Preparation method of catalyst based on positive electrode material of retired lithium cobalt oxide battery and application of catalyst in electrolyzed water

Abstract

The invention relates to the technical field of resource recovery and high-value utilization technologies and catalyst preparation, in particular to a preparation method of a catalyst based on a retired lithium cobalt oxide battery positive electrode material and application of the catalyst in electrolyzed water. The preparation method of the catalyst comprises the following steps: (a) charging a decommissioned lithium cobalt oxide battery to a target voltage at a high temperature in a constant current manner, and then keeping the voltage for more than 6 hours at the target voltage; (b) disassembling the retired lithium cobalt oxide battery, collecting a lithium cobalt oxide material of a positive electrode part, and grinding to obtain a catalyst; the target voltage is higher than the charging cut-off voltage of the retired lithium cobalt oxide battery. According to the method, the defect density of the catalyst is improved, active sites are enriched, meanwhile, structural evolution is promoted, structural collapse is effectively avoided, and the catalytic activity and long-term catalytic stability of the prepared catalyst in the water electrolysis oxygen evolution reaction are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resource recycling and high-value utilization and catalyst preparation, in particular to a catalyst preparation method based on retired lithium cobalt oxide battery positive electrode material and application thereof in water electrolysis. BACKGROUND

[0002] With the wide application of lithium ion batteries in the consumer electronics field, lithium cobalt oxide batteries have become one of the mainstream choices due to their high energy density and stable performance, but the resource waste and environmental problems caused by their large-scale retirement have become increasingly serious. According to statistics, among the retired lithium batteries produced globally each year, lithium cobalt oxide batteries account for more than 40%. Traditional recycling technologies include pyrometallurgy and hydrometallurgy, the former has high energy consumption and is prone to produce harmful gases, and the latter has complex process and great difficulty in waste liquid treatment. In addition, although these methods can partially extract cobalt resources, they are difficult to realize high-value utilization, and there is a risk of lithium element loss and secondary pollution in the recycling process.

[0003] At the same time, as a key link of clean energy technology, the water electrolysis hydrogen production has a slow oxygen evolution reaction (OER) kinetics, and it is urgent to develop efficient catalysts to reduce overpotential and energy consumption. Cobalt-based materials (such as cobaltic oxide, cobalt oxyhydroxide, etc.) are of great concern due to their excellent catalytic activity, but the preparation of such materials depends on newly mined cobalt resources, which is costly and unsustainable.

[0004] Under this background, if the cobalt resources in the retired lithium cobalt oxide batteries can be recycled and converted into high-performance OER catalysts, not only can the resource waste and environmental pressure caused by retired batteries be alleviated from the source, but also a low-cost and sustainable catalyst supply path for water electrolysis hydrogen production can be provided, realizing the high-value utilization of retired lithium cobalt oxide battery resources.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a catalyst preparation method based on retired lithium cobalt oxide battery positive electrode material and application thereof in water electrolysis. The method of the present application realizes low-cost and environmentally friendly recycling of retired lithium cobalt oxide battery positive electrode material, and provides a high-value utilization approach. The prepared catalyst exhibits excellent catalytic performance in alkaline water electrolysis oxygen evolution reaction.

[0007] In order to achieve the above-mentioned purpose of the present application, the first aspect of the present application provides a catalyst preparation method based on retired lithium cobalt oxide battery positive electrode material, comprising the following steps: (a) charging the retired lithium cobalt oxide battery at a high temperature to a target voltage at a constant current, and then maintaining the voltage at the target voltage for 6 hours or more; (b) disassembling the retired lithium cobalt oxide battery treated in step (a), collecting the lithium cobalt oxide material of the positive electrode part, and grinding to obtain the catalyst; wherein the target voltage is higher than the charge cut-off voltage of the retired lithium cobalt oxide battery.

[0008] Further, the high temperature is 50-60℃.

[0009] Further, the duration of the maintaining voltage is 6-12 h.

[0010] Further, the nominal voltage of the retired lithium cobalt oxide battery is 3.7-3.8 V, and the charge cut-off voltage of the retired lithium cobalt oxide battery is 4.2-4.4 V.

[0011] Further, the target voltage is 4.2-5 V, preferably 4.5-5 V.

