Method for repairing waste lithium iron phosphate positive electrode material by modifying with tetrabutyl silicate and application in deep sea field

Abstract

The application discloses a method for repairing waste lithium iron phosphate positive electrode material by modifying with tetrabutyl orthosilicate and application of the method in deep sea field. The waste lithium iron phosphate positive electrode material is subjected to ultrasonic treatment and drying; the dried waste lithium iron phosphate positive electrode material is subjected to ball milling to obtain waste lithium iron phosphate powder; the waste lithium iron phosphate powder is mixed with tetrabutyl orthosilicate and dissolved in anhydrous ethanol, and then subjected to ball milling again to obtain a mixed material; the mixed material is subjected to drying treatment, and then heated to 450-550 DEG C and subjected to oxidation treatment to obtain a mixed oxide; the mixed oxide, lithium carbonate and glucose are mixed and subjected to ball milling to obtain a mixed powder sample; the mixed powder sample is heated to 650-750 DEG C and subjected to high-temperature solid-phase sintering to obtain a repaired lithium iron phosphate positive electrode material. The tetrabutyl orthosilicate modified waste lithium iron phosphate positive electrode material prepared by the method can be applied to the deep sea field.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a method for modifying and repairing waste lithium iron phosphate cathode materials with tetrabutyl silicate and its application in the deep-sea field. Background Technology

[0002] Lithium-ion batteries, especially lithium iron phosphate batteries, have become one of the mainstream choices for power batteries and energy storage systems due to their excellent thermal stability, long cycle life, and relatively low cost. Furthermore, lithium-ion batteries are widely used in deep-sea applications. However, the average lifespan of these batteries is only 5-8 years, and the resulting large number of waste batteries, if not properly disposed of, will lead to resource waste and environmental pollution. Therefore, developing economical and environmentally friendly battery recycling technologies, particularly the direct repair and high-value utilization of cathode materials, has become crucial.

[0003] Currently, the recycling methods for cathode materials from spent lithium iron phosphate batteries are mainly divided into three categories: pyrometallurgy, hydrometallurgy, and direct recycling. Pyrometallurgy involves high-temperature smelting to reduce and enrich the metal components in the battery material into alloys or slag. This method is simple and has a large processing capacity, but it has significant drawbacks: extremely high energy consumption, easy volatilization and loss of valuable elements such as lithium and phosphorus, low recovery rate, and the generation of harmful gases during the high-temperature process, which is environmentally unfriendly. For lithium iron phosphate materials that do not contain high-value cobalt and nickel, pyrometallurgical recycling is less economically viable. Hydrometallurgy is currently the mainstream commercial technology, recovering metals in the form of salts through acid leaching, extraction, and precipitation. The advantages of this method are high metal recovery rate and high product purity. However, its process is long and complex, consuming large amounts of acid and alkali reagents and generating difficult-to-treat wastewater, resulting in high environmental costs. Furthermore, this method completely destroys the crystal structure of lithium iron phosphate, constituting "downgraded recycling" and failing to fully utilize its original material science value.

[0004] Direct recycling (or repair and regeneration) is an emerging technology that aims to minimize damage to the material's structure by directly restoring its electrochemical performance through methods such as lithium replenishment and heat treatment. Theoretically, this method has significant advantages, including a short process, low energy consumption, minimal chemical consumption, and environmental friendliness, and is considered the most promising approach to achieving closed-loop cycling of lithium iron phosphate. However, existing direct repair technologies often only partially restore material performance. Repaired materials typically exhibit inferior cycle stability and rate performance compared to new materials, and they struggle to repair irreversible structural damage caused by deep degradation.

[0005] Pyrometallurgical and hydrometallurgical processes suffer from inherent drawbacks such as high energy consumption, heavy pollution, or complex processes, while existing direct recycling methods face bottlenecks in performance recovery. Therefore, there is an urgent need to develop a novel remediation and regeneration technology that can retain the environmental and economic advantages of direct recycling while significantly improving the original performance of materials. Introducing new elements into lithium iron phosphate (LFP) has thus become a new research direction. Silicon possesses high ion-accommodating capacity and structural regulation capabilities. Introducing appropriate silicon doping into the LFP lattice can optimize lithium-ion diffusion channels through ion substitution and surface coating, thereby improving the material's rate performance and kinetic characteristics. Simultaneously, the stable bonding structures formed by silicon within the material and at interfaces can effectively alleviate volume effects during charging and discharging, enhance particle structural integrity, and improve the cycle stability of recycled materials. However, conventional silicon doping methods are mostly late-stage physical composites, resulting in uneven silicon dispersion and weak bonding with the matrix, making it difficult to achieve simultaneous modification and structural strengthening during regeneration. Achieving in-situ, uniform silicon doping during the direct regeneration of LFP is of great significance for improving the comprehensive performance of recycled materials and realizing the high-value utilization of retired LFP. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for repairing waste lithium iron phosphate cathode materials using tetrabutyl silicate modification and its application in the deep-sea field. This invention achieves significant performance improvements by modifying waste lithium iron phosphate with silicon, and constructs high-performance lithium-ion batteries based on this material. Through silicon-based modification, this invention not only successfully overcomes the bottleneck of incomplete performance recovery in traditional direct repair methods, but also enables the comprehensive performance of recycled materials to reach the level of commercial materials, adding a new recycling path for the high-value recycling of waste lithium iron phosphate batteries that combines environmental friendliness, economic efficiency, and high-performance output potential.

