Methods for recycling graphite and recycled graphite

Abstract

This disclosure relates to a method (100) for producing recycled graphite, the method (100) comprising: a step of supplying a recycled graphite concentrate containing one or more of carboxymethylcellulose and styrene-butadiene rubber; a step (120) of pre-treating the recycled graphite concentrate by subjecting it to an oxidizing environment at a temperature in the range of 250 to 380°C, thereby reducing the total concentration of carboxymethylcellulose and styrene-butadiene rubber to less than 0.25%; and a step (130) of heat-treating the pre-treated recycled graphite concentrate by subjecting it to a non-oxidizing environment at a temperature of at least 2300°C. The present invention also describes recycled graphite, the use of recycled graphite, and batteries containing recycled graphite.

Description

Technical Field

[0001] The present invention relates to the field of graphite recycling.

Background Art

[0002] In recent years, the demand for graphite has increased significantly, mainly due to its use as an anode material in lithium-ion batteries (LIBs).

[0003] Due to the limited lifespan of LIBs and growing environmental concerns, the recycling of end-of-life (EoL) lithium-ion batteries (EoL-LIBs) has attracted attention in recent years. The recycling of EoL-LIBs has conventionally focused on the extraction of metals such as cobalt, nickel, and copper, but the recycling of graphite is also gaining attention. Graphite is recovered not only from EoL-LIBs but also from graphite residues remaining from the production of battery anodes and cells. Recycling is generally carried out today using one or more of wet refining, dry refining, and direct recycling.

[0004] The dry refining method is currently the most common method for recycling EoL-LIBs. This process generally involves a combination of chemical treatment and high-temperature treatment, but is often used only for the purpose of recovering metals such as nickel and cobalt. To recover other materials with a high overall recycling rate, such as graphite, from EoL-LIBs, recycling by wet refining and / or direct recycling may be employed instead of or in addition to the dry refining method.

[0005] Wet smelting recycling generally involves a separation process, followed by the leaching of black mass. Separation can be carried out using flotation methods such as selective flotation or pyrolysis-ultrasonic-assisted flotation, while leaching can be carried out using acids or bases. Flotation methods generally have the disadvantage of not being able to achieve the desired purity, while the use of acids or bases for leaching has the disadvantage of generating undesirable environmental waste. Furthermore, materials such as binders and heavy metals are not properly removed in wet smelting recycling, leading to their high density in the recycled graphite.

[0006] Direct recycling, as the name suggests, is a relatively simple method of mechanically extracting negative electrode materials such as graphite. Direct recycling may involve a pulverization process followed by a sieving process to extract particles of a specific size. Since direct recycling generally does not involve refining the recycled graphite, the recycled graphite will contain a large amount of impurities such as metals, dust, and residual binders.

[0007] The objective of this invention is to provide a method for recycling graphite that addresses some of the problems in the prior art. [Overview of the project] [Means for solving the problem]

[0008] A first aspect of the present invention provides a method for producing recycled graphite. This method includes the steps of: supplying a reclaimed graphite concentrate containing one or more of carboxymethylcellulose and styrene-butadiene rubber; pre-treating the reclaimed graphite concentrate by subjecting it to an oxidizing environment at a temperature in the range of 250 to 380°C, thereby reducing the total concentration of carboxymethylcellulose and styrene-butadiene rubber in the reclaimed graphite concentrate to less than 0.25% by mass; and heat-treating the pre-treated reclaimed graphite concentrate by subjecting it to a non-oxidizing environment at a temperature of at least 2300°C.

[0009] In embodiments of the present invention, the method further includes a step of mixing a pre-treated regenerated graphite concentrate with an unused binder to form a blend, prior to a step of heat-treating the pre-treated regenerated graphite concentrate, wherein the step of heat-treating the pre-treated regenerated graphite concentrate includes subjecting the blend to a non-oxidizing environment at a temperature of at least 2300°C.

[0010] In another embodiment of the present invention, the ratio between the virgin binder and the pre-treated reclaimed graphite concentrate in the blend is in the range of 3 to 12% by mass, preferably in the range of 6 to 8% by mass.

[0011] In yet another embodiment of the present invention, in the pretreatment step of the regenerated graphite concentrate, the regenerated graphite concentrate is subjected to an oxidizing environment at a temperature of no more than 350°C.

[0012] In yet another embodiment of the present invention, the pretreatment step of the regenerated graphite concentrate is carried out such that the total concentration of carboxymethylcellulose and styrene-butadiene rubber in the pretreated regenerated graphite concentrate is less than 0.2% by mass.

[0013] In yet another embodiment of the present invention, the heat treatment step of the pre-treated regenerated graphite concentrate is carried out by subjecting the pre-treated regenerated graphite concentrate to a non-oxidizing environment at a temperature in the range of 2300°C to 2900°C.

