A ternary positive electrode material based on citric acid-assisted hydrothermal low-temperature lithium supplementing and a preparation method and application thereof

Abstract

The application discloses a kind of based on citric acid auxiliary hydrothermal low-temperature lithium supplement ternary positive electrode material and its preparation method and application, belong to lithium ion battery electrode material technical field.The method with the preprocessed waste NCM material as precursor, through ICP accurate quantitative analysis, using lithium citrate complex solution is hydrothermal lithium supplement, then after processing and high temperature annealing, prepared regenerated ternary positive electrode material.The method is simple, green and environmentally friendly, realizes the high-value recycling of waste battery material.Through citric acid complexation and low-temperature hydrothermal coordination strategy, the crystal defects and lithium deficiency of the material are integrated repaired, the obtained material has complete layered structure, stable interface, excellent electrochemical performance, the capacity retention rate is higher than 84% after 70 cycles at 1C rate, significantly better than the un-repaired material, has the potential for large-scale application in power battery and energy storage field.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, and particularly relates to a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment, its preparation method and application. Background Technology

[0002] Ternary nickel-cobalt-manganese oxides (NCMs) are considered highly promising cathode materials for lithium-ion batteries due to their high specific capacity, excellent rate performance, and long cycle stability. However, their large-scale application still faces challenges due to the irreversible phase transition from layered to spinel to rock salt phase during cycling. The structural stability of the cathode material is a key factor determining battery life and capacity retention.

[0003] Currently, commercially available NCM materials commonly suffer from lattice distortion, surface lithium plating, and inert NiO formation during long-term cycling, leading not only to rapid capacity decay but also a significant decrease in safety and stability at high voltages. Lithium replenishment technology has attracted considerable attention due to its ability to reconstruct crystal structures and improve cycle life. However, conventional lithium replenishment methods often suffer from difficulties in precisely controlling the amount of lithium replenished, insufficient reaction uniformity, poor interface stability, or complex and demanding processes, making it difficult to meet the requirements of high-performance power batteries.

[0004] Therefore, developing a low-cost, green regeneration method that can effectively repair crystal defects, suppress phase transitions, and improve structural stability is an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment, its preparation method, and its applications. The preparation method of this invention offers controllable and reproducible processes; the crystal morphology and electrochemical performance of the material can be precisely controlled by adjusting the lithium replenishment system ratio and annealing parameters. The prepared material exhibits excellent cycle stability, high specific capacity, and structural integrity, making it particularly suitable for use in power lithium-ion batteries and energy storage batteries, meeting the requirements of new energy vehicles and grid energy storage for long battery life, high safety, high rate capability, and low cost.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment includes the following steps: Using pretreated waste NCM material as a precursor, the ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment was obtained through ICP quantitative analysis, citric acid complexation lithium replenishment, hydrothermal reaction, post-treatment and annealing. The citric acid complex lithium supplementation uses a lithium citrate complex solution (Li2HCit solution), which is obtained by complexing citric acid and lithium hydroxide (LiOH·H2O) in a molar ratio of 1:1-2.5.

[0007] Optionally, the molar ratio of citric acid to lithium hydroxide (LiOH·H2O) is 1:1, 1:1.5, 1:2, or 1:2.5.

[0008] Optionally, the pretreatment process is as follows: the waste NCM material is soaked in DME (dimethyl ether) solution to remove the electrolyte, cut into pieces and then soaked in NMP (methylpyrrolidone) solution, followed by washing, drying and heat treatment to obtain the precursor.

[0009] Furthermore, the heat treatment temperature is 350-500℃, the holding time is 3-5 h, and the atmosphere is air or an inert atmosphere.

[0010] Optionally, the Li / NCM molar ratio in the precursor is 0.2:1; NCM consists of three transition metal elements: nickel (Ni), cobalt (Co), and manganese (Mn).

[0011] Optionally, the concentration of the lithium citrate complex solution is 1 mol / L.

[0012] Optionally, the hydrothermal reaction is carried out at a temperature of 100°C for 6 hours.

[0013] Optionally, the post-treatment and annealing steps are as follows: the hydrothermal product is washed alternately with deionized water and anhydrous ethanol, dried, mixed and ground with lithium compensator, and annealed under an inert atmosphere.

[0014] Furthermore, the drying temperature is 100-120℃, and the time is 3-5 hours; The lithium compensator is Li2CO3, and the addition amount is 5% mol equivalent; The annealing temperature was 850°C and the time was 4 hours.