[0007] To achieve the above objectives, the technical solution designed by the present invention is as follows: This invention provides a method for modifying and repairing waste lithium iron phosphate cathode materials with tetrabutyl silicate, comprising the following steps: (1) The waste lithium iron phosphate cathode material is ultrasonically treated 4 to 5 times and then dried; (2) The dried waste lithium iron phosphate cathode material is ball-milled to obtain waste lithium iron phosphate powder; (3) The waste lithium iron phosphate powder and tetrabutyl silicate are mixed and dissolved in anhydrous ethanol, and then ball-milled again to obtain a mixed material; the mass-volume ratio of the waste lithium iron phosphate powder and tetrabutyl silicate is 1: (0.1188~0.251). (4) The mixed material is dried and transferred to a muffle furnace. Then, under an air atmosphere, it is heated to 450~550℃ and kept at that temperature for oxidation treatment. After cooling, the mixed oxide is obtained. (5) Mix the mixed oxide, lithium carbonate and glucose, and ball mill them to obtain a mixed powder sample; (6) Under a hydrogen-argon mixed atmosphere, the mixed powder sample is heated to 650~750℃, held at the temperature for high-temperature solid-state sintering, and cooled to obtain the modified repaired lithium iron phosphate cathode material.

[0008] Further, in step (1), the frequency of ultrasonic treatment is 100~120 kHz, the duration of ultrasonic treatment is 8~12 minutes / time, and the drying temperature is 65~75℃; In steps (2) and (3), the grinding beads used in the ball mill have a particle size of 1 mm and 3 mm, the ratio of 1 mm grinding beads to 3 mm grinding beads is (10~12):1, the rotation speed of the ball mill is 350~450 rpm, and the ball milling time is 3.5~4.5 hours.

[0009] Furthermore, the ultrasonic treatment frequency is 120 kHz, the ultrasonic treatment time is 10 minutes / time, and the drying temperature is 70°C. The ratio of 1 mm grinding beads to 3 mm grinding beads is 12:1, the ball milling speed is 400 rpm, and the ball milling time is 4 hours; The mass-to-volume ratio of the waste lithium iron phosphate powder, tetrabutyl silicate, and anhydrous ethanol is 1:0.1968.

[0010] Furthermore, in step (4), the heating rate is 4~5℃ / min, and the oxidation treatment time is 5.5~6.5 hours; In step (5), the grinding beads used in the ball mill have particle sizes of 1 mm and 3 mm, the ratio of 1 mm grinding beads to 3 mm grinding beads is (10~12):1, the ball milling speed is 500~600 rpm, and the ball milling time is 7.5~8.5 hours; the mass ratio of the mixed oxide, lithium carbonate and glucose is 100:(8.5~9.5):(10~12); the particle size of the mixed powder sample is 100~500 nm. In step (6), the hydrogen-argon mixed atmosphere consists of 5% hydrogen and 95% argon, the heating rate is 4~5℃ / min, and the high-temperature solid-phase sintering time is 9~11 hours.

[0011] Furthermore, in step (4), the temperature is raised to 500°C at a rate of 5°C / min, and the oxidation treatment time is 6 hours. In step (5), the ratio of 1 mm grinding beads to 3 mm grinding beads is 10:1, the ball milling speed is 500 rpm, and the ball milling time is 8 hours; the mass ratio of the mixed oxide, lithium carbonate, and glucose is 100:8.95:10.9. In step (6), the temperature is raised to 700°C at a rate of 5°C / min, and the high-temperature solid-phase sintering time is 10 hours.

[0012] The present invention also provides a repaired lithium iron phosphate cathode material obtained by the method described.

[0013] The present invention also provides an application of the aforementioned repaired lithium iron phosphate cathode material in the preparation of lithium iron phosphate batteries.

[0014] The present invention also provides a repaired lithium iron phosphate cathode sheet, wherein the repaired lithium iron phosphate cathode sheet comprises the repaired lithium iron phosphate cathode material.

[0015] The present invention also provides a repaired lithium iron phosphate battery, wherein the repaired lithium iron phosphate battery comprises the repaired lithium iron phosphate positive electrode sheet.

[0016] The present invention also provides an application of the repaired lithium iron phosphate battery in the deep-sea field.

