Method for electrochemically assisted delithiation assisted failure lithium iron phosphate direct regeneration
By combining electrochemical pre-delithiation with solid-phase lithium replenishment, the problem of uneven lithium ratio during the regeneration of spent lithium iron phosphate batteries with different failure levels was solved, achieving efficient and safe large-scale regeneration and improving material performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU UNIV
- Filing Date
- 2026-02-27
- Publication Date
- 2026-06-05
Smart Images
Figure CN122158778A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of waste battery recycling technology, specifically to a method for the direct regeneration of failed lithium iron phosphate batteries assisted by electrochemical delithiation. Background Technology
[0002] The application of lithium-ion batteries continues to grow, with lithium iron phosphate (LFP) batteries gaining a significant market share in energy storage and electric vehicles due to their advantages of low cost, high safety, and long cycle life. Given the 5-9 year lifespan of lithium-ion batteries, the recycling of used lithium batteries is particularly important. Efficiently recycling these used batteries is not only crucial for the recycling of resources such as lithium, iron, and phosphorus, but also plays a vital role in reducing the environmental damage caused by mining and lowering carbon emissions.
[0003] While current mainstream pyrometallurgical and hydrometallurgical recycling technologies can process batteries containing precious metals such as cobalt and nickel, they face challenges with LFP batteries, which have lower economic value. Pyrometallurgical processes rely on high-temperature smelting at 800-1500℃ to extract metals, generating large amounts of CO2 and sulfur and nitrogen oxides. Hydrometallurgical processes, although achieving high metal recovery rates, require strong acid leaching and complex separation processes, resulting in processing costs as high as 80% of those for virgin material production. In contrast, direct regeneration technology directly restores the performance of cathode materials through physicochemical repair, without the need for high-temperature decomposition or corrosive reagents. This can reduce energy consumption by 40%-60% and carbon emissions by more than 70%, making it the optimal solution for LFP battery recycling.
[0004] The core of direct regeneration technology lies in precisely repairing the structural defects of LFP materials. Long-term recycling leads to an increase in lithium vacancy defects in the material. Solid-phase lithium replenishment, by mixing and calcining the failed material with lithium carbonate (Li₂CO₃) or lithium hydroxide (LiOH), can repair these lithium vacancy defects. It is important to note that the amount of lithium salt added in this method must be precisely matched to the lithium vacancy concentration in the material. A small amount of lithium cannot completely repair the lithium vacancy defects, while excessive lithium will increase the alkalinity of the material surface, cause gelation of the battery slurry, and degrade performance.
[0005] However, the differential degradation of batteries has become a bottleneck for the industrial application of this technology. Even for the same battery pack, the lithium loss of different cell cathode materials can vary by as much as 15-30 mol%. During large-scale batch processing, it is difficult to ensure uniform diffusion of lithium ions, which can easily lead to uneven local lithium replenishment or lithium residue, resulting in poor performance of the repair materials. Summary of the Invention
[0006] This invention addresses the shortcomings of existing technologies by providing a method for the direct regeneration of failed lithium iron phosphate batteries assisted by electrochemical delithiation. It combines pre-delithiation with solid-phase lithium replenishment, pre-uniforming the lithium deficiency of spent lithium iron phosphate batteries with varying degrees of failure through an electrochemical charging process. Further, through standardized lithium allocation and high-temperature calcination, large-scale direct regeneration of spent lithium iron phosphate is achieved. This solves the bottleneck and challenge of current solid-phase regeneration methods, which struggle to accurately allocate lithium for batteries with different failure levels to achieve large-scale regeneration, thus promoting the industrialization of this technology.
[0007] To address the aforementioned technical problems, the first aspect of this invention provides a method for the direct regeneration of electrochemically delithiated lithium iron phosphate, comprising the following steps:
[0008] S1. Precharge waste lithium iron phosphate batteries with different failure levels, and unify the lithium deficiency on the positive electrode side by controlling the charging rate and cutoff voltage.
