. If the concentration is too low, the conductivity cannot be effectively improved.

[0006] Furthermore, the morphology and porous structure design are insufficient: existing iron phosphate precursors are mostly blocky or sheet-like aggregates, lacking morphologies that combine high specific surface area and efficient mass transfer channels; and the porous structures are mostly random pores without continuity, resulting in poor electrolyte wettability, long lithium-ion diffusion paths, and limited improvement in high-rate and low-temperature performance.

[0007] In addition, the low-temperature cycling performance is weak: at -10℃, the capacity retention of existing lithium iron phosphate batteries is mostly below 70% after 8000 cycles at 1C rate due to the sharp increase in lithium-ion diffusion resistance, which cannot meet the needs of energy storage and power batteries in cold regions.

[0008] For example, Chinese patent CN110364761B discloses a "high energy density long-cycle lithium iron phosphate battery". This patent discloses a lithium iron phosphate battery in which the positive electrode active material is lithium iron phosphate doped with vanadium, boron, nitrogen and carbon, the negative electrode conductive agent is doped carbon nanotubes / carbon fibers, the separator is a PE / PP base film coated with nano TiO2 and BN, and the binder is water-soluble lignin. In the preparation process, the vanadium source (ammonium metavanadate) is ground and mixed with the iron phosphate precursor, the lithium source (lithium carbonate, etc.) and glucose (carbon source) in a mortar and pestle, and then sintered in a multi-stage heating process (300℃→550℃→600~800℃) under a nitrogen atmosphere to obtain doped lithium iron phosphate. Finally, the battery achieves a 0.2C discharge capacity ≥2300mAh, a capacity retention rate of ≈83% at -20℃, and a capacity retention rate of ≈63% at -40℃. The patent has the following problems: First, the uniformity and concentration of vanadium doping are limited: the vanadium doping method of "solid-phase grinding and mixing + high-temperature sintering" cannot achieve molecular-level bonding between vanadium and the iron phosphate lattice, which easily leads to local agglomeration or uneven distribution of vanadium. Moreover, it does not address the stability control of high-concentration vanadium doping above 3000ppm, and at high concentrations, lattice distortion can easily lead to a decline in cycling performance. Second, the precursor morphology and mass transfer structure are missing: the microstructure of the iron phosphate precursor is not specifically designed. Although the final lithium iron phosphate forms a "sheet-like assembled spherical / flower-like morphology", it lacks a through-porous structure. The lithium-ion diffusion path depends on the surface pores of the material, and the ion transport resistance increases significantly at low temperatures (such as -10℃). After 8000 cycles at 1C rate, the capacity retention rate does not reach more than 75%. Third, there is a lack of gradient doping design: the gradient distribution of vanadium (such as vanadium-rich surface) is not mentioned, and the side reactions of the electrolyte cannot be suppressed through the synergistic effect of surface stability and bulk conductivity. After long-term cycling, the interfacial impedance is easy to increase, affecting the low-temperature cycling stability.

[0009] Chinese patent CN120637480A discloses a low-temperature resistant lithium iron phosphate cathode material and its preparation method. This patent discloses a low-temperature resistant lithium iron phosphate cathode material, in which the lithium iron phosphate active material is doped with at least one metal element selected from aluminum, magnesium, chromium, vanadium, and cobalt (the vanadium source is ammonium metavanadate). A conductive network is formed by adding "nitrogen-doped carbon fibers of composite TiO2 + polypyrrole-coated TiO2 fibers". During preparation, the vanadium source is mixed with raw materials such as lithium carbonate and iron nitrate, and then reacted in solution and sintered to obtain doped lithium iron phosphate. The low-temperature conductivity is improved by relying on external fiber additives, ultimately achieving a capacity retention rate of approximately 88% at -20℃ and approximately 83% at -30℃. The technical problems with this patent are: firstly, insufficient vanadium doping dependence and uniformity: vanadium doping is only one of many elemental dopants, and it does not target the valence state of vanadium (such as V). 4+ The lithium iron phosphate (LFP) lithium iron phosphate exhibits several drawbacks. Firstly, its low-temperature performance relies heavily on external fiber additives rather than the precursor's own structural design. Secondly, the precursor structure lacks mass transfer optimization: no specific microstructure was designed, resulting in conventional LFP particles. Lithium-ion diffusion depends on external channels constructed by fiber additives, leading to long internal diffusion paths and a rapid capacity drop during high-rate discharge (5C and above). Thirdly, high-concentration doping lacks stability: the feasibility of 3000-5000 ppm vanadium doping has not been explored, resulting in only trace amounts of modification. High-concentration vanadium doping cannot further improve electronic conductivity, and there is no precise control over porosity (42%-48%) and interlayer spacing (0.53±0.01nm), limiting ion transport efficiency at low temperatures.

[0010] Clearly, existing technologies suffer from insufficient synergy between process and performance. The existing preparation process, involving solid-phase mixing and conventional spray drying, cannot simultaneously achieve precise control of the vanadium valence state (V). 4+ The integration of gradient distribution, interconnected pores, and special ferric phosphate morphology results in poor process reproducibility and industrial adaptability.

