A method for recovering graphite from waste lithium-ion battery mixture

Abstract

The present invention relates to the field of lithium-ion battery recycling, and in particular to a method for recovering graphite from a mixture of waste lithium-ion batteries. The method comprises the following steps: primary acid leaching: subjecting the heat-treated raw material to a first acid leaching using a primary acid leaching reagent; secondary acid leaching: subjecting the mixture subjected to the primary acid leaching to a second acid leaching using a secondary acid leaching reagent; and alkaline leaching: subjecting the mixture subjected to the secondary acid leaching to impurities removal using an alkaline solution; the raw material being a mixture of positive and negative electrodes or negative electrode materials of waste lithium-ion batteries; the primary acid leaching reagent being an inorganic acid and / or an oxidant; and the secondary acid leaching reagent being an organic acid mixed solution with a surfactant added. The method provided by the present invention for recovering high-purity graphite from the positive and negative electrode mixture / negative electrode materials of crushed waste lithium-ion batteries has the characteristics of high graphite recovery rate, high graphite purity, and a wide range of applications.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion battery recycling, and in particular to a method for recycling graphite from waste lithium ion battery mixture. Background Art

[0002] In recent years, sales of new energy vehicles have steadily increased. As a core component that impacts the range and safety performance of new energy vehicles, the development level of lithium-ion batteries directly determines the scale and development of the new energy vehicle industry. Currently, the production of lithium-ion power batteries has reached record highs. Lithium-ion power batteries have a service life of approximately 5-7 years. In 2020, the cumulative number of retired power batteries in the market reached 200,000 tons. By 2025, the number of retired lithium-ion batteries is expected to reach 640,000 tons, of which power batteries will account for more than half. The recycling of lithium-ion batteries has gradually become a research hotspot.

[0003] The existing invention disclosure number is CN101710632, and its name is a method for recovering graphite from waste batteries. The invention uses alkaline leaching, acid leaching, and secondary acid leaching to remove impurities from the battery materials obtained by crushing and separating, and then washes and dries and then repairs them at high temperature to obtain recycled graphite. Current research on the recovery of graphite from waste batteries mainly focuses on the recovery of graphite from a single pair of negative electrode materials. However, current industrial production cannot meet the requirements for the separate separation of the negative electrode materials of waste batteries, and can only recover the positive and negative electrode mixtures. It is currently difficult to recover high-purity graphite from battery mixtures, and the purity of the recovered graphite is not high, the recovery rate is also low, and the structure of the recovered graphite is poor. Therefore, there is an urgent need in this field to provide a new method for recovering graphite from waste lithium batteries. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method for recovering graphite from waste lithium-ion battery mixture.

[0005] The method for recovering graphite from waste lithium-ion battery mixture provided by the present invention comprises the following steps:

[0006] Primary acid leaching: The heat-treated raw materials are subjected to the first acid leaching using a primary acid leaching reagent;

[0007] Secondary acid leaching: the mixture treated by the primary acid leaching is subjected to a second acid leaching using a secondary acid leaching reagent;

[0008] Alkali leaching: removing impurities from the mixture treated by the secondary acid leaching using an alkaline solution;

[0009] The raw material is a mixed positive and negative electrode material or negative electrode material from waste lithium-ion batteries; the primary acid leaching reagent is an inorganic acid and / or an oxidant; and the secondary acid leaching reagent is a mixed organic acid solution containing a surfactant. The present invention utilizes a two-step acid leaching process (mineral acid / oxidant-organic acid / surfactant) followed by a three-step alkaline leaching process, significantly improving graphite impurity removal. This provides a new approach to waste battery processing and enables better resource recycling. The method provided by the present invention for recovering high-purity graphite from the mixed positive and negative electrode material / negative electrode material of crushed waste lithium-ion batteries has the advantages of high graphite recovery rate, high graphite purity, high extraction efficiency, and a wide range of applications.

[0010] Preferably, the method for recovering graphite from waste lithium-ion battery mixture provided by the present invention comprises the following steps:

[0011] 1) Heat treatment: heat-treating the positive and negative electrode mixture or the negative electrode material of the waste lithium-ion battery to obtain a heat-treated mixture;

[0012] 2) Primary acid leaching: The heat-treated mixture is subjected to a first acid leaching using a primary acid leaching reagent, wherein the primary acid leaching reagent is a mixed solution of H2SO4 and H2O2, a mixed solution of H2SO4 and HNO3, or HNO3, with a liquid-to-solid ratio preferably being 10-50:1, and filtered and washed until neutral to obtain a mixture after primary acid leaching;

[0013] 3) Secondary acid leaching: The mixture after the primary acid leaching is subjected to a second acid leaching using a secondary acid leaching reagent, wherein the secondary acid leaching reagent is a mixed solution of an organic acid to which a surfactant is added, and the liquid-to-solid ratio is preferably 100-300:1. The mixture is filtered and washed until neutral to obtain a mixture after the secondary acid leaching. The organic acid in the secondary acid leaching reagent is preferably a mixed solution of methanesulfonic acid and citric acid, and the surfactant is preferably hexadecyltrimethylammonium bromide. In the present invention, by using specific primary and secondary acid leaching reagents and conditions, the synergistic effect of the secondary acid leaching reagent and the surfactant (especially the mixed acid of methanesulfonic acid and citric acid and hexadecyltrimethylammonium bromide) is better exerted, thereby better reducing the content of metal impurities in the graphite.

