Method for recovering positive active material from waste positive pole piece

Abstract

The invention provides a method for recovering a positive active material from a waste positive pole piece, which comprises the following steps: (1) carrying out quenching treatment on the positive pole piece in liquid nitrogen to obtain a quenched positive pole piece; (2) heating and soaking the quenched positive pole piece in a stripping solution, carrying out ultrasonic treatment, and carrying out solid-liquid separation to obtain slurry containing a positive active material; the stripping liquid comprises an organic solvent and an oxidizing agent. According to the method provided by the invention, the positive electrode active material can directly fall off, and impurities such as a current collector are effectively prevented from being introduced.

Description

Technical Field

[0001] This invention relates to the field of cathode material recycling technology, and in particular to a method for recycling cathode active materials from waste cathode sheets. Background Technology

[0002] Since its successful commercialization, lithium-ion batteries have been widely used in mobile electronic devices, electric vehicles, and power grids due to their long lifespan, high energy density, and wide operating temperature range. In recent years, with increasing attention to energy and environmental issues, the demand for developing new energy vehicles, hybrid vehicles, or electric vehicles has further expanded.

[0003] The continuous development of the electric vehicle industry has brought about the issue of how to dispose of electric vehicle batteries after they are scrapped. Currently, the positive electrode material of electric vehicle batteries is mainly ternary material. If these waste batteries are not disposed of properly, they will have an impact on the environment: First, the decomposition of waste electrolyte in the battery will produce harmful substances such as HF, which will harm human health and the environment; second, the transition metals such as nickel, cobalt, and manganese in the battery also have certain hazards and will have an adverse impact on the environment.

[0004] On the other hand, used batteries are a resource in themselves, and especially given the current scarcity of energy and resources, the resource utilization and processing of used batteries is particularly important. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for recovering positive electrode active materials from waste positive electrode sheets. By using rapid cooling and a specific stripping solution for stripping, the positive electrode active material can be directly stripped from the current collector, avoiding the entry of impurities such as those in the current collector into the positive electrode active material. Subsequent recycling and separation are also simpler, and the method has broad application prospects.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for recovering positive electrode active materials from waste positive electrode sheets, the method comprising the following steps:

[0008] (1) The positive electrode sheet is rapidly cooled in liquid nitrogen to obtain a rapidly cooled positive electrode sheet;

[0009] (2) The rapidly cooled positive electrode sheet is placed in a stripping solution for heating and immersion, and then subjected to ultrasonic treatment. After solid-liquid separation, a slurry containing positive electrode active material is obtained. The stripping solution includes an organic solvent and an oxidant.

[0010] This invention first involves rapid cooling in liquid nitrogen, where the temperature is extremely low, subjecting the positive electrode sheet to a precipitous cooling environment. This is followed by heating and immersion. The temperature difference between the liquid nitrogen and heating / immersion environments causes the material in the positive electrode sheet to first contract and then expand. Due to the difference in thermal expansion coefficients between the current collector and the positive electrode active material layer, the positive electrode active material film layer peels off from the current collector after the rapid cooling and heating / immersion. A peeling solution is used simultaneously to assist in the peeling process, achieving efficient and simple separation of the positive electrode active material from the current collector. The resulting slurry containing the positive electrode active material, free of current collector impurities, can be repaired and reused, demonstrating broad application prospects.

[0011] Preferably, the positive electrode sheet in step (1) includes a positive electrode sheet containing a ternary positive electrode active material.

[0012] Preferably, the current collector of the positive electrode sheet includes an aluminum foil current collector.