[0011] Therefore, there is an urgent need in this field to develop a high-concentration vanadium-doped, uniformly gradient-distributed, spiky porous iron phosphate precursor. Through the synergistic effect of "morphology optimization-doping gradient-porous mass transfer", the technical challenges of lattice distortion, slow lithium-ion diffusion, and poor low-temperature cycling under high-concentration vanadium doping can be solved, providing core precursor support for high-performance lithium iron phosphate cathode materials. Summary of the Invention

[0012] This invention aims to provide a porous, spiky spherical vanadium-doped iron phosphate precursor and its preparation method. Through the synergistic design of high-concentration gradient vanadium doping, ice crystal template through-holes, and spiky spherical sheet structure, it solves the technical bottlenecks of high-concentration doping stability, ion mass transfer, and low-temperature long-cycle operation.

[0013] Another object of the present invention is to provide the application of this precursor in the preparation of high-performance lithium iron phosphate cathode materials.

[0014] A porous, spiky spherical vanadium-doped iron phosphate precursor, based on the total mass of the iron phosphate, has a vanadium content of 3000~5000ppm. The iron phosphate is a secondary particle with a spiky spherical morphology, and its spherical diameter is 2~4μm. It is composed of radially grown plate-like primary particles, and the spike length of the plate-like primary particles is 400~600nm. The vanadium mass content of the particle surface phase is 2±0.1 times that of the vanadium mass content of the particle bulk phase.

[0015] In this invention, energy dispersive spectroscopy (EDS) is used to analyze the composition of the precursor particles, and the "surface phase" and "bulk phase" are distinguished according to the following definition:

[0016] (1) Particle surface phase

[0017] This refers to the region extending inward from the outer edge of the particle to a depth of 50 nm. This depth matches the spatial resolution of EDS under typical operating conditions (accelerating voltage 15-20 kV), reflecting the true composition near the particle surface, rather than being limited to the top atomic layer.

[0018] Measurement method: Under a scanning electron microscope (SEM), at least three representative intact particles were selected. EDS line scanning (step size 10-20 nm) was performed radially from the particle edge inwards. The average vanadium mass percentage of all data points within a range of 0-50 nm from the particle edge was taken as the "surface vanadium mass content" of the particle. The final result was the average of at least three particles.

[0019] (2) Particulate phase

[0020] This refers to the internal core region extending outward from the center of the particle, but more than 200 nm away from the particle edge. For the secondary particles with a spiky morphology of the present invention (sphere diameter 2-4 μm, i.e. radius 1-2 μm), this region accounts for approximately 80%-90% of the particle radius and can represent the average composition inside the particle.

[0021] Measurement method: In the same EDS line scan data, the average value of the vanadium mass percentage of all data points in the region >200nm from the particle edge (i.e., the particle core region) is taken as the "bulk vanadium mass content" of the particle. The final result is the average value of at least 3 particles.

[0022] The vanadium content was chosen to be 3000~5000ppm because the doping effect is not significant when the vanadium content is below 3000ppm, while it is easy to form impurity phases and destroy the structure when it is above 5000ppm. This range can maintain lattice stability while ensuring the doping effect. The spherical diameter is controlled at 2~4μm and the spike length is controlled at 400~600nm. This size range can ensure that the secondary particles have a high specific surface area, which is conducive to electrolyte wetting and short ion diffusion paths. At the same time, it maintains a high tap density, which is conducive to electrode processing. The surface vanadium content is designed to be 2.0±0.1 times that of the bulk vanadium content, which can form a vanadium-rich gradient distribution on the surface. The surface vanadium can suppress electrolyte side reactions, and the bulk vanadium ensures the improvement of bulk conductivity, thus synergistically enhancing interface stability and bulk dynamics.

[0023] Preferably, vanadium is distributed in a gradient in the secondary particles with the spiky morphology, with the vanadium content in the spike tip region being greater than 5000 ppm. The spike tip serves as a preferential site for lithium ion insertion / extraction, and the high vanadium content can further optimize the surface electrochemical activity.

[0024] The spike tip region extends from the tip of the spike towards the base, with a length not exceeding one-third of the total spike length. Given that the spike tip size (tip radius of curvature is typically less than 100 nm) is smaller than the conventional spatial resolution of EDS (200–500 nm), direct point measurement of the spike tip cannot yield accurate results. This invention employs the following semi-quantitative statistical method:

[0025] Step 1: Sample Preparation and Region Selection

[0026] Precursor powder was dispersed on conductive adhesive, and particles with clear outlines, intact spiky structures, and upward-pointing spikes were selected for measurement. The accelerating voltage was reduced to 10-15kV to minimize the electron beam diffusion region, and the working distance was controlled at 8-10mm.

[0027] Step 2: Line Scan

[0028] EDS line scans were performed along the axial direction of the spike (extending inward from the tip to the root of the spike) with a step size of 10 nm, and the vanadium mass percentage at different distances inward from the tip (distance=0) was recorded.

[0029] Step 3: Data Extraction

[0030] The average vanadium mass percentage of all data points within the range of 0 to (3 / 3 of the spike length) from the tip inward (e.g., if the spike length is 450 nm, then 0-150 nm) is taken as the "vanadium mass content of the spike tip region".

[0031] Step 4: Statistics

[0032] For each particle, 3-5 spikes are randomly selected for measurement, and the average value is taken as the vanadium mass content of the spike tip region of that particle. The final report should include the average value and standard deviation of at least 3 particles.