[0012] Further, in the constant current charging, the current is 0.01-0.5 C.

[0013] Further, in the process of maintaining voltage, the retired lithium cobalt oxide battery is charged with a current of ≤0.5 C to maintain the voltage at the target voltage.

[0014] Further, the collecting of the lithium cobalt oxide material of the positive electrode part comprises: soaking the disassembled positive electrode part in an organic solvent, separating the lithium cobalt oxide material, and then washing and drying the lithium cobalt oxide material.

[0015] The second aspect of the present application provides a catalyst prepared by the catalyst preparation method based on the positive electrode material of the retired lithium cobalt oxide battery provided in the first aspect of the present application.

[0016] Further, the catalyst has a micron-level layered structure.

[0017] Further, the average particle size of the catalyst is 2 μm±0.2 μm.

[0018] The third aspect of the present application provides the application of the catalyst of the second aspect of the present application in the oxygen evolution reaction of water electrolysis.

[0019] Compared with the prior art, the present application has the following beneficial effects: (1) The present application realizes precise deep delithiation and controllable structure reconstruction of the positive electrode material of the lithium cobalt oxide battery by high-pressure pressure maintaining treatment of the retired lithium cobalt oxide battery at high temperature; the process is realized by electrochemical overcharging to a target high pressure at high temperature, inducing a large number of oxygen vacancies and various defects in the material, thereby significantly improving the active site density; then, the voltage is maintained at high temperature and small current, which promotes the transformation of the material to the thermodynamic stable state while inducing the ordered evolution of vacancies and defects, so that the catalyst prepared by the method avoids structural collapse while improving the defect density and rich active sites, thereby significantly improving the intrinsic catalytic activity and long-term catalytic stability in the electrolytic water oxygen evolution reaction; (2) The preparation method of the present application is simple and controllable, only needs to adjust the temperature, the target voltage of charging, the time of maintaining voltage, etc., without complex post-treatment, low cost and green environmental protection; and the method of the present application is compatible with existing battery charging and discharging systems, and is easy to scale up production. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0021] Figure 1 The electrochemical test LSV curve of the material provided for different embodiments and comparative examples of the present application; Figure 2 The photo of the retired lithium cobalt oxide battery after treatment in Example 2 of the present application is provided; Figure 3 The XRD comparison chart of the material provided for Examples 1-3 and Comparative Example 2 of the present application is provided; Figure 4 The scanning electron microscope chart of the material provided for Example 2 of the present application is provided; Figure 5 The transmission electron microscope chart of the material provided for Example 2 of the present application is provided; Figure 6 The transmission electron microscope chart of the material provided for Example 4 of the present application is provided. DETAILED DESCRIPTION

[0022] The technical solutions of the present application will be described clearly and completely below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0023] The electrochemical method for treating lithium cobalt oxide battery is a fast way to convert lithium cobalt oxide material into a catalyst. However, the current electrochemical recycling method usually only aims at the delithiation treatment of the positive electrode material of the lithium cobalt oxide battery, and its operation range is limited to the charge cut-off voltage of the battery. The inventors of the present application found in the research that when the retired lithium cobalt oxide battery is overcharged, the stability of the delithiated material is significantly reduced. Specifically, under the condition of high-voltage overcharging, the instability of the lattice oxygen easily causes local lattice collapse and atomic dislocation, and then generates a large number of oxygen vacancies and multiple types of structural defects. Although this process can expose more active sites and give the material potential high catalytic activity, the subsequent structural collapse seriously limits its application. Based on this, the present application proposes a new process: after the retired lithium cobalt oxide battery is deeply delithiated at high voltage, the defects and vacancies are induced to evolve and accurately controlled by combining temperature regulation and small current voltage holding, so that they are gradually converted into thermodynamically stable structures, thereby balancing high defect density and structural stability, and realizing long-term high-efficiency catalytic performance. The method of the present application is not only an effective application of defect engineering, but also opens up a new way for the high-value utilization of retired lithium cobalt oxide batteries.