[0014] In yet another embodiment of the present invention, the step of heat-treating the pre-treated regenerated graphite concentrate is carried out such that the concentration of one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon in the heat-treated regenerated graphite concentrate is less than 100 ppmw, preferably less than 20 ppmw.

[0015] In yet another embodiment of the present invention, the method further includes a step of mixing the pre-treated recycled graphite concentrate with an untreated raw material before a step of heat-treating the pre-treated recycled graphite concentrate, where the untreated raw material is selected from one or more of petroleum coke, unused synthetic graphite, and natural graphite. The heat-treating step of the pre-treated recycled graphite concentrate is carried out by subjecting the pre-treated recycled graphite concentrate to a non-oxidizing environment at a temperature of at least 2300°C.

[0016] In yet another embodiment of the present invention, the recycled graphite concentrate contains at least 90%, preferably at least 95%, and more preferably at least 99% carbon.

[0017] In yet another embodiment of the present invention, the recycled graphite concentrate contains up to 1% by mass of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon.

[0018] In yet another embodiment of the present invention, the recycled graphite concentrate is a negative electrode scrap.

[0019] In yet another embodiment of the present invention, the pretreatment step of the recycled graphite concentrate includes a sub-step of subjecting the recycled graphite concentrate to an oxidation environment at a temperature within the range of 250 to 380 °C, thereby reducing the total concentration of carboxymethyl cellulose and styrene-butadiene rubber to less than 0.25% by mass, and then subjecting the recycled graphite concentrate from step i) to an oxidation environment at a temperature within the range of 500 to 600 °C, preferably 550 to 600 °C.

[0020] A second aspect of the present invention is to provide recycled graphite containing at most 0.25% by mass, preferably at most 0.2% by mass, of any one or more of carboxymethyl cellulose, styrene-butadiene rubber, and their residues, and containing at most 0.01% by mass, preferably at most 0.005% by mass, of any one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon.

[0021] In an embodiment of the present invention, the recycled graphite has a tap density of at least 1 g / cc and / or an SSABET of at most 2.0 m 2 / g.

[0022] A third aspect of the present invention is to provide the use of recycled graphite.

[0023] A third aspect of the present invention is to provide a battery containing recycled graphite.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 shows a schematic diagram of the method according to the present invention. [[ID= 31]] [Figure 2] FIG. 2 is a schematic diagram of various embodiments of the method according to the present invention. [Figure 3]Figure 3 is a schematic diagram of an example of a value chain for obtaining and using recycled graphite according to the present invention. [Figure 4] Figure 4 shows X-ray fluorescence analysis data indicating the sublimation temperature (°C) of various metals in the recycled graphite concentrate. [Figure 5] Figure 5 shows thermogravimetric analysis data of a sample of untreated recycled graphite concentrate and six samples of recycled graphite concentrate that were subjected to pretreatment at various temperatures and times in an oxidizing environment. [Figure 6] Figure 6 is a table showing the pretreatment conditions of the six samples in Figure 5 before thermogravimetric analysis, as well as the total binder amount and binder residue amount in the six pretreated samples and the untreated recycled graphite concentrate. [Figure 7] Figure 7 is a table showing qualitative data selected from samples of recycled graphite obtained by the method according to the present invention, samples of recycled graphite obtained by other methods, and samples of unused graphite. [Figure 8] Figure 8 is a table showing qualitative data of an untreated graphite concentrate and a sample of recycled graphite obtained from the same graphite concentrate by the method of the present invention. [Figure 9] Figure 9 shows an example of input parameters for the pretreatment step by the method of the present invention.

Mode for Carrying Out the Invention

[0025] General and specific representative embodiments of the present invention are described below. The accompanying drawings are referenced. However, it should be noted that the drawings represent only representative embodiments, and other features and embodiments may also fall within the scope of the invention as described in the claims. Furthermore, reference expressions such as "a" and "an" should not be interpreted as excluding the plural form. In this specification, the term "invention" may be used interchangeably with the term "disclosure." The term "producing" may be used interchangeably with the term "obtaining."

[0026] Unless otherwise defined, all technical terms, symbols, and other scientific or technical terms used herein shall have the meaning generally understood by those skilled in the art relating to the present invention. However, certain technical terms, symbols, and other scientific or technical terms may be specifically defined as shown below.

[0027] This invention provides a method for producing / obtaining recycled graphite from recycled graphite concentrates. The invention also provides recycled graphite, uses of recycled graphite, and batteries containing recycled graphite. This method can be considered a method for recycling graphite.

