A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries

Abstract

The present invention relates to a method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries, belonging to the field of resource utilization of lithium battery waste. In the present invention, the waste negative electrode of the lithium-ion battery is directly subjected to high-temperature heat treatment, and then screened to obtain crude graphite powder and crude copper powder; the crude graphite powder is mixed evenly with a chlorinating agent and then subjected to chlorination grinding to obtain a mixture; the mixture is added to ammonia water for ammonia leaching, and solid-liquid separation is carried out, and the solid is dried to obtain high-purity graphite. The present invention directly conducts high-temperature heat treatment to reduce metal oxides such as Ni, Co, Mn, and Li in the negative electrode graphite to metal elements, and enriches and separates them through Cu, protects the morphology of graphite, removes non-metal impurities such as S, P, and F, and removes a small amount of metal impurities contained in the graphite through chlorination grinding and ammonia leaching, and improves the grade of the recovered graphite to 99.9%, realizing the high-purity and high-efficiency recovery of graphite.

Description

Technical Field

[0001] The present invention relates to a method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries, belonging to the field of resource utilization of lithium battery waste. Background Art

[0002] The content of graphite in waste LIBs is between 12 wt.% and 21 wt.%, and the negative electrode active material contains up to 97% of carbon materials such as graphite. The increasing demand for graphite (the demand growth of graphite is estimated to be 250,000 t per year) has promoted the inevitable trend of recycling negative electrode materials. At present, few researchers focus on the recycling of negative electrode graphite in waste lithium-ion batteries, and most of the negative electrode graphite is consumed as a reducing agent.

[0003] In recent years, preliminary progress has been made in the recycling of graphite negative electrode materials for lithium-ion batteries. Yang et al. used sulfuric acid solution as the leaching agent, and achieved complete separation of copper foil and graphite at a leaching time of 5 min and a sulfuric acid concentration of 0.9 mol·L -1 When the concentration was reached, Yang et al. used a two-step calcination plus acid leaching method to achieve the recovery of graphite, Cu, Li, and Al. At 1.5 mol·L -1 Hydrochloric acid, S / L atomic ratio of 100 g·L -1 And at a leaching time of 1 h, by adjusting the pH value from 7 to 9, 99.9% of Cu and Al can be extracted, and 90% of graphite can be recovered. The hydrometallurgical process has a low operating temperature and can effectively recover the lithium salt in the negative electrode. However, due to the presence of insoluble lithium salts such as LiF, this process will consume a large amount of strong acids (sulfuric acid, hydrochloric acid) and will also produce more toxic hydrofluoric acid. At the same time, in order to remove electrolytes and binders such as PVDF, it is usually necessary to calcine the electrode waste in an inert atmosphere, causing a certain degree of environmental pollution. Summary of the Invention

[0004] In view of the problems of large consumption of acidic leaching agent, long treatment time, and low purity of recovered graphite in the existing wet recycling of graphite, the present invention proposes a method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries, that is, directly performing high-temperature heat treatment to reduce metal oxides such as Ni, Co, Mn, and Li in the negative electrode graphite to metal elements, and enriching and separating them through Cu, protecting the morphology of graphite, removing non-metallic impurities such as S, P, and F, removing a small amount of metal impurities contained in graphite by chlorination, grinding, and ammonia leaching, and increasing the grade of the recovered graphite to 99.9%, realizing the high-purity and high-efficiency recovery of graphite.

[0005] A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries, the specific steps are as follows:

[0006] (1) Directly perform high-temperature heat treatment on the waste negative electrode of the lithium-ion battery, and screen to obtain coarse graphite powder and coarse copper powder;

[0007] (2) Mix the coarse graphite powder and the chlorinating agent evenly and then carry out chlorination grinding to obtain a mixture;

[0008] (3) Add the mixture to ammonia water for ammonia leaching, carry out solid-liquid separation, and dry the solid to obtain high-purity graphite.

[0009] The main component of the waste negative electrode in the step (1) is graphite, and it also contains a binder, a current collector and positive electrode waste.

[0010] The positive electrode waste is lithium nickelate, lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate or lithium iron phosphate.

[0011] The heating method of the high-temperature heat treatment is direct heating, induction heating or microwave heating.

[0012] The temperature of the high-temperature heat treatment in the step (1) is 1100-1500 °C, and the time is 10-60 min.

[0013] The chlorinating agent in the step (2) is copper chloride, calcium chloride, magnesium chloride or aluminum chloride; preferably, the chlorinating agent is copper chloride.