[0009] S2. Disassemble and process the waste lithium iron phosphate battery to obtain positive electrode material with consistent lithium deficiency, and then test and evaluate the lithium iron ratio of the positive electrode material.
[0010] S3. According to the target lithium-iron ratio, the cathode material is mixed with lithium salt and then calcined under a protective atmosphere to obtain a regenerated lithium battery cathode material.
[0011] This invention pre-charges the batteries before repairing the failed lithium iron phosphate cathode material, standardizing the lithium deficiency at the cathode of lithium iron phosphate batteries with different degrees of failure. These batteries are then mixed with an external lithium source for solid-phase regeneration. Since different spent lithium iron phosphate batteries exhibit varying degrees of capacity loss, the corresponding lithium deficiency in the cathode material varies significantly. Repairing and regenerating these batteries requires quantifying the lithium deficiency of each battery and precisely matching the amount of external lithium source, which greatly increases the challenge of industrializing solid-phase regeneration methods.
[0012] In this invention, the more lithium vacancies in LFP, the lower the reset barrier of the reverse Fe. This indicates that controlling the lithium content of the cathode material by voltage is positively correlated with the performance of the repair result; that is, the higher the charging voltage, the more lithium vacancies in the degraded material, and the better the repair performance of the cathode material.
[0013] This invention's pre-charge treatment can delithiate the positive electrode material under the influence of an electric field. By controlling the cutoff voltage, the lithium deficiency of lithium iron phosphate with different degrees of failure can be controlled at a uniform level. After further lithium source matching and high-temperature annealing, large-scale direct regeneration of waste lithium iron phosphate can be achieved.
[0014] Furthermore, in S1, the charging rate is 0.1-0.5C, and the cutoff voltage is 3.5-5V, preferably 3.8-4.4V. If the rate is too low, it will not affect delithiation, but it will lead to excessively long charging time and low efficiency; while if the rate is too high, lithium ions cannot be completely delithiated from the positive electrode, and due to impedance effects, it is impossible to achieve a uniform amount of lithium deficiency in positive electrode materials with different degrees of failure. Similarly, if the voltage is too low, lithium ions cannot be completely delithiated; if the voltage is too high, it will lead to excessive delithiation of the material, structural collapse, and subsequent irreparable damage, and the electrolyte will decompose, causing safety hazards.
[0015] Furthermore, waste lithium batteries are not limited to waste lithium iron phosphate batteries, but can also include waste lithium nickel cobalt manganese oxide batteries and lithium manganese oxide batteries.
[0016] Furthermore, in S3, the target lithium-iron ratio is 1-1.06. A low lithium content cannot compensate for lithium volatilization during high-temperature calcination; while an excessively high lithium content leads to increased alkalinity of the recycled material, affecting the uniformity of the slurry and reducing battery performance.
[0017] Furthermore, in S3, the lithium salt is selected from lithium carbonate and / or lithium hydroxide.
[0018] Furthermore, in S3, the calcination temperature is 600-800℃, preferably 650-750℃. If the temperature is too low, lithium ion diffusion is slow, and lithium replenishment cannot be completed in a short time; if the temperature is too high, the particles will agglomerate, resulting in poor electrochemical performance of the material.
[0019] Furthermore, in S3, the calcination treatment time is 3-6 hours.
[0020] Furthermore, in S3, the protective atmosphere is nitrogen and / or argon.
[0021] Furthermore, in S2, the disassembly process specifically involves: disassembling the battery to obtain a positive electrode sheet, immersing the positive electrode sheet in NMP for treatment, scraping off the positive electrode powder, and then cleaning and drying it.
[0022] Furthermore, in S2, the immersion treatment is carried out at a temperature of 70-90°C for 3-6 hours.
[0023] Furthermore, in S2, the drying conditions are: vacuum drying at 110-130°C.