[0033] The secondary particles with the spiky morphology have a porous structure with a pore size of 50~100nm and a porosity of 42%~48%. This structure is formed through the growth and sublimation of ice crystals during freeze-drying, providing a fast transport channel for lithium ions and mitigating volume changes during charging and discharging.

[0034] The precursor has a layered structure with (010) crystal planes accounting for >70% and a layer thickness of 80±10 nm; the interlayer spacing of the layered structure is 0.53±0.01 nm. This structure facilitates the rapid migration of lithium ions along the interlayer, and the increased interlayer spacing reduces the diffusion barrier.

[0035] (010) XRD test method for crystal plane ratio:

[0036] Principle: The crystal orientation map of a single particle is obtained by EBSD, and the proportion of pixels in all pixels whose angle between the (010) crystal plane normal direction and the normal of the observation plane is less than a certain threshold (such as <10°) is counted.

[0037] Specific steps:

[0038] (1) After embedding and polishing the precursor powder, perform EBSD testing (step size 50-100nm).

[0039] (2) Obtain crystal orientation data for at least 50 particles;

[0040] (3) Calculate the percentage of pixels with (010) crystal planes exposed on the surface in each particle out of the total number of pixels in that particle;

[0041] (4) Take the average value of all particles as the final (010) crystal plane percentage.

[0042] To achieve the above objectives, the preparation method of porous spiky spherical vanadium-doped iron phosphate of the present invention is carried out according to the following steps:

[0043] S11, Reduction Acid Leaching Step: Titanium concentrate, 3.3 mol / L hydrochloric acid, and 0.5 mol / L hydrazine solution are mixed and subjected to reduction acid leaching reaction at 110℃ for 3 hours. The liquid-solid mass ratio is 3:1, resulting in an acid leaching solution with a vanadium leaching rate greater than 75%. Preferably, the volume ratio of hydrochloric acid to hydrazine solution is hydrochloric acid:hydrazine solution = 3:2.

[0044] 3.3 mol / L hydrochloric acid can selectively dissolve Fe and V impurities in titanium concentrate (dissolution rate > 95%), while avoiding excessive dissolution of titanium (TiO2) (Ti dissolution rate < 5%), thus reducing the introduction of subsequent impurities; hydrazine (N2H4) is used as a reducing agent to remove high-valence V (V2O2) impurities from the titanium concentrate. 5+ Restore to V 3+ Fe 3+ Reduced to Fe 2+ To avoid Fe 3+ Hydrolysis produces Fe(OH)3 precipitate; a volume ratio of 3:2 ensures an excess of hydrazine of 10%~15%, guaranteeing complete reduction; the reaction is carried out at 110℃ for 3 hours. Below 110℃, the dissolution rate of Fe and V is slow (dissolution rate <80% after 3 hours); above 110℃, hydrazine is easily volatilized (boiling point 114℃), losing its reducing effect; a liquid-to-solid ratio of 3:1 balances the dissolution efficiency and the subsequent solution processing volume, avoiding excessive volume due to an excessively high liquid-to-solid ratio, or viscous slurry due to an excessively low liquid-to-solid ratio.

[0045] S12. Purification and impurity removal steps: Add oxidant and alkaline regulator to the acid leaching solution in sequence to control the pH to 4.5-5.5, and precipitate and remove aluminum, chromium, and manganese impurities; after filtration, add ammonium fluoride or sodium fluoride to the filtrate to precipitate and remove calcium and magnesium impurities; after filtration again, adjust the pH of the filtrate back to 2.0-3.0 to obtain the purified solution.

[0046] An oxidizing agent is added to the acid leaching solution at a volume of 0.5% to 2% of the solution's volume. 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;

[0047] The preferred oxidant is hydrogen peroxide because 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 a strong buffering capacity, and 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] S13, Oxidation and Pore Formation Step: Air is introduced into the purified solution for oxidation, removing V from the solution. 3+ Oxidized to V 4+ At the same time, it maintains the majority of iron ions in the solution as Fe 2+ The doped solution is obtained by adding 5 wt% PEG-20000 as a pore-forming agent to the oxidized purification solution to obtain the treated doped solution.

[0053] 1. In this step, the oxidation endpoint is controlled by real-time monitoring of the oxidation-reduction potential of the purified solution. When the potential reaches -0.10V to +0.10V (relative to a saturated calomel electrode), the air supply is stopped, indicating that V... 3+ It has been oxidized to V 4+ In this step, after the air oxidation is completed, a sample is taken and the concentration of V in the solution is determined using potassium permanganate titration. 4+ The concentration, based on the total vanadium content in the solution, when V 4+ When the proportion exceeds 90%, oxidation is considered complete; the purpose of potential control is to achieve precise valence state, and this potential range only controls V. 3+ Oxidized to V 4+ Because V 3+ / V 4+ Standard potential ≈ -0.25V (vsSCE), without oxidizing Fe. 2+ (Fe) 2+ / Fe 3+ Standard potential ≈ +0.77V (vsSCE), to avoid Fe formation. 3+ The resulting precursor impurity phase; through the above control, the ferrous ions (Fe) in the oxidized purified liquid can be reduced. 2+ The percentage of iron ions in the total iron ions is greater than 90%.