[0015] A ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment prepared according to the above preparation method.

[0016] Optionally, the ternary cathode material retains more than 84% of its capacity after 70 cycles at 1C.

[0017] The above-mentioned ternary cathode materials are used in power batteries, energy storage batteries or consumer electronic devices.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: (1) The ternary cathode material preparation method based on citric acid-assisted lithium replenishment provided by this invention is simple, low-cost, and environmentally friendly. This invention uses waste or low-performance NCM as raw material to achieve the recycling and high-value utilization of battery materials, significantly reducing the production cost of cathode materials, while reducing resource waste and environmental pollution. Through the synergistic strategy of citric acid complexation, precise ICP quantification, hydrothermal lithium replenishment, and high-temperature annealing, the integrated repair of material defects, phase transitions, and lithium deficiency problems is achieved. The reaction conditions are mild, easy to repeat, and can be scaled up, which is in line with the concept of sustainable development.

[0019] (2) The lithium-supplemented ternary cathode material prepared by this invention has excellent structural and electrochemical characteristics, providing a material basis for high-performance lithium-ion batteries. Through precise lithium control and annealing reconstruction, the material has a complete layered structure, no impurities, stable interface, and unobstructed lithium-ion conduction channels, effectively suppressing phase transitions and volume effects during cycling. Citric acid complexation coating can reduce side reactions and improve interfacial conductivity, enabling the material to have both high specific capacity, long cycle life, and excellent rate performance.

[0020] (3) The lithium-ion battery prepared by this invention exhibits excellent electrochemical performance and cycle stability. The half-cell assembled based on this material retains more than 84% of its capacity after more than 70 cycles at 1C rate, with a coulombic efficiency close to 100%. Under high voltage platform, the structure does not collapse and the capacity does not drop sharply, and the performance is significantly better than unrepaired waste NCM and conventional lithium replenishment materials. At the same time, the repair process is simple and the regeneration cost is low, which gives it strong market competitiveness and application potential in the fields of power battery cascade utilization and low-cost manufacturing of energy storage batteries. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 shows the cycle performance curve of the lithium-ion half-cell prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment ternary cathode material (ZS-NCM).

[0022] Figure 2 shows the first charge-discharge specific capacity curve of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment at 0.5C rate.

[0023] Figure 3 shows the rate performance curve of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment.

[0024] Figure 4 shows a scanning electron microscope (SEM) image of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment.

[0025] Figure 5 shows the refined X-ray diffraction (XRD) pattern of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] This invention discloses a method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment, the steps of which include: Using waste or low-performance NCM materials as precursors, a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium supplementation is obtained through pretreatment separation, ICP quantitative analysis, citric acid complexation lithium supplementation, hydrothermal reaction, post-treatment and annealing.

[0032] In some optional embodiments, the pretreatment step includes: immersing the positive electrode material with aluminum foil in a DME (dimethyl ether) solution for 12 hours to remove the electrolyte, cutting it into small pieces, immersing it in an NMP (methylpyrrolidone) solution at 80°C for 0.5 hours, then washing and drying it; heating the dried sample in a tube furnace at a heat treatment temperature of 350-500°C for 3-5 hours in an air or inert atmosphere.

[0033] Pretreatment is a crucial step in removing impurities and restoring material activity. Temperatures that are too low (<350℃) will result in incomplete removal of binders and conductive agents, and residual organic matter will carbonize and cover active sites in subsequent reactions, directly affecting lithium replenishment and material conductivity. Temperatures that are too high (>500℃) may lead to lattice oxygen loss, layered structure collapse, or even excessive oxidation and the formation of impurity phases in the NCM material, significantly reducing its electrochemical performance. This invention, by controlling heat treatment at 350-500℃, effectively removes residual PVDF, conductive carbon black, and other impurities while preserving the original layered framework structure of the material to the greatest extent possible, providing an ideal precursor structure for subsequent lithium replenishment and repair.

[0034] In some optional embodiments, the ICP quantitative analysis step includes: digesting the NCM material with aqua regia at high temperature in a digestion vessel, diluting it with dilute nitric acid, and then performing ICP elemental analysis to determine the contents of Li, Ni, Co, and Mn and calculate the Li / NCM ratio; The aqua regia was prepared by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1, and the digestion temperature was 160℃; the Li / NCM molar ratio was measured to be 0.2:1.

