High-magnification regenerated lithium iron phosphate based on near-surface Fe-O bond and lithium ion transmission tetrahedron channel targeted regulation and preparation method of high-magnification regenerated lithium iron phosphate

Abstract

The invention discloses a preparation method of high-rate regenerated lithium iron phosphate based on near-surface Fe-O bond and lithium ion transport tetrahedron channel targeted regulation, and the preparation method comprises the following steps: (1) mixing lithium iron phosphate, waste lithium iron phosphate and a lithium source additive, carrying out wet ball milling to obtain a suspension, and drying to obtain powder; (2) performing multi-stage heating on the powder in an inert atmosphere, and recycling tail gas generated in the heating process as a reducing agent to obtain high-rate regenerated lithium iron phosphate; the multi-stage heating comprises the following steps: in the first stage, calcining at 300-450 DEG C for 1-3 hours; and in the second stage, calcining at 600-700 DEG C for 8-12 hours. According to the method, the lithium iron phosphate with high rate capability and cycle capacity retention ratio is successfully prepared while the waste lithium iron phosphate is repaired.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery energy storage technology, specifically to a high-rate regenerated lithium iron phosphate and its preparation method based on near-surface Fe-O bonds and targeted regulation of lithium-ion transport tetrahedral channels. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, long cycle life, and a wide operating temperature range, and have been widely used in consumer electronics, power system peak shaving and frequency regulation, and electric vehicles. A lithium-ion battery typically consists of a positive electrode material, a negative electrode material, an electrolyte, a separator, a current collector, and a casing. As one of the most critical and cost-intensive components (accounting for over 50%), the positive electrode material determines key indicators of the lithium-ion battery, including electrode potential, energy density, voltage plateau stability, cycle stability, and chemical stability, significantly impacting the battery's electrochemical performance, lifespan, and safety.

[0003] Currently, the mainstream lithium-ion battery cathode materials on the market can generally be divided into the following two types: layered structure cathode materials (lithium cobalt oxide LCO: LiCoO2, ternary nickel cobalt manganese oxide NCM: Li 1.0 Ni x Co y Mn z Lithium cobalt oxide (LiFePO4) is the earliest commercially available cathode material for lithium-ion batteries, boasting a high theoretical specific capacity (274 mAh / g), a stable layered space group (R-3m space group), and mature manufacturing processes. Due to the extremely high price of cobalt ore, ternary nickel-cobalt-manganese lithium oxide was developed by partially replacing cobalt with nickel and manganese. Depending on the different proportions of nickel, cobalt, and manganese, ternary nickel-cobalt-manganese lithium oxide is further divided into several different types. Its average theoretical specific capacity is 278 mAh / g, and it possesses a stable α-NaFeO2 layered structure. Because the reduced cobalt content in ternary nickel-cobalt-manganese lithium oxide effectively controls costs and maintains a high theoretical specific capacity, it has begun to be widely used in the electric vehicle field. The two-dimensional lithium-ion diffusion channels in layered cathode materials allow for rapid lithium-ion extraction and insertion. However, during cycling, transition metals such as nickel, cobalt, and manganese are extracted from the interlayer and exchange with lithium ions, forming harmful rock salt and spinel phases on the surface and inside. This leads to a sharp reduction in the number of active lithium ions (significantly decreasing battery capacity), collapse of the layered structure, and puncture phenomena. This property makes layered cathode materials less safe, and several recent electric vehicle explosions have been mainly caused by ternary lithium batteries.

[0004] In contrast, olivine-structured lithium iron phosphate cathode materials involve only a single conversion reaction during charge-discharge cycling. Furthermore, LiFePO4 and FePO4 share the same structure and similar volume, exhibiting minimal volume change in the cathode material during charge-discharge cycles, thus demonstrating excellent stability and safety. However, the one-dimensional lithium-ion diffusion channels in lithium iron phosphate cathode materials result in poor conductivity and rate performance. Therefore, researchers have enhanced the conductivity of lithium iron phosphate cathode materials through methods such as carbon coating (e.g., Chinese patent CN120933348A discloses a carbon-coated lithium iron phosphate cathode material and its preparation method) and transition metal cation doping (e.g., CN105428648A discloses a method for preparing lithium iron phosphate cathode material, in which water-soluble lithium ions and doped metal ions are embedded in the iron phosphate matrix), thus addressing the issue of low energy density at high charge-discharge currents. This is of great significance for the application of lithium iron phosphate batteries.