[0017] The principle of this invention: Oceans cover approximately 71% of the Earth's surface, with deep-sea areas exceeding 200 meters in depth accounting for over 85% of the total ocean volume. These deep-sea areas are rich in mineral and biological resources and represent a frontier of technological competition among nations. Meanwhile, coastal sand is primarily composed of silicon dioxide (SiO2). Silicon is the second most abundant element in the Earth's crust after oxygen, and in the marine environment, it exists widely as dissolved silicates or suspended particles. Inspired by the natural corrosion resistance, high-pressure resistance, and structural stability of silicon, this invention utilizes tetrabutyl silicate (TBOS), an organosilicon source, to achieve in-situ, uniform silicon doping during the remediation of waste lithium iron phosphate. This transforms silicon into nano-silica and a lithium silicate interface phase, constructing a stable Si-O bonded, three-dimensional hybrid conductive network. Lithium iron phosphate materials inherently possess excellent thermal stability and overcharge resistance. After silicon-based modification, the surface carbon coating and the lithium silicate interface phase further suppress the risk of thermal runaway. This battery can operate safely in the high-salt, high-humidity, and sealed deep-sea environment, making it suitable for scenarios with the highest safety requirements, such as manned submersibles and deep-sea laboratories.

[0018] During the oxidation heat treatment stage, the uniformly dispersed silicon source is transformed into nano-silica, mainly distributed on the surface and grain boundaries of the iron phosphate / iron oxide particles. In the subsequent reduction and resynthesis stage, under high temperature and reducing atmosphere, silica can undergo a solid-state reaction with the lithium carbonate component to generate a uniform lithium silicate compound, forming a strongly bonded Si-OP bond on the material surface.

[0019] The solid-state sintering stage in a tube furnace allows lithium silicate and silicon-carbon produced by glucose pyrolysis to work synergistically, creating a more efficient three-dimensional hybrid conductive network between particles and on the surface, providing a modification mechanism for the material.

[0020] The beneficial effects of this invention are: Addressing the prominent issues of high energy consumption and low recovery rate of valuable elements in existing pyrometallurgical processes, complex and highly polluting hydrometallurgical processes, and insufficient performance recovery in traditional direct repair methods, this invention introduces a silicon source (tetrabutyl silicate, TBOS) into the direct repair process. This allows silicon to play multiple roles in structural enhancement and functional optimization during material regeneration: During the oxidation stage, nano-silica formed by silicon is uniformly dispersed in material defects and grain boundaries, acting as nucleation support and structural buffer; during the reduction and resynthesis stage, some silicon species enter the crystal lattice or form stable interface phases, significantly enhancing the crystal stability of the regenerated LiFePO4 olivine phase and effectively suppressing structural distortion and particle pulverization during the cycle; simultaneously, the silicon component and the carbon coating layer synergistically construct a highly efficient three-dimensional hybrid conductive network, significantly improving the material's electronic conductivity and lithium-ion migration capability.

[0021] The repair method provided by this invention is characterized by its simple process, green economy, and strong adaptability, making it easy to achieve large-scale production. The silicon-modified lithium iron phosphate cathode material regenerated using this method exhibits excellent cycle stability, high-rate performance, and reliable safety, and can be directly used to assemble high-performance lithium-ion batteries, meeting the application needs of energy storage systems, electric vehicles, and other fields. This provides a practical and feasible technical path for the high-value recycling and resource recycling of waste lithium iron phosphate batteries. Attached Figure Description

[0022] Figure 1 To repair the X-ray diffraction pattern of lithium iron phosphate cathode material RLFP-8at%; In the diagram, 2θ refers to the diffraction angle; Figure 2 To restore the TEM image of lithium iron phosphate cathode material RLFP-8at% at 100 nm; Figure 3 To restore the TEM image of lithium iron phosphate cathode material RLFP-8at% at 50 nm; Figure 4 To restore the TEM image of lithium iron phosphate cathode material RLFP-8at% at 10 nm; Figure 5 for Figure 4 TEM image of region 1 at 0.192 nm; Figure 6 for Figure 4 TEM image of region 2 at 0.192 nm; Figure 7 for Figure 4 TEM image of region 3 at 0.192 nm; Figure 8The lattice spacing diagram is obtained by inverse Fourier transform of TEM at the 10nm scale; Figure 9 To repair the SEM image of lithium iron phosphate cathode material RLFP-8at%; Figure 10 To repair the Si element distribution map of lithium iron phosphate cathode material RLFP-8at%; Figure 11 To repair the C element distribution map of lithium iron phosphate cathode material RLFP-8at%; Figure 12 To repair the Fe element distribution map of lithium iron phosphate cathode material RLFP-8at%; Figure 13 To repair the P element distribution map of lithium iron phosphate cathode material RLFP-8at%; Figure 14 To repair the O element distribution map of lithium iron phosphate cathode material RLFP-8at%; Figure 15 The X-ray photoelectron spectrum of Fe2p in the repaired lithium iron phosphate cathode material RLFP-8at% is shown. Figure 16 To repair the C1s X-ray photoelectron spectrum of lithium iron phosphate cathode material RLFP-8at%; Figure 17 To repair the X-ray photoelectron spectrum of Si2p in lithium iron phosphate cathode material RLFP-8at%; Figure 18 The graph shows the cycling performance of a battery based on the repaired lithium iron phosphate cathode material RLFP-8at% at a current density of 0.2 C. Figure 19 The charge-discharge curves of the battery based on the repaired lithium iron phosphate cathode material RLFP-8at% at a current density of 0.2 C are shown. Figure 20 The graph shows the electrochemical performance of a battery based on the repaired lithium iron phosphate cathode material RLFP-8at% at different current densities. Figure 21 This is a diagram of a battery fabricated based on the repaired lithium iron phosphate cathode material RLFP-8at% undergoing long-cycle testing at a high current density of 5 C. Figure 22 The graph shows a comparison of the 30-cycle performance of batteries made from repaired lithium iron phosphate cathode materials RLFP-8at%, RLFP-5at%, and RLFP-10at% and RLFP-15at%, and RLFP-25at%, respectively, at 0.2 C. Figure 23The graph shows a comparison of the first cycle performance at 0.2 C for batteries made from repaired lithium iron phosphate cathode material RLFP-8at% and repaired lithium iron phosphate cathode material RLFP-inorganic silicon, respectively. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can understand it.