[0035] This invention introduces ICP precise quantitative technology, which can accurately determine the degree of lithium deficiency inside the material, providing precise data support for subsequent lithium replenishment. Severe lithium deficiency will lead to intensified phase transitions and rapid capacity decay during cycling, while excessive lithium replenishment will trigger side reactions, generate impurity phases, and reduce cycling stability. Therefore, precise quantitative measurement is the core key to achieving efficient, uniform, and controllable lithium replenishment and repair.

[0036] In some alternative embodiments, the citric acid complexation lithium supplementation step includes: preparing a lithium citrate solution by mixing citric acid with LiOH·H2O in a certain proportion and adjusting the pH to acidic.

[0037] Furthermore, the concentration of the Li2HCit solution was 1 mol / L, and the molar ratio of citric acid to LiOH·H2O was 1:2.

[0038] Citric acid, as an acidic substance, can selectively dissolve the rock salt phase NiO on the surface of ternary cathode materials without reacting with the materials themselves. The presence of the NiO impurity phase increases the energy barrier for lithium replenishment, blocking the lithium replenishment pathway. Eliminating the surface NiO impurity phase not only improves the lithium-ion diffusion coefficient but also creates more oxygen vacancies.

[0039] In some alternative embodiments, the hydrothermal reaction step includes: stirring the NCM precursor with the above mixture, adding a 4 mol / L lithium hydroxide aqueous solution, transferring it into a hydrothermal reactor for hydrothermal reaction, and then naturally cooling.

[0040] Furthermore, the hydrothermal temperature was 100℃, the time was 6h, the volume of the reaction liquid did not exceed 2 / 3 of the reactor volume, and the concentration of LiOH in the system was 4mol / L.

[0041] Under hydrothermal conditions at 100℃, lithium ions can slowly and uniformly embed into the lattice defects of the material, effectively repairing oxygen vacancies and phase transition damage areas, while not destroying the original layered structure of the material. This lays a stable foundation for subsequent high-temperature annealing and crystallization, significantly improving the structural integrity and electrochemical reversibility of the material.

[0042] In some alternative embodiments, the post-processing and annealing steps include: washing the hydrothermal product alternately with deionized water and anhydrous ethanol, drying it, mixing and grinding it with a lithium compensator, annealing it at high temperature in an inert atmosphere, and then naturally cooling it.

[0043] Furthermore, the washing process alternates between deionized water and anhydrous ethanol, washing 5 times until the pH of the supernatant reaches 10; the drying temperature is 100-120℃, and the time is 3-5 hours; the lithium compensator is Li2CO3, and the addition amount is 5% mol equivalent (i.e., the amount of lithium carbonate added is 5% of the amount of the ternary cathode material (untreated waste NCM material)); the annealing temperature is 850℃, the time is 4 hours, and the atmosphere is argon.

[0044] The annealing process enables material recrystallization, lattice repair, and irreversible elimination of NiO impurities. It also effectively compensates for lithium volatilization during high-temperature sintering, restoring the material to a regular α-NaFeO2 layered structure and significantly improving cycle stability, rate performance, and structural reliability.

[0045] The present invention also provides a ternary cathode material prepared by the above preparation method based on citric acid-assisted hydrothermal low-temperature lithium replenishment.

[0046] The ternary cathode material prepared by this invention has a complete layered crystal structure, with irreversible NiO impurities completely eliminated, high lattice order, uniform surface, and stable interface. After lithium replenishment, the material exhibits high specific capacity, low polarization, excellent cycle stability, and high coulombic efficiency in the 3.0-4.3V voltage range, significantly improving the overall performance of lithium-ion batteries.

[0047] This invention provides an application of the above-mentioned ternary cathode material in lithium-ion batteries.

[0048] The present invention provides an electrode, the active component of which includes the above-mentioned ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment.

[0049] The present invention provides a lithium-ion battery comprising the electrodes described above.

[0050] In some alternative embodiments, the lithium-ion battery is a button / pouch power battery, the electrolyte is a conventional lithium salt organic electrolyte, and the voltage window is 3.0-4.3V.

[0051] The present invention also provides an application of the above-mentioned lithium-ion battery in new energy vehicles, energy storage power stations, 3C consumer electronics, grid energy storage and other equipment.

[0052] All raw materials used in this invention were purchased from the market.

[0053] The technical solution of the present invention will be further illustrated by the following embodiments.