[0013] Preferably, the molar ratio of nickel, cobalt and manganese in the positive electrode sheet in step (1) is 1~8:0.5~1:1, wherein the number of nickel parts can be, for example, 1, 1.8, 2.6, 3.4, 4.2, 4.9, 5.7, 6.5, 7.3 or 8, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] The amount of cobalt can be, for example, 0.5, 0.56, 0.62, 0.67, 0.73, 0.78, 0.84, 0.89, 0.95 or 1, but is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0015] Preferably, the quenching time in step (1) is 0.5 to 1 hour, for example, it can be 0.5 hours, 0.56 hours, 0.62 hours, 0.67 hours, 0.73 hours, 0.78 hours, 0.84 hours, 0.89 hours, 0.95 hours or 1 hour, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the organic solvent in the stripping solution in step (2) includes any one or a combination of at least two of dimethyl sulfoxide, N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone, wherein typical but non-limiting combinations are a combination of dimethyl sulfoxide and N,N-dimethylacetamide, a combination of N,N-dimethylformamide and N,N-methylpyrrolidone, a combination of N-methylpyrrolidone and N,N-dimethylacetamide, or a combination of dimethyl sulfoxide and N-methylpyrrolidone.

[0017] Preferably, the oxidant includes any one or a combination of at least two of ozone, hydrogen peroxide, or potassium permanganate, wherein typical but non-limiting combinations are a combination of ozone and hydrogen peroxide, a combination of ozone and potassium permanganate, a combination of potassium permanganate and hydrogen peroxide, or a combination of potassium permanganate, ozone, and hydrogen peroxide.

[0018] Preferably, the mass ratio of the oxidant to the organic solvent in step (2) is 0.25 to 1:1, for example, it can be 0.25:1, 0.34:1, 0.42:1, 0.5:1, 0.59:1, 0.67:1, 0.75:1, 0.84:1, 0.92:1 or 1:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] The present invention preferably controls the mass ratio of oxidant to organic solvent within the above-mentioned range, which can significantly improve the stripping effect of positive electrode active material, while effectively avoiding the current collector from entering the active slurry.

[0020] Preferably, the heating and soaking temperature in step (2) is 60~80℃, for example, it can be 60℃, 63℃, 65℃, 67℃, 69℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] The present invention preferably controls the heating and soaking temperature within the above-mentioned range, which can improve the stripping effect while reducing the leaching of aluminum current collectors in the stripped slurry. Specifically, the binder in waste positive electrode sheets is generally PVDF. When the heating and soaking temperature is too low, the stripping solution is difficult to effectively dissolve PVDF, and the recovery rate of positive electrode active material decreases; when the heating and soaking temperature is too high, the dissolution rate of PVDF is accelerated, and the oxidizing power of potassium permanganate is enhanced. Under 90°C conditions, it is very likely to react with the current collector aluminum foil, introducing Al impurities.

[0022] Preferably, the power of the ultrasonic treatment in step (2) is 50~500W, for example, it can be 50W, 100W, 150W, 200W, 250W, 300W, 350W, 400W, 450W or 500W, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the ultrasonic treatment time is 2 to 5 hours, for example, 2 hours, 2.4 hours, 2.7 hours, 3 hours, 3.4 hours, 3.7 hours, 4 hours, 4.4 hours, 4.7 hours or 5 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the solid-liquid ratio of the positive electrode sheet to the stripping solution after rapid cooling in step (2) is 0.1~1g / mL, for example, it can be 0.1g / mL, 0.2g / mL, 0.3g / mL, 0.4g / mL, 0.5g / mL, 0.6g / mL, 0.7g / mL, 0.8g / mL, 0.9g / mL or 1g / mL, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] As a preferred technical solution of the present invention, the method includes the following steps:

[0026] (1) The positive electrode sheet is rapidly cooled in liquid nitrogen for 0.5~1h to obtain the rapidly cooled positive electrode sheet;

[0027] (2) The rapidly cooled positive electrode sheet is placed in a stripping solution and heated to 60-80°C and ultrasonically treated for 2-5 hours at a power of 50-500W, with a solid-liquid ratio of 0.1-1 g / mL. Then, a slurry containing positive electrode active material is obtained by solid-liquid separation. The stripping solution includes an organic solvent and an oxidant, with a mass ratio of oxidant to organic solvent of 0.25-1:1.

