A method for efficiently leaching spent ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*.

Abstract

This invention discloses a method for efficiently leaching spent ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in synergy with *Lactobacillus plantarum*. It belongs to the field of spent lithium battery recycling technology and includes: 1) preparing battery cathode powder; preparing an anaerobic basal culture medium for *Lactobacillus plantarum* and performing deoxygenation treatment; 2) inoculating *Lactobacillus plantarum* and adding spent battery cathode powder into the anaerobic basal culture medium, leaching and acclimatizing under anaerobic conditions, followed by subculturing, gradually increasing the solid-liquid ratio gradient to acclimatize the bacteria; 3) inoculating *Lactobacillus plantarum* bacteria into the anaerobic basal culture medium and activating them under anaerobic conditions; adding spent battery cathode powder and metal nanoparticles to the anaerobic basal culture medium to prepare a leaching medium, inoculating the activated *Lactobacillus plantarum* to construct a bioleaching system, and co-culturing under anaerobic conditions at 35℃–37℃. Under the synergistic effect of the metal nanoparticles, the bacteria metabolize and mediate the leaching of valuable metals.

Description

Technical Field

[0001] This invention belongs to the field of recycling technology for waste lithium batteries, specifically relating to a method for efficiently leaching the positive electrode powder of waste ternary lithium-ion batteries using metal nanoparticles in conjunction with Lactobacillus plantarum under anaerobic conditions. Background Technology

[0002] With the large-scale expansion of the new energy vehicle and energy storage industries, lithium nickel cobalt manganese oxide (NCM) ternary lithium-ion batteries, with their advantages of high energy density and long cycle life, have become the mainstream cathode material for power and energy storage batteries, and their market share continues to rise. NCM ternary lithium-ion batteries are rich in metals such as lithium, nickel, cobalt, and manganese, possessing extremely high resource regeneration and economic value. Achieving efficient recycling of spent NCM batteries can not only alleviate the pressure on primary mineral resource supply and reduce dependence on external resources, but also avoid environmental pollution and human health risks caused by heavy metal loss, making it a key link in achieving the green and circular development of the lithium battery industry.

[0003] Currently, waste NCM batteries have entered their mass end-of-life period. Existing mainstream recycling processes mainly include pyrometallurgy and hydrometallurgy. Pyrometallurgy relies on high-temperature roasting, resulting in high energy consumption, significant metal volatilization losses, and the emission of toxic fumes. Chemical hydrometallurgy requires large amounts of strong inorganic acids or alkalis, placing extremely high demands on the corrosion resistance of reaction equipment and generating large quantities of acidic and alkaline wastewater, leading to high environmental remediation costs, which is inconsistent with the concept of green circular development.

[0004] As a green alternative technology, bioleaching has attracted much attention due to its low energy consumption and environmental friendliness. However, existing bioleaching research is mostly limited to strongly acidophilic strains, which can only survive in extremely acidic environments (pH < 2), resulting in significant challenges in subsequent acidic wastewater treatment. In contrast, *Lactobacillus plantarum*, as a mild acidophilic bacterium with anaerobic adaptability, has good potential for industrial application. However, existing single-strain systems suffer from bottlenecks such as slow kinetic rates and incomplete leaching during the leaching process, and their metabolic acid production capacity and redox regulation levels are insufficient to meet the industrial demands for rapid recycling of waste batteries.

[0005] Therefore, how to synergistically enhance the mild bioleaching system by introducing inorganic functional materials to improve the reduction and dissolution efficiency of metal elements in spent NCM batteries has become a key technical challenge urgently needing to be solved in the field of biometallurgy. Some metal nanoparticles, due to their excellent redox activity and electrochemical conductivity, can theoretically serve as electron conduction mediators or micro-electrochemical reaction centers, promoting the reduction and destruction of the cathode material's crystal structure and the rapid release of ions. Currently, there are no reports on research based on the anaerobic leaching of spent NCM batteries using metal nanoparticles in conjunction with *Lactobacillus plantarum*. This technology is expected to provide a novel and innovative technical solution for the green, low-cost, and efficient resource recycling of spent lithium-ion batteries. Summary of the Invention

[0006] To address the technical bottlenecks of slow reaction kinetics and incomplete leaching of valuable metals in existing mild bioleaching systems, this invention provides a method for efficiently leaching spent NCM battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with Lactobacillus plantarum.

[0007] This invention constructs a "biological-abiotic" synergistic system with *Lactobacillus plantarum* by using metal nanoparticles as electron transfer media and micro-electrochemical reaction centers. Under anaerobic conditions, the metal nanoparticles utilize their redox activity and electrochemical conductivity to synergize with *Lactobacillus plantarum* in metabolic acid production and extracellular electron transfer, thereby accelerating the lattice disruption and metal ion dissolution of the cathode material.

[0008] This method significantly improves the leaching rate and metal recovery rate in a weakly acidic anaerobic system, achieving efficient, green, and low-cost recycling of valuable metals from waste NCM batteries, and providing a novel synergistic enhancement pathway for battery recycling processes.

[0009] The technical solution provided by this invention:

[0010] A method for efficiently leaching spent ternary lithium-ion battery cathode powder using metal nanoparticles in conjunction with *Lactobacillus plantarum* under anaerobic conditions includes the following steps:

[0011] Step 1: Pre-processing;

[0012] The pretreatment process includes the preparation of battery cathode powder and the preparation of anaerobic basic culture medium, and there is no specific order between the two.