[0005] However, the above-mentioned enhancement methods involve complex preparation steps. How to enhance the performance of lithium iron phosphate through a simpler method is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide a high-rate regenerated lithium iron phosphate and its preparation method based on near-surface Fe-O bonds and targeted regulation of lithium-ion transport tetrahedral channels. This method can successfully prepare lithium iron phosphate with high rate performance and cycle capacity retention while repairing waste lithium iron phosphate.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing high-rate regenerated lithium iron phosphate based on near-surface Fe-O bonds and targeted regulation of lithium-ion transport tetrahedral channels, the method comprising: (1) After mixing lithium iron phosphate, waste lithium iron phosphate and lithium source additives, the mixture is wet ball milled to obtain a suspension, and then dried to obtain powder; (2) The powder is heated in an inert atmosphere in multiple stages, and the tail gas generated during the heating process is recycled as a reducing agent to obtain high-rate regenerated lithium iron phosphate; The multi-stage heating process includes: the first stage, calcination at 300~450℃ for 1~3 hours; and the second stage, calcination at 600~700℃ for 8~12 hours.

[0008] The technical principle of this invention is as follows: the precursor used in the preparation method of this invention for high-rate regenerated lithium iron phosphate is original unused lithium iron phosphate and a certain mass fraction of waste lithium iron phosphate. The waste lithium iron phosphate is heated in multiple stages to provide a strong electronegative heterogeneous interface regulator, thereby controlling the near-surface Fe-O bonds and tetrahedral transport channels. Combined with the tail gas recirculation co-heating process, the prepared lithium iron phosphate possesses both high-rate performance and good cycle performance. Specifically: by constructing a strong electronegative heterogeneous interface on the surface, the electronic hybridization of the near-surface Fe-O bonds is weakened, successfully controlling the Fe-O bond length. Simultaneously, the volume of the O1-O2-O3-O3 tetrahedron between the PO4 tetrahedron and the FeO6 octahedron increases. This increase in tetrahedral volume widens the near-surface lithium ion

[010] transport channels, thus increasing the number of active lithium ions that can be extracted and inserted under high-rate charge and discharge currents, significantly improving the rate performance of the lithium iron phosphate cathode material.

[0009] In step (1), the lithium iron phosphate is selected from commercial lithium iron phosphate (model: DY-3) and waste lithium iron phosphate obtained from waste power batteries (SOH≈50%).

[0010] In step (1), the lithium source additive is lithium carbonate, lithium hydroxide or lithium acetate.

[0011] In step (1), the amount of waste lithium iron phosphate added is 10-70 wt% of lithium iron phosphate, and the percentage is a mass percentage.

[0012] Preferably, the amount of waste lithium iron phosphate added is 11-43 wt% of the total lithium iron phosphate, where the percentage is by mass. This invention further improves the rate performance of the prepared lithium iron phosphate by further controlling the amount of waste lithium iron phosphate added.

[0013] Preferably, the amount of waste lithium iron phosphate added is 25-43 wt% of the total lithium iron phosphate, where the percentage is by mass. At this added amount, the prepared lithium iron phosphate exhibits higher rate performance.

[0014] In step (2), the multi-stage heating includes: a first stage of calcination at 350~450℃; and a second stage at 600~700℃. This invention further improves the rate performance of the prepared lithium iron phosphate by controlling the multi-stage heating temperature.

[0015] In step (2), the high-rate regenerated lithium iron phosphate is obtained by heating and then naturally cooling down. The heating rate during the heating process is 2℃ / min.

[0016] The present invention also provides a high-rate regenerated lithium iron phosphate obtained by the above preparation method.

[0017] Furthermore, compared to the lithium iron phosphate in step (1), the Fe-O bond length of the high-rate regenerated lithium iron phosphate is longer, while the O1-O2-O3-O3 tetrahedral volume of the interstices between the PO4 tetrahedron and the FeO6 octahedron increases.