[0028] Compared with the prior art, the present invention has at least the following beneficial effects:

[0029] The method for recovering positive electrode active material from waste positive electrode sheets provided by this invention enables the direct stripping of positive electrode active material from the current collector, avoiding the entry of impurities such as those from the current collector into the positive electrode active material. The slurry containing positive electrode active material has a low aluminum content, less than 0.03 wt%, with nickel recovery rates exceeding 99.3%, cobalt recovery rates exceeding 98.5%, manganese recovery rates exceeding 99.8%, and lithium recovery rates exceeding 99.5%. Subsequent separation of individual elements is unnecessary; only the proportions of the corresponding elements need to be adjusted and impurities removed to obtain the positive electrode active material slurry, which can be directly reused, demonstrating broad application prospects. Detailed Implementation

[0030] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0031] Example 1

[0032] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets, the preparation method comprising the following steps:

[0033] (1) Positive electrode sheet (current collector is aluminum foil, positive electrode active material is LiNi) 0.8 Co 0.1 Mn0.1 O2) was rapidly cooled in liquid nitrogen for 40 minutes to obtain the rapidly cooled positive electrode sheet;

[0034] (2) The rapidly cooled positive electrode sheet was placed in the stripping solution and heated to 75°C and ultrasonically treated for 3 hours at a power of 250W, and then filtered to obtain a slurry containing positive electrode active material. The stripping solution includes dimethyl sulfoxide and potassium permanganate, and the mass ratio of potassium permanganate to dimethyl sulfoxide is 0.3:1.

[0035] Example 2

[0036] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets, the preparation method comprising the following steps:

[0037] (1) Positive electrode sheet (current collector is aluminum foil, positive electrode active material is LiNi) 0.7 Co 0.1 Mn 0.2 O2) was rapidly cooled in liquid nitrogen for 30 minutes to obtain the rapidly cooled positive electrode sheet;

[0038] (2) The quenched positive electrode sheet is placed in the stripping solution and heated to 80°C and ultrasonically treated for 2 hours at a power of 50W, and then filtered to obtain a slurry containing positive electrode active material. The stripping solution includes N-methylpyrrolidone and hydrogen peroxide, and the mass ratio of hydrogen peroxide to N-methylpyrrolidone is 1:1.

[0039] Example 3

[0040] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets, the preparation method comprising the following steps:

[0041] (1) Positive electrode sheet (current collector is aluminum foil, positive electrode active material is LiNi) 0.6 Co 0.2 Mn 0.2 O2) was rapidly cooled in liquid nitrogen for 60 min to obtain the rapidly cooled positive electrode sheet;

[0042] (2) The rapidly cooled positive electrode sheet was placed in the stripping solution and heated to 60°C and ultrasonically treated for 5 hours at a power of 500W, and then filtered to obtain a slurry containing positive electrode active material. The stripping solution included N,N-dimethylacetamide and potassium permanganate, and the mass ratio of potassium permanganate to N,N-dimethylacetamide was 0.25:1.

[0043] Example 4

[0044] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1, except that the heating and soaking temperature is 50°C. It will not be described again here.

[0045] Example 5

[0046] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1, except that the heating and soaking temperature is 90°C. It will not be described again here.

[0047] Example 6

[0048] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. Except for the mass ratio of potassium permanganate to dimethyl sulfoxide in step (2) being 0.2:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0049] Example 7

[0050] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. Except for the mass ratio of potassium permanganate to dimethyl sulfoxide in step (2) being 1.2:1, the preparation method is the same as in Example 1, and will not be repeated here.

[0051] Example 8

[0052] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1, except that potassium permanganate is replaced with hydrogen peroxide, and will not be described again here.

[0053] Example 9

[0054] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1, except that potassium permanganate is replaced with ozone, and will not be described again here.

[0055] Example 10

[0056] This embodiment provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1, except that dimethyl sulfoxide is replaced with acetone, and will not be described again here.

[0057] Comparative Example 1

[0058] This comparative example provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1 except that liquid nitrogen quenching is not performed, and will not be repeated here.