[0024] The present application provides a catalyst preparation method based on the positive electrode material of the retired lithium cobalt oxide battery in the first aspect, which comprises the following steps: (a) charging the retired lithium cobalt oxide battery at a high temperature to a target voltage at a constant current, and then maintaining the voltage at the target voltage for 6 hours or more; (b) disassembling the retired lithium cobalt oxide battery treated in step (a), collecting the lithium cobalt oxide material of the positive electrode part, and grinding to obtain a catalyst; Wherein, the target voltage is higher than the charge cut-off voltage of the retired lithium cobalt oxide battery.

[0025] In the preparation method of the present application, through the process of high temperature, high pressure and pressure holding, on the one hand, the positive electrode material of the lithium cobalt oxide battery is deeply delithiated, and a high-density complex defect network (Li vacancy, oxygen vacancy, lattice distortion, and stacking fault coordination) is induced, which significantly increases the active sites of the material. On the other hand, temperature regulation promotes the transformation of the material to a thermodynamic stable state, and the ordered evolution of vacancies and defects is induced at the target voltage by using a small current pressure holding process. Through the synergy of multiple aspects, while increasing the defect density and enriching the active sites, the structural collapse is effectively avoided, and the catalytic activity and long-term catalytic stability of the obtained catalyst in the electrolytic water oxygen evolution reaction are significantly improved.

[0026] Moreover, the present application uses low-cost retired lithium cobalt oxide batteries as raw materials, and directly converts them into high-efficiency alkaline electrolytic water oxygen evolution reaction catalysts through a one-step method, which not only realizes the efficient and green recycling of retired lithium cobalt oxide batteries, but also fits the current carbon reduction and sustainable development theme, and at the same time opens up a new application path for high-value utilization.

[0027] The operation of the present application is compatible with various battery charging and discharging systems and is easy to scale up production. In the subsequent embodiments, only the new Wei battery cabinet "WGDW series (automatic fire extinguishing and explosion-proof type)" is exemplarily used as the charging and discharging environment, and the new Wei battery test equipment NEWARE BTS8.0.1 (64-bit) software version is used.

[0028] In the specific embodiments of the present application, the retired lithium cobalt oxide battery can be derived from mobile phones, digital cameras, notebook computers, mobile power supplies, etc., and is not limited thereto.

[0029] In the specific embodiments of the present application, the nominal voltage of the retired lithium cobalt oxide battery is 3.7-3.8 V, for example, it can be 3.7 V, 3.72 V, 3.75 V, 3.78 V, 3.8 V, or a range formed by any two of them; the charge cut-off voltage of the retired lithium cobalt oxide battery is 4.2-4.4 V, for example, it can be 4.2 V, 4.25 V, 4.3 V, 4.35 V, 4.4 V, or a range formed by any two of them.

[0030] The retired lithium cobalt oxide battery is obtained after the lithium cobalt oxide battery meets the retirement conditions after being used for a period of time. The retirement conditions include safety performance and electrical performance. It should be noted that the retired lithium cobalt oxide battery of the present application refers to: when the rated capacity of the battery is attenuated to below 80% of the initial nominal capacity, the battery is retired.

[0031] In the specific embodiments of the present application, the high temperature is 50-60℃, for example, it can be 50℃, 52℃, 55℃, 58℃, 60℃ or a range consisting of any two of them. The temperature of the charging and maintaining voltage of step (a) of the present application can be independently selected from 50-60℃. Controlling the temperature within the above range is more conducive to ensuring the balance between the deep delithiation and controllable structural reconstruction of the lithium cobalt oxide positive electrode material. When the temperature is too low, not only is the degree of delithiation low, but the temperature is also insufficient to cause the material to transition to a thermodynamically stable state; when the temperature is too high, it will exacerbate the collapse of the material structure, making it difficult to reconstruct a stable defect structure with high catalytic activity.

[0032] In the specific embodiments of the present application, the current in the constant current charging is 0.01-0.5 C, for example, it can be 0.01 C, 0.05 C, 0.1 C, 0.2 C, 0.3 C, 0.4 C, 0.5 C or a range consisting of any two of them. Controlling the current in the constant current charging within the above range helps to maintain the integrity of the material bulk structure, providing a basis for the subsequent reconstruction and evolution of the material internal defects. When the current is too large, lithium ions are rapidly and massively removed, resulting in a dramatic increase in lattice stress and leading to structural collapse; when the current is too small, it is not conducive to improving production efficiency.