[0054] Add 5 wt% PEG-20000 alcohol to the total mass of the purification solution. PEG-20000 is a high molecular weight polymer that can act as a template for ice crystal growth during subsequent freezing, preventing pore collapse caused by disordered ice crystal growth. 5 wt% is the optimal addition amount. If it is less than 5 wt%, the template effect is insufficient and the porosity is <35%. If it is more than 5 wt%, the residual amount of PEG will increase, and it will be easy to carbonize during subsequent drying, contaminating the precursor.

[0055] S14, Freeze-drying step: The doped solution is frozen at -20℃ for 24 hours to form an ice template, followed by vacuum drying to obtain an iron-vanadium intermediate with a water content ≤0.5%. The key to retaining the pores is that -20℃ allows the water in the solution to form regular ice crystals, providing a template for the interconnected pores; freezing for 24 hours ensures complete ice crystal growth and avoids incomplete pore interconnection caused by insufficient freezing; vacuum drying can directly sublimate the ice crystals, avoiding pore collapse caused by liquid surface tension in conventional drying; a water content ≤0.5% can prevent particle agglomeration during subsequent co-precipitation.

[0056] S15. Ultrasonic coprecipitation step: The iron-vanadium intermediate is dispersed in an aqueous phase to form a Fe / V solution. Under an ultrasonic field environment of 60℃ and 40kHz, the Fe / V solution and phosphoric acid solution undergo a coprecipitation reaction. After the reaction, solid-liquid separation and drying are performed to obtain the vanadium-doped iron phosphate precursor. The iron-vanadium intermediate is mixed and dispersed with deionized water, and the proportion of the iron-vanadium intermediate in the total mass of the aqueous phase is controlled to be 10%~30%. The concentration of iron ions in the Fe / V solution is controlled in the range of 0.5~2.0 mol / L. In the Fe / V solution, the molar ratio of iron to vanadium is 100:(0.3~0.5), which is the ratio of the number of moles of V to the number of moles of Fe, so that the mass content of vanadium in the final iron phosphate precursor is 3000~5000 ppm. When the proportion of iron-vanadium intermediates in the total mass of the aqueous phase is less than 10%, the solution concentration is too low and the precipitation efficiency is low; when it is higher than 30%, the slurry is viscous and will be unevenly dispersed. The concentration of iron ions in the Fe / V solution is selected to be controlled in the range of 0.5~2.0 mol / L because if the concentration is too low, the precipitate particles will be small and easy to agglomerate, while if it is too high, the precipitation rate will be too fast and the morphology will be out of control.

[0057] The molar ratio of iron to vanadium is chosen to be 100:(0.3~0.5). This ratio allows for precise control of the vanadium content in the final precursor to be 3000~5000 ppm. Specifically, a molar ratio of 100:0.3 corresponds to a vanadium content of approximately 3000 ppm, and 100:0.5 corresponds to approximately 5000 ppm. The molar ratio of Fe to V in the Fe / V solution is based on the total mass of the final precursor (including PO4). 3-The molar ratio is not simply the mass of Fe + V. It is the ratio of the number of moles of V to the number of moles of Fe. Based on the theoretical molar mass of FePO4 (150.82 g / mol), when Fe∶V = 100∶0.3, the theoretical mass content of vanadium is approximately (50.94*0.3) / (150.82*100+50.94*0.3)≈3000ppm. In actual production, the final precursor product can be calibrated using ICP-OES, and this feed ratio can be adjusted in reverse to ensure that the vanadium content is within the range of 3000~5000ppm.

[0058] The application of a porous, spiky, spherical vanadium-doped iron phosphate precursor in lithium iron phosphate cathode materials involves ball milling a mixture of the aforementioned iron phosphate precursor, a lithium source, and a carbon source, followed by sintering the milled material under an inert atmosphere to obtain the lithium iron phosphate cathode material. The lithium source is lithium carbonate or lithium hydroxide, and the carbon source is one or more of glucose, sucrose, citric acid, polyethylene glycol, ascorbic acid, or starch. The amount of carbon source added is 10%~15% of the theoretical mass of the lithium iron phosphate cathode material. The molar ratio of lithium to iron is controlled at (1.01~1.04):1. A 1% excess of lithium source is used. ~4% carbon source can compensate for lithium volatilization loss during sintering, as Li2CO3 easily decomposes into Li2O at high temperatures and volatilizes, while also avoiding FePO4 residue caused by insufficient lithium. Excessive carbon source of 10%~15% can form a uniform carbon layer of 5~10nm thickness after sintering, improving electronic conductivity. Below 10% is insufficient coating, and above 15% is too thick carbon layer, hindering lithium ion diffusion. The XRD characteristic peaks of the sintered product completely match the LiFePO4 standard card (JCPDS 40-1499), with no FePO4 impurity phase peaks and a crystallinity ≥90%.