[0013] a. Preparation of battery positive electrode powder:

[0014] Waste NCM ternary lithium-ion batteries are discharged, then the positive electrode is disassembled and the adhesive on the surface of the positive electrode is removed. After crushing, the impurities and large particles are removed by sieving to obtain waste NCM ternary lithium-ion battery positive electrode powder.

[0015] b. Preparation of anaerobic basal culture medium:

[0016] An anaerobic basal culture medium for *Lactobacillus plantarum* was prepared with the following components: peptone 10.0 g / L, beef extract 8.0 g / L, yeast extract 4.0 g / L, glucose 20.0 g / L, dipotassium hydrogen phosphate 2.0 g / L, diammonium hydrogen citrate 2.0 g / L, sodium acetate 5.0 g / L, magnesium sulfate 0.2 g / L, manganese sulfate 0.04 g / L, and Tween 80 1.0 g / L. The prepared culture medium was then subjected to deoxygenation treatment.

[0017] Step 2: Domestication of Lactobacillus plantarum;

[0018] Lactobacillus plantarum was inoculated into a prepared anaerobic basal culture medium, and waste NCM ternary lithium-ion battery cathode powder was added. An initial solid-liquid ratio and initial bacterial concentration were set, and leaching and acclimatization culture was carried out under anaerobic conditions at 35℃–37℃. After the initial acclimatization culture, subculture was performed to stabilize the strain's adaptability. Subsequently, the solid-liquid ratio of the system was gradually increased to conduct gradient acclimatization, obtaining Lactobacillus plantarum strains adapted to high solid-liquid ratios.

[0019] Step 3: Co-leaching of valuable metals;

[0020] The *Lactobacillus plantarum* bacteria obtained in step 2 were inoculated into the anaerobic basal culture medium prepared in step 1b and cultured and activated under anaerobic conditions at 35℃–37℃. Waste NCM ternary lithium-ion battery cathode powder and metal nanoparticles were added to the anaerobic basal culture medium prepared in step 1b according to a mass ratio of 5:(0.5~3) to prepare a leaching culture medium. The activated *Lactobacillus plantarum* was then inoculated into this leaching culture medium to construct a bioleaching system. This bioleaching system was co-cultured under anaerobic conditions at 35℃–37℃. Under the synergistic effect of the metal nanoparticles, the bacteria metabolized and mediated the leaching of valuable metals from the battery cathode powder. The metal nanoparticles included copper nanoparticles, iron nanoparticles, and iron(III) oxide nanoparticles.

[0021] The above-mentioned method for efficiently leaching spent ternary lithium-ion battery cathode powder using metal nanoparticles in conjunction with *Lactobacillus plantarum* under anaerobic conditions, wherein:

[0022] In step 1a, the waste NCM ternary lithium-ion batteries are fully immersed in a 10%–20% sodium chloride solution for discharge treatment, which is controlled to last 1–7 days. During this period, the brine is replaced and the batteries are turned over periodically to ensure uniform and sufficient discharge on the electrode surface, ultimately reducing the voltage of the waste NCM ternary lithium-ion batteries to below 0.5 V. The discharged waste ternary lithium-ion batteries are then transferred to an oven for drying at 40℃–65℃. This step effectively removes free water and crystal water from the battery's internal pores and surface, reducing safety issues such as short circuits and thermal runaway caused by residual energy and moisture during subsequent disassembly and crushing. After drying, the battery casing, separator, positive electrode, and negative electrode are separated. The separated positive electrode is then cut into small pieces with a length and width not exceeding 5.0 cm. The small electrode pieces were then placed in a container filled with N,N-dimethylformamide (DMF) and immersed in a 60°C oven for 1–6 hours, with stirring every hour to enhance contact between the electrode and DMF, accelerate the separation of the binder from the positive electrode substrate, improve dissolution efficiency, and reduce binder residue. After immersion, the positive electrode pieces were removed and rinsed with deionized water, repeated 3–6 times until the pH of the deionized water stabilized near neutral to ensure all residual DMF was removed. The cleaned positive electrode pieces were then placed back in the oven and dried at 60°C–70°C for 12–24 hours until the moisture evaporated and the electrode mass remained constant. Finally, the constant-mass positive electrode pieces were pulverized and vibrated using a pulverizer, and then sieved through a 100-mesh standard inspection sieve to remove impurities. The product collected from the sieve was the uniformly dispersed battery positive electrode powder. To prevent oxidation from moisture, the obtained positive electrode powder was sealed and stored in a dark, dry environment (relative humidity ≤ 30%) for subsequent bioleaching.

[0023] In step 1b, special attention must be paid to the problem of bacterial growth due to nutritional characteristics and the protection of heat-sensitive nutrients. Because the anaerobic basal medium (i.e., MRS broth medium) is rich in protein nutrients such as peptone, beef extract, and yeast extract, as well as sugars such as glucose, it is highly susceptible to bacterial growth. Furthermore, high temperatures can damage the structure of heat-sensitive nutrients in the medium. Therefore, it is necessary to strictly control the sterilization temperature, pressure, and time to balance sterilization effectiveness with nutrient retention. The prepared MRS broth medium should be evenly dispensed into sterile bottles, with each bottle not exceeding 2 / 3 of its volume to prevent boiling and overflow during sterilization. Since the subsequent culture of *Lactobacillus plantarum* requires a strictly anaerobic environment, a degassing step must be added before sterilization: sterile nitrogen gas is slowly introduced into the bottle to replace the air, continuing for 10-60 minutes depending on the solution volume, to completely remove dissolved oxygen from the medium and prevent residual oxygen from affecting the subsequent anaerobic metabolic activity of *Lactobacillus plantarum*. After degassing, seal the bottle opening and place the bottle body steadily into the inner tray of the high-pressure steam sterilizer. Close the sterilizer and set the parameters: sterilization temperature 116℃-120℃, sterilization pressure 0.07 MPa-0.09 MPa, sterilization time 10 min-20 min, and start the sterilization program.