[0054] Example 1 A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment includes the following steps: S1. The waste ternary cathode sheet was washed with DME, dried in an 80℃ oven for 12 hours, cut into pieces with scissors, and then soaked in NMP solution for 0.5 hours to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 400°C at 5°C / min in an air atmosphere. It is held at this temperature for 4 hours for heat treatment. After natural cooling, pure NCM precursor FQ-NCM is obtained. S3. Dissolve 0.1g of NCM precursor in aqua regia, digest in a digestion vessel at 160℃, dilute with 0.01% dilute nitric acid and perform ICP test, the ratio of Li / NCM was found to be 0.2:1; S4. Prepare 10 mL of 1 mol / L Li2HCit solution: Mix citric acid and LiOH·H2O at a molar ratio of 1:2, stir well to form a mixed solution; S5. Take 12.9g of FQ-NCM, add the above Li2HCit solution and FQ-NCM and mix and stir. Add deionized water to 2 / 3 of the volume of the reaction vessel, add LiOH・H2O to the concentration of 4mol / L, seal and react at 100℃ for 6h. After cooling, collect the black solid crystallized at the bottom. S6. Wash the black solid with deionized water and anhydrous ethanol alternately 5 times until the pH of the supernatant is 10, and dry it in an oven at 100℃ for 4 hours to obtain the hydrothermal product. S7. Grind the hydrothermal product with 5% mol equivalent Li2CO3 for 45 min, place it in a tube furnace under argon atmosphere and heat to 850℃ at 5℃ / min, hold for 4 h for annealing and crystallization, and then cool naturally. S8. Grind and sieve the annealed product to obtain a ternary cathode material based on citric acid-assisted lithium supplementation, denoted as ZS-NCM.

[0055] Example 2 A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment includes the following steps: S1. The waste ternary cathode sheet was washed with DME, dried in an 80℃ oven for 12 hours, cut into pieces with scissors, and then soaked in NMP solution for 0.5 hours to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 400°C at 5°C / min in an air atmosphere. It is held at this temperature for 2 hours for heat treatment. After natural cooling, pure NCM precursor FQ-NCM is obtained. S3. Dissolve 0.1g of NCM precursor in aqua regia, digest in a digestion vessel at 160℃, dilute with 0.01% dilute nitric acid and perform ICP test, the ratio of Li / NCM was found to be 0.2:1; S4. Prepare 10 mL of 1 mol / L LiH2Cit solution: Mix citric acid and LiOH·H2O in a 1:1 molar ratio, stir well and adjust the pH to acidic to form a mixed solution; S5. Take 12.9g of FQ-NCM, add Li2HCit solution and mix and stir. Add deionized water to 2 / 3 of the volume of the reaction vessel, add LiOH・H2O to the concentration of 4mol / L, seal and react at 100℃ for 6h. After cooling, collect the black solid crystallized at the bottom. S6. Wash the black solid with deionized water and anhydrous ethanol alternately 5 times until the pH of the supernatant is 10, and dry it in an oven at 110℃ for 4 hours to obtain the hydrothermal product. S7. Grind the hydrothermal product with 5% mol equivalent Li2CO3 for 45 min, place it in a tube furnace under argon atmosphere and heat to 850℃ at 5℃ / min, hold for 4 h for annealing and crystallization, and then cool naturally. S8. Grind and sieve the annealed product to obtain a ternary cathode material based on citric acid-assisted lithium supplementation, denoted as ZS-NCM-1.

[0056] Example 3 A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment includes the following steps: S1. The waste ternary cathode sheet was washed with DME, dried in an 80℃ oven for 12 hours, cut into pieces with scissors, and then soaked in NMP solution for 0.5 hours to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 400°C at 5°C / min in an air atmosphere. It is held at this temperature for 2 hours for heat treatment. After natural cooling, pure NCM precursor FQ-NCM is obtained. S3. Dissolve 0.1g of NCM precursor in aqua regia, digest in a digestion vessel at 160℃, dilute with 0.01% dilute nitric acid and perform ICP test, the ratio of Li / NCM was found to be 0.2:1; S4. Prepare 10 mL of 1 mol / L Li2HCit solution: Mix citric acid and LiOH·H2O in a 1:2 molar ratio, stir well and adjust the pH to acidic to form a mixed solution; S5. Take 12.9g of FQ-NCM, add Li2HCit solution and mix and stir. Add deionized water to 2 / 3 of the volume of the reaction vessel, add LiOH・H2O to the concentration of 4mol / L, seal and react at 100℃ for 6h. After cooling, collect the black solid crystallized at the bottom. S6. Wash the black solid with deionized water and anhydrous ethanol alternately 5 times until the pH of the supernatant is 10, and dry it in an oven at 110℃ for 4 hours to obtain the hydrothermal product. S7. Grind the hydrothermal product with 5% mol equivalent Li2CO3 for 45 min, place it in a tube furnace under argon atmosphere and heat to 850℃ at 5℃ / min, hold for 4 h for annealing and crystallization, and then cool naturally. S8. Grind and sieve the annealed product to obtain a ternary cathode material based on citric acid-assisted lithium supplementation, denoted as ZS-NCM-1.5.