[0024] The beneficial effects of this invention are:
[0025] This invention first pre-charges spent lithium iron phosphate batteries. By controlling the charging rate and cutoff voltage during the charging process, the lithium deficiency of lithium iron phosphate battery materials with different degrees of failure is unified. This provides feasibility for the unified lithium matching of cathode materials of spent lithium iron phosphate batteries and large-scale direct regeneration, solving the challenge of existing solid-phase technology that requires precise lithium matching for cathode materials with different degrees of lithium deficiency.
[0026] The method of this invention is simple to operate, has a short cycle, and low energy consumption. The corresponding recycled battery materials obtained, after being reassembled into full cells, exhibit electrochemical performance comparable to that of full cells assembled with commercial electrode materials, and have universality, which can further promote the industrialization of this technology. Attached Figure Description
[0027] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0028] Figure 1 The XRD patterns of lithium iron phosphate after delithiation at different magnification rates in Examples 1, 1, and 2 of the present invention are shown.
[0029] Figure 2 These are XRD patterns of lithium iron phosphate after delithiation at different cutoff voltages in Examples 1, 2, and 3 of the present invention.
[0030] Figure 3 These are optical photographs of the lithium iron phosphate electrode of the 80% degraded battery in Example 1 and the ICP test results of different regions before and after delithiation.
[0031] Figure 4 These are the ICP results of the 50%, 65%, and 80% degraded materials in Example 1 before and after electrochemical delithiation;
[0032] Figure 5 These are charge / discharge test diagrams of the lithium iron phosphate assembled batteries in Example 1 and Comparative Examples 9-10.
[0033] Figure 6 This is a long-cycle test diagram of the battery assembled with the recycled lithium iron phosphate cathode material in Example 1. Detailed Implementation
[0034] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0035] This embodiment relates to a method for the direct regeneration of electrochemically delithiated lithium iron phosphate, comprising the following steps:
[0036] S1. Precharge waste lithium iron phosphate batteries with different failure levels, and unify the lithium deficiency on the positive electrode side by controlling the charging rate and cutoff voltage.
[0037] S2. Disassemble and process the waste lithium iron phosphate battery to obtain positive electrode material with consistent lithium deficiency, and then test and evaluate the lithium iron ratio of the positive electrode material.
[0038] S3. According to the target lithium-iron ratio, the cathode material is mixed with lithium salt and then calcined under a protective atmosphere to obtain a regenerated lithium battery cathode material.
[0039] This embodiment pre-charges the batteries before repairing the failed lithium iron phosphate (LFP) cathode material, standardizing the lithium deficiency at the cathode of LFP batteries with different failure levels. These batteries are then mixed with an external lithium source for solid-phase regeneration. Since different spent LFP batteries exhibit varying degrees of capacity loss, the corresponding lithium deficiency in the cathode material varies significantly. Repairing and regenerating these batteries requires quantifying the lithium deficiency of each battery and precisely matching the amount of external lithium source, greatly increasing the challenge for industrial-scale solid-phase regeneration. The results from the embodiment and comparative examples show that the more lithium vacancies in LFP, the lower the reset barrier of the anti-Fe. This indicates a positive correlation between voltage-controlled lithium content in the cathode material and the repair performance; that is, the higher the charging voltage, the more lithium vacancies in the degraded material, and the better the repair performance of the cathode material. This embodiment uses pre-charging treatment, which delithiates the cathode material under an electric field. By controlling the cutoff voltage, the lithium deficiency of LFP batteries with different failure levels can be controlled at a uniform level. Through further unified lithium source matching and high-temperature annealing treatment, large-scale direct regeneration of waste lithium iron phosphate batteries can be achieved. The waste lithium batteries are not limited to waste lithium iron phosphate batteries, but can also include waste nickel-cobalt-manganese lithium batteries and manganese lithium batteries.
[0040] In a preferred embodiment, in S1, the charging rate is 0.1-0.5C, and the cutoff voltage is 3.5-5V, preferably 3.8-4.4V. A lower charging rate will not affect delithiation, but will result in excessively long charging time and low efficiency. Conversely, a higher charging rate will prevent lithium ions from completely removing from the positive electrode, and due to impedance effects, it will be impossible to achieve a uniform amount of lithium deficiency in positive electrode materials with different failure levels. Similarly, a lower voltage will prevent complete delithiation of lithium ions, while a higher voltage will lead to excessive delithiation of the material, structural collapse that cannot be repaired, and electrolyte decomposition, posing a safety hazard.