[0059] Comparative Example 2

[0060] This comparative example provides a method for recovering positive electrode active material from waste positive electrode sheets. Except for the cold treatment in step (1) at -15°C, the preparation method is the same as in Example 1, and will not be repeated here.

[0061] Comparative Example 3

[0062] This comparative example provides a method for preparing a ternary cathode material. The preparation method is the same as that in Example 1 except that potassium permanganate is not added, and will not be repeated here.

[0063] Comparative Example 4

[0064] This comparative example provides a method for recovering positive electrode active materials from waste positive electrode sheets. The preparation method is the same as in Example 1 except that dimethyl sulfoxide is replaced with water, and will not be described again here.

[0065] Test method: The aluminum, nickel, manganese, cobalt and lithium contents in the above-mentioned slurry containing positive electrode active material were tested by ICP, and the recovery rates of nickel, cobalt, manganese and lithium were calculated based on the nickel, manganese, cobalt and lithium contents in the original positive electrode sheet.

[0066] The test results of the above embodiments and comparative examples are shown in Table 1.

[0067] Table 1

[0068]

[0069] The following points can be observed from Table 1:

[0070] (1) As can be seen from the comprehensive examples 1 to 3, the method for recovering positive electrode active material from waste positive electrode sheets provided by the present invention can obtain a slurry containing positive electrode active material by first performing liquid nitrogen rapid cooling treatment and then heating and soaking. The aluminum content in the slurry containing positive electrode active material is low, only within 0.03wt%, the recovery rate of nickel is above 99.3%, the recovery rate of cobalt is above 98.5%, the recovery rate of manganese is above 99.8%, and the recovery rate of lithium is above 99.5%. Since the aluminum content in the positive electrode slurry obtained by stripping is low and nickel, cobalt, manganese and lithium are basically recovered, there is no need to separate each element in the subsequent process. Only the proportion of the corresponding elements can be compounded and impurities removed to obtain the positive electrode active material slurry, which can be directly reused and has broad application prospects.

[0071] (2) As can be seen from Examples 1 and 4-5, the dissolution rate of PVDF slowed down at the heating and soaking temperature of 50°C in Example 4, resulting in a decrease in the recovery rate of each element under the same conditions. In Example 5, when the heating and soaking temperature was 90°C, the dissolution rate of PVDF accelerated, and the oxidizing power of potassium permanganate was enhanced. At 90°C, it is very likely to react with the aluminum foil current collector, introducing Al impurities, which would require the slurry to undergo a complex separation process. This shows that the present invention controls the heating and soaking temperature within a reasonable range, which can balance the recovery rate of the positive electrode active material elements and the aluminum impurity content of the recovered slurry.

[0072] (3) It can be seen from the combined examples 1 and 6 to 7 that the mass ratio of potassium permanganate to dimethyl sulfoxide in example 6 is too low, which cannot guarantee the oxidation effect of the stripping solution and causes a decrease in recovery rate. In example 7, the mass ratio of potassium permanganate to dimethyl sulfoxide is too high, and some potassium permanganate will not participate in the reaction, resulting in waste of raw materials. Moreover, the content of dimethyl sulfoxide is too low, which will weaken the dissolution effect on PVDF and thus affect the stripping effect. This shows that the present invention preferably controls the mass ratio of oxidant to dimethyl sulfoxide within a reasonable range, which can improve the stripping effect.

[0073] (4) As can be seen from the combined examples 1 and 8 to 9, the present invention preferably uses a specific oxidant, which has a better stripping effect and can at the same time avoid the leaching of aluminum.

[0074] (5) As can be seen from the combined examples 1 and 10, acetone was used instead of dimethyl sulfoxide in Example 10. Acetone is a weakly polar solvent and has poor solubility for PVDF. When acetone is used, the stripping effect is weakened because PVDF cannot be completely dissolved, resulting in a lower recovery rate.