[0024] In step 2, the waste NCM ternary lithium-ion battery cathode powder prepared in step 1a is added to the anaerobic basic culture medium prepared in step 1b. The initial solid-liquid ratio is set to 1.0 g / L, and the initial bacterial concentration is 10. 7 The bacterial culture was carried out at 35℃–37℃ under anaerobic conditions in a constant temperature and humidity shaker for leaching and acclimatization (the anaerobic environment was ensured by purging sterile nitrogen gas to prevent dissolved oxygen in the culture medium). The OD value of the bacterial culture at 600.0 nm was monitored periodically. 600 The pH of the culture medium and the bacterial concentration were measured (once a day). When the bacterial concentration stabilized at 10... 9 The initial acclimatization culture was completed when the bacterial concentration was [number of cells / mL] and the pH was 3.5–4.0. Under aseptic conditions in an anaerobic glove box, an appropriate amount of the acclimatized bacterial culture was taken and transferred to fresh anaerobic basal medium containing the same solid-liquid ratio and components. The culture was maintained at 35–37°C under anaerobic conditions, and the above culture process was repeated until the bacterial concentration stabilized at 10[number of cells / mL]. 9The concentration of cells / mL was recorded for one subculture. Three consecutive subcultures were performed to ensure that the *Lactobacillus plantarum* strain could stably adapt to the anaerobic basal medium containing spent NCM ternary lithium-ion battery cathode powder, thus initially establishing tolerance to the powder. After subculture acclimatization, the strain's adaptability was further enhanced by gradually increasing the solid-liquid ratio. During each acclimatization, the solid-liquid ratio of the spent NCM ternary lithium-ion battery cathode powder was increased by 1.0 g / L, while other culture conditions (35℃–37℃, anaerobic environment, anaerobic basal medium) remained constant. Each subculture was continued until the bacterial concentration stabilized at 10⁻⁶ cells / mL. 9 After reaching a cell / mL concentration, proceed to the next gradient acclimatization step. Repeat the above gradient acclimatization steps sequentially until the solid-liquid ratio of the system is increased to 5.0 g / L, and the *Lactobacillus plantarum* strain can still maintain a stable bacterial concentration of 10 g / mL after cultivation under this solid-liquid ratio condition. 9 The acclimatization process was considered complete when the number of cells / mL reached a certain level, ultimately yielding a strain of *Lactobacillus plantarum* that could stably adapt to the high solid-liquid ratio of waste NCM and exhibited good leaching adaptability. Finally, a bacterial culture was prepared and stored at -80°C for subsequent anaerobic leaching.

[0025] In step 3, the *Lactobacillus plantarum* strain that has been cryopreserved and acclimatized in step 2 is taken and, in a sterile anaerobic glove box, is prepared at an initial bacterial concentration of 10... 7 Inoculate the culture medium at a rate of cells / mL into the anaerobic basal medium after deoxygenation treatment in step 1b, and culture anaerobically in a shaker at 35℃–37℃ for 12–18 h. Monitor the OD of the bacterial culture in real time during the culture process. 600 Value, when OD 600 When the bacterial growth rate reaches approximately 1.8, indicating that the strain has entered the logarithmic growth phase, activation is complete. This activation process can eliminate the inhibitory effect of low-temperature preservation on the strain's metabolism, effectively increasing the proliferation rate and metabolic activity of the bacteria after inoculation, and providing a stable and efficient source of bacteria for subsequent bioleaching experiments.

[0026] Inside an anaerobic sterile glove box, the anaerobic basic culture medium prepared in step 1b is used. The anaerobic environment is maintained throughout to minimize the influence of oxygen and prevent the formation of metal oxides that could hinder the reduction reaction. Waste NCM ternary lithium-ion battery cathode powder and metal nanoparticles are added to the culture medium at a mass ratio of 5:(0.5~3), and stirred until homogeneous to obtain the leaching medium. The preparation process requires shaking to ensure the powder is fully dispersed and free from agglomeration, guaranteeing uniform contact between the metal nanoparticles and the cathode powder, allowing the reduction reaction to proceed fully. The waste NCM ternary lithium-ion battery cathode material described in this invention includes models such as NCM111, NCM523, and NCM622. The metal nanoparticles are preferably copper nanoparticles with a particle size range of 30 nm-50 nm.