[0041] In a preferred embodiment, in S3, the target lithium-iron ratio is 1-1.06. A low lithium content cannot compensate for lithium volatilization during high-temperature calcination; while an excessively high lithium content leads to increased alkalinity of the recycled material, affecting the uniformity of the slurry and reducing battery performance. The lithium salt is selected from lithium carbonate and / or lithium hydroxide. The calcination temperature is 600-800℃, preferably 650-750℃. If the temperature is too low, lithium ion diffusion is slow, making it impossible to complete lithium replenishment in a short time; if the temperature is too high, particles will agglomerate, resulting in poor electrochemical performance of the material. The calcination time is 3-6 hours; the protective atmosphere is nitrogen and / or argon.
[0042] In a preferred embodiment, in S2, the disassembly process specifically involves: disassembling the battery to obtain a positive electrode sheet, immersing the positive electrode sheet in NMP for treatment, scraping off the positive electrode powder, and then cleaning and drying it; the immersion treatment temperature is 70-90℃ and the time is 3-6h; the drying conditions are: vacuum drying at 110-130℃.
[0043] Example 1
[0044] This embodiment relates to a method for the direct regeneration of electrochemically delithiated lithium iron phosphate, comprising the following steps:
[0045] (1) The battery was electrochemically cycled at a rate of 1 C, and the capacity was reduced to 40%, 60% and 80%, respectively.
[0046] (2) Charge the battery from step (1) at a rate of 0.1 C, with a cutoff voltage of 3.8 V.
[0047] (3) Disassemble the battery in step (2), separate the positive electrode sheet, immerse it in NMP (N-methylpyrrolidone), stir at 80°C for 4 h, scrape off the positive electrode powder, wash it repeatedly with NMP 3 times, and dry it overnight at 120°C in a vacuum oven to obtain the failed lithium iron phosphate positive electrode material.
[0048] (4) Take the pre-delithiation cathode material from step (3) and perform acid leaching, measure ICP, and evaluate the lithium iron ratio of the three failed battery cathode materials after pre-discharge. The results show that the lithium iron ratio of the three cathode materials is consistent (the lithium iron ratio of only one cathode material needs to be tested in subsequent Examples 1-6 and Comparative Examples 1-8).
[0049] (5) The pre-delithiation cathode material obtained in step (3) is mixed and then mixed with lithium carbonate. The lithium-iron ratio of the mixed material is 1.04.
[0050] (6) The mixture obtained in step (5) is subjected to high-temperature annealing at 650 °C under a nitrogen atmosphere for 4 h to obtain the regenerated lithium iron phosphate cathode material.
[0051] Example 2
[0052] The difference between this embodiment and Embodiment 1 is that the cutoff voltage is 4.4V, while the other steps and parameters remain unchanged.
[0053] Example 3
[0054] The difference between this embodiment and Embodiment 1 is that the high-temperature annealing temperature is 750°C, while other steps and parameters remain unchanged.
[0055] Example 4
[0056] The difference between this embodiment and Embodiment 1 is that the high-temperature annealing time is 6 hours, while other steps and parameters remain unchanged.
[0057] Example 5
[0058] The difference between this embodiment and embodiment 1 is that the lithium-iron ratio of the mixed material in step (5) is 1.06, while the other steps and parameters remain unchanged.
[0059] Example 6
[0060] The difference between this embodiment and embodiment 1 is that the lithium-iron ratio of the mixed material in step (5) is 1.0, while the other steps and parameters remain unchanged.
[0061] Comparative Example 1
[0062] The difference between this comparative example and Example 1 is that the charging rate in step (2) is 1C, while the other steps and parameters remain unchanged.