[0033] In the specific embodiments of the present application, the target voltage is 4.2-5 V, for example, it can be 4.2 V, 4.3 V, 4.4 V, 4.45 V, 4.5 V, 4.55 V, 4.6 V, 4.65 V, 4.7 V, 4.75 V, 4.8 V, 4.9 V, 5 V or a range consisting of any two of them, preferably 4.5-5 V. The appropriate target voltage is more conducive to achieving a balance between high defect density and structural stability. When the target voltage is too low, it is insufficient to induce high active sites (such as vacancy defects, atomic disorder, etc.), the defect density is low, and the number of active sites is insufficient; when the target voltage is too high, it will cause excessive delithiation, the structure formed will irreversibly collapse, resulting in poor structural stability and hindering the catalytic process.

[0034] In the specific embodiments of the present application, the duration of the maintaining voltage is 6-24 h, for example, it can be 6 h, 8 h, 12 h, 16 h, 20 h, 24 h or a range consisting of any two of them. When the duration of the maintaining voltage is insufficient, it cannot induce the ordered evolution of vacancies and defects, resulting in low defect density and poor catalytic activity; when the duration of the maintaining voltage is too long, not only does it affect production efficiency, but it can also cause further structural collapse and further reduce the atomic layer spacing, changing from the original O3 phase to the more inert rock salt phase and spinel phase, reducing the efficiency and stability of the catalyst.

[0035] In the specific embodiment of the present application, the voltage of the retired lithium cobalt oxide battery is maintained at the target voltage by charging the retired lithium cobalt oxide battery at a current of ≤0.5 C.

[0036] In actual operation, after the retired lithium cobalt oxide battery is charged at a constant current to the target voltage, the charging is stopped. Due to self-discharge of the battery, the voltage of the battery decreases over time. After stopping charging for 5-10 s, the retired lithium cobalt oxide battery is continuously charged at a current of ≤0.5 C until the target voltage is reached, and the charging is stopped, which is one cycle; such a cycle is repeated until the voltage is maintained at the target voltage for 6 h or more.

[0037] In the specific embodiment of the present application, maintaining the voltage at the target voltage for 6 h or more includes: (S1) After stopping charging the battery for 5-10 s, charging at a current of 0.01-0.5 C to the target voltage, and then stopping charging; (S2) Repeat step (S1) until the battery voltage is maintained at the target voltage for 6 h or more.

[0038] As in different embodiments, in step (S1), the current can be 0.01 C, 0.05 C, 0.1 C, 0.2 C, 0.3 C, 0.4 C, 0.5 C, or a range formed by any two of them. By cyclic charging at high temperature and small current, the voltage is maintained, which can induce the ordered evolution of vacancies and defects, thereby avoiding structural collapse while maintaining high defect density and abundant active sites, significantly improving the stability and long-term catalytic performance of the catalyst.

[0039] In actual operation, the above operation can be completed by using a battery charging and discharging system with conventional settings, which will not be described here.

[0040] The present application can induce and control the evolution of defects and vacancies by temperature regulation and small current voltage maintenance, gradually converting them into thermodynamically stable structures, thereby balancing high defect density and structural stability, and achieving long-term high-efficiency catalytic performance.

[0041] In the specific embodiment of the present application, after the operation of step (a) is completed, the retired lithium cobalt oxide battery is not discharged and is directly disassembled.

[0042] In the specific embodiment of the present application, collecting the lithium cobalt oxide material from the positive electrode part includes: soaking the positive electrode part obtained by disassembly in an organic solvent, separating the lithium cobalt oxide material, and then washing and drying the lithium cobalt oxide material.

[0043] In the detailed description of the present application, the organic solvent includes, but is not limited to, at least one of ethanol, isopropanol, N-methyl pyrrolidone and acetone. The amount of the organic solvent is not limited, and the positive electrode part can be completely soaked.

[0044] In the detailed description of the present application, the organic solvent includes isopropanol and N-methyl pyrrolidone. Further, the volume ratio of isopropanol and N-methyl pyrrolidone is 1: (0.1-10).