[0027] The activated Lactobacillus plantarum culture was inoculated into the leaching medium to make the initial bacterial concentration of the system 10. 7 A homogeneous and stable *Lactobacillus plantarum* bioleaching system was constructed by gently inverting and mixing the sample at a concentration of cells / mL. This system was then co-cultured anaerobically in a constant temperature and humidity shaker at 35℃–37℃. During co-culture, *Lactobacillus plantarum* and metal nanoparticles synergistically enhanced leaching: *Lactobacillus plantarum* secreted leaching media such as lactic acid through metabolism, gradually dissolving the crystal structure of the cathode powder from waste NCM ternary lithium-ion batteries; while the metal nanoparticles, utilizing their excellent redox activity and good electron transport capabilities, acted as highly efficient electron mediators and reducing agents in the anaerobic system, disrupting the metal oxide lattice structure through micro-redox reactions and accelerating interfacial electron transfer rates, thus promoting the reduction and dissolution of high-valence metal ions. This synergistic enhancement system effectively solves the bottleneck problems of low leaching efficiency, slow reaction kinetics, and long leaching cycles of *Lactobacillus plantarum* alone at high solid-liquid ratios in existing technologies. The co-culture period lasted 5-10 days to ensure sufficient metabolism of the strain and complete leaching of valuable metals. Samples were taken at regular intervals, and the pH value was measured using a pH meter and the OD value was measured using a spectrophotometer. 600 The bacterial cell concentration was characterized by a value, and the solution was then filtered through a 0.22 μm aqueous microporous membrane to obtain the filtrate. The concentration of metal ions in the filtrate was then measured and the leaching percentage was calculated.

[0028] The core of this invention lies in optimizing the bioleaching efficiency of waste NCM ternary lithium-ion battery cathode materials under anaerobic conditions by introducing a synergistic system of metal nanoparticles and *Lactobacillus plantarum*. This method uses metal nanoparticles as an electron mediator and reducing agent, significantly enhancing the coupling efficiency between metabolic acid production and metal reduction in *Lactobacillus plantarum*. Leveraging the high reactivity at the nanoscale, it overcomes the technical bottleneck of slow leaching and low leaching rates of single organisms at high solid-liquid ratios, providing a novel technical solution for the green and efficient recycling of waste lithium batteries.

[0029] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0030] This invention differs from the traditional aerobic leaching environment of Lactobacillus plantarum by using an anaerobic environment to maintain the reducing properties of the system. By introducing metal nanoparticles to construct a "biological-abiotic" synergistic system with Lactobacillus plantarum, the excellent redox activity and electrochemical conductivity of the metal nanoparticles are utilized to significantly enhance the efficiency of acid production by the strain and the reduction and dissolution rate of solid metals. Under mild anaerobic conditions, the leaching cycle is greatly shortened, and the leaching efficiency of valuable metals such as nickel, cobalt, manganese, and lithium is significantly improved. Attached Figure Description

[0031] Figure 1This is a flowchart of the method for efficiently leaching waste NCM ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with Lactobacillus plantarum. Detailed Implementation

[0032] The cathode material of the waste NCM ternary lithium-ion battery described in this invention is selected from lithium nickel cobalt manganese oxide 111, lithium nickel cobalt manganese oxide 523, lithium nickel cobalt manganese oxide 622, etc. The metal nanoparticles described in this invention are copper nanoparticles, iron nanoparticles, and iron tetroxide nanoparticles, wherein the copper nanoparticles are all commercially available models with a particle size of 30 nm–50 nm.

[0033] Example 1

[0034] A method for efficiently leaching waste NCM111 ternary lithium-ion battery cathode powder under anaerobic conditions using copper nanoparticles in conjunction with *Lactobacillus plantarum*, such as... Figure 1 As shown, the specific operation steps are as follows:

[0035] Step 1: Pre-processing;

[0036] The pretreatment process includes the preparation of battery cathode powder and the preparation of anaerobic basic culture medium, and there is no specific order between the two.

[0037] a. Preparation of battery positive electrode powder:

[0038] Waste NCM111 ternary lithium-ion batteries were fully immersed in a 10%–20% sodium chloride solution for discharge treatment for 1–7 days. The brine was changed and the batteries were turned over every day during this period, ensuring the voltage of the waste NCM111 ternary lithium-ion batteries stabilized below 0.5 V. After discharge, the waste NCM111 ternary lithium-ion batteries were transferred to an oven for drying at 40℃–65℃. After drying, the battery casing, separator, positive electrode, and negative electrode were separated step-by-step using insulated disassembly equipment. The separated positive electrode was then cut into small pieces, each no more than 5.0 cm in length and width. These small electrode pieces were then placed in a container containing DMF and immersed in a 60℃ oven for 1–6 hours, with stirring performed every hour. After soaking, remove the positive electrode sheet and wash it in deionized water, repeating this process 3–6 times until the pH of the deionized water stabilizes near neutral. Place the washed positive electrode sheet back into an oven and dry it at 60℃–70℃ for 12 h–24 h until the moisture evaporates and the electrode sheet mass becomes constant. Finally, pulverize and vibrate the constant-mass positive electrode sheet using a pulverizer to separate the positive electrode powder from the substrate. Sieve the powder through a 100-mesh standard inspection sieve to remove impurities, and collect the undersize product, which is the uniformly dispersed battery positive electrode powder.

[0039] The concentration of metal elements in the obtained battery cathode powder was analyzed using a chemical digestion method: 0.08 g of battery cathode powder was taken and 5.0 mL of digestion solution (HCl:HNO3=3:1, v / v) was added. The solution was placed in a crucible on a hot plate and heated to 230℃ for digestion. After cooling, the volume was adjusted to 100.0 mL with 1% dilute nitric acid. The concentration of metal ions in the digestion solution was measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The calculated lithium content in the battery cathode powder was 65.5 mg / g, nickel content was 236.9 mg / g, cobalt content was 183.8 mg / g, and manganese content was 192.3 mg / g.