[0063] Comparative Example 2
[0064] The difference between this comparative example and Example 1 is that the charging rate in step (2) is 3C, while the other steps and parameters remain unchanged.
[0065] Comparative Example 3
[0066] The difference between this comparative example and Example 1 is that the charging cutoff voltage in step (2) is 3.38V, while the other steps and parameters remain unchanged.
[0067] Comparative Example 4
[0068] The difference between this comparative example and Example 1 is that the high-temperature annealing temperature in step (6) is 850°C, while the other steps and parameters remain unchanged.
[0069] Comparative Example 5
[0070] The difference between this comparative example and Example 1 is that the high-temperature annealing temperature in step (6) is 550°C, while the other steps and parameters remain unchanged.
[0071] Comparative Example 6
[0072] The difference between this comparative example and Example 1 is that the high-temperature annealing time in step (6) is 2 hours, while the other steps and parameters remain unchanged.
[0073] Comparative Example 7
[0074] The difference between this comparative example and Example 1 is that the lithium-iron ratio of the mixed material in step (5) is 0.98, while the other steps and parameters remain unchanged.
[0075] Comparative Example 8
[0076] The difference between this comparative example and Example 1 is that the lithium-iron ratio of the mixed material in step (5) is 1.08, while the other steps and parameters remain unchanged.
[0077] Comparative Example 9
[0078] The difference between this comparative example and Example 1 is that step (2) of charging and delithiation is omitted. Instead, the different batteries in step (1) are directly disassembled to obtain positive electrode materials, which are then mixed and directly regenerated with lithium to obtain lithium iron phosphate.
[0079] Comparative Example 10
[0080] Commercial lithium iron phosphate.
[0081] Test case
[0082] The parameters of Examples 1-6 and Comparative Examples 1-8, the Li / Fe ratio after electrochemical delithiation, and the initial specific capacity of the recycled material are shown in Table 1.
[0083] Table 1
[0084] Group Precharge rate (C) Precharge cutoff voltage (V) Li / Fe ratio after electrochemical delithiation <![CDATA[Calcination temperature ( o °C)]]> Sintering time (h) Lithium supplementation (Li / Fe) Initial specific capacity of recycled materials (mAh / g) Example 1 0.1 3.8 0.10 650 4 1.04 158.24 Example 2 0.1 4.4 0.09 650 4 1.04 158.38 Example 3 0.1 3.8 0.09 750 4 1.04 157.11 Example 4 0.1 3.8 0.10 650 6 1.04 159.46 Example 5 0.1 3.8 0.08 650 4 1.06 158.20 Example 6 0.1 3.8 0.09 650 4 1.00 157.89 Comparative Example 1 1 3.8 0.21 650 4 1.04 149.10 Comparative Example 2 3 3.8 0.30 650 4 1.04 145.81 Comparative Example 3 0.1 3.38 0.53 650 4 1.04 148.2 Comparative Example 4 0.1 3.8 0.09 850 4 1.04 145.9 Comparative Example 5 0.1 3.8 0.07 550 4 1.04 149.2 Comparative Example 6 0.1 3.8 0.08 650 2 1.04 151.2 Comparative Example 7 0.1 3.8 0.08 650 4 0.98 150.4 Comparative Example 8 0.1 3.8 0.10 650 4 1.08 149.0
[0085] As shown in Table 1, after electrochemical pre-charging, lithium ions in the cathode material can be effectively removed. Referring to Examples 1, 1-2, 1-2, and 3, the lower the rate (0.1 C) and the higher the voltage (above 3.8 V), the more significant the lithium removal effect. However, too low a rate leads to long charging time and low processing efficiency, while too high a voltage causes electrode liquid decomposition, battery swelling, and safety hazards. Referring to Examples 1 and 4-5, too low a calcination temperature results in slow lithium ion diffusion, making it impossible to complete the repair of lithium vacancy defects within the set time. Too high a calcination temperature leads to particle agglomeration and decreased electrochemical performance. Referring to Examples 1, 6, 1, and 7-8, insufficient calcination time and lithium replenishment outside the optimized range defined in this patent both result in poor electrical performance.