[0014] 4) Alkali leaching: soaking the mixture obtained by secondary acid leaching with an alkaline leaching agent, preferably with a liquid-to-solid ratio of 50 to 150:1, filtering and washing until neutral, and drying to obtain recovered graphite;

[0015] Preferably, in step 1), the heat treatment is performed in an atmosphere of air, at a temperature of 450-700° C., for a time of 1-3 hours.

[0016] Further preferably, in step 2), when the primary acid leaching reagent is a mixed solution of H2SO4 and H2O2, the concentration of H2SO4 is 2-5 mol / L, and the amount of H2O2 is 4 vol%-12 vol%. In the present invention, the above-mentioned acid leaching reagent at the preferred concentration is combined with an oxidant to improve the removal effect of copper impurities.

[0017] Preferably, in step 3), the organic acid in the secondary acid leaching reagent is a mixed solution of methanesulfonic acid and citric acid, and the surfactant is cetyltrimethylammonium bromide. The present invention utilizes a specific organic acid mixture and surfactant to synergistically work with the acid leaching reagent to effectively remove nickel and cobalt impurities, further improving graphite purity.

[0018] More preferably, in step 3), the concentration of the methanesulfonic acid is 1-6 mol / L, the concentration of the citric acid is 0.5-3 mol / L, and the amount of the surfactant is 5-100 mg / L.

[0019] More preferably, in step 2), the leaching time is 0.5-2 h, and the reaction temperature is 30-90 °C.

[0020] More preferably, in step 3), the leaching time is 0.5-1.5 h, and the reaction temperature is 30-90 °C.

[0021] Preferably, in step 4), the alkaline leaching agent is a NaOH solution, and the concentration of the alkaline leaching agent is 0.5-3 mol / L.

[0022] More preferably, in step 4), the leaching time is 0.5-2 h, and the reaction temperature is 30-90 °C.

[0023] Further preferably, in steps 2) to 4), the reaction product needs to be filtered and washed until neutral, and dried at 60±5°C for 1±0.2h.

[0024] The method for recovering graphite from a waste lithium-ion battery mixture provided by the present invention comprises the following steps:

[0025] 1) Heat treatment: The recovered battery positive and negative electrode mixture is heat treated in an air atmosphere at a temperature of 450-700°C for 1-3 hours;

[0026] 2) Primary acid leaching: Leach the mixture after alkali leaching with a mixed solution of H2SO4 and H2O2, filter and wash until neutral, and dry to obtain the acid-leached mixture. The concentration of H2SO4 is 2-5 mol / L, the amount of H2O2 is 4 vol%-12 vol%, the leaching time is 0.5-2 h, the reaction temperature is 30-90 °C, and the liquid-to-solid ratio is 10-50:1;

[0027] 3) Secondary acid leaching: cetyltrimethylammonium bromide is added to a mixed organic acid solution of 1-6 mol / L methanesulfonic acid and 0.5-3 mol / L citric acid, with a surfactant dosage of 5-100 mg / L. After the solutions are evenly mixed, the acid-leached mixture is subjected to secondary acid leaching, filtered, washed to neutrality, and dried. The leaching time is 0.5-1.5 h, the reaction temperature is 30-90° C., and the liquid-to-solid ratio is 100-300:1.

[0028] 4) Alkali leaching: Soak the calcined positive and negative electrode mixture in NaOH solution, filter and wash until neutral, and dry to obtain the alkali-leached mixture. The concentration of NaOH solution is 0.5 mol / L~3 mol / L, the reaction time is 0.5~2h, the reaction temperature is 30~90℃, and the liquid-solid ratio is 50~150:1.

[0029] The present invention has at least the following beneficial effects: it utilizes a combination of a two-step acid leaching process (inorganic acid / oxidant-organic acid / surfactant) and a three-step alkaline leaching process, enabling better recovery of high-purity graphite from the positive and negative electrode mixtures / negative electrode materials of crushed waste lithium-ion batteries. This significantly improves the graphite impurity removal process, provides a new approach to waste battery processing, and better achieves resource recycling. The method of the present invention can be used not only to extract high-purity graphite from the positive and negative electrode mixtures of waste lithium-ion batteries, but can also be used to directly extract high-purity graphite from the negative electrode materials of waste lithium-ion batteries. The method of the present invention has the advantages of high graphite recovery rate, high graphite purity, high extraction efficiency, and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is the XRD pattern of the raw materials used in the examples of the present invention.