[0040] b. Preparation of anaerobic basal culture medium:

[0041] An anaerobic basal culture medium for *Lactobacillus plantarum* was prepared with the following components: peptone 10.0 g / L, beef extract 8.0 g / L, yeast extract 4.0 g / L, glucose 20.0 g / L, dipotassium hydrogen phosphate 2.0 g / L, diammonium hydrogen citrate 2.0 g / L, sodium acetate 5.0 g / L, magnesium sulfate 0.2 g / L, manganese sulfate 0.04 g / L, and Tween 80 1.0 g / L. To meet the requirements of subsequent anaerobic culture of *Lactobacillus plantarum*, sterile nitrogen gas was continuously purged into the prepared anaerobic basal culture medium for 10–60 min before sealing to completely remove dissolved oxygen and avoid affecting the metabolism of *Lactobacillus plantarum*. After degassing, the container was sealed and placed in an autoclave. Sterilization was initiated at 118℃, 0.08 MPa, and 15 min.

[0042] Step 2: Domestication of Lactobacillus plantarum;

[0043] Inoculate *Lactobacillus plantarum* into the anaerobic basal culture medium prepared in step 1b, and add battery positive electrode powder. Set the initial solid-liquid ratio to 1.0 g / L and the initial bacterial concentration to 10. 7 Cells / mL, anaerobic cultured in a shaker at 35℃–37℃ until the bacterial concentration reached 102. 9 Cells / mL. Then, an appropriate amount of bacterial culture was taken from the anaerobic glove box and transferred to a new anaerobic basal medium with the same solid-liquid ratio for subculturing. This process was repeated three times to stabilize the strain's adaptability. Subsequently, the solid-liquid ratio was gradually increased by 1.0 g / L each time, performing a gradient acclimatization until the solid-liquid ratio reached 5.0 g / L and the bacterial concentration stabilized at 10⁻⁶ cells / mL. 9When the bacterial culture reaches a cell / mL ratio, the domestication is considered complete, and a strain of *Lactobacillus plantarum* adapted to a high solid-liquid ratio is obtained. The bacterial culture is then mixed with the cryoprotectant glycerol at a 1:1 volume ratio to prepare a bacterial culture protectant, which is then stored in a -80°C freezer.

[0044] Step 3: Co-leaching of valuable metals;

[0045] Take the *Lactobacillus plantarum* bacteria cultured in step 2 that has been adapted to a high solid-liquid ratio by storing it in a -80℃ freezer, and inoculate it into the anaerobic basal medium prepared in step 1b. Activate the medium by culturing it at 35℃–37℃ under anaerobic conditions for 12–18 hours. During this period, monitor its growth status using a UV-Vis spectrophotometer until the OD... 600 Once the bacterial count reaches approximately 1.8, the bacteria enter the logarithmic growth phase, and then leaching experiments are performed. Add 80.0 mL of the anaerobic basal culture medium prepared in step 1b to a 100.0 mL serum bottle, and inoculate the activated *Lactobacillus plantarum* into the medium, controlling the initial bacterial concentration to 10⁻⁶. 7 Cells / mL. Battery cathode powder and copper nanoparticles were added to the anaerobic basal medium prepared in step 1b, controlling the solid-liquid ratio of the battery cathode powder to 5.0 g / L and the solid-liquid ratio of the copper nanoparticles to 3.0 g / L to prepare the leaching medium. Activated *Lactobacillus plantarum* was inoculated into this leaching medium to construct the bioleaching system. The start of the leaching experiment was recorded as 0 h, and the system was placed in a constant temperature shaker for anaerobic culture at 37℃. The leaching experiment lasted for 7 days, with samples taken every other day. A parallel control group was also set up, with all experimental operations and parameters kept consistent except for the absence of copper nanoparticles in the system, such as culture medium composition, solid-liquid ratio, culture conditions, and sampling methods, to compare and verify the synergistic enhancing effect of copper nanoparticles on the bioleaching process.

[0046] pH and cell concentration changes were monitored during sampling. The collected samples were filtered using a 0.22 μm aqueous filter, and the concentrations of lithium, cobalt, nickel, and manganese ions in the leachate were measured using ICP-OES. The leaching percentage was then calculated. Seven days later, the percentage of lithium ions in the leachate of the leaching system without copper nanoparticles was only 62.7%, the percentage of nickel ions was only 46.3%, the percentage of cobalt ions was only 56.5%, and the percentage of manganese ions was only 46.9%. However, the percentage of lithium ions in the leachate of the synergistic leaching system with added copper nanoparticles was 95.4%, the percentage of nickel ions was 79.8%, the percentage of cobalt ions was 97.4%, and the percentage of manganese ions was 79.9%. The results indicate that copper nanoparticles can enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM111 ternary lithium-ion battery cathode powder under anaerobic conditions, increasing the leaching efficiency of lithium by 1.5 times and the leaching efficiency of nickel, cobalt, and manganese by 1.7 times.