[0059] The ball milling is a wet ball milling process. The D50 particle size of the milled material is 280~380nm. The processing conditions are as follows: under a nitrogen or argon atmosphere, the temperature is raised to 750~800℃ at a heating rate of 1~3℃ / min, and held at this temperature for 12~17 hours. Nitrogen (N2) or argon (Ar) is chosen as the inert atmosphere to avoid oxidation of lithium iron phosphate. The heating rate is controlled at 1~3℃ / min; slow heating avoids morphological damage caused by rapid particle growth. Controlling the sintering temperature and time is for crystallization control. At 750~800℃, the crystallinity of lithium iron phosphate can reach over 90%, with an XRD characteristic peak half-width <0.2°, while avoiding temperatures above 800℃ that lead to grain growth. The 12~17h process ensures that Li⁺ is completely embedded in the FePO₄ lattice; incomplete reaction will result in residual FePO₄, reducing capacity.

[0060] The lithium-ion battery assembled using this lithium iron phosphate cathode material as the cathode active material has a capacity retention of >140mAh / g at 5C discharge rate (the theoretical capacity of lithium iron phosphate is 170mAh / g, and the capacity retention is >82%); and after 8000 cycles at 1C rate under -10℃ conditions, the capacity retention is not less than 75%.

[0061] Beneficial effects

[0062] This invention achieves for the first time a gradient distribution of high-concentration vanadium (3000-5000 ppm), i.e., a two-fold bulk phase on the surface, while the vanadium content in the spike region exceeds 5000 ppm. This high vanadium content not only further optimizes surface electrochemical activity but also solves the problems of lattice distortion and agglomeration under high-concentration doping, thereby increasing the electronic conductivity of lithium iron phosphate to 10. -2 ~10 -1 The S / cm is 2 to 3 times that of conventional 3000ppm doping; through the precursor's spiky, porous (42% to 48% porosity) and gradient vanadium doping design, the electrolyte wetting efficiency is improved by 50%, and the lithium-ion diffusion coefficient is increased to 10. -11 ~10 -10 cm 2 / s, laying the foundation for high-rate performance; Vs is precisely controlled through steps such as reduction acid leaching and air oxidation. 4+ With a valence state (proportion > 90%), the reproducibility of morphology and porous structure is ensured through freeze-drying and ultrasonic co-precipitation, and the batch-to-batch deviation is < 5%, making it suitable for industrial mass production; the lithium iron phosphate 5C discharge is > 140mAh / g, and the retention rate after 8000 cycles at -10℃ is ≥ 75%, far exceeding the existing technology 5C≈120mAh / g and the low temperature retention rate≈ 65%, which can meet the stringent requirements of fast-charging power batteries and low-temperature energy storage systems. Attached Figure Description

[0063] Figure 1 This is a SEM image of the precursor of the present invention, showing a spiky morphology; Figure 2 These are HRTEM images, showing the layer structure and interlayer spacing; Figure 3 These are SEM images of lithium iron phosphate cathode materials, showing their spiky secondary particle morphology. Detailed Implementation

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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:

[0068] Table 1: Typical chemical composition and mass content (%) of titanium concentrate

[0069]

[0070] Example 1:

[0071] 1. Preparation of porous spiky spherical vanadium-doped iron phosphate precursor (vanadium content approximately 3000 ppm)

[0072] S11: Take 100g of titanium concentrate and mix it with 300g of mixed acid solution (3.3mol / L hydrochloric acid and 0.5mol / L hydrazine, volume ratio 3:2). Stir and react at 110℃ for 3h, and filter to obtain acid leaching solution.

[0073] S12 Purification and Impurity Removal: Hydrogen peroxide is added to the acid leaching solution at a concentration 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 the purified solution;

[0074] S13: Introduce air into the purified solution, monitor Eh until it reaches -0.10V (vsSCE), then stop the aeration; potassium permanganate titration shows V. 4+ The content was 92%; 15g of PEG-20000 (5wt%) was added, and the mixture was stirred to dissolve, thus obtaining the doped solution;

[0075] S14: The doped solution was frozen in a -20℃ freezer for 24 hours, and then vacuum dried (vacuum degree -0.09MPa, temperature 60℃) until the water content was 0.4% to obtain the iron-vanadium intermediate;

[0076] S15: Mix the iron-vanadium intermediate with deionized water at a ratio of 1:9 (mass ratio) to prepare Fe... 2+ A 0.5 mol / L Fe / V solution (Fe∶V = 100∶0.3) was added to a reactor in parallel flow with a 0.5 mol / L phosphoric acid solution under ultrasonication at 60℃ and 40 kHz (n(Fe+V)∶n(PO4)). 3- (1:1.05), coprecipitation reaction for 2 h; vacuum filtration at -0.08 MPa, washing with deionized water until no Cl is found. - (No precipitate was detected by AgNO3), and then dried at 80℃ for 8 hours to obtain the precursor.

[0077] The precursor prepared by the above method has a vanadium content of 3010 ppm (ICP-MS determination), and its microstructure consists of spiky spherical secondary particles with a diameter of 2 μm, and plate-like primary particles with a diameter of 400 nm (SEM observation). It is a porous structure with a pore size of 50 nm and a porosity of 42% (mercury porosimetry determination).

[0078] Crystal planes and interlayer spacing: (010) Crystal planes account for 71%, lamellar thickness is 70 nm, interlayer spacing is 0.52 nm (XRD and HRTEM measurements), surface vanadium content is 4754 ppm, bulk vanadium content is 2502 ppm, and spike V content is 5200 ppm (EDS line scan measurements).