[0045] In the detailed description of the present application, the soaking time is 1-24 h, for example, 1 h, 2 h, 6 h, 10 h, 12 h, 16 h, 20 h, 24 h or a range consisting of any two of them; the soaking temperature is 30-60℃, for example, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃ or a range consisting of any two of them.

[0046] In the detailed description of the present application, during the soaking process, ultrasonic or stirring is performed. The duration of ultrasonic and stirring is not limited, and the lithium cobaltate material can be detached from the positive electrode current collector.

[0047] In the detailed description of the present application, after soaking, the lithium cobaltate material can be obtained by separation methods such as filtration or centrifugation.

[0048] In the detailed description of the present application, the washing includes water washing and / or ethanol washing. Further, the separated lithium cobaltate material can be first subjected to water washing, and then subjected to ethanol washing. The number of water washing and ethanol washing is not limited, for example, each can be independently selected from 1-5 times.

[0049] In the detailed description of the present application, the drying temperature is 50-60℃, and the drying time is 12-24 h.

[0050] In the detailed description of the present application, the grinding treatment method includes ball milling.

[0051] In the detailed description of the present application, in the ball milling, the ball-to-material ratio is (50-200): 1, for example, 50:1, 80:1, 100:1, 120:1, 150:1, 180:1, 200:1 or a range consisting of any two of them.

[0052] In the detailed description of the present application, in the ball milling, N-methyl pyrrolidone is used as the ball milling medium. Further, the ratio of lithium cobaltate material to ball milling medium is 1 g: (10-20) mL, for example, compared to 1 g of lithium cobaltate material to be subjected to ball milling, the amount of ball milling medium can be 10 mL, 12 mL, 15 mL, 18 mL, 20 mL or a range consisting of any two of them.

[0053] In the specific embodiments of the present application, the ball milling speed is 300-500 rpm, for example, it can be 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm or a range consisting of any two of them.

[0054] In the specific embodiments of the present application, it also includes washing and drying the material after ball milling. The washing and drying operations can refer to the washing and drying operations after separating the lithium cobalt oxide material, which will not be repeated here.

[0055] The second aspect of the present application provides a catalyst prepared by the method for preparing a catalyst based on the positive electrode material of the retired lithium cobalt oxide battery provided by the first aspect of the present application.

[0056] In the specific embodiments of the present application, the catalyst has a micron-level layered structure. The catalyst obtained by the method of the present application has a micron-level layered structure, showing high specific surface area and abundant active sites.

[0057] In the specific embodiments of the present application, the average particle size of the catalyst is 2 μm±0.2 μm, for example, it can be 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm or a range consisting of any two of them.

[0058] The third aspect of the present application provides the use of the catalyst of the second aspect of the present application in the oxygen evolution reaction of water electrolysis.

[0059] The retired lithium cobalt oxide battery used in the following specific embodiments of the present application is from a soft-pack battery used for toys, which is from Xi'an Jingwei Neng Electronic Technology Co., Ltd., model PL404048-950 mAh, rated capacity 950 mAh, nominal voltage 3.7 V.

[0060] Example 1 The present embodiment provides a method for preparing a catalyst based on the positive electrode material of the retired lithium cobalt oxide battery, which comprises the following steps: (1) The retired lithium cobalt oxide battery is charged at a constant current of 0.5 C to 4.2 V at 60℃, and the voltage is maintained at 4.2 V for 12 h at 60℃; wherein, after the battery voltage reaches 4.2 V, the charging is stopped for 10 s, and then the battery is charged at a constant current of 0.1 C to 4.2 V; the foregoing operation is repeated until the battery voltage is maintained at 4.2 V for 12 h.

[0061] (2) The battery treated in step (1) is not discharged, and the positive electrode part is directly disassembled and soaked in N-methyl pyrrolidone and isopropyl alcohol at a volume ratio of 1:1 at 30°C for 6 h, ultrasonic treatment is performed during the soaking for about 1 h, and centrifugal separation is performed to obtain a lithium cobalt oxide material; the lithium cobalt oxide material is washed with water for 3 times and washed with ethanol for 3 times, and then dried in an oven at 60°C for 24 h to collect the material.