[0047] Example 2

[0048] A method for efficiently leaching waste NCM523 ternary lithium-ion battery cathode powder under anaerobic conditions using copper nanoparticles in conjunction with *Lactobacillus plantarum*, such as... Figure 1 As shown, the specific operation steps are as follows:

[0049] Step 1: As in step 1a of Example 1, prepare the cathode powder of waste NCM523 ternary lithium-ion batteries; as in step 1b of Example 1, prepare the anaerobic basic culture medium.

[0050] Step 2: As in Step 2 of Example 1, acclimate Lactobacillus plantarum to the positive electrode powder of waste NCM523 ternary lithium-ion batteries;

[0051] Step 3: As in Step 3 of Example 1, copper nanoparticles are used to leach valuable metals from the cathode powder of waste NCM523 ternary lithium-ion batteries. As in Step 3 of Example 1, a parallel control group is set up. The control group system does not contain copper nanoparticles and only uses Lactobacillus plantarum for leaching experiments. All other conditions and operations are the same.

[0052] The results of leaching waste NCM523 ternary lithium-ion battery cathode powder with copper nanoparticles in conjunction with *Lactobacillus plantarum* in Example 2 are as follows: Calculations show that the waste NCM523 ternary lithium-ion battery cathode powder prepared in step 1 contains 61.0 mg / g of lithium, 339.3 mg / g of nickel, 131.6 mg / g of cobalt, and 182.7 mg / g of manganese. After leaching for 7 days with a solid-liquid ratio of 5.0 g / L and without the addition of copper nanoparticles, the percentage of lithium ions in the leachate was only 42.8%, the percentage of nickel ions was only 54.2%, the percentage of cobalt ions was only 55.6%, and the percentage of manganese ions was only 53.1%; while the percentage was lower with a solid-liquid ratio of 3.0 g / L. The leachate containing the synergistic leaching system of g / L copper nanoparticles had a lithium ion content of 99.0%, a nickel ion content of 100.0%, a cobalt ion content of 100.0%, and a manganese ion content of 100.0%. The results showed that copper nanoparticles could enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM523 ternary lithium-ion battery cathode powder under anaerobic conditions, increasing the leaching efficiency of lithium by 2.3 times, the leaching efficiency of nickel and cobalt by 1.8 times, and the leaching efficiency of manganese by 1.9 times.

[0053] Example 3

[0054] A method for efficiently leaching waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions using copper nanoparticles in conjunction with *Lactobacillus plantarum*, such as... Figure 1 As shown, the specific operation steps are as follows:

[0055] Step 1: As in step 1a of Example 1, prepare the cathode powder of waste NCM622 ternary lithium-ion batteries; as in step 1b of Example 1, prepare the anaerobic basic culture medium.

[0056] Step 2: As in Step 2 of Example 1, acclimate Lactobacillus plantarum to the positive electrode powder of waste NCM622 ternary lithium-ion batteries;

[0057] Step 3: As in Step 3 of Example 1, copper nanoparticles are used to synergistically leach valuable metals from the cathode powder of waste NCM622 ternary lithium-ion batteries. The solid-liquid ratio of copper nanoparticles is designed to be 0.5 g / L, 1.5 g / L, or 3.0 g / L. As in Step 3 of Example 1, a parallel control group is set up. The control group system does not contain copper nanoparticles and only uses Lactobacillus plantarum for leaching experiments. All other conditions and operations are the same.

[0058] The results of leaching waste NCM622 ternary lithium-ion battery cathode powder with copper nanoparticles in conjunction with *Lactobacillus plantarum* in Example 3 are as follows: Calculations show that the waste NCM622 ternary lithium-ion battery cathode powder prepared in step 1 contains 64.4 mg / g of lithium, 320.5 mg / g of nickel, 109.6 mg / g of cobalt, and 107.0 mg / g of manganese. After leaching for 7 days with a solid-liquid ratio of 5.0 g / L and without the addition of copper nanoparticles, the percentage of lithium ions in the leachate was only 61.0%, the percentage of nickel ions was only 62.0%, the percentage of cobalt ions was only 60.1%, and the percentage of manganese ions was only 57.1%. The leachate containing a synergistic leaching system with copper nanoparticles at a solid-liquid ratio of 0.5 g / L had a lithium ion content of 71.5%, a nickel ion content of 75.9%, a cobalt ion content of 72.7%, and a manganese ion content of 70.7%. The results indicate that 0.5 g / L copper nanoparticles can slightly enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions, increasing the leaching efficiency of lithium, nickel, cobalt, and manganese to 1.2 times the original efficiency. Increasing the solid-liquid ratio of copper nanoparticles, when a synergistic leaching system was formed by adding copper nanoparticles with a solid-liquid ratio of 1.5 g / L, resulted in a leaching solution containing 81.7% lithium ions, 82.1% nickel ions, 82.4% cobalt ions, and 82.9% manganese ions. These results indicate that increasing the copper nanoparticle content can further enhance the leaching effect of *Lactobacillus plantarum* on lithium, nickel, cobalt, and manganese in waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions, increasing the leaching efficiency of lithium and nickel to 1.3 times that of the original system, cobalt to 1.4 times, and manganese to 1.5 times. Further increasing the solid-liquid ratio of copper nanoparticles, when a synergistic leaching system was formed by adding copper nanoparticles with a solid-liquid ratio of 3.0 g / L, the percentage content of lithium ions, nickel ions, cobalt ions, and manganese ions in the leachate was 100.0%. The results showed that the optimal mass ratio of battery cathode powder to copper nanoparticles was 5:3. At this ratio, copper nanoparticles could significantly enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions, increasing the leaching efficiency of lithium and nickel to 1.6 times that of the original system, cobalt to 1.7 times, and manganese to 1.8 times.