[0086] Figure 1 The XRD patterns of lithium iron phosphate after delithiation at different magnification rates are shown for Examples 1, 1, and 2. In Example 1, the low magnification rate of 0.1 C can achieve complete conversion of the lithium iron phosphate phase to iron phosphate; while in Comparative Examples 1 and 2, the higher magnification rates of 1 C and 3 C cannot achieve complete lithium extraction.
[0087] Figure 2 XRD patterns of lithium iron phosphate after delithiation at different cutoff voltages in Examples 1, 2, and 3 are shown. In Examples 1 and 2, cutoff voltages of 3.8 V and 4.4 V achieved complete conversion from lithium iron phosphate to iron phosphate; however, in Comparative Example 3, the lower voltage of 3.38 V failed to achieve complete lithium extraction. Considering safety factors, the optimal charging cutoff voltage is 3.8 V.
[0088] Figure 3 These are optical photographs of the lithium iron phosphate (LFP) electrode of the 80% degraded battery in Example 1, along with ICP test results for different regions before and after delithiation. Before delithiation, LFP had a high lithium-iron ratio. After delithiation under 0.1 C-3.8 V conditions, the LFP-3.8V material had a uniform lithium content of approximately Li / Fe = 0.1.
[0089] Figure 4 These are the ICP results for the 50%, 65%, and 80% degraded materials in Example 1 before and after electrochemical delithiation. This indicates that the materials from batteries with different degrees of degradation, after lithium extraction under 0.1 C-3.8 V conditions, have similar lithium contents, with Li / Fe = 0.1. This provides a guarantee for the direct regeneration of directly mixed materials.
[0090] Figure 5The figures show the charge-discharge test results of lithium iron phosphate assembled batteries in Example 1 and Comparative Examples 9-10. It can be seen that the material in Example 1, which underwent pre-charging treatment, has more uniformly dispersed lithium vacancy defects, more complete repair, and better cycle stability, approaching that of commercial lithium iron phosphate. In contrast, the material in Comparative Example 9, which was directly lithium-ionized without charging and delithiation, has poorer performance.
[0091] Figure 6 The image shows a long-cycle test of a battery assembled using the recycled lithium iron phosphate cathode material from Example 1, demonstrating its excellent cycle stability.
[0092] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.
Claims
1. A method for direct regeneration of degraded lithium iron phosphate assisted by electrochemical delithiation, characterized in that, Includes the following steps: S1. Precharge waste lithium iron phosphate batteries with different failure levels, and unify the lithium deficiency on the positive electrode side by controlling the charging rate and cutoff voltage. S2. Disassemble and process the waste lithium iron phosphate battery to obtain positive electrode material with consistent lithium deficiency, and then test and evaluate the lithium iron ratio of the positive electrode material. S3. According to the target lithium-iron ratio, the cathode material is mixed with lithium salt and then calcined under a protective atmosphere to obtain a regenerated lithium battery cathode material.
2. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S1, the charging rate is 0.1-0.5C and the cutoff voltage is 3.5-5V.
3. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S3, the target value for the lithium-iron ratio is 1-1.
06.
4. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S3, the lithium salt is selected from lithium carbonate and / or lithium hydroxide.
5. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S3, the calcination temperature is 600-800℃.
6. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S3, the calcination treatment time is 3-6 hours.
7. The method for direct regeneration of degraded lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S3, the protective atmosphere is nitrogen and / or argon.
8. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 1, characterized in that, In S2, the disassembly process specifically involves: disassembling the battery to obtain a positive electrode sheet, immersing the positive electrode sheet in NMP for treatment, scraping off the positive electrode powder, and then cleaning and drying it.
9. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 8, characterized in that, In S2, the immersion treatment is carried out at a temperature of 70-90°C for 3-6 hours.
10. The method for direct regeneration of failed lithium iron phosphate assisted by electrochemical delithiation as described in claim 8, characterized in that, In S2, the drying conditions are: vacuum drying at 110-130℃.