[0062] (3) The material obtained in step (2) is weighed with N-methyl pyrrolidone at a ratio of 1 g:15 mL, added into a ball mill, and ball milled at 500 rpm for 24 h at a ball-to-material ratio of 100:1 (zirconium bead milling is used); the material after ball milling is collected, washed with water for 3 times, washed with ethanol for 3 times, and then dried in an oven at 60°C for 24 h to obtain a catalyst.

[0063] Example 2 The embodiment provides a catalyst preparation method based on a retired lithium cobalt oxide battery positive electrode material, including the following steps: (1) The retired lithium cobalt oxide battery is charged at a current of 0.5 C to 4.5 V at 60°C, and the voltage is maintained at 4.5 V for 12 h at 60°C; wherein the voltage maintained at 4.5 V for 12 h includes: after the battery voltage reaches 4.5 V, the charging is stopped for 10 s, and then the charging is performed at a current of 0.1 C to 4.5 V; the foregoing operation is repeated until the battery voltage is maintained at 4.5 V for 12 h.

[0064] (2) The battery treated in step (1) is not discharged, and the positive electrode part is directly disassembled and soaked in N-methyl pyrrolidone and isopropyl alcohol at a volume ratio of 1:1 at 30°C for 6 h, ultrasonic treatment is performed during the soaking for about 1 h, and centrifugal separation is performed to obtain a lithium cobalt oxide material; the lithium cobalt oxide material is washed with water for 3 times and washed with ethanol for 3 times, and then dried in an oven at 60°C for 24 h to collect the material.

[0065] (3) The material obtained in step (2) is weighed with N-methyl pyrrolidone at a ratio of 1 g:15 mL, added into a ball mill, and ball milled at 500 rpm for 24 h at a ball-to-material ratio of 100:1 (zirconium bead milling is used); the material after ball milling is collected, washed with water for 3 times, washed with ethanol for 3 times, and then dried in an oven at 60°C for 24 h to obtain a catalyst.

[0066] Example 3 The embodiment provides a catalyst preparation method based on a retired lithium cobalt oxide battery positive electrode material, including the following steps: (1) The retired lithium cobalt oxide battery is charged at 0.5 C to 4.8 V at 60 °C, and the voltage is maintained at 4.8 V for 12 h at 60 °C; wherein, the voltage is maintained at 4.8 V for 12 h includes: after the battery voltage reaches 4.8 V, stop charging for 10 s, and then charge at 0.1 C to 4.8 V; repeat the foregoing operation until the battery voltage is maintained at 4.8 V for 12 h.

[0067] (2) The battery treated in step (1) is not discharged, and the positive electrode part is directly disassembled and soaked in a volume ratio of 1:1 N-methyl pyrrolidone and isopropyl alcohol at 30 °C for 6 h, and ultrasonic treatment is performed during the soaking for about 1 h. Centrifugal separation obtains lithium cobalt oxide material; after the lithium cobalt oxide material is washed with water 3 times and ethanol 3 times, it is dried in an oven at 60 °C for 24 h, and the material is collected.

[0068] (3) The material obtained in step (2) is weighed with N-methyl pyrrolidone at a ratio of 1 g:15 mL, added to a ball mill, ball-milled at a ball-to-material ratio of 100:1 (zirconium bead ball milling) at 500 rpm for 24 h, and the material after ball milling is collected, washed with water 3 times and ethanol 3 times, and dried in an oven at 60 °C for 24 h to obtain a catalyst.

[0069] Example 4 This example refers to the preparation method of Example 2, the only difference being that in step (1), the duration of maintaining the voltage at 4.5 V is different, and the specific difference is as follows: In this example, the duration of maintaining the voltage at 4.5 V is 24 h.

[0070] Comparative Example 1 Comparative Example 1 refers to the preparation method of Example 1, the only difference being that step (1) is different.

[0071] Step (1) of Comparative Example 1 includes: the retired lithium cobalt oxide battery is charged at 0.5 C to 4.5 V at 30 °C, and the charging is terminated.

[0072] Comparative Example 2 Comparative Example 2 refers to the preparation method of Example 1, the only difference being that step (1) is different.

[0073] Step (1) of Comparative Example 2 includes: the retired lithium cobalt oxide battery is not charged, and is directly disassembled.