[0024] Example 1 A method for modifying and repairing waste lithium iron phosphate cathode materials with tetrabutyl silicate 1 1. Disassemble the waste lithium iron phosphate soft-pack batteries to obtain waste lithium iron phosphate electrode sheets (capacity decayed to 70~80% of the rated capacity). Cut them into 2.5 cm × 2.5 cm pieces with a weight of 1 g. Use ultrapure water to separate the aluminum foil current collector and waste lithium iron phosphate positive electrode material from the waste lithium iron phosphate electrode sheets for later use.

[0025] 2. The waste lithium iron phosphate cathode material is subjected to five high-frequency ultrasonic treatments at a frequency of 120 kHz and a duration of 10 minutes per treatment. This is to initially remove the small amount of adhesive adsorbed on the surface of the waste lithium iron phosphate cathode material. Then, the waste lithium iron phosphate cathode material is placed in a 70℃ oven for drying.

[0026] 3. The dried 100 mg of waste lithium iron phosphate cathode material was ball-milled into powder using a planetary ball mill. The ball mill jar was an agate ball mill jar with a capacity of 50 ml. The agate ball mill beads had particle sizes of 1 mm and 3 mm, with a ratio of 12:1 between 1 mm and 3 mm agate ball mill beads. The number of 1 mm agate ball mill beads was 12 and the number of 3 mm agate ball mill beads was 1. The ball milling speed was set to 400 rpm and the time was controlled to 4 hours to obtain waste lithium iron phosphate (SLFP) powder.

[0027] 4. Mix 100 mg of waste lithium iron phosphate powder with 19.68 μL of tetrabutyl silicate (TBOS) (the amount of lithium iron phosphate is 0.634 mmol, the amount of TBOS is 0.055 mmol, and the atomic percentage of lithium iron phosphate:TBOS is controlled at 92:8) in 1.2 mL of anhydrous ethanol. Then, ball mill the mixture again in a planetary ball mill for 4 hours to ensure that the TOBS and lithium iron phosphate materials are evenly distributed. The ball milling process is carried out in a planetary ball mill with the same parameters as in step 3 to obtain the mixed material SLFP-T.

[0028] 5. After ball milling, the mixed material SLFP-T is removed and dried in a 70℃ oven. After drying, the mixed material is transferred to a ceramic boat and placed in a muffle furnace. Under air atmosphere, it is heated to 500℃ at a heating rate of 5℃ / min and held at this temperature for 6 hours. Finally, it is naturally cooled to room temperature (25℃) to complete the oxidation treatment of the material, obtaining a mixed oxide including iron(III) oxide, lithium oxide, iron phosphate, and silicon oxide, for later use.

[0029] 6. Take 500 mg of mixed oxide and transfer it to a ball mill jar. At the same time, take 44.75 mg of lithium supplement Li2CO3 and 54.5 mg of carbon source glucose and add them to the ball mill jar. Glucose accounts for 10 wt% as a carbon source for carbon coating. Perform ball milling treatment in a planetary ball mill. The ball mill jar is an agate ball mill jar with a capacity of 50 ml. The particle sizes of the agate grinding beads are 1 mm and 3 mm. The ratio of 1 mm agate grinding beads to 3 mm agate grinding beads is 10:1. The number of 1 mm agate grinding beads is 10 and the number of 3 mm agate grinding beads is 1. The ball milling speed is set to 500 rpm and the time is controlled to 8 hours to obtain a mixed powder sample (particle size of 100~500 nm).