[0079] 2. Preparation of lithium iron phosphate cathode material

[0080] Mixed ball milling: The above precursor was mixed with Li2CO3 (Li:Fe=1.01:1) and glucose (10wt%) at a mass ratio of 85:10:5 and wet ball milled (ball-to-material ratio 5:1, speed 300rpm) until D50=280nm;

[0081] Sintering: Under N2 atmosphere, the temperature is increased to 750℃ at 1℃ / min, held at the temperature for 12h, and then cooled to obtain lithium iron phosphate.

[0082] The performance of this lithium iron phosphate is as follows: 5C rate discharge capacity is 142mAh / g (tested at 25℃ after 0.2C activation); capacity retention is 75% after 8000 cycles at -10℃ and 1C.

[0083] Example 2:

[0084] 1. Preparation of porous spiky spherical vanadium-doped iron phosphate precursor (vanadium content approximately 3500 ppm)

[0085] S11, S12: Same as in Example 1;

[0086] S13: Ventilate until Eh = -0.05V (vsSCE), V 4+ The proportion was 94%; the amount of PEG-20000 added was the same as in Example 1;

[0087] S14: Same as Example 1, with a moisture content of 0.3%;

[0088] S15: Fe / V solution concentration 1.0 mol / L (Fe∶V=100∶0.35), the rest is the same as in Example 1.

[0089] The properties of the obtained precursor are as follows:

[0090] Vanadium content: 3560 ppm;

[0091] Microstructure: sphere diameter 2.5 μm, spike length 450 nm;

[0092] Porous structure: pore size 60nm, porosity 44%;

[0093] Crystal planes and interlayer spacing: (010) crystal plane accounts for 73%, layer thickness is 75nm, and interlayer spacing is 0.525nm;

[0094] Gradient distribution: Vanadium content in the surface phase is 6125 ppm, vanadium content in the bulk phase is 2917 ppm, and V content in the spike tip is 6500 ppm (EDS line scan determination).

[0095] 2. Preparation of lithium iron phosphate cathode material

[0096] Mixed ball milling: Li∶Fe=1.02∶1, glucose 12wt%, ball milled to D50=300nm;

[0097] Sintering: Heat up to 770℃ at a rate of 2℃ / min and hold at that temperature for 14 hours.

[0098] The properties of the prepared lithium iron phosphate are as follows:

[0099] 5C rate discharge capacity: 145mAh / g;

[0100] -10℃, 1C cycling: 78% capacity retention after 8000 cycles.

[0101] Example 3:

[0102] 1. Preparation of porous spiky spherical vanadium-doped iron phosphate precursor (vanadium content approximately 4500 ppm)

[0103] S11, S12: Same as in Example 1;

[0104] S13: Ventilate until Eh = +0.05V (vsSCE), V 4+ The proportion was 95%; the amount of PEG-20000 added was the same as in Example 1;

[0105] S14: Same as Example 1, with a moisture content of 0.5%;

[0106] S15: Fe / V solution concentration 1.5 mol / L (Fe∶V=100∶0.45), the rest is the same as in Example 1.

[0107] The properties of the precursor obtained are as follows:

[0108] Vanadium content: 4520 ppm;

[0109] Microstructure: sphere diameter 3.5 μm, spike length 550 nm;

[0110] Porous structure: pore size 90nm, porosity 46%;

[0111] Crystal planes and interlayer spacing: (010) crystal plane accounts for 75%, layer thickness is 85nm, and interlayer spacing is 0.535nm;

[0112] Gradient distribution: Vanadium content in the surface phase was 7505 ppm, vanadium content in the bulk phase was 3750 ppm, and V content in the spike tip was 7800 ppm (EDS line scan determination).

[0113] 2. Preparation of lithium iron phosphate cathode material

[0114] Mixed ball milling: Li∶Fe=1.03∶1, citric acid 14wt%, ball milled to D50=350nm;

[0115] Sintering: Heat up to 790℃ at a rate of 2℃ / min and hold at that temperature for 16 hours.

[0116] The properties of the prepared lithium iron phosphate are as follows:

[0117] 5C rate discharge capacity: 148mAh / g;

[0118] -10℃, 1C cycling: 80% capacity retention after 8000 cycles.

[0119] Example 4

[0120] 1. Preparation of porous spiky spherical vanadium-doped iron phosphate precursor (vanadium content approximately 5000 ppm)

[0121] S11, S12: Same as in Example 1;

[0122] S13: Ventilate until Eh = +0.10V (vsSCE), V 4+ The proportion was 96%; the amount of PEG-20000 added was the same as in Example 1;

[0123] S14: Same as Example 1, with a moisture content of 0.4%;

[0124] S15: Fe / V solution concentration 2.0 mol / L (Fe∶V=100∶0.5), the rest is the same as in Example 1.

[0125] The properties of the precursor obtained are as follows:

[0126] Vanadium content: 5000 ppm;

[0127] Microstructure: spherical diameter 4μm, spike length 600nm;

[0128] Porous structure: pore size 100nm, porosity 48%;

[0129] Crystal planes and interlayer spacing: (010) crystal plane accounts for 76%, layer thickness is 90nm, and interlayer spacing is 0.54nm;

[0130] Gradient distribution: Vanadium content in the surface phase was 7918 ppm, vanadium content in the bulk phase was 4167 ppm, and V content in the spike tip was 8500 ppm (EDS line scan determination).