[0032] Figure 2 This is the XRD pattern of the product obtained in Example 1 of the present invention.

[0033] Figure 3 This is a SEM image of the product obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following examples are used to illustrate the present invention, but are not used to limit the scope of the present invention. If the specific technology or conditions are not specified in the embodiments, they shall be carried out in accordance with the technology or conditions described in the literature in this field, or in accordance with the product instructions. The implementation conditions in the embodiments can be further adjusted according to specific experimental conditions or factory conditions. The implementation conditions that are not specified are generally the conditions in conventional experiments. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0035] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0036] In the following examples of the present invention, the content of C element in the crushed mixture of the positive and negative electrodes used is 5.43%. Example 1

[0037] Weigh 10 g of the crushed mixture of the positive and negative electrodes and calcine it at 600 °C for 1 h to complete the heat treatment.

[0038] The heat-treated graphite was leached with 5 mol / L H2SO4 and 12 vol% H2O2, with a liquid-to-solid ratio of 30:1, a leaching temperature of 90°C, and a leaching time of 1 h. It was filtered, washed until neutral, and then dried.

[0039] Add 0.015g of hexadecyltrimethylammonium bromide to 300mL of pure water and mix for 5 minutes. Add methanesulfonic acid and citric acid to the solution to prepare a mixed solution with a methanesulfonic acid concentration of 3 mol / L and a citric acid concentration of 0.5 mol / L. Add the acid-leached graphite to the mixed solution at a liquid-to-solid ratio of 150:1. Add a magnet and stir magnetically at 90°C for 1 hour. Then, wash with pure water until neutral and filter to dryness.

[0040] The graphite after the secondary acid leaching was alkali leached using 100mL 2mol / L NaOH solution, with a liquid-to-solid ratio of 150:1, a leaching temperature of 90°C, and an alkali leaching time of 1h. After the reaction, it was filtered and washed to neutrality. The graphite after alkali leaching was washed 5 times, each time with 200mL of pure water.

[0041] After washing and drying, the carbon content of the graphite can be measured by a carbon-sulfur analyzer and the carbon content in the dried mixture can reach 82%, with a recovery rate of 84.2%. Figure 3 As shown in Figure 2, the flake structure of graphite is still well maintained. Figure 1-Figure 2 It can be seen that most of the impurities are removed after treatment using the method of this embodiment. Example 2

[0042] Weigh 10 g of the crushed mixture of the positive and negative electrodes and calcine it at 600 °C for 1 h to complete the heat treatment.

[0043] The heat-treated graphite was leached using 4 mol / L H2SO4 and 8 vol% H2O2, with a liquid-to-solid ratio of 20:1, a leaching temperature of 60°C, and a leaching time of 1 h. It was filtered, washed until neutral, and then dried.

[0044] Add 0.025g of hexadecyltrimethylammonium bromide to 300mL of pure water and mix for 5 minutes. Add methanesulfonic acid and citric acid to the solution to prepare a mixed solution with a methanesulfonic acid concentration of 3 mol / L and a citric acid concentration of 0.5 mol / L. Add the acid-leached graphite to the mixed solution at a liquid-to-solid ratio of 200:1. Add a magnet and stir magnetically at 60°C for 1 hour. Then, wash with pure water until neutral and filter dry.

[0045] The graphite after the secondary acid leaching was alkali leached using 100mL 1mol / L NaOH solution, with a liquid-solid ratio of 100:1, a leaching temperature of 60°C, and an alkali leaching time of 1h. After the reaction, it was filtered and washed to neutrality. The graphite after alkali leaching was washed 5 times, each time using 200mL of pure water.

[0046] After washing and drying, the carbon content of the graphite in the dried mixture can be measured using a carbon-sulfur analyzer, and the recovery rate is 85.5%. Example 3

[0047] Weigh 10 g of the crushed mixture of the positive and negative electrodes and calcine it at 600 °C for 1 h to complete the heat treatment.

[0048] The heat-treated graphite was leached with 4 mol / L H2SO4 and 8 vol% H2O2, with a liquid-to-solid ratio of 30:1, a leaching temperature of 60°C, a leaching time of 1.5 h, filtered, washed to neutrality, and then dried.

[0049] Add 0.005g of hexadecyltrimethylammonium bromide to 300mL of pure water and mix for 5 minutes. Add methanesulfonic acid and citric acid to the solution to prepare a mixed solution with a methanesulfonic acid concentration of 5 mol / L and a citric acid concentration of 0.5 mol / L. Add the acid-leached graphite to the mixed solution at a liquid-to-solid ratio of 200:1. Add a magnet and stir magnetically at 60°C for 1 hour. Then, wash with pure water until neutral and filter dry.