[0014] When screening, the aperture of the sieve hole is 200-400 mesh.

[0015] The mass ratio of the coarse graphite powder to the chlorinating agent in the step (2) is 60-75:1.

[0016] The chlorination grinding method is vibration grinding, ball grinding or high-energy ball grinding, and the ball grinding time is 10-30 min.

[0017] The concentration of ammonia water in the step (3) is 6-10%, the molar ratio of metal to ammonia in the mixture is 1:2.2-2.5, and the leaching time is 30-60 min.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention can process broken or unbroken graphite negative electrode waste, reduce industrial treatment procedures, and minimize the incorporation of positive electrode waste as much as possible;

[0020] (2) The present invention uses high-temperature roasting of the negative electrode graphite waste, uses Cu as a carrier, enriches the reduced metal elements such as Ni, Co, Mn, and Li, protects the morphology of graphite, and removes most of the volatile impurities such as F, P, and S;

[0021] (3) The present invention uses copper chloride as a chlorinating agent to grind the roasted negative electrode graphite and leach it with ammonia water. The total metal content in the graphite is less than 20 ppmw, and the content of other impurities is not higher than 40 ppmw, realizing high-purity and high-efficiency recovery of graphite. Description of the Drawings

[0022] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0024] Example 1: The material content of the discarded graphite negative electrode in this example is shown in Table 1.

[0025] Table 1 Material content of waste graphite negative electrode

[0026]

[0027] A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries (see Figure 1 ), the specific steps are as follows:

[0028] (1) 100 g of waste graphite negative electrode of lithium ion battery was directly heated to 1500° C. in a resistance furnace with Ar gas, and subjected to high temperature heat treatment for 10 min. The mixture was cooled in the furnace, and sieved through a 400-mesh copper standard test sieve to obtain a coarse copper powder on the sieve and 75.02 g of a sieve under the sieve whose main component was graphite. The Cu content of the sieve under the sieve was 0.57%, the content of other metal impurities was 0.05%, and the total amount of non-metallic impurities such as F, P, and S was 0.07%;

[0029] (2) After the coarse graphite powder and the chlorinating agent (copper chloride) are uniformly mixed, the mixture is chlorinated and ground in a planetary ball mill with a revolution speed of 700 rpm and a transmission ratio of 2 for 10 minutes to obtain a mixture; the mass ratio of the coarse graphite powder to the chlorinating agent (copper chloride) is 75:1;

[0030] (3) adding the mixture into 10 wt.% ammonia water for ammonia leaching for 30 min, separating the solid and the liquid, and drying the solid to obtain high-purity graphite; wherein the solid-liquid ratio of the mixture to the ammonia water is 1:1 in g:mL;

[0031] According to ICP analysis, the total metal content in the high-purity recycled graphite is 13ppmw, and the total amount of other non-metallic impurities is 32ppmw;

[0032] The waste negative electrode is treated under high temperature conditions, so that a small amount of positive electrode material mixed in the negative electrode is reduced to a metal element by graphite and enriched by molten Cu, which greatly reduces the metal content in the graphite; the indirect heating of the resistance furnace does not have a stirring effect, and the sedimentation behavior is ignored. The molten Cu particles basically maintain their original size. The use of a 400-mesh test sieve can separate the Cu particles from the graphite system as much as possible, reducing the amount of subsequent additives such as copper chloride and ammonia water; during leaching, the ashed diaphragm powder will float on the surface of the leaching solution, and the non-metallic impurities such as F and S in the graphite can be further removed through the leaching process.

[0033] Example 2: The waste graphite anode in this example is the same as that in Example 1.

[0034] A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries (see Figure 1 ), and the specific steps are as follows:

[0035] (1) 100 g of the waste graphite anode of lithium-ion batteries is directly heated to 1100 °C in an induction furnace with Ar flowing through, and subjected to high-temperature heat treatment for 60 min, then cooled in the furnace. After screening through a 200-mesh copper standard test sieve, the oversize product is coarse copper powder, and the undersize product with a main component of graphite is 75.09 g. The Cu content in the undersize product is 0.63%, the content of other metal impurities is 0.04%, and the total content of non-metal impurities such as F, P, and S is 0.12%.

[0036] (2) After uniformly mixing the coarse graphite powder with a chlorinating agent (copper chloride), it is subjected to chlorination grinding in a planetary ball mill with a revolution speed of 700 rpm and a transmission ratio of 2 for 30 min to obtain a mixture; the mass ratio of the coarse graphite powder to the chlorinating agent (copper chloride) is 60:1.