[0057] Example 4 A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment includes the following steps: S1. The waste ternary cathode sheet was washed with DME, dried in an 80℃ oven for 12 hours, cut into pieces with scissors, and then soaked in NMP solution for 0.5 hours to obtain the precursor. S2. The precursor is placed in a tube furnace and heated to 400°C at 5°C / min in an air atmosphere. It is held at this temperature for 2 hours for heat treatment. After natural cooling, pure NCM precursor FQ-NCM is obtained. S3. Dissolve 0.1g of NCM precursor in aqua regia, digest in a digestion vessel at 160℃, dilute with 0.01% dilute nitric acid and perform ICP test, the ratio of Li / NCM was found to be 0.2:1; S4. Prepare 10 mL of 1 mol / L Li₂HCit solution: Mix citric acid and LiOH·H₂O at a molar ratio of 1:2.5, stir well and adjust the pH to acidic to form a mixed solution; S5. Take 12.9g of FQ-NCM, add Li2HCit solution and mix and stir. Add deionized water to 2 / 3 of the volume of the reaction vessel, add LiOH・H2O to the concentration of 4mol / L, seal and react at 100℃ for 6h. After cooling, collect the black solid crystallized at the bottom. S6. Wash the black solid with deionized water and anhydrous ethanol alternately 5 times until the pH of the supernatant is 10, and dry it in an oven at 110℃ for 4 hours to obtain the hydrothermal product. S7. Grind the hydrothermal product with 5% mol equivalent Li2CO3 for 45 min, place it in a tube furnace under argon atmosphere and heat to 850℃ at 5℃ / min, hold for 4 h for annealing and crystallization, and then cool naturally. S8. Grind and sieve the annealed product to obtain a ternary cathode material based on citric acid-assisted lithium supplementation, denoted as ZS-NCM-2.5.

[0058] Comparative Example 1 A method for preparing a common ternary cathode material includes the following steps: S1. The waste ternary cathode sheet is washed with DME, dried in an 80℃ oven for 12 hours, cut into pieces with scissors, and then soaked in NMP solution to obtain the precursor. S2. Place the precursor directly in a tube furnace and heat it to 400°C at 5°C / min in an air atmosphere. Hold it at that temperature for 2 hours for heat treatment, and then allow it to cool naturally. S3. Wash the heat-treated product with deionized water and dry it in a vacuum oven at 80°C for 12 hours to obtain ordinary regenerated ternary cathode material, denoted as Raw-NCM.

[0059] Comparative Example 2 (Deviation from optimal hydrothermal process: low-temperature hydrothermal, defects not repaired) The difference between this comparative example and Example 1 of the present invention is that the hydrothermal reaction temperature is lowered (the optimal 100°C repair condition is not reached), that is, the 100°C in step S5 of Example 1 is modified to 60°C. All other process parameters are completely the same, which is used to verify the key role of the optimal hydrothermal temperature in lattice repair and defect lithium replenishment. Finally, a low-temperature hydrothermal regenerated ternary material is obtained, denoted as LT-NCM.

[0060] Differences in test results: The relatively low hydrothermal temperature cannot drive lithium ions to fully migrate and fill oxygen vacancies, resulting in incomplete removal of NiO impurities on the material surface, incomplete repair of lattice defects, and high lithium ion diffusion resistance. This sample exhibits poor cycle stability, rapid capacity decay, and significantly lower rate performance than the optimal sample of this invention; specifically, after 70 cycles, the capacity retention is only 81.2%, and the discharge specific capacity at 0.5C is 130 mAh / g. This demonstrates that a hydrothermal temperature of 100℃ is a key process parameter for defect repair.