[0028] Recycled graphite concentrates may generally be defined herein as recycled graphite-containing materials. Recycled graphite concentrates may include, for example, graphite separated from EoL-LIBs and one or more LIBs, and may also or optionally include graphite left over from the manufacture of LIBs. Graphite left over from the manufacture of LIBs is generally referred to as graphite scrap and may be graphite recycled from any manufacturing process involved in the manufacture of LIBs (e.g., negative electrode scrap). Examples of specific manufacturing processes include, but are not limited to, slurry mixing, electrode casting, and cell assembly. Figure 3 schematically shows an example of a source of recycled graphite concentrates.

[0029] Method 100 according to the present invention includes, as schematically shown in Figure 1, a step 110 of supplying a recycled graphite concentrate, a step 120 of pre-treating the recycled graphite concentrate, and a step 130 of heat-treating the pre-treated recycled graphite concentrate. The pre-treatment step 120 of the recycled graphite concentrate is generally configured to remove at least some of a specific binder and / or binder residue from the recycled graphite concentrate. The heat-treating step 130 of the pre-treated recycled graphite concentrate may generally be configured to remove at least some of a metallic impurity from the pre-treated recycled graphite concentrate. The heat-treated and pre-treated recycled graphite concentrate may be referred to herein as recycled graphite.

[0030] The pretreatment step 120 of the regenerated graphite concentrate may be carried out by subjecting the regenerated graphite concentrate to an oxidizing environment at a temperature in the range of 250 to 380°C, as schematically shown in Figure 1. The pretreatment step 120 is carried out to remove at least partially from the regenerated graphite concentrate one or more of carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR), and optionally one or more of their residues, by oxidation. Thus, the regenerated graphite concentrate may contain one or more of CMC, SBR, and their residues. Here, residues may refer, for example, to molecules remaining from the thermal decomposition and / or chemical decomposition of CMC and / or SBR. In this specification, the terms CMC and SBR may generally be interpreted to include CMC and SBR residues, respectively.

[0031] CMC, SBR, and their residues may be present in recycled graphite concentrates due to the use of these binders in the manufacture of negative and / or positive electrodes for lithium-ion batteries (LIBs). More specifically, CMC and / or SBR may be used, for example, as part of the LIB cell manufacturing process, in the coating process of the negative electrode material on copper foil. It will be understood by those skilled in the art that whether a recycled graphite concentrate contains binders, binder residues, or a combination of both depends on the exact source of the recycled graphite concentrate.

[0032] In the pretreatment step of recycled graphite concentrates, it has been found that using a temperature in the range of 250°C to 380°C is suitable for removing one or more of CMC, SBR, and their residues. The inventors have found that CMC and its residues can be removed from recycled graphite concentrates by subjecting them to an oxygen-containing environment at a temperature as low as 250°C, as shown, for example, in Figure 5. The inventors have found that SBR and its residues can be removed from recycled graphite concentrates by subjecting them to an oxygen-containing environment at a temperature as low as 300°C, as shown in Figure 5. Therefore, according to embodiments of the present invention, the pretreatment step of recycled graphite concentrates can be carried out by subjecting the recycled graphite concentrates to an oxidizing environment at a temperature of at least 250°C or at least 300°C, the exact temperature of which can be selected depending on whether the recycled graphite concentrate contains CMC, SBR, or both CMC and SBR.

[0033] Figures 5 and 6 show thermogravimetric analysis data for a sample of recycled graphite concentrate that had not undergone any pretreatment, as well as six samples of recycled graphite concentrate that had been pretreated in an oxidizing environment at various temperatures, airflow conditions, and times. The former sample is labeled "Recycled Graphite Concentrate," and the latter six samples are labeled "Examples 1-6." All of the Examples 1-6 samples contained the same amount of pre-treatment binder CMC and SBR as the untreated recycled graphite concentrate. The thermogravimetric analysis data in Figure 5 shows a first shoulder at approximately 250°C-300°C and a second shoulder around 300°C-380°C, more specifically around 300°C-350°C, for several samples. The first shoulder indicates that CMC can be removed at temperatures as low as 250°C–300°C, and the second shoulder indicates that SBR can be removed at temperatures as low as 300°C–380°C, more specifically around 300°C–350°C. As shown in Figure 6, the material of Example 6 was pretreated by being subjected to an oxidizing environment at 350°C for 60 minutes before being measured by thermogravimetric analysis. The thermogravimetric analysis data for Example 6 in Figure 5 shows neither shoulders nor significant weight loss, which means that Example 6 did not contain substantial amounts of CBC and SBR before thermogravimetric analysis. Therefore, the CMC and SBR present in Example 6 before the above pretreatment were largely removed during the pretreatment.

[0034] From an energy-saving viewpoint, the pretreatment step for recycled graphite concentrate is preferably kept at the lowest possible temperature, with the upper limit being the temperature required to remove one or more of the CMC, SBR, and their residues present in the recycled graphite concentrate. If the recycled graphite concentrate does not contain SBR, the pretreatment step for the recycled graphite concentrate can be carried out at a temperature in the range of, for example, 250°C to 300°C. If the recycled graphite concentrate contains SBR, the pretreatment step for the recycled graphite concentrate can be carried out at a temperature as low as 300°C to 380°C, preferably 300°C to 350°C.