[0074] Comparative Example 3 Comparative Example 3 refers to the preparation method of Example 2, the only difference being that in step (1), the duration of maintaining the voltage at 4.5 V is different, and the specific difference is as follows: In Comparative Example 3, the duration of the 4.5 V holding voltage was 0 h.

[0075] Experimental Example The materials obtained in different examples and comparative examples were subjected to electrochemical tests, and the test scenario was the alkaline electrolytic water oxygen evolution reaction. The tests of all the materials were performed under the same conditions, and the test method was as follows, and the test results are shown in Figures 1-2 The materials were loaded on carbon paper at 2 mg / cm 2 , and the electrolyte was 1 mol / L potassium hydroxide. Ag / AgCl and carbon rod were the reference electrode and the counter electrode, respectively. The scan rate of LSV test was 2 mV / s, and the automatic compensation was 85%.

[0076] Figure 1 The electrochemical test LSV curves of the materials provided in different examples and comparative examples of the application are shown in Table 1. Table 1 is the overpotential at 10 mA / cm 2 and the CP stability test at 10 mA / cm 2 current density of the materials obtained by the chronoamperometry method. From Figure 1 and Table 1, it can be seen that the electrochemical performance of the materials provided in different examples and comparative examples has great difference. Among them, Comparative Example 2, as a retired lithium cobalt oxide without high-temperature charging treatment, has the maximum overpotential at 10 mA / cm 2 position and the shortest stable running time, indicating that it needs a larger starting potential for catalyzing the alkaline oxygen evolution reaction, has poor catalytic performance and low efficiency, and is not suitable as a catalyst for the alkaline electrolytic water oxygen evolution reaction.

[0077] According to the overpotential and stability duration data of Examples 1-3, it is found that under different cutoff voltages, at 60℃, and under the pressure holding for 12 h, all have better data and better catalytic performance. Relatively speaking, Example 2 has the lowest overpotential and the longest stable running time (stable running for more than 100 h). Analysis shows that as the voltage increases, the battery overcharging degree increases, and the lithium extraction amount increases. Under the same high temperature and holding voltage duration, the overpotential at 10 mA / cm 2 position is further reduced. Example 2 only needs an overpotential of 334 mV at 10 mA / cm 2 , showing the best alkaline electrolytic water oxygen evolution catalytic performance. However, as the cutoff voltage further increases, in Example 3, the overcharging voltage is 4.8 V, and the catalytic performance does not further improve, which is because the excessive overcharging voltage leads to excessive lithium extraction, and the structure formed is irreversibly collapsed, and the structure is more unstable, hindering the catalytic process.

[0078] ​According to the results, examples 4 and comparative example 3 with different holding time are prepared for example 2 with optimal performance, and the performance of which is compared in table 1, it can be seen that no matter how long or short the holding time is, it will reduce the catalytic efficiency and stability. It can be seen that the holding time is the key to ensure that the positive material of the retired lithium cobalt oxide battery is converted into a high-efficiency catalyst. Comparative example 3 without holding has poor overpotential and stability, which is due to the fact that the vacancies and defects formed after the positive material of the lithium cobalt oxide battery is delithiated need to increase the stability of the structure, regulate the type of structural defects and improve the catalytic performance under the condition of high temperature and holding voltage. However, example 4 with further holding for 24 h, the internal atomic structure and arrangement of which has further changed, part of the vacancies as active centers collapses to affect the catalytic activity, and part of the dislocation defects further twists to cause unstable structure, etc. These conditions make the overpotential of the catalyst increase and the stable running time decrease.

[0079] In addition, comparative example 1 as a low-temperature comparative example of example 2 shows worse catalytic performance than example 2, which indicates that the evolution of the internal structure and the regulation of defects need higher temperature to promote the formation thereof. In summary, the vacancies and defects formed after the positive material of the lithium cobalt oxide battery is delithiated need to realize the promotion of the evolution of the internal structure and the regulation of defects, and improve the catalytic performance under the condition of appropriate high temperature and a certain time of holding voltage.