[0030] 7. Take 500 mg of the mixed powder sample and place it in a ceramic boat. Then transfer it to a tube furnace for high-temperature solid-state sintering. The reducing atmosphere is a hydrogen-argon mixture containing 5% hydrogen and 95% argon. At the same time, control the heating rate of the tube furnace to 5℃ / min, raise it from room temperature to 700℃, hold it at that temperature for 10 hours, and then let it cool naturally to obtain the modified repaired lithium iron phosphate cathode material RLFP-8at.

[0031] Example 2 A method for remediating waste lithium iron phosphate cathode materials by modifying with tetrabutyl silicate 2 The method in this embodiment is the same as in Embodiment 1, except that in step 4, 100 mg of waste lithium iron phosphate powder is thoroughly mixed with 11.88 μL of tetrabutyl silicate (the amount of lithium iron phosphate is 0.634 mmol, the amount of TBOS is 0.033 mmol, and the atomic percentage of lithium iron phosphate:TBOS is controlled at 95:5) in 1.2 mL of anhydrous ethanol. This yields the modified repaired lithium iron phosphate cathode material RLFP-5at%.

[0032] Example 3 A method for remediating waste lithium iron phosphate cathode materials by modifying with tetrabutyl silicate 3 The method in this embodiment is the same as in Embodiment 1, except that in step 4, 100 mg of waste lithium iron phosphate powder is thoroughly mixed with 25.10 μL of tetrabutyl silicate (the amount of lithium iron phosphate is 0.634 mmol, the amount of TBOS is 0.704 mmol, and the atomic percentage of lithium iron phosphate:TBOS is controlled at 90:10) in 1.2 mL of anhydrous ethanol. This yields the modified repaired lithium iron phosphate cathode material RLFP-10at%.

[0033] Comparative Example 1 A method for modifying and repairing waste lithium iron phosphate cathode materials D1 The method used in this comparative example is the same as in Example 1, except that step 4 is omitted, and the waste lithium iron phosphate (SLFP) powder is processed in step 5 after step 3. This yields the repaired lithium iron phosphate cathode material SLFP+LCO.

[0034] Comparative Example 2 A method for modifying and repairing waste lithium iron phosphate cathode materials D2 The method for this comparative example is the same as in Example 1, except that in step 4, 100 mg of waste lithium iron phosphate powder and 39.32 μL of tetrabutyl silicate (the amount of lithium iron phosphate is 0.634 mmol, the amount of TBOS is 0.112 mmol, and the atomic percentage of lithium iron phosphate:TBOS is controlled at 85:15) are thoroughly mixed in 1.2 mL of anhydrous ethanol. This yields the modified and repaired lithium iron phosphate cathode material RLFP-15at%.

[0035] Comparative Example 3 A method for modifying and repairing waste lithium iron phosphate cathode materials D3 The method for this comparative example is the same as in Example 1, except that in step 4, 100 mg of waste lithium iron phosphate powder and 55.7 μL of tetrabutyl silicate (the amount of lithium iron phosphate is 0.634 mmol, the amount of TBOS is 0.159 mmol, and the atomic percentage of lithium iron phosphate:TBOS is controlled at 80:20) are thoroughly mixed in 1.2 mL of anhydrous ethanol. This yields the modified repaired lithium iron phosphate cathode material RLFP-20at%.

[0036] Comparative Example 4 A method for modifying and repairing waste lithium iron phosphate cathode materials D4 The method used in this comparative example is the same as in Example 1, except that in step 4, 100 mg of waste lithium iron phosphate powder and 8.7 mg of inorganic silicon source (lithium silicate Li4SiO4) are thoroughly mixed in 1.2 mL of anhydrous ethanol. This yields the modified, repaired lithium iron phosphate cathode material RLFP-inorganic silicon.

[0037] Performance Test 1 1. X-ray diffraction (XRD) analysis was performed on the repaired lithium iron phosphate cathode material RLFP-8at% from Example 1 and the commercial lithium iron phosphate standard card (card number #40-1499).

[0038] 2. The repaired lithium iron phosphate cathode material RLFP-8at% prepared in Example 1 was analyzed by transmission electron microscopy (TEM) and TEM-EDS elemental scanning analysis.

[0039] 3. X-ray photoelectron spectroscopy (XPS) analysis was performed on the repaired lithium iron phosphate cathode material RLFP-8at% from Example 1. The results are as follows: Figures 1-17 As shown.

[0040] (1) Combination Figure 1 As shown, the repaired lithium iron phosphate cathode material RLFP-8at% matches the crystal structure of commercial lithium iron phosphate standard cards, proving that waste lithium iron phosphate can be effectively repaired.