[0059] Example 4

[0060] A method for efficiently leaching waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions using iron nanoparticles in conjunction with *Lactobacillus plantarum*, such as... Figure 1 As shown, the specific operation steps are as follows:

[0061] Step 1: As in step 1a of Example 1, prepare the cathode powder of waste NCM622 ternary lithium-ion batteries; as in step 1b of Example 1, prepare the anaerobic basic culture medium.

[0062] Step 2: As in Step 2 of Example 1, acclimate Lactobacillus plantarum to the positive electrode powder of waste NCM622 ternary lithium-ion batteries;

[0063] Step 3: As in Step 3 of Example 1, iron nanoparticles (particle size 50 nm-50 μm) are used to synergistically leach valuable metals from waste NCM622 ternary lithium-ion battery cathode powder. As in Step 3 of Example 1, a parallel control group is set up. Iron nanoparticles are not added to the control group system, and all other conditions and operations are the same.

[0064] The results of leaching waste NCM622 ternary lithium-ion battery cathode powder with iron nanoparticles in conjunction with *Lactobacillus plantarum* in Example 4 are as follows: Calculations show that the waste NCM622 ternary lithium-ion battery cathode powder prepared in step 1 contains 64.4 mg / g of lithium, 320.5 mg / g of nickel, 109.6 mg / g of cobalt, and 107.0 mg / g of manganese. After leaching for 7 days with a solid-liquid ratio of 5.0 g / L and without the addition of iron nanoparticles, the percentage of lithium ions in the leachate was only 61.0%, the percentage of nickel ions was only 62.0%, the percentage of cobalt ions was only 60.1%, and the percentage of manganese ions was only 57.1%. The leachate containing a synergistic leaching system with iron nanoparticles at a solid-liquid ratio of 3.0 g / L had a lithium ion content of 89.0%, a nickel ion content of 83.9%, a cobalt ion content of 79.3%, and a manganese ion content of 68.0%. The results indicate that iron nanoparticles can enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM622 ternary cathode powder under anaerobic conditions, but its effect is weaker than that of copper nanoparticles at the same addition amount.

[0065] Example 5

[0066] A method for efficiently leaching waste NCM622 ternary lithium-ion battery cathode powder under anaerobic conditions using iron oxide nanoparticles in conjunction with *Lactobacillus plantarum*. Figure 1 As shown, the specific operation steps are as follows:

[0067] Step 1: As in step 1a of Example 1, prepare the cathode powder of waste NCM622 ternary lithium-ion batteries; as in step 1b of Example 1, prepare the anaerobic basic culture medium.

[0068] Step 2: As in Step 2 of Example 1, acclimate Lactobacillus plantarum to the positive electrode powder of waste NCM622 ternary lithium-ion batteries;

[0069] Step 3: As in Step 3 of Example 1, iron oxide nanoparticles (average particle size 50 nm) are used to synergistically leach valuable metals from waste NCM622 ternary lithium-ion battery cathode powder. As in Step 3 of Example 1, a parallel control group is set up. The control group system does not contain iron oxide nanoparticles, and all other conditions and operations are the same.

[0070] The results of leaching waste NCM622 ternary lithium-ion battery cathode powder with iron oxide nanoparticles in conjunction with *Lactobacillus plantarum* in Example 5 are as follows: Calculations show that the waste NCM622 ternary lithium-ion battery cathode powder prepared in step 1 contains 64.4 mg / g of lithium, 320.5 mg / g of nickel, 109.6 mg / g of cobalt, and 107.0 mg / g of manganese. After leaching for 7 days with a solid-liquid ratio of 5.0 g / L and without the addition of iron oxide nanoparticles, the percentage of lithium ions in the leachate is only 61.0%, the percentage of nickel ions is only 62.0%, the percentage of cobalt ions is only 60.1%, and the percentage of manganese ions is only 57.1%. The leachate containing a synergistic leaching system with 3.0 g / L iron oxide nanoparticles as the solid-liquid ratio had a lithium ion content of 70.9%, a nickel ion content of 75.1%, a cobalt ion content of 72.1%, and a manganese ion content of 68.3%. The results indicate that iron oxide nanoparticles can enhance the leaching effect of Lactobacillus plantarum on lithium, nickel, cobalt, and manganese in waste NCM622 ternary cathode powder under anaerobic conditions, but its effect is weaker than that of copper nanoparticles at the same addition amount.