[0035] Therefore, the pretreatment step for recycled graphite concentrates can generally be carried out by subjecting the recycled graphite concentrate to an oxidizing environment at a temperature of at least 250°C or at least 300°C. The exact temperature here can be selected depending on whether the recycled graphite concentrate contains CMC, SBR, or both CMC and SBR. The pretreatment step for recycled graphite concentrates can further be carried out by subjecting the recycled graphite concentrate to an oxidizing environment at a temperature of at most 300°C, 350°C, or 380°C. The exact temperature here can be selected depending on whether the recycled graphite concentrate contains CMC, SBR, or both CMC and SBR. To avoid unwanted oxidation of the graphite in the recycled graphite concentrate while simultaneously achieving the removal of CMC, SBR, or both CMC and SBR, an upper limit of 380°C, preferably 350°C, is preferred. The conditions in the pretreatment step for recycled graphite concentrates can generally be selected to remove a desired proportion of one or more of CMC, SBR, and their residues from the recycled graphite concentrate. The pretreatment step for the regenerated graphite concentrate can be carried out more specifically to reduce the concentration of CBC, SBR, and optionally their residues in the pretreated regenerated graphite concentrate to less than 0.25% by mass, preferably less than 0.2% by mass. It has been found that removing CBC and / or SBR before the heat treatment step at elevated temperatures is preferable to obtain a high tap density and a low Brunauer, Emmett, and Teller (BET) surface area of ​​the pretreated regenerated graphite concentrate after the subsequent heat treatment step. The latter is shown in Figure 7, where the sample in Example 1 was subjected to the pretreatment according to the present invention before heat treatment at high temperatures, while the sample in Example 3 was subjected to heat treatment at high temperatures only. Generally, a tap density of at least 1 g / cc and / or at most 2 m 2 / g (for example, 2.0m) 2 It was found that recycled graphite material having a BET specific surface area (SSA BET) of 1 / g can be obtained.

[0036] As those skilled in the art will understand with knowledge of the present invention, the exact amounts of CMC, SBR and their residues removed from the regenerated graphite concentrate during the pretreatment step can vary based on a combination of several process parameters. Such parameters include the duration of the pretreatment, the temperature during pretreatment, the degree of agitation during pretreatment, the particle size of the regenerated graphite concentrate, the amount of regenerated graphite concentrate to be pretreated, and the oxygen concentration in the oxidizing environment. The pretreatment step for the regenerated graphite concentrate generally proceeds, for example, within a range of 0.5 to 5 hours, preferably within a range of 0.5 to 2 hours, and more preferably within a range of 0.5 to 1 hour. Figure 6 shows some examples of conditions in the pretreatment step for the regenerated graphite concentrate.

[0037] The pretreatment process for recycled graphite concentrates generally involves exposing the recycled graphite concentrate to an oxidizing environment. As those skilled in the art will understand with knowledge of the present invention, the oxygen concentration in the oxidizing environment can vary. For example, the oxygen concentration in the oxidizing environment can be the same as the oxygen concentration in the air. More generally, the oxygen concentration in the oxidizing environment can be in the range of 10% to 20%. However, those skilled in the art will understand that the precise oxygen concentration in the oxidizing environment can be selected based on a balance estimate. That is, the oxygen concentration in the oxidizing environment is selected depending on the duration and temperature of the pretreatment process, as well as the amount of non-graphite carbon to be removed present in the recycled graphite concentrate. A rough approximation that can be used to estimate the time required to remove a certain amount of non-graphite carbon from a regenerated graphite concentrate during pretreatment can be obtained by solving the following equation for time: Time [min] × Gas flow [l / min] × Gas pressure [atm] ÷ 22.4 l / mol × O2 concentration gas [%] × O2 yield [%] = RGC [kg] × Binder / carbon amount [%] × Carbon fraction / fixed carbon [%] × 12 g / mol. The table in Figure 9 includes examples of input parameters for the pretreatment process.

[0038] The pretreatment process for regenerated graphite concentrates can generally be carried out in any suitable pretreatment apparatus, such as a rotary kiln, a heat mixer, a tubular furnace, a fluidized bed reactor, or similar equipment. As those skilled in the art will understand with knowledge of the present invention, the pretreatment process for regenerated graphite concentrates can be carried out in a pretreatment apparatus configured to expose the regenerated graphite concentrates to an oxidizing environment at a temperature in the range of 250°C to 380°C, or possibly 250°C to 350°C. More specifically, the pretreatment apparatus may be configured to expose the pretreated regenerated graphite concentrates to an oxygen-containing purging gas. The pretreatment apparatus may include, for example, a reaction chamber, a heat source, a thermostat, a gas inlet, and a gas outlet.