[0018] Compared with the prior art, the present invention has the following advantages: 1. The high-rate regenerated lithium iron phosphate cathode material prepared by this invention exhibits high rate performance and high energy density at high charge-discharge currents, exceeding that of currently mainstream commercially available lithium iron phosphate. For example, the discharge specific capacity is 146.9 mAh / g at 1C (1C=170 mAh / g, the same below), 137.6 mAh / g at 2C, 125 mAh / g at 5C, 107.9 mAh / g at 10C, 94.4 mAh / g at 15C, and 70.0 mAh / g at 30C.

[0019] 2. The high-rate regenerated lithium iron phosphate cathode material prepared by this invention also exhibits high capacity retention during cycling. For example, in long-cycle performance tests at 1C rate, the prepared material retains 95% of its capacity after 200 cycles, 93% after 300 cycles, 83% after 500 cycles, and 70% after 1000 cycles. In long-cycle performance tests at 5C rate, the capacity retention is 84% ​​after 400 cycles.

[0020] 3. This invention successfully prepares high-rate regenerated lithium iron phosphate using original, unused lithium iron phosphate and waste lithium iron phosphate. Through multi-stage heating, the strong electronegativity regulator in the waste lithium iron phosphate is decomposed in a controllable manner, further regulating the near-surface Fe-O bonds and O1-O2-O3-O3 tetrahedra, thereby obtaining excellent rate performance and cycle performance. By circulating and co-heating the exhaust gas (mainly inert gas, H2, and HF), the reducing gas generated in the multi-stage heating steps is returned to the tube furnace to create a reducing environment, achieving the simultaneous repair of waste lithium iron phosphate and successful preparation of high-rate lithium iron phosphate. Attached Figure Description

[0021] Figure 1 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 1 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 2 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 2 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 3The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 3 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 4 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 4 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 5 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 5 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 6 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 6 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 7 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 7 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 8 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Comparative Example 1 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 9 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Comparative Example 2 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 10 The graph shows a comparison of the cycle performance of high-rate regenerated lithium iron phosphate obtained in Comparative Example 3 with waste lithium iron phosphate and commercial lithium iron phosphate at different rates, where the charge and discharge voltage range is 2.5-4.2V. Figure 11 This is a comparison chart of the long-cycle performance of high-rate regenerated lithium iron phosphate obtained in Example 2 with waste lithium iron phosphate and commercial lithium iron phosphate at 5C. Figure 12 The cyclic voltammetry curves of the high-rate regenerated lithium iron phosphate obtained in Example 2 at different scan rates are shown. Figure 13 The image shows the lithium-ion transport rate fitting diagram of the high-rate regenerated lithium iron phosphate obtained in Example 2 under different scan rates during cyclic voltammetry testing. Figure 14 In-situ X-ray diffraction pattern of waste lithium iron phosphate material; Figure 15 In-situ X-ray diffraction pattern of commercial lithium iron phosphate materials; Figure 16 The in-situ X-ray diffraction pattern of the high-ratio regenerated lithium iron phosphate material obtained in Example 2; Figure 17 Thermogravimetric-infrared spectroscopy (TGA-IR) image of the high-rate regenerated lithium iron phosphate material prepared in Example 2; Figure 18 X-ray diffraction patterns of waste lithium iron phosphate material, high-rate regenerated lithium iron phosphate material obtained in Example 2, and commercial lithium iron phosphate. Figure 19 Rieteld refinement image of X-ray diffraction of waste lithium iron phosphate; Figure 20 Rietveld refined X-ray diffraction pattern for commercial lithium iron phosphate; Figure 21 This is a Rietveld refinement image of the high-rate regenerated lithium iron phosphate obtained in Example 2. Detailed Implementation

[0022] In this invention, the invention will be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] Example 1 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 11wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 350°C and keep it at that temperature for 2 hours. Then heat it to 650°C and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 1 .

[0024] Example 2 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 350°C and keep it at that temperature for 2 hours. Then heat it to 650°C and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm using a punching machine, while the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm. Furthermore, 1 m³ of LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g.