Claims

1. A method for efficiently leaching spent ternary lithium-ion battery cathode powder using metal nanoparticles in conjunction with *Lactobacillus plantarum* under anaerobic conditions, characterized in that... Includes the following steps: Step 1: Pre-processing; The pretreatment process includes the preparation of battery cathode powder and the preparation of anaerobic basic culture medium, and there is no specific order between the two. a. Preparation of battery positive electrode powder: Waste NCM ternary lithium-ion batteries are discharged, then the positive electrode is disassembled and the adhesive on the surface of the positive electrode is removed. After crushing, the impurities and large particles are removed by sieving to obtain waste NCM ternary lithium-ion battery positive electrode powder. b. Preparation of anaerobic basal culture medium: Prepare an anaerobic basal culture medium for Lactobacillus plantarum and deoxygenate it; Step 2: Domestication of Lactobacillus plantarum; Lactobacillus plantarum was inoculated into the prepared anaerobic basal culture medium, and waste NCM ternary lithium-ion battery positive electrode powder was added. The initial solid-liquid ratio and initial bacterial concentration were set, and the culture was carried out under anaerobic conditions at 35℃–37℃. After the first culture was completed, the culture was passaged. The solid-liquid ratio of the system was gradually increased to carry out gradient culture to obtain Lactobacillus plantarum strains adapted to high solid-liquid ratios. Step 3: Co-leaching of valuable metals; Take the *Lactobacillus plantarum* bacteria obtained in step 2 and inoculate them into the anaerobic basal culture medium prepared in step 1b. Activate the culture under anaerobic conditions at 35℃–37℃. Add the waste NCM ternary lithium-ion battery cathode powder and metal nanoparticles to the anaerobic basal culture medium prepared in step 1b according to a mass ratio of 5:(0.5~3) to prepare a leaching culture medium. Inoculate the activated *Lactobacillus plantarum* into this leaching culture medium to construct a bioleaching system. Co-culture the system under anaerobic conditions at 35℃–37℃. Under the synergistic effect of the metal nanoparticles, the bacteria metabolize and mediate the leaching of valuable metals. The metal nanoparticles include copper nanoparticles, iron nanoparticles, and iron(III) oxide nanoparticles.

2. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... In step 1a, the waste NCM ternary lithium-ion battery is fully immersed in a sodium chloride solution with a mass concentration of 10%–20% for discharge treatment, so that the voltage of the waste NCM ternary lithium-ion battery is stably reduced to below 0.5 V. After cleaning, drying, crushing and sieving, the positive electrode powder of the battery is obtained.

3. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... In step 1b, the anaerobic basal culture medium for *Lactobacillus plantarum* comprises: 10.0 g / L peptone, 8.0 g / L beef extract, 4.0 g / L yeast extract, 20.0 g / L glucose, 2.0 g / L dipotassium hydrogen phosphate, 2.0 g / L diammonium hydrogen citrate, 5.0 g / L sodium acetate, 0.2 g / L magnesium sulfate, 0.04 g / L manganese sulfate, and 1.0 g / L Tween 80. The prepared anaerobic basal culture medium is dispensed into sterile bottles, and sterile nitrogen is introduced for deoxygenation. Subsequently, it is autoclaved at a temperature of 116℃-120℃, a pressure of 0.07 MPa-0.09 MPa, and a time of 10 min-20 min.

4. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... In step 2, the waste NCM ternary lithium-ion battery cathode powder prepared in step 1a is added to the anaerobic basic culture medium prepared in step 1b. The initial solid-liquid ratio is set to 1.0 g / L, and the initial bacterial concentration is 10. 7 The bacterial concentration was increased to 10 cells / mL and cultured under anaerobic conditions at 35℃–37℃ until it stabilized. 9 The initial acclimatization culture was completed at a concentration of cells / mL and a pH of 3.5–4.

0. Subsequent subcultures were conducted under the same conditions. After subculture acclimatization, the strain's adaptability was enhanced by gradually increasing the solid-liquid ratio. During each acclimatization, the solid-liquid ratio of the waste NCM ternary lithium-ion battery cathode powder was increased by 1.0 g / L, while other culture conditions remained constant. Each gradient was cultured until the bacterial concentration stabilized at 10⁻⁶ cells / mL. 9 After reaching a concentration of cells / mL, the next gradient acclimatization step is performed, and this gradient acclimatization step is repeated until the solid-liquid ratio of the system is increased to 5.0 g / L, and the concentration of *Lactobacillus plantarum* strain can still be stably maintained at 10 g / mL after cultivation under this solid-liquid ratio condition. 9 When the number of cells / mL reaches a certain threshold, the acclimatization process is considered complete.

5. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... In step 3, the *Lactobacillus plantarum* strain that has been cryopreserved and acclimatized in step 2 is taken and, in a sterile anaerobic glove box, is prepared at an initial bacterial concentration of 10... 7 An inoculum of *Lactobacillus plantarum* cells / mL was inoculated into the anaerobic basal medium after deoxygenation treatment in step 1b, and cultured at 35℃–37℃ under anaerobic conditions for 12h–18h; activation was completed when the strain entered the logarithmic growth phase; the anaerobic basal medium prepared in step 1b was taken, and waste NCM ternary lithium-ion battery cathode powder and metal nanoparticles were added to the medium, and stirred evenly to obtain the leaching medium; the activated *Lactobacillus plantarum* bacterial solution was inoculated into the leaching medium to make the initial bacterial concentration of the system 10. 7 The cells / mL were then used to co-culture the bioleaching system under anaerobic conditions at 35℃–37℃. During co-culture, Lactobacillus plantarum and metal nanoparticles synergistically enhanced leaching and promoted the reduction and dissolution of high-valence metal ions.

6. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... The waste NCM ternary lithium-ion battery cathode materials include NCM111, NCM523, and NCM622.

7. The method for efficiently leaching waste ternary lithium-ion battery cathode powder under anaerobic conditions using metal nanoparticles in conjunction with *Lactobacillus plantarum*, as described in claim 1, is characterized in that... The metal nanoparticles are copper nanoparticles with a particle size range of 30 nm to 50 nm.

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