[0039] The pretreatment step for recycled graphite concentrate may, according to embodiments of the present invention, include two sub-steps, namely sub-step i) and sub-step ii). In sub-step i), the recycled graphite concentrate is subjected to an oxidizing environment at a temperature in the range of 250 to 380°C. Thus, the pretreatment step for recycled graphite concentrate may reduce the total concentration of CBC and SBR to less than 0.25% by mass, and their residues to less than 0.25% by mass. In sub-step ii), the recycled graphite concentrate from sub-step i) is subjected to an oxidizing environment at a temperature in the range of 500 to 600°C, preferably 550 to 600°C. Sub-step ii) may be performed here to remove conductive additives such as carbon black from the recycled graphite concentrate, while simultaneously limiting the oxidation of graphite in the recycled graphite concentrate compared to when the entire pretreatment step for recycled graphite concentrate is performed at a temperature in the range of 500 to 600°C. By employing separate sub-steps i) and ii), it is possible to perform a long heat treatment at a low temperature (in the range of 250-380°C) followed by a short heat treatment at a higher temperature (in the range of 500-600°C). The adoption of such sub-steps i) and ii) makes it possible to remove CBC and SBR, as well as other conductive additives such as carbon black, from the recycled graphite concentrate while limiting the oxidation of graphite in the recycled graphite concentrate. For example, sub-step i) can be continued for time X, and sub-step ii) for time Y, where X > Y. Those skilled in the art will understand, with knowledge of the present invention, that X and Y can vary based on the precise properties of the recycled graphite concentrate. As an example, X may be 1 hour and Y may be 10 minutes.

[0040] According to certain embodiments of the present invention, the recycled graphite concentrate may be electrode scrap, for example, anode scrap. Here, electrode scrap may be graphite electrode scrap from electrode manufacturing, more specifically anode manufacturing, for example, defective products. Anode scrap may typically contain graphite, SBR, and CMC, for example, with graphite being 95-97% by mass and the total amount of SBR and CMC being 3-5% by mass. Anode scrap may contain copper impurities, as it can be obtained, for example, by separation from copper foil. As an example, anode scrap may contain 0.1-2% by mass of copper. Anode scrap may not contain binders other than, for example, SBR and CMC. In other words, anode scrap may be graphite anode scrap, i.e., spent graphite anode material.

[0041] Method 100 according to the present invention includes a step 130 of heat-treating a pre-treated recycled graphite concentrate, as schematically shown in Figure 1. The heat-treating step 130 of the pre-treated recycled graphite concentrate is carried out after the pre-treatment step and involves subjecting the pre-treated recycled graphite concentrate to a non-oxidizing environment at a temperature of at least 2300°C. The duration of the heat-treating step 130 of the pre-treated recycled graphite concentrate may be, for example, in the range of 0.5 to 5 hours, more preferably in the range of 1 to 3 hours. The pre-treated recycled graphite concentrate can be understood here as a material containing the recycled graphite concentrate that has undergone the above pre-treatment step 120.

[0042] A non-oxidizing environment in the process of heat-treating pre-treated recycled graphite concentrates is generally an environment in which oxygen is not intentionally added. An example of a non-oxidizing environment is an environment that is constantly purged with an inert gas such as argon or nitrogen. The total oxygen concentration in the non-oxidizing environment is generally at most 0.1%, preferably at most 0.05%, and more preferably at most 0.01%. The non-oxidizing environment is selected here to limit the oxidation of the graphite components of the pre-treated recycled graphite concentrates. However, those skilled in the art will understand that some degree of undesirable oxidation may be unavoidable during the heat treatment of the graphite components of the pre-treated recycled graphite concentrates. Undesirable oxidation may occur, for example, due to the presence of oxygen impurities in the purging gas used, residual moisture or air in the equipment used to carry out the heat treatment, or leakage of air in the equipment used to carry out the heat treatment.

