KR20230038844A - Method for rcycling cathode active material and rycycled cathode active material - Google Patents

Abstract

The present invention relates to a method for recovering a positive electrode active material and a positive electrode active material recovered therefrom, and more specifically, to a method for recovering a positive electrode active material and a positive electrode active material recovered therefrom, wherein the method comprises the steps of: (a) recovering a positive electrode active material by heat treating a waste positive electrode, which includes a current collector and a positive electrode active material layer coated thereon, at 300 to 650℃ in air; (b) washing the recovered positive electrode active material with a basic aqueous lithium compound solution at 40 to 100℃; and (c) adding a lithium precursor to the washed positive electrode active material and annealing the same at 400 to 1000℃ in air. According to the present invention, provided are the method for recovering a positive electrode active material and the positive electrode active material recovered therefrom with excellent electrochemical performance, resistance characteristics, and capacity characteristics, wherein an F component remaining on a surface of the recovered positive electrode active material is thoroughly removed with a small amount of cleaning solution to greatly reduce wastewater generation and greatly improve rate performance of a battery, the method is eco-friendly by not using acid and thus reduces process costs by not requiring neutralization and wastewater treatment, the positive electrode active material is recycled without decomposition such that there is no wasted metal element, the current collector is not dissolved to allow recovery of the current collector, organic solvents are not used for safety without a risk of toxic gases or explosions, and the method is suitable for mass production by using easy-to-manage processes such as heat treatment and sedimentation.

Description

Regeneration method of cathode active material and cathode active material regenerated therefrom

The present invention relates to a method for regenerating a cathode active material and a cathode active material regenerated therefrom, and more particularly, to cleanly remove the F component remaining on the surface of the regenerated cathode active material with a small amount of washing solution, greatly reducing the generation of wastewater and at the same time It significantly improves rate performance, is eco-friendly because it does not use acid, and reduces process costs because it does not require neutralization and wastewater treatment. It does not dissolve the whole, so it can be recovered, and it is safe without the risk of toxic gas or explosion because it does not use an organic solvent, and it is suitable for mass production using a process that is easy to manage such as heat treatment or sedimentation. The present invention relates to a regenerated cathode active material having excellent electrochemical performance, resistance characteristics, and capacity characteristics after being regenerated therefrom.

A lithium secondary battery consists of a positive electrode whose positive active material layer is coated on a metal foil such as aluminum, a negative electrode whose negative active material layer is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing, and between the positive and negative electrodes. It consists of an electrolyte that allows lithium ions to move.

The positive electrode active material layer mainly uses a lithium-based oxide as an active material, and the negative electrode active material layer mainly uses a carbon material as an active material. The lithium-based oxide generally contains rare metals such as cobalt, nickel, or manganese. Research on recovering and recycling rare metals from cathodes of lithium secondary batteries that are discarded or scraps of anodes generated in the manufacturing process of lithium secondary batteries (hereinafter, referred to as 'waste anodes') has been extensively conducted.

Conventional technologies for recovering rare metals from waste anodes are mostly methods of dissolving the waste anode with hydrochloric acid, sulfuric acid or nitric acid, extracting cobalt, manganese, nickel, etc. with an organic solvent, and then using them as raw materials for synthesizing cathode active materials. .

However, the method of extracting rare metals using an acid has a problem of environmental pollution, a neutralization process and a wastewater treatment process are required, which greatly increases process cost, and has disadvantages in that lithium, the main metal of the cathode active material, cannot be recovered.

In order to overcome these disadvantages, a method of directly recycling the cathode active material from the waste anode without decomposition (direct recycled method) has recently been studied, and in this way, calcination, solvent dissolution, aluminum Four degrees are introduced: aluminum foil dissolution, crushing & screening.

However, although the firing method has a simple process, there are disadvantages in that foreign substances that deteriorate the output performance of the battery are generated on the surface of the regenerated cathode active material, waste gas is generated, and energy consumption is high.

In addition, the solvent dissolution method can obtain a regenerated cathode active material with a relatively clean surface, but the solvent such as N-methyl-2-pyrrolidone (NMP) used to dissolve the binder is a toxic gas and has a risk of explosion, so stability is poor. There is a disadvantage that a poor and expensive solvent recovery process is required.

In addition, the aluminum foil melting method has good process stability, low process cost, and easy binder removal, but foreign substances that are difficult to remove are generated on the surface of the recycled cathode active material, and hydrogen gas is generated during the aluminum foil removal process, resulting in an explosion risk. There is a downside to that.

Finally, the crushing and screening method has the advantage of being the simplest process, but it is difficult to completely separate the current collector and the positive electrode active material, and the particle size distribution of the positive electrode active material changes during the crushing process, and the binder remains, resulting in regenerated positive electrode active material There is a disadvantage that the battery characteristics of the deterioration.

Therefore, there is an urgent need to develop a method for reproducing a cathode active material with improved output performance without metal elements discarded from the waste anode at a low cost and in an environmentally friendly manner.

In order to solve the problems of the prior art as described above, the present invention greatly reduces the generation of wastewater and greatly improves the rate performance of the battery by clearly removing the F component remaining on the surface of the regenerated cathode active material with a small amount of washing liquid. It is eco-friendly because it does not use acid, and process cost is reduced because it does not require neutralization and wastewater treatment, and since the cathode active material is reproduced as it is without disassembling, there are no wasted metal elements and it is possible to recover it because it does not dissolve the current collector. It is an object of the present invention to provide a method for regenerating a cathode active material suitable for mass production by using a safe, easy-to-manage process such as heat treatment or sedimentation without the use of organic