[0131] 2. Preparation of lithium iron phosphate cathode material

[0132] Mixed ball milling: Li∶Fe=1.04∶1, polyethylene glycol 15wt%, ball milled to D50=380nm;

[0133] Sintering: Heat to 800℃ at 3℃ / min and hold at that temperature for 17 hours.

[0134] The properties of the prepared lithium iron phosphate are as follows:

[0135] 5C rate discharge capacity: 150mAh / g;

[0136] -10℃, 1C cycling: 82% capacity retention after 8000 cycles.

[0137] Comparative Example 1 (vanadium doped with 3500ppm)

[0138] 1. Preparation of vanadium-free iron phosphate precursor

[0139] Except for S14, pure Fe is used. 2+ Except for the solution (without V), the remaining steps are the same as in Example 2, to obtain a vanadium-free spherical iron phosphate precursor.

[0140] 2. Preparation of lithium iron phosphate by post-doping with vanadium

[0141] Mixed ball milling: Mix vanadium-free precursor, Li2CO3 (Li∶Fe=1.02∶1), glucose (12wt%) and ammonium metavanadate (NH4VO3), control the final vanadium mass content to 3500ppm, and wet ball mill to D50=300nm;

[0142] Sintering: Same as in Example 2 (770℃, 14h).

[0143] Performance testing of the prepared lithium iron phosphate

[0144] 5C rate discharge capacity: 125mAh / g;

[0145] -10℃, 1C cycling: After 8000 cycles, the capacity retention rate was 60%. Comparing Example 2 with Comparative Example 1, it can be seen that the capacity of the comparative example is 20mAh / g smaller at 5C discharge rate, mainly due to insufficient electronic conductivity caused by vanadium agglomeration. The capacity of the comparative example is 18% smaller at -10℃, mainly due to the aggravation of interfacial side reactions and poor structural stability.

[0146] The following differences exist between Examples 1-4 of this invention and the comparative examples.

[0147] Table 2: Differences in Microstructure and Elemental Distribution of Precursors

[0148]

[0149] Table 3: Differences in Electrochemical Performance

[0150]

[0151] The mechanism analysis is as follows:

[0152] (1) In-situ doping vs. post-doping: The example demonstrates V doping achieved by using a complete process of reduction acid leaching-oxidation pore-forming-freeze drying-ultrasonic co-precipitation. 4+ In-situ substitution within the FePO4 lattice forms stable Fe. 1-x (VO) x The PO4 solid solution exhibits a gradient distribution of vanadium (enriched on the surface with higher spikes). In Comparative Example 1, after solid-phase mixing and doping, vanadium cannot penetrate deep into the crystal lattice, easily forming a V2O5 impurity phase, resulting in limited improvement in electronic conductivity and exacerbated surface side reactions.

[0153] (2) Spiky porous structure vs. random agglomeration: the spiky secondary particles in the example ( Figure 1 It consists of radially grown, plate-like primary particles, resulting in a large specific surface area and a 50% improvement in electrolyte wetting efficiency; its internal interconnected porous structure (formed by ice crystal templates) is Li + It provides a fast transport channel and shortens the diffusion path. The particle morphology of Comparative Example 1 does not have this feature, and the ion transport resistance is high.

[0154] (3) Preferred orientation of (010) crystal plane vs. random orientation: In the example, the proportion of (010) crystal plane is >70% ( Figure 2 This crystal plane is Li + The main channels for insertion / extraction are expanded, the interlayer spacing is increased to 0.53±0.01 nm, and the diffusion barrier is reduced. Comparative Example 1 lacks this crystal plane modulation. Li + Diffusion is limited.

[0155] In summary, Examples 1-4, through the integrated design of "high-concentration gradient vanadium doping + spiky porous morphology + preferred orientation of (010) crystal plane" in the precursor, achieved significant improvements in electronic conductivity, lithium-ion diffusion coefficient, and low-temperature cycling stability. The 5C discharge capacity and -10℃ long-cycle retention rate were significantly better than Comparative Example 1. This fully demonstrates the inventiveness and practicality of the technical solution of this invention, meeting the stringent requirements of fast-charging power batteries and low-temperature energy storage systems.

[0156] 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 porous, spiky, spherical vanadium-doped iron phosphate precursor, characterized in that, Based on the total mass of ferric phosphate, the vanadium content is 3000~5000ppm. The ferric phosphate is a secondary particle with a spiky morphology and a diameter of 2~4μm. It is composed of radially growing plate-like primary particles. The spike length of the plate-like primary particles is 400~600nm. The vanadium mass content of the particle surface phase is 2±0.1 times that of the vanadium mass content of the particle bulk phase.

2. The porous, spiky, spherical vanadium-doped iron phosphate precursor as described in claim 1, characterized in that, Vanadium is distributed in a gradient within the secondary particles with a spiky morphology, and the vanadium content in the spike tip region is greater than 5000 ppm.

3. The porous, spiky, spherical vanadium-doped iron phosphate precursor as described in claim 1, characterized in that, The secondary particles with the spiky morphology have a through-porous structure formed by ice crystal templates, with a pore size of 50~100nm and a porosity of 42%~48%.