[0050] The graphite after the secondary acid leaching was alkali leached using 100mL 1mol / L NaOH solution, with a liquid-solid ratio of 100:1, a leaching temperature of 90°C, and an alkali leaching time of 1h. After the reaction, it was filtered and washed to neutrality. The graphite after alkali leaching was washed 5 times, each time using 200mL of pure water.

[0051] After washing and drying, the carbon content of the graphite in the dried mixture can be measured using a carbon-sulfur analyzer, and the recovery rate is 79.5%.

[0052] Comparative Example 1

[0053] Weigh 10 g of the crushed mixture of the positive and negative electrodes and calcine it at 600 °C for 1 h to complete the heat treatment.

[0054] The heat-treated graphite was leached using 4 mol / L H2SO4 and 8 vol% H2O2, with a liquid-to-solid ratio of 20:1, a leaching temperature of 90°C, and a leaching time of 1 h. It was filtered, washed until neutral, and then dried.

[0055] A mixed solution of 3 mol / L methanesulfonic acid and 0.5 mol / L citric acid was prepared. The crushed material after the first acid leaching was subjected to a second leaching using an organic mixed acid with a liquid-to-solid ratio of 150:1. A magnet was added and magnetic stirring was carried out at 90°C for 1 hour. The material was then washed with pure water until neutral and filtered and dried.

[0056] After washing and drying, the carbon content of the graphite in the dried mixture can be measured using a carbon-sulfur analyzer, and the recovery rate is 68.7%.

[0057] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for recovering graphite from waste lithium-ion battery mixture, characterized in that: Use the following steps: 1) Heat treatment: heat-treating the positive and negative electrode mixture or the negative electrode material of the waste lithium-ion battery to obtain a heat-treated mixture; 2) Primary acid leaching: The heat-treated mixture is subjected to a first acid leaching using a primary acid leaching reagent, wherein the primary acid leaching reagent is a mixed solution of H2SO4 and H2O2, a mixed solution of H2SO4 and HNO3, or HNO3, with a liquid-to-solid ratio of 10 to 50:1, filtered and washed until neutral, and dried to obtain a mixture after primary acid leaching; 3) Secondary acid leaching: The mixture after the primary acid leaching is subjected to a second acid leaching using a secondary acid leaching reagent, wherein the secondary acid leaching reagent is a mixed solution of an organic acid to which a surfactant is added, with a liquid-to-solid ratio of 100 to 300:

1. The mixture is filtered, washed until neutral, and dried to obtain a mixture after secondary acid leaching. The organic acids in the secondary acid leaching reagent are methanesulfonic acid and citric acid, and the surfactant is hexadecyltrimethylammonium bromide. In the secondary acid leaching reagent, the amount of the surfactant is 5 to 100 mg / L, the concentration of the methanesulfonic acid is 1 to 6 mol / L, and the concentration of the citric acid is 0.5 to 3 mol / L. 4) Alkali leaching: The mixture after the secondary acid leaching is soaked in an alkaline leaching agent with a liquid-to-solid ratio of 50 to 150:1, filtered and washed until neutral, and dried to obtain recovered graphite.

2. The method for recovering graphite from waste lithium-ion battery mixture according to claim 1, wherein In step 1), the heat treatment is carried out in an atmosphere of air, at a temperature of 450-700°C, for a time of 1-3 hours.

3. The method for recovering graphite from waste lithium-ion battery mixture according to claim 1, wherein In step 2), when the primary acid leaching reagent is a mixed solution of H2SO4 and H2O2, the concentration of H2SO4 is 2-5 mol / L, and the amount of H2O2 is 4 vol%-12 vol%.

4. The method for recovering graphite from waste lithium-ion battery mixture according to claim 1, wherein In step 2), the leaching time is 0.5-2 h, and the reaction temperature is 30-90 °C; in step 3), the leaching time is 0.5-1.5 h, and the reaction temperature is 30-90 °C.

5. The method for recovering graphite from waste lithium-ion battery mixture according to claim 1, wherein In step 4), the alkaline leaching agent is a NaOH solution, and the concentration of the alkaline leaching agent is 0.5-3 mol / L.

6. The method for recovering graphite from waste lithium-ion battery mixture according to claim 1, wherein: In step 4), the leaching time is 0.5~2 h, and the reaction temperature is 30~90 °C.

7. The method for recovering graphite from waste lithium-ion battery mixture according to any one of claims 1 to 6, characterized in that: In steps 2) to 4), the reaction product needs to be filtered and washed until neutral, and then dried at 60±5°C for 1±0.2h.

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