[0025] The electrochemical rate performance of this embodiment is shown in [reference needed]. Figure 2 High-rate, long-cycle performance is shown in [reference needed]. Figure 11 The lithium-ion transport kinetics of the high-rate regenerated lithium iron phosphate obtained in this embodiment were fitted using cyclic voltammetry curves at different scan rates. The results are shown in [Figure Number]. Figure 12 , 13 To further visualize the reversibility of phase transitions in materials during charging and discharging, in-situ X-ray diffraction was performed on the high-rate regenerated lithium iron phosphate, waste lithium iron phosphate, and commercial lithium iron phosphate obtained in this embodiment during charging and discharging. The results are shown in [Figure number missing]. Figure 14 , 15 16; To investigate the weight loss rate and phase changes of the material during the preparation process, the thermogravimetric-infrared spectroscopy (TGA) test results during the preparation process in this embodiment are shown in [reference needed]. Figure 17 To investigate the volume change of near-surface tetrahedra in the materials, X-ray diffraction Rietvield was performed on the high-performance lithium iron phosphate obtained in this embodiment, waste lithium iron phosphate, and commercial lithium iron phosphate. The results are shown in [Figure number missing]. Figure 19 , 20 ,twenty one.

[0026] Example 3 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 43wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 350°C and keep it at that temperature for 2 hours. Then heat it to 650°C and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 3 .

[0027] Example 4 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 66wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 350°C and keep it at that temperature for 2 hours. Then heat it to 650°C and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 4 .

[0028] Example 5 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 300℃ and keep it at that temperature for 1 hour, then heat it to 600℃ and keep it at that temperature for 8 hours. Then, cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2℃ / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm); before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion; subsequently, cycle performance and rate performance were measured in the Neware battery testing system, with an operating voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 5 .

[0029] Example 6 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to wet ball milling with ethanol. Ball milling beads were added at a ball-to-material ratio of 10:1 and the mixture was ball milled at 600rpm for 2h. Then the ball-milled suspension was transferred to a beaker and dried in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 400℃ and keep it at that temperature for 3 hours. Then heat it to 600℃ and keep it at that temperature for 10 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2℃ / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process;

[0030] (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was then uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 6 .

[0031] Example 7 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to ethanol wet ball milling. Ball milling beads were added at a ball-to-material ratio of 10:1 and ball milling was carried out at 600rpm for 2h. Then the suspension after ball milling was transferred to a beaker and placed in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Heat it to 450℃ and keep it at that temperature for 2 hours under an inert atmosphere. Then heat it to 700℃ and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2℃ / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system, with a working voltage range of 2.5-4.2V (for Li...).+ / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this embodiment is shown in [reference]. Figure 7 .

[0032] Comparative Example 1 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 100wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to ethanol wet ball milling. Ball milling beads were added at a ball-to-material ratio of 10:1 and ball milled at 600rpm for 2h. Then the ball milled suspension was transferred to a beaker and placed in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Under the protection of an inert atmosphere, heat it to 350°C and keep it at that temperature for 2 hours. Then heat it to 650°C and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm). Before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion. Cycle performance and rate performance were then measured using the Neware battery testing system. The operating voltage range was 2.5-4.2V (for Li...). + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this comparative example is shown in [reference]. Figure 8 .

[0033] Comparative Example 2 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to ethanol wet ball milling. Ball milling beads were added at a ball-to-material ratio of 10:1 and ball milling was carried out at 600rpm for 2h. Then the suspension after ball milling was transferred to a beaker and placed in a forced-air drying oven at 80℃ for 12h. (2) Multi-stage heating: Take out the dried powder in step (1), press it into tablets and place it in a tube furnace. Heat it to 200℃ and keep it at that temperature for 2 hours under an inert atmosphere. Then heat it to 800℃ and keep it at that temperature for 12 hours. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2℃ / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively.

[0034] (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm); before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion; subsequently, cycle performance and rate performance were measured using the Neware battery testing system; the operating voltage range was 2.5-4.2V (for Li + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this comparative example is shown in [reference]. Figure 9 .