[0037] (3) The mixture is added to ammonia water with a concentration of 6 wt.% for ammonia leaching for 30 min, and then solid-liquid separation is carried out. The solid is dried to obtain high-purity graphite; the solid-liquid ratio of the mixture to ammonia water is g:mL = 1:2.

[0038] Analyzed by ICP, the total metal content in the high-purity recovered graphite is 15 ppmw, and the total content of other non-metal impurities is 40 ppmw.

[0039] Changing the heating method to induction heating, the metal receives the Lorentz force in the induction coil, and it is easier to generate larger metal particles. Most of the Cu can be separated from the graphite system by using a 200-mesh test sieve; during the movement of the molten Cu particles, the metal impurities around the movement path will be enriched, further reducing the content of impurity metals in the system; the heating and cooling processes of induction heating are relatively fast, and the diaphragm is not completely ashed. Compared with Example 1, the content of non-metal impurities is slightly higher.

[0040] Example 3: The waste graphite anode in this example is the same as that in Example 1.

[0041] A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries (see Figure 1 ), and the specific steps are as follows:

[0042] (1) 100 g of the waste graphite anode of a lithium-ion battery was directly heated to 1300 °C in a microwave oven with Ar flowing through it and heat-treated at high temperature for 30 min, then cooled in the furnace. After screening through a 400-mesh copper standard test sieve, the oversize product was crude copper powder, and the undersize product with a main component of graphite was 74.99 g. The Cu content in the undersize product was 0.61%, the content of other metal impurities was 0.08%, and the total amount of non-metal impurities such as F, P, and S was 0.09%.

[0043] (2) After mixing the crude graphite powder evenly with a chlorinating agent (copper chloride), it was chlorinated and ground in a planetary ball mill with a revolution speed of 700 rpm and a transmission ratio of 2 for 20 min to obtain a mixture; the mass ratio of the crude graphite powder to the chlorinating agent (copper chloride) was 65:1.

[0044] (3) The mixture was added to ammonia water with a concentration of 6 wt.% for ammonia leaching for 45 min, followed by solid-liquid separation, and the solid was dried to obtain high-purity graphite; the solid-liquid ratio of the mixture to ammonia water was g:mL = 1:1.8.

[0045] By ICP analysis, the total metal content in the high-purity recycled graphite was 20 ppmw, and the total amount of other non-metal impurities was 38 ppmw.

[0046] Changing the heating method to microwave heating, microwave selective heating makes it easier for graphite, which is more absorbent of microwaves, to absorb waves, resulting in an uneven temperature distribution in the system. Impurities closer to the graphite are more likely to be reduced, leading to a relatively high content of impurity metals; the microwave heating method does not have a stirring effect on the reactants. Selecting a 400-mesh test sieve can separate the Cu particles in the graphite as much as possible; the heating and cooling processes of microwave heating are relatively fast, and the diaphragm is not sufficient to be completely ashed, resulting in a relatively high content of non-metal impurities compared with Example 1.

[0047] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries, characterized in that, The specific steps are as follows: (1) Directly conduct high-temperature heat treatment on the waste negative electrode of the lithium-ion battery, and screen to obtain crude graphite powder and crude copper powder; the temperature of the high-temperature heat treatment is 1100~1500 °C, and the time is 10~60 min; the main component of the waste negative electrode is graphite, and it also contains a binder, a current collector, and positive electrode waste; the positive electrode waste is lithium nickelate, lithium cobaltate, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium iron phosphate; (2) Mix the crude graphite powder evenly with a chlorinating agent and conduct chlorination grinding to obtain a mixture; the chlorinating agent is copper chloride; (3) Add the mixture to ammonia water for ammonia leaching, conduct solid-liquid separation, and dry the solid to obtain high-purity graphite.

2. The method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries according to claim 1, characterized in that: The chlorination grinding time in step (2) is 10~30 min.

3. The method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries according to claim 1, characterized in that: The mass ratio of the crude graphite powder to the chlorinating agent in step (2) is 60~75:

1.

4. The method for recovering high-purity graphite from the negative electrode of waste lithium-ion batteries according to claim 1, characterized in that: In step (3), the ammonia water concentration is 6~10%, the molar ratio of metal to ammonia in the mixture is 1:2.2~2.5, and the leaching time is 30~60 min.

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