[0043] The process of heat-treating the pre-treated recycled graphite concentrate may be carried out to reduce the amount of metallic impurities present in the pre-treated recycled graphite concentrate. According to the present invention, the temperature in the heat-treating process of the pre-treated recycled graphite concentrate is at least 2300°C. The inventors have found that 2300°C is the sublimation threshold for most metallic impurities commonly found in recycled graphite concentrates, excluding iron, nickel, titanium, vanadium, etc. Figure 4 shows the sublimation temperatures of various metallic impurities in the pre-treated graphite concentrate, as measured by X-ray fluorescence analysis (XRF). It has been found that heat treatment in a non-oxidizing environment at a temperature of at least 2300°C, preferably at least 2400°C, removes copper, silicon, manganese, magnesium, sodium, chromium, calcium, phosphorus, and aluminum from the recycled graphite concentrate. Furthermore, it has been found that heat treatment in a non-oxidizing environment at a temperature of at least 2800°C causes sublimation and subsequent removal of iron and nickel. When recycled graphite is used as a negative electrode material, iron is particularly undesirable in recycled graphite because it causes undesirable electrochemical side reactions that shorten the lifespan of the LIB. Figure 4 shows that sublimation of vanadium and titanium occurs at temperatures of at least 2900°C. Since vanadium and titanium are rarely found in significant concentrations in LIBs, it may not be necessary to perform a heat treatment step of pre-treated recycled graphite concentrate at temperatures above 2900°C. According to a particular embodiment of the present invention, the heat treatment step of the pre-treated recycled graphite concentrate is performed by subjecting the pre-treated recycled graphite concentrate to a non-oxidizing environment at a temperature in the range of 2300°C to 2900°C, preferably in the range of 2400°C to 2900°C, and more preferably in the range of 2800°C to 2900°C. It is considered desirable to keep the temperature during heat treatment as low as possible, more specifically below 2900°C, in order to obtain the aforementioned sublimation while simultaneously reducing wear on the equipment and limiting power consumption compared to using higher temperatures.The heat treatment may be carried out at a maximum of 3200°C, which has been found to be the minimum threshold at which many elements with higher sublimation points, such as titanium and vanadium, can be removed to 20 ppmw or less. In certain embodiments of the present invention, the heat treatment step of the pre-treated recycled graphite concentrate is carried out so that the concentration of one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon in the heat-treated recycled graphite concentrate, i.e., the sum of their concentrations, is less than 100 ppmw, preferably less than 20 ppmw. Since some metals are electrochemically active and can cause undesirable side reactions during repeated cycles, high purity recycled graphite, when used as the negative electrode material for new LIBs, can generally lead to a longer lifespan for LIBs.

[0044] Figure 8 shows the total amount of metal impurities in an untreated recycled graphite concentrate sample and the same recycled graphite concentrate sample that was pretreated in a heated mixer under an air atmosphere at 350°C for 60 minutes and then heat-treated at 3000°C for 2 hours. Here, it can be seen that the total amount of metal impurities exceeds 1.5% by mass in the untreated recycled graphite concentrate, while it is less than 0.01% by mass in the recycled graphite concentrate subjected to heat treatment.

[0045] In embodiments where the regenerated graphite concentrate is anode scrap, the step of heat-treating the pre-treated regenerated graphite concentrate may be carried out by subjecting the pre-treated regenerated graphite concentrate to a non-oxidizing environment at a temperature in the range of 2300°C to 2500°C, preferably 2300°C to 2400°C. The temperature range may be selected to remove one or more of copper and silicon from the anode scrap, as silicon may be present in the anode scrap at a concentration of more than 1% by weight. The upper temperature limit may be selected here to limit wear and power consumption of the equipment and / or to limit the generation of off-gas / emissions. At least some of the iron present in the anode scrap may be removed by magnetic separation.

[0046] The process of heat-treating the pre-treated regenerated graphite concentrate may, for example, be carried out in an induction furnace. As those skilled in the art will understand with knowledge of the present invention, the heat-treating process of the pre-treated regenerated graphite concentrate may be carried out in a heat treatment apparatus configured to expose the pre-treated regenerated graphite concentrate to a non-oxidizing environment at a temperature of at least 2300°C. More specifically, the heat treatment apparatus may be configured to expose the pre-treated regenerated graphite concentrate to a temperature of at least 2300°C while simultaneously exposing the pre-treated regenerated graphite concentrate to an inert purging gas at all times. Thus, the heat-treating process of the pre-treated regenerated graphite concentrate may further involve condensing metallic impurities from the purge gas in a condenser unit, where the condenser unit may be separated from the induction furnace used to carry out the heat-treating process of the pre-treated regenerated graphite concentrate. The latter is preferable to using a conventional Acheson furnace in which metallic impurities accumulate in the furnace.

[0047] The method of the present invention can generally be carried out using a wide range of recycled graphite concentrates. However, the recycled graphite concentrate preferably contains at least 90%, preferably at least 95%, and more preferably at least 99% carbon. This level of carbon may allow for limiting the duration of the pretreatment and heat treatment steps, and may also allow for a high proportion of graphite in the recycled graphite obtained by the method. A carbon content of at least 90% in the recycled graphite concentrate may be considered a lower limit to make the method of the present invention practically feasible, i.e., to avoid having to perform each step for a duration that would impair the economics of the method, cause unwanted wear of the equipment, and / or impose excessively high requirements for off-gas / emissions handling. Furthermore, or optionally, the recycled graphite concentrate may contain limited amounts of metallic impurities before being treated with the method according to the present invention. In certain embodiments of the present invention, the recycled graphite concentrate may contain copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon, i.e., up to 1% by mass in cumulative amounts. The amount of metal impurities in question may allow for a limited duration of the required heat treatment process, enable acceptable equipment wear, and / or allow for limited generation of off-gas / emissions.