[0041] (2) Combination Figures 2-14 As shown, the crystal structure of the repaired lithium iron phosphate cathode material RLFP-8at% is well-organized, and the lattice spacing in Fourier transform images is 0.192 nm, corresponding to the (302) crystal plane. Figures 2-4 ),and Figures 5-7 The results demonstrate that the lattice spacing uniformity of the repaired lithium iron phosphate cathode material RLFP-8at% has achieved excellent results, indicating that the lattice has been effectively repaired. Energy dispersive spectroscopy elemental analysis confirms the uniform distribution of carbon, iron, phosphorus, and oxygen elements in the repaired lithium iron phosphate cathode material RLFP-8at% (…). Figures 11-14 The elemental distribution of the repaired lithium iron phosphate cathode material RLFP-8at% prepared by this invention is uniform. Figure 9 ), Figure 10 The results confirm the effectiveness of Si doping, and the resulting crystal structure and phase purity meet commercial requirements and commercial standards.

[0042] (3) Combination Figures 15-17 As shown, Fe2p X-ray photoelectron spectroscopy was used to test the valence state changes of Fe on the surface of the repaired lithium iron phosphate cathode material RLFP-8at%: the fitted peak at 709.1 eV represents Fe(II) 2p3 / 2, while the Fe(III) peak was not observed, indicating that the repaired lithium iron phosphate cathode material RLFP-8at% contains abundant Fe. 2+ This indicates that the composition and structure of the waste lithium iron phosphate were restored. Figure 15 The valence state of C was determined by X-ray photoelectron spectroscopy. After repair, the CF bond peak disappeared, while obvious C-C and CO peaks were present. The repair was successful and effective. Figure 16The valence state of Si in the electrode was obtained by X-ray photoelectron spectroscopy. The stable valence state of silicon during charge and discharge not only indicates that Si plays a framework role at the P site during redox processes, but also provides a reliable and non-collapsed transport environment for lithium ions. Figure 17 ).

[0043] (4) Simultaneously through Figure 8 TEM-EDS elemental surface scan results and Figure 17 Si2p X-ray photoelectron spectroscopy confirmed the successful incorporation of Si into the repaired lithium iron phosphate. TEM-EDS elemental surface scanning results showed that Si was uniformly dispersed in LiFePO4, and the Fe, P, and O elements were highly matched with the matrix particle outlines. C achieved complete coating of the active material, demonstrating the material's excellent elemental uniformity and structural integrity. XPS analysis indicated that Fe existed stably in the +2 valence state in the repaired lithium iron phosphate cathode material RLFP-8at%, while Si existed in a coated form. During charge and discharge, a reversible valence state evolution occurred, achieving the electrochemical lithium storage activity of silicon. Simultaneously, the volume expansion of silicon was synergistically suppressed through chemical bonding and carbon coating, preventing structural collapse.

[0044] Example 4 Preparation of repaired lithium iron phosphate positive electrode RLFP-8at%. 1. Take the repaired lithium iron phosphate cathode material RLFP-8at% (active material), Ketjen black (conductive agent) and polyvinylidene fluoride (binder) prepared in Example 1 and put them into the grinding tube in a mass ratio of 8:1:1. Dry grind them three times at 4000 rpm in a portable grinder for 2 minutes each time.

[0045] 2. Add N-methylpyrrolidone and perform wet milling twice, under the same conditions as the dry milling in step 1. The mass-to-volume ratio of the lithium iron phosphate cathode material RLFP-8at% to N-methylpyrrolidone should be 170 mg / mL. Coat the mixed solution evenly onto carbon-coated aluminum foil, controlling the active material loading on each foil to be 2-3 mg / cm³. 2 Then, it was dried in an oven at 70℃ for 10 h to obtain the repaired lithium iron phosphate positive electrode sheet RLFP-8at.

[0046] Example 5 Preparation of repaired lithium iron phosphate positive electrode RLFP-5at%. The preparation method of this embodiment is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material RLFP-5at from Example 2.

[0047] Example 6 Preparation of repaired lithium iron phosphate positive electrode RLFP-10at% The preparation method of this embodiment is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material RLFP-10at of Example 3.

[0048] Comparative Example 5 Preparation of repaired lithium iron phosphate positive electrode SLFP+LCO The preparation method of this comparative example is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material SLFP+LCO of Comparative Example 1.

[0049] Comparative Example 6 Preparation of repaired lithium iron phosphate positive electrode RLFP-15at%. The preparation method of this comparative example is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material RLFP-15at of Comparative Example 2.

[0050] Comparative Example 7 Preparation of repaired lithium iron phosphate positive electrode RLFP-20at% The preparation method of this comparative example is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material RLFP-20at of Comparative Example 3.

[0051] Comparative Example 8 Preparation of repaired lithium iron phosphate positive electrode RLFP-inorganic silicon The preparation method of this comparative example is the same as that of Example 4, except that the active material is the repaired lithium iron phosphate cathode material RLFP-inorganic silicon of Comparative Example 4.