[0080] Table 1 overpotential and stable running time of different materials under 10 mA / cm 2

[0081] In order to explore the mechanism of the structural change of the treated material and the improvement of the catalytic performance thereof, the present application carries out systematic characterization of the material from macro to micro. Figure 2 It is the photo of the retired lithium cobalt oxide battery after disassembly after the treatment of example 2 of the present application by step (1), and from the figure, it can be seen that a large amount of positive material falls off and adheres to the negative electrode and the separator. This indicates that the positive electrode is seriously delithiated under the condition of high temperature and long time holding voltage. Figure 3 It is the XRD comparison chart of the materials provided by examples 1-3 and comparative example 2 of the present application, and from the figure, it can be seen that the 003 crystal plane of the lithium cobalt oxide of examples 1-3 moves to the left compared with comparative example 2, which indicates that the spacing between the two cobalt oxide layers increases, which is also due to the fact that a large amount of Li layer is delithiated. In addition, a large amount of electrolyte is decomposed during the delithiation process, which destroys the material structure, and it is inferred that a large amount of vacancy defects and atomic dislocation defects are generated in the positive electrode part of the lithium cobalt oxide. The morphology of the material provided by example 2 is observed by scanning electron microscope (SEM), as shown in Figure 4 ​As shown, the retired lithium cobalt oxide positive electrode material treated by electrochemistry and ball milling has a micron-level layered structure (average particle size of 2 pm ± 0.2 pm, particle size distribution of 0.5-3 pm), high specific surface area and rich active sites. Further, the atomic arrangement of the material provided in Example 2 was observed by transmission electron microscopy (TEM), as shown in FIG. 2. Figure 5 As shown, the material after electrochemical treatment has significant atomic layer misalignment and bending. The atomic interlayer spacing in these regions changes, and the charge distribution state is different from that of the original material, forming more active active sites, which is one of the key reasons for its better performance. However, long-term pressure retention further affects its internal structure, from Figure 6 It can be seen from FIG. 4 that the atomic layers of Example 4 are severely misaligned and the structure is locally disordered, which may exacerbate the risk of Co dissolution and structural collapse.

[0082] In summary, the material of Example 2 induces high active sites (such as vacancy defects and atomic misalignment) under specific treatment, accelerates the evolution of material defect structure, and effectively controls the stability of the structure, so the material exhibits the best catalytic performance and has commercial potential.

[0083] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a catalyst based on retired lithium cobalt oxide battery cathode material, characterized in that, Includes the following steps: (a) Charge the retired lithium cobalt oxide battery at a constant current at high temperature to the target voltage, and then maintain the voltage at the target voltage for more than 6 hours; (b) Disassemble the retired lithium cobalt oxide battery after step (a), collect the lithium cobalt oxide material in the positive electrode part, grind it to obtain the catalyst; The target voltage is higher than the charging cutoff voltage of the retired lithium cobalt oxide battery.

2. The preparation method according to claim 1, characterized in that, The high temperature is 50–60°C.

3. The preparation method according to claim 1, characterized in that, The duration of the voltage holding period is 6 to 12 hours.

4. The preparation method according to claim 1, characterized in that, It has at least one of the following characteristics: (1) The nominal voltage of the retired lithium cobalt oxide battery is 3.7 to 3.8 V, and the charging cut-off voltage of the retired lithium cobalt oxide battery is 4.2 to 4.4 V; (2) The target voltage is 4.2 to 5 V.

5. The preparation method according to claim 1, characterized in that, In the constant current charging, the current is 0.01 to 0.5C.

6. The preparation method according to claim 1, characterized in that, During the voltage maintenance process, the decommissioned lithium cobalt oxide battery is charged with a current of ≤0.5 C to maintain the voltage at the target voltage.

7. The preparation method according to claim 1, characterized in that, The process of collecting the lithium cobalt oxide material from the positive electrode portion includes: immersing the disassembled positive electrode portion in an organic solvent to separate the lithium cobalt oxide material, and then washing and drying the lithium cobalt oxide material.

8. A catalyst based on retired lithium cobalt oxide battery cathode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The catalyst according to claim 8, characterized in that, It has at least one of the following characteristics: (1) The catalyst has a micron-scale layered structure; (2) The average particle size of the catalyst is 2 μm ± 0.2 μm.

10. The application of the catalyst according to claim 8 or 9 in the oxygen evolution reaction of water electrolysis.

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