[0048] Recycled graphite concentrates can generally undergo pretreatment steps without being subjected to acid immersion first. Methods for producing recycled graphite may even omit the acid immersion step altogether.

[0049] In certain recycling processes, it may be preferable to process recycled graphite concentrates with a carbon content of less than 90% and a metal impurity concentration of more than 1%. Given the quality of such recycled graphite concentrates, it may be possible to improve the overall quality of the recycled graphite concentrate or pre-treated recycled graphite concentrate by mixing it with unused raw materials, for example, those containing more than 90% carbon and / or less than 1% metal impurity. Figure 2 schematically illustrates a particular embodiment of the present invention, in which method 100 further comprises a step 140 of mixing the pre-treated recycled graphite concentrate with untreated raw materials before a step 130 of heat-treating the pre-treated recycled graphite concentrate. The unused raw materials may be selected from, for example, petroleum coke, unused synthetic graphite, and natural graphite. The unused raw materials may contain, for example, at least 90% carbon and at most 1% by mass of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon, i.e., in cumulative amounts.

[0050] The pre-treated recycled graphite concentrate may be mixed with other additives prior to step 130, in which the pre-treated recycled graphite concentrate is heat-treated, as schematically shown in Figure 2. Such additives may include, for example, unused binders. Unused binders may be defined here as one or more of coal tar pitch, petroleum pitch, or asphalt / bitumen. In certain embodiments of the present invention, a method for producing recycled graphite from graphite concentrates may further include step 150, in which the pre-treated recycled graphite concentrate and unused binders are mixed to form a blend prior to step 130, in which the pre-treated recycled graphite concentrate is heat-treated. Adding unused binders to the pre-treated recycled graphite concentrate prior to heat treatment 130 may be done to agglomerate and coat the graphite particles prior to heat treatment 130. The ratio between the binder and the pre-treated reclaimed graphite concentrate in the blend may preferably be in the range of 3 to 12% by mass, more preferably in the range of 6 to 8% by weight. The latter range has been empirically shown to result in improved cohesiveness after the subsequent heat treatment 130. The method 100 for producing recycled graphite from graphite concentrate may further include a step 160 in which the blend is cohesive at a temperature in the range of 800 to 1100°C, prior to the step 130 in which the pre-treated reclaimed graphite is heat-treated. Such cohesiveness 160 has been shown to result in a lower degree of orientation of the recycled graphite obtained from method 100 compared to when cohesiveness is not performed. The step 140 in which the pre-treated reclaimed graphite concentrate is mixed with unused raw materials may generally be performed before or after the optional step 150 in which the pre-treated reclaimed graphite concentrate and unused binder are mixed to form a blend. The process of heat-treating pre-treated recycled graphite concentrates can cause partial or complete graphitization of the unused binder.

[0051] The present invention also provides recycled graphite containing at least 0.25% by mass, preferably at most 0.2% by mass, CBC and SBR and optionally their residues, and at least 0.01% by mass, preferably at most 0.005% by mass, one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon. Therefore, the total amount of CBC, SBR and their residues is at most 0.25% by mass, preferably at most 0.2% by mass. Therefore, the total amount of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon may be at most 0.01% by mass, preferably at most 0.005% by mass. The recycled graphite further has a tap density of at least 1 g / cc and at most 2 m 2 / g, for example 2.0m 2 It may have one or more of the BET specific surface area (SSA BET) per g. Recycled graphite can generally be obtained by any embodiment of the method according to the present invention. Therefore, binder residue can generally refer to one or more residues of CBC and SBR, for example, molecules remaining from the thermal and / or chemical decomposition of the binder.

[0052] Recycled graphite can generally be used in the manufacture of negative electrodes for lithium-ion batteries (LIBs). As will be understood by those skilled in the art, the exact method of manufacturing the negative electrode may vary. Accordingly, one aspect of the present invention provides a battery comprising recycled graphite according to a second aspect of the present invention. Another aspect of the present invention involves using the recycled graphite described herein in the negative electrode of a battery.

[0053] example: Figure 7 shows an overview of various materials obtained using different representative methods, labeled as Examples 1-3.

[0054] Example 1: Recycled graphite concentrate was pre-treated in a heated mixer under an air atmosphere at 350°C for 60 minutes. The pre-treated material was then heat-treated at 3000°C for 2 hours.