[0052] Example 7 Preparation of Repaired Lithium Iron Phosphate Battery RLFP-8at% The repaired lithium iron phosphate positive electrode RLFP-8at% from Example 4 was cut into positive electrode sheets with a diameter of 10 mm using a punching machine. Lithium sheet was used as the negative electrode material, a 17 mm diameter polypropylene (PP) membrane was used as the separator, and lithium-ion secondary electrolyte LB-002 was used as the electrolyte. CR2016 coin cells were assembled in an argon glove box to obtain the repaired lithium iron phosphate battery RLFP-8at.

[0053] Example 8 Preparation of Repaired Lithium Iron Phosphate Battery RLFP-5at% The preparation method of this embodiment is the same as that of embodiment 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode RLFP-5at from embodiment 5.

[0054] Example 9 Preparation of Repaired Lithium Iron Phosphate Battery RLFP-10at% The preparation method of this embodiment is the same as that of embodiment 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode RLFP-10at of embodiment 6.

[0055] Comparative Example 9 Preparation of repaired lithium iron phosphate battery SLFP+LCO The preparation method of this comparative example is the same as that of Example 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode SLFP+LCO of Comparative Example 5.

[0056] Comparative Example 10 Preparation of Repaired Lithium Iron Phosphate Battery RLFP-15at% The preparation method of this comparative example is the same as that of Example 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode RLFP-15at of Comparative Example 6.

[0057] Comparative Example 11 Preparation of Repaired Lithium Iron Phosphate Battery RLFP-20at% The preparation method of this comparative example is the same as that of Example 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode RLFP-20at of Comparative Example 7.

[0058] Comparative Example 12 Preparation of RLFP-inorganic silicon for repairing lithium iron phosphate batteries The preparation method of this comparative example is the same as that of Example 7, except that the positive electrode is the repaired lithium iron phosphate positive electrode RLFP-inorganic silicon of Comparative Example 8.

[0059] Performance Test 2 The performance of the repaired lithium iron phosphate batteries RLFP-8at%, RLFP-5at%, and RLFP-10at% from Examples 7-9, and the repaired lithium iron phosphate batteries SLFP+LCO, RLFP-15at%, RLFP-20at%, and RLFP-inorganic silicon from Comparative Examples 9-12 were tested in the range of 2.5-4.2 V. The results are as follows: Figures 18-23 And as shown in Table 1.

[0060] Table 1 Performance test of repaired lithium iron phosphate batteries 1. Combination Figures 18-19As shown, the repaired lithium iron phosphate battery RLFP-8at% exhibits a high initial coulombic efficiency of 97.91% and retains a high specific capacity of 146.19 mAh / g after 100 cycles. This demonstrates that the repaired lithium iron phosphate cathode material prepared based on the method of this invention possesses high specific capacity and coulombic efficiency, as well as good capacity retention.

[0061] 2. Combining Figure 20 As shown, the repaired lithium iron phosphate battery RLFP-8at% exhibited average specific capacities of 148.03 mAh / g, 142.39 mAh / g, 135.87 mAh / g, 126.60 mAh / g, and 107.91 mAh / g at current densities of 0.2, 0.5, 1.0, 2.0, and 5.0 C, respectively. Even after switching to a current density of 0.2 C, the capacity still recovered to a high specific capacity of 146.80 mAh / g. This demonstrates that the repaired lithium iron phosphate cathode material prepared based on the method of this invention possesses excellent rate performance and superior reversibility.

[0062] 3. Combining Figure 21 As shown, the repaired lithium iron phosphate battery RLFP-8at% still provides a high specific capacity of 89.51 mAh / g after 500 cycles at a current density of 5 C. This indicates that the repaired lithium iron phosphate cathode material prepared based on the method of this invention has good long-cycle performance.

[0063] 4. Combination Figure 22 As shown, under 0.2C cycling, excessive TBOS doping leads to performance degradation. When the TBOS doping reaches 15 at%, the average charge specific capacity after 30 cycles is only 108.92 mAh / g; when it reaches 20 at%, the average charge specific capacity after 30 cycles is only 75.69 mAh / g. Therefore, controlling the TBOS doping at 8 at% yields the best performance for repairing lithium iron phosphate batteries.

[0064] 5. Combination Figure 23 As shown, the repaired lithium iron phosphate battery RLFP-8at% achieved a specific charge capacity of 153.72 mAh / g in the first cycle, while the repaired lithium iron phosphate battery RLFP-inorganic silicon only achieved 131.38 mAh / g in the first cycle. This is because the organosilicon TBOS has a smaller molecular size, allowing for better bonding with lithium iron phosphate during synthesis. In contrast, the inorganic silicon Li4SiO4 particles are larger and cannot effectively synergize with lithium iron phosphate during synthesis, thus its performance improvement cannot match that of organosilicon.