[0061] Comparative Example 3 (Deviation from optimal lithium replenishment process: Insufficient lithium replenishment agent dosage) The difference between this comparative example and Example 1 of the present invention is that the amount of lithium compensator added is changed from the optimal 5% mol equivalent to 2% mol equivalent, resulting in insufficient lithium replenishment. The rest of the process is completely the same, and it is used to verify the necessity of precise lithium replenishment process for structural repair and electrochemical performance improvement.

[0062] S1. Wash the waste ternary cathode with deionized water, dry it in an 80℃ oven for 12 hours, cut it into small pieces with scissors, and then soak it in NMP solution to obtain NCM precursor. S2. Prepare a 1 mol / L Li2HCit mixed solution (citric acid to LiOH·H2O molar ratio 1:2), add 4 mol / L LiOH aqueous solution to the precursor and stir thoroughly, then transfer to a hydrothermal reactor; S3. Set the hydrothermal reaction temperature to 100℃, keep it at that temperature for 6 hours, and then allow it to cool naturally. S4. Wash the hydrothermal product with deionized water and anhydrous ethanol alternately for 5 times until the pH of the supernatant is 10, and then dry it in an oven at 110℃ for 4 h. S5. The dried product is mixed and ground evenly with 2% mol equivalent Li2CO3 (lower than the optimal lithium supplementation ratio), and annealed at 850℃ for 4 h under argon atmosphere. After natural cooling, the under-lithium recycled ternary material is obtained, denoted as Low-Li-NCM.

[0063] Experimental results: The material prepared in Comparative Example 3 retained 80.3% of its capacity after 70 cycles, and its discharge specific capacity at 0.5C rate was 123 mAh / g.

[0064] Effect verification The ZS-NCM material prepared in Example 1 and the Raw-NCM material prepared in Comparative Example 1 were assembled into CR2032 coin cells in an argon-filled glove box (H2O < 0.01 ppm, O2 < 0.01 ppm) for electrochemical performance testing. Using lithium metal as the negative electrode, Celgard 2400 as the separator, and a 1M LiPF6 EC / DMC (volume ratio 1:1) solution as the electrolyte, the following electrochemical performance tests were conducted: I. Cyclic performance test: Charge and discharge test was conducted under constant temperature conditions with a voltage range of 3.0-4.3V and a current density of 1C (1C = 180 mA / g).

[0065] II. Rate Performance Test: Charge and discharge tests at different rates (0.1C, 0.2C, 0.5C, 1C, 2C, 3C, 5C).

[0066] III. Structural Characterization and Rietveld Refinement: X-ray diffraction (XRD) tests were performed on the ZS-NCM material, and Rietveld refinement analysis was conducted using FullProf software to further explore its crystal structure.

[0067] IV. Analysis of charge-discharge voltage curves at a current density of 0.5C.

[0068] Figure 1 shows the cycle performance curves of the lithium-ion half-cell based on the citric acid-assisted hydrothermal low-temperature lithium replenishment ternary cathode material (ZS-NCM) prepared in Example 1 (the lower curve corresponds to the left Y-axis (unit: mAh / g), representing the specific capacity, which records the actual discharge capacity change of the battery in each cycle at 1C rate; the upper curve corresponds to the right Y-axis (unit: %), representing the coulombic efficiency, which records the ratio of the discharged capacity to the charged capacity during each charge-discharge cycle). Figure 1As shown, the modified ZS-NCM material achieved an initial charge-discharge specific capacity of approximately 132 mAh / g, demonstrating high utilization of active materials. After 70 cycles, the discharge specific capacity remained at 115 mAh / g, with a capacity retention rate as high as 84.9%. Compared to the waste recycled material in Comparative Example 1 that did not undergo lithium replenishment treatment (capacity retention rate less than 10%), the material prepared in this invention showed significantly improved cycle stability. This proves that citric acid-assisted hydrothermal lithium replenishment effectively repaired oxygen and lithium vacancies on the material surface, inhibited electrolyte erosion of the electrode material, and reduced the irreversible phase transition from the layered phase to the spinel phase, thereby significantly improving the cycle life of the material.

[0069] Figure 2 shows the first charge-discharge specific capacity curve of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment at 0.5C rate. Figure 2 As shown, at a current density of 0.5C, the charge-discharge curves of the ZS-NCM material exhibit typical ternary material voltage plateaus, with an average operating voltage of approximately 3.7V. The charge-discharge curves demonstrate good symmetry, and the voltage difference (polarization voltage) between the charge-discharge plateaus is small, further verifying the material's excellent reversible lithium storage performance and low internal resistance characteristics. This is consistent with the cycle and rate test results mentioned above.