[0055] Example 2: Recycled graphite concentrate was pretreated in a heated mixer at 350°C under an air atmosphere for 60 minutes. Next, the pretreated recycled graphite concentrate was mixed with a pitch binder to form a blend, which was then agglomerated and heat-treated at 1000°C until it contained 8% pitch. The agglomerated blend was then heat-treated at 3000°C for 2 hours to produce recycled graphite.

[0056] Example 3: Recycled graphite concentrate was directly heat-treated at 3000°C for 2 hours.

Claims

1. A method (100) for producing recycled graphite, wherein the method (100) is A step of supplying a recycled graphite concentrate containing one or more of carboxymethylcellulose and styrene-butadiene rubber, A step (120) of pre-treating the recycled graphite concentrate by subjecting it to an oxidizing environment at a temperature in the range of 250 to 380°C, thereby reducing the total concentration of carboxymethylcellulose and styrene-butadiene rubber in the recycled graphite concentrate to less than 0.25% by mass, and (130) A step in which the pre-treated recycled graphite concentrate is heat-treated by subjecting it to a non-oxidizing environment at a temperature of at least 2300°C. A method for manufacturing recycled graphite, including the following.

2. Prior to the step of heat-treating the pre-treated recycled graphite concentrate (130), the pre-treated recycled graphite concentrate is mixed with an unused binder (150) to form a blend, The step (130) of heat-treating the pre-treated recycled graphite concentrate includes subjecting the blend to a non-oxidizing environment at a temperature of at least 2300°C. The method according to claim 1, further comprising:

3. The method according to claim 2, wherein the ratio of the unused binder in the blend to the pre-treated recycled graphite concentrate is in the range of 3 to 12% by mass, preferably in the range of 6 to 8% by mass.

4. The method according to any one of claims 1 to 3, wherein in the pretreatment step (120) of the regenerated graphite concentrate, the regenerated graphite concentrate is subjected to an oxidizing environment at a temperature of no more than 350°C.

5. The method according to any one of claims 1 to 4, wherein the pretreatment step (120) of the recycled graphite concentrate is carried out such that the total concentration of carboxymethylcellulose and styrene-butadiene rubber in the pretreated recycled graphite concentrate is less than 0.2% by mass.

6. The method according to any one of claims 1 to 5, wherein the heat treatment step (130) of the pre-treated recycled graphite concentrate is carried out by subjecting the pre-treated recycled graphite concentrate to a non-oxidizing environment at a temperature in the range of 2300°C to 2900°C.

7. The method according to any one of claims 1 to 6, wherein the heat treatment step (130) of the pre-treated recycled graphite concentrate is carried out such that the concentration of one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon in the heat-treated recycled graphite concentrate is less than 100 ppmw, preferably less than 20 ppmw.

8. The above method (100) Prior to the heat treatment step (130) of the pre-treated recycled graphite concentrate, the step (140) includes mixing the pre-treated recycled graphite concentrate with unused raw materials. The aforementioned unused raw material is selected from one or more of the following: petroleum coke, unused synthetic graphite, and natural graphite. The heat treatment step (130) of the pre-treated recycled graphite concentrate is carried out by subjecting the pre-treated recycled graphite concentrate to a non-oxidizing environment at a temperature of at least 2300°C. The method according to any one of claims 1 to 7, further comprising:

9. The method according to any one of claims 1 to 8, wherein the recycled graphite concentrate contains at least 90%, preferably at least 95%, and more preferably at least 99% carbon.

10. The method according to any one of claims 1 to 9, wherein the recycled graphite concentrate contains up to 1% by mass of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon.

11. The method according to any one of claims 1 to 10, wherein the recycled graphite concentrate is anode scrap.

12. The pretreatment step for the recycled graphite concentrate is, i) A sub-step in which the recycled graphite concentrate is subjected to an oxidizing environment at a temperature in the range of 250 to 380°C, thereby reducing the total concentration of carboxymethylcellulose and styrene-butadiene rubber to less than 0.25% by mass, and after that ii) A sub-step in which the regenerated graphite concentrate from step i) is subjected to an oxidizing environment at a temperature in the range of 500 to 600°C, preferably in the range of 550 to 600°C. A method according to any one of claims 1 to 11, including the method described in any one of claims 1 to 11.

13. Recycled graphite comprising at most 0.25% by mass, preferably at most 0.2% by mass, of one or more of carboxymethylcellulose, styrene-butadiene rubber, and their residues, and at most 0.01% by mass, preferably at most 0.005% by mass, of one or more of copper, nickel, magnesium, iron, manganese, aluminum, lithium, sulfur, and silicon.

14. The recycled graphite has a tap density of at least 1 g / cc and / or at most 2.0 m ２ The recycled graphite according to claim 13, having a BET specific surface area of ​​1 / g.

15. Use of recycled graphite according to claim 13 or 14 in the negative electrode of a battery.

16. A battery comprising recycled graphite according to claim 13 or 14.

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