[0065] 6. As shown in Table 1, the batteries in Examples 1-3 still maintain a high specific capacity after 100 cycles, indicating that the lithium iron phosphate particles repaired by the method of this application have good capacity retention. Comparative Example 1, compared to Examples 1-3, did not add tetrabutyl silicate (TBOS) for modification, but only added Li2CO3 for lithium replenishment repair. Its first-cycle charge capacity, first-cycle discharge capacity, and capacity retention after 100 cycles were significantly lower than those of Examples 1-3, which added tetrabutyl silicate (TBOS). This indicates that the addition of tetrabutyl silicate (TBOS) is beneficial for the regeneration of lithium iron phosphate and the maintenance of its charge and discharge capacity.

[0066] In summary, this invention significantly improves the specific capacity, cycle stability, and rate performance of lithium iron phosphate materials through silicon doping modification, solving the technical problems of low specific capacity and volume expansion failure of traditional lithium iron phosphate materials, and has excellent prospects for industrial application.

[0067] All other parts not described in detail are existing technologies. Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for modifying and repairing waste lithium iron phosphate cathode materials with tetrabutyl silicate, characterized in that: Includes the following steps: (1) The waste lithium iron phosphate cathode material is ultrasonically treated 4 to 5 times and then dried; (2) The dried waste lithium iron phosphate cathode material is ball-milled to obtain waste lithium iron phosphate powder; (3) The waste lithium iron phosphate powder and tetrabutyl silicate are mixed and dissolved in anhydrous ethanol, and then ball-milled again to obtain a mixed material; the mass-volume ratio of the waste lithium iron phosphate powder and tetrabutyl silicate is 1: (0.1188~0.251). (4) The mixed material is dried and transferred to a muffle furnace. Then, under an air atmosphere, it is heated to 450~550℃ and kept at that temperature for oxidation treatment. After cooling, the mixed oxide is obtained. (5) Mix the mixed oxide, lithium carbonate and glucose and ball mill them to obtain a mixed powder sample; the mass ratio of the mixed oxide, lithium carbonate and glucose is 100: (8.5~9.5): (10~12). (6) Under a hydrogen-argon mixed atmosphere, the mixed powder sample was heated to 650~750℃, held at the temperature for high-temperature solid-state sintering, and cooled to obtain the modified repaired lithium iron phosphate cathode material. In steps (2) and (3), the grinding beads used in the ball mill have a particle size of 1 mm and 3 mm, the ratio of 1 mm grinding beads to 3 mm grinding beads is (10~12):1, the rotation speed of the ball mill is 350~450 rpm, and the ball milling time is 3.5~4.5 hours.

2. The method according to claim 1, characterized in that: In step (1), the frequency of ultrasonic treatment is 100~120 kHz, the duration of ultrasonic treatment is 8~12 minutes / time, and the drying temperature is 65~75℃.

3. The method according to claim 2, characterized in that: The ultrasonic treatment frequency is 120 kHz, and the ultrasonic treatment time is 10 minutes per cycle; the drying temperature is 70℃. The ratio of 1 mm grinding beads to 3 mm grinding beads is 12:1, the ball milling speed is 400 rpm, and the ball milling time is 4 hours; The mass-to-volume ratio of the waste lithium iron phosphate powder to tetrabutyl silicate is 1:0.1968.

4. The method according to claim 1, characterized in that: In step (4), the heating rate is 4~5℃ / min, and the oxidation treatment time is 5.5~6.5 hours; In step (5), the grinding beads used in the ball mill have a particle size of 1 mm and 3 mm, the ratio of 1 mm grinding beads to 3 mm grinding beads is (10~12):1, the ball milling speed is 500~600 rpm, and the ball milling time is 7.5~8.5 hours; the particle size of the mixed powder sample is 100~500 nm. In step (6), the hydrogen-argon mixed atmosphere consists of 5% hydrogen and 95% argon, the heating rate is 4~5℃ / min, and the high-temperature solid-phase sintering time is 9~11 hours.

5. The method according to claim 4, characterized in that: In step (4), the temperature is raised to 500°C at a rate of 5°C / min, and the oxidation treatment time is 6 hours. In step (5), the ratio of 1 mm grinding beads to 3 mm grinding beads is 10:1, the ball milling speed is 500 rpm, and the ball milling time is 8 hours; the mass ratio of the mixed oxide, lithium carbonate, and glucose is 100:8.95:10.

9. In step (6), the temperature is raised to 700°C at a rate of 5°C / min, and the high-temperature solid-phase sintering time is 10 hours.

6. A repaired lithium iron phosphate cathode material obtained by the method according to any one of claims 1 to 5.

7. The application of the repaired lithium iron phosphate cathode material as described in claim 6 in the preparation of lithium iron phosphate batteries.

8. A method for repairing lithium iron phosphate positive electrode sheets, characterized in that: The repaired lithium iron phosphate cathode sheet comprises the repaired lithium iron phosphate cathode material as described in claim 6.

9. A method for repairing lithium iron phosphate batteries, characterized in that: The repaired lithium iron phosphate battery includes the repaired lithium iron phosphate positive electrode sheet as described in claim 8.

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