[0075] (6) As can be seen from the combined examples 1 and 6, the absence of sodium bisulfate in example 5 prevents the leaching system from forming a weakly acidic environment, which severely inhibits the selective leaching efficiency of lithium. Furthermore, the premature dissolution of nickel, cobalt, and manganese due to pH loss of control completely destroys the stepwise recovery process, resulting in a significant decrease in the recovery rate and purity of all valuable metals.

[0076] (7) In Comparative Example 1, no liquid nitrogen quenching was performed, and the recovery rate of metal elements was significantly lower than that in Example 1. In Comparative Example 2, the quenching temperature was higher, and the results showed that its metal element recovery rate was comparable to that of Comparative Example 1. In Comparative Example 3, no potassium permanganate was added, so the oxidation effect could not be achieved, and the metal element recovery rate decreased significantly. In Comparative Example 4, dimethyl sulfoxide was replaced with water, which made it difficult to achieve a good stripping effect, and the metal element leaching rate decreased severely. This shows that the present invention, by combining liquid nitrogen quenching, a specific stripping solution composition, and a heating and soaking process, can improve the recovery rate of nickel, cobalt, manganese, and lithium, and reduce the amount of aluminum entering the slurry.

[0077] The present invention has been illustrated with the above embodiments to illustrate its detailed features, but the present invention is not limited to the above detailed features, that is, it does not mean that the present invention must rely on the above detailed features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected technical features, additions of auxiliary technical features, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering positive electrode active materials from waste positive electrode sheets, characterized in that, The method includes the following steps: (1) The positive electrode sheet is rapidly cooled in liquid nitrogen to obtain a rapidly cooled positive electrode sheet; (2) The quenched positive electrode sheet is placed in a stripping solution for heating and soaking and ultrasonic treatment, and then subjected to solid-liquid separation to obtain a slurry containing positive electrode active material; the stripping solution includes organic solvent and oxidant.

2. The method according to claim 1, characterized in that, The positive electrode sheet mentioned in step (1) includes a positive electrode sheet containing a ternary positive electrode active material; Preferably, the current collector of the positive electrode sheet includes an aluminum foil current collector.

3. The method according to claim 1 or 2, characterized in that, The molar ratio of nickel, cobalt and manganese in the positive electrode sheet mentioned in step (1) is 1~8:0.5~1:

1.

4. The method according to claims 1-3, characterized in that, The rapid cooling process described in step (1) takes 0.5 to 1 hour.

5. The method according to any one of claims 1 to 4, characterized in that, The organic solvent in the stripping solution described in step (2) includes any one or a combination of at least two of dimethyl sulfoxide, N,N-dimethylacetamide, N,N-dimethylformamide or N-methylpyrrolidone; Preferably, the oxidant includes any one or a combination of at least two of ozone, hydrogen peroxide, or potassium permanganate.

6. The method according to any one of claims 1 to 5, characterized in that, The mass ratio of the oxidant to the organic solvent in step (2) is 0.25 to 1:

1.

7. The method according to any one of claims 1 to 6, characterized in that, The heating and soaking temperature in step (2) is 60~80℃.

8. The method according to any one of claims 1 to 7, characterized in that, The power of the ultrasonic treatment in step (2) is 50~500W; Preferably, the ultrasonic treatment time is 2-5 hours.

9. The method according to any one of claims 1 to 8, characterized in that, The solid-liquid ratio of the positive electrode sheet to the stripping solution after rapid cooling in step (2) is 0.1~1g / mL.

10. The method according to any one of claims 1 to 9, characterized in that, The method includes the following steps: (1) The positive electrode sheet is rapidly cooled in liquid nitrogen for 0.5~1h to obtain the rapidly cooled positive electrode sheet; (2) The rapidly cooled positive electrode sheet is placed in a stripping solution and heated to 60-80°C and ultrasonically treated for 2-5 hours at a power of 50-500W, with a solid-liquid ratio of 0.1-1 g / mL. Then, a slurry containing positive electrode active material is obtained by solid-liquid separation. The stripping solution includes an organic solvent and an oxidant, with a mass ratio of oxidant to organic solvent of 0.25-1:1.

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