[0035] Comparative Example 3 (1) Pretreatment: Commercial lithium iron phosphate (model: DY-3), 25wt% waste lithium iron phosphate and lithium source additives equivalent to 50mol% of waste lithium iron phosphate were subjected to ethanol wet ball milling. Ball milling beads were added at a ball-to-material ratio of 10:1 and ball milling was carried out at 600rpm for 2h. Then the suspension after ball milling was transferred to a beaker and placed in a forced-air drying oven at 80℃ for 12h. (2) Take out the dried powder from step (1), press it into tablets and place it in a tube furnace. Heat it to 650°C and keep it at that temperature for 12 hours under an inert atmosphere. Then cool it down naturally to obtain the high-rate regenerated lithium iron phosphate prepared. The heating rate during the heating process is 2°C / min. (3) Tail gas recirculation and co-heating: The tail gas generated in step (2) multi-stage heating is preheated and returned to the tubular furnace to provide a good reducing environment for the co-heating process; (4) Slurry preparation and coating: The prepared high-rate regenerated lithium iron phosphate, binder, and conductive carbon black were ground in an agate mortar at a mass ratio of 8:1:1 for 15 minutes. Then, NMP solution (N-methylpyrrolidone) was added, and grinding continued until a uniform slurry was formed. The slurry was uniformly coated onto aluminum foil and dried at 120°C for 12 hours to obtain an active material loading of 3-4 mg / cm³. 2 The positive electrode strip is formed into a circular electrode with a diameter of 11 mm by a punching machine, and the negative electrode uses a lithium sheet with a diameter of 15 mm and a thickness of 0.45 mm; in addition, 1 m LiPF6 in Celgard2500 and EC:DEC:DMC (volume ratio 1:1:1) are used as the separator and electrolyte, respectively. (5) Button cell assembly and testing: CR2025 button cells were prepared in a glove box filled with argon (H2O < 0.01 ppm, O2 < 0.01 ppm); before testing, the button cells were placed in a 25°C constant temperature chamber for 12 hours to ensure complete electrolyte immersion; subsequently, cycle performance and rate performance were measured using the Neware battery testing system; the operating voltage range was 2.5-4.2V (for Li + / Li potential), nominal capacity 170 mAh / g, electrochemical performance of this comparative example is shown in [reference]. Figure 10 .

Claims

1. A method for preparing high-rate regenerated lithium iron phosphate based on near-surface Fe-O bonds and targeted regulation of lithium-ion transport tetrahedral channels, characterized in that, The preparation method includes: (1) After mixing lithium iron phosphate, waste lithium iron phosphate and lithium source additives, the mixture is wet ball milled to obtain a suspension, and then dried to obtain powder; (2) The powder is heated in an inert atmosphere in multiple stages, and the tail gas generated during the heating process is recycled as a reducing agent to obtain high-rate regenerated lithium iron phosphate; The multi-stage heating process includes: the first stage, calcination at 300~450℃ for 1~3 hours; and the second stage, calcination at 600~700℃ for 8~12 hours.

2. The preparation method according to claim 1, characterized in that, In step (1), the lithium source additive is lithium carbonate, lithium hydroxide or lithium acetate.

3. The preparation method according to claim 1, characterized in that, In step (1), the amount of waste lithium iron phosphate added is 10-70 wt% of lithium iron phosphate, and the percentage is a mass percentage.

4. The preparation method according to claim 3, characterized in that, The amount of waste lithium iron phosphate added is 11-43 wt% of lithium iron phosphate, and the percentage is a mass percentage.

5. The preparation method according to claim 4, characterized in that, The amount of waste lithium iron phosphate added is 25-43 wt% of lithium iron phosphate, and the percentage is a mass percentage.

6. The preparation method according to claim 1, characterized in that, In step (2), the multi-stage heating includes: a first stage, calcination at 350~450℃; and a second stage, calcination at 600~700℃.

7. A high-rate regenerated lithium iron phosphate obtained by the preparation method according to any one of claims 1-6.

8. The high-rate regenerated lithium iron phosphate according to claim 7, characterized in that, Compared to the lithium iron phosphate in step (1), the Fe-O bond length of the high-rate regenerated lithium iron phosphate is longer, and the O1-O2-O3-O3 tetrahedron volume between the PO4 tetrahedron and the FeO6 octahedron is increased.

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