[0070] Figure 3 shows the rate performance curve of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment. Figure 3 As shown, charge-discharge tests at different rates (0.1C, 0.2C, 0.33C, 0.5C, 1C, 3C, 5C) demonstrate that this material exhibits excellent high-rate charge-discharge capabilities. At a low current density of 0.1C, the specific capacity reaches over 180 mAh / g; as the current density gradually increases to 0.5C, the specific capacity approaches 140 mAh / g; and when the current density gradually increases to 5C, the material still releases a specific capacity of over 85 mAh / g. Furthermore, when the current density returns to 0.1C, the specific capacity recovers to its initial value, proving that its structure remains stable under high-current impact. This excellent rate performance is attributed to the uniform microstructure created by citric acid complexation, which reduces the diffusion resistance of lithium ions and improves conductivity.

[0071] Figure 4 shows a scanning electron microscope (SEM) image of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment. Figure 4 As shown, the material exhibits a typical NaFeO2 layered structure (R-3m space group) and contains no other impurities.

[0072] Figure 5 shows the refined X-ray diffraction (XRD) pattern of the ternary cathode material (ZS-NCM) prepared in Example 1 based on citric acid-assisted hydrothermal low-temperature lithium replenishment. The refined results show that Rp (residual factor) is only 2.17%, Rwp (weighted residual factor) is 2.85%, Ycalc (calculated diffraction intensity) and Yobs (experimental diffraction intensity) have extremely high fit, and Rexp (expected residual) is only 1.72%. The refined data indicate that the crystal structure model of the material matches the actual diffraction data very well, and the material has good crystallinity. Furthermore, the refined results show no obvious cation mixing phenomenon in the material (i.e., the proportion of Ni occupying Li sites is extremely low), which provides a solid structural basis for the material's high electrochemical activity and low polarization.

[0073] In summary, the ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment provided by this invention achieves atomic-level uniform distribution of lithium source through the synergistic effect of hydrothermal method and annealing treatment, utilizing the strong complexing ability of citric acid. This effectively repairs surface defects of waste materials and reconstructs the crystal structure of the material. The prepared ZS-NCM material not only recycles waste battery resources but also endows the material with high specific capacity, excellent cycle stability, and rate performance comparable to newly prepared materials. Its preparation process is simple, environmentally friendly, and low-cost, making it particularly suitable as a cathode material for high-performance lithium-ion batteries. It has extremely high application value and broad application prospects in the fields of electric vehicle power battery recycling and large-scale energy storage.

[0074] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment, characterized in that, Includes the following steps: Using pretreated waste NCM material as a precursor, the Li / NCM molar ratio in the precursor, citric acid complexation for lithium replenishment, hydrothermal reaction, post-treatment, and annealing were determined by ICP quantitative analysis to obtain the ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment. The citric acid complex lithium supplementation uses a lithium citrate complex solution, which is obtained by complexing citric acid and lithium hydroxide in a molar ratio of 1:1-2.

5.

2. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 1, characterized in that, The pretreatment process is as follows: the waste NCM material is immersed in DME solution to remove the electrolyte, cut into pieces and then immersed in NMP solution, followed by washing, drying and heat treatment to obtain the precursor.

3. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 2, characterized in that, The heat treatment temperature is 350-500℃, and the holding time is 3-5 h.

4. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 2, characterized in that, The Li / NCM molar ratio in the precursor is 0.2:1; The concentration of the lithium citrate complex solution is 1 mol / L.

5. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 1, characterized in that, The hydrothermal reaction was carried out at a temperature of 100°C for 6 hours.

6. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 1, characterized in that, The post-treatment and annealing steps are as follows: the hydrothermal product is washed alternately with deionized water and anhydrous ethanol, dried, mixed and ground with lithium compensator, and annealed under an inert atmosphere.

7. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 6, characterized in that, The lithium compensator is Li2CO3.

8. The preparation method of a ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment according to claim 6, characterized in that, The annealing temperature was 850°C and the time was 4 hours.

9. A ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment, prepared by the preparation method according to any one of claims 1-8.

10. The application of the ternary cathode material based on citric acid-assisted hydrothermal low-temperature lithium replenishment as described in claim 9 in power batteries, energy storage batteries, or consumer electronic devices.

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