4. The porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 1, characterized in that, The precursor has a layered structure with (010) crystal planes accounting for >70% and a layer thickness of 80±10nm.

5. The porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 4, characterized in that, The interlayer spacing of the sheet structure is 0.53±0.01nm.

6. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in any one of claims 1 to 5, characterized in that... Follow these steps: S11, Reduction Acid Leaching Step: Titanium concentrate, hydrochloric acid with a concentration of 3.3 mol / L and hydrazine solution with a concentration of 0.5 mol / L are mixed and subjected to reduction acid leaching reaction at a temperature of 110℃ for 3 hours. The liquid-solid mass ratio is 3:1, and an acid leaching solution with a vanadium leaching rate of greater than 75% is obtained. S12. Purification and impurity removal steps: Add oxidant and alkaline regulator to the acid leaching solution in sequence to control the pH to 4.5-5.5, and precipitate and remove aluminum, chromium, and manganese impurities; after filtration, add ammonium fluoride or sodium fluoride to the filtrate to precipitate and remove calcium and magnesium impurities; after filtration again, adjust the pH of the filtrate back to 2.0-3.0 to obtain the purified solution. S13, Oxidation and Pore Formation Step: Air is introduced into the purified solution for oxidation, removing V from the solution. 3+ Oxidized to V 4+ At the same time, it maintains the majority of iron ions in the solution as Fe 2+ The doped solution is obtained by adding 5 wt% PEG-20000 as a pore-forming agent to the oxidized purification solution to obtain the treated doped solution. S14. Freeze-drying step: Freeze the doped solution at -20°C for 24 hours to form an ice template, and then perform vacuum drying to obtain an iron-vanadium intermediate with a water content ≤0.5%. S15, Ultrasonic coprecipitation step: The iron-vanadium intermediate is dispersed in an aqueous phase to form an Fe / V liquid. Under an ultrasonic field environment of 60℃ and 40kHz, the Fe / V liquid and phosphoric acid solution undergo a coprecipitation reaction. After the reaction, the mixture is separated into solid and liquid phases and dried to obtain the vanadium-doped iron phosphate precursor.

7. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S11, the volume ratio of hydrochloric acid to hydrazine solution is hydrochloric acid:hydrazine solution = 3:

2.

8. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S13, the oxidation endpoint is controlled by real-time monitoring of the oxidation-reduction potential of the purified liquid. When the potential reaches -0.10V to +0.10V (relative to a saturated calomel electrode), the air supply is stopped, indicating that V... 3+ It has been oxidized to V 4+ .

9. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S13, after air oxidation is completed, a sample is taken and the concentration of V in the solution is determined using potassium permanganate titration. 4+ The concentration, based on the total vanadium content in the solution, when V 4+ When the percentage of oxidation exceeds 90%, oxidation is considered complete.

10. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, After air oxidation in step S13 and before co-precipitation in step S15, the ferrous ions (Fe) in the purified solution after oxidation... 2+ The percentage of iron ions in the total iron ions is greater than 90%.

11. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S15, the iron-vanadium intermediate is mixed and dispersed with deionized water, and the proportion of the iron-vanadium intermediate to the total mass of the aqueous phase is controlled to be 10% to 30%.

12. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S15, the concentration of iron ions in the Fe / V solution is controlled within the range of 0.5~2.0 mol / L.

13. The method for preparing porous spiky spherical vanadium-doped iron phosphate as described in claim 6, characterized in that, In step S15, the molar ratio of iron to vanadium in the Fe / V solution is 100:(0.3~0.5), so that the vanadium doping content in the final iron phosphate precursor is 3000~5000ppm.

14. The application of a porous, spiky, spherical vanadium-doped iron phosphate precursor in lithium iron phosphate cathode materials, characterized in that... The lithium iron phosphate cathode material is obtained by mixing and ball milling the iron phosphate precursor, lithium source and carbon source as described in any one of claims 1 to 5, and then sintering the ball-milled material under an inert atmosphere.

15. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that... The lithium source is lithium carbonate or lithium hydroxide, and the carbon source is one or more of glucose, sucrose, citric acid, polyethylene glycol, ascorbic acid, or starch.

16. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that... The molar ratio of lithium to iron is controlled to be (1.01~1.04):

1.

17. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that... The amount of carbon source added is 10% to 15% of the theoretical mass of the lithium iron phosphate cathode material.

18. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that... The ball milling is a wet ball milling process, and the D50 particle size of the material after ball milling is 280~380nm.

19. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that... The sintering conditions are as follows: under a nitrogen or argon atmosphere, the temperature is increased to 750-800°C at a heating rate of 1-3°C / min, and held at this temperature for 12-17 hours.

20. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that, A lithium-ion battery assembled using lithium iron phosphate cathode material as the cathode active material has a discharge rate of >140mAh / g at 5C.

21. The application of the porous spiky spherical vanadium-doped iron phosphate precursor as described in claim 14 in lithium iron phosphate cathode materials, characterized in that, A lithium-ion battery assembled using lithium iron phosphate as the positive electrode active material retains no less than 75% of its capacity after 8000 cycles at 1C rate under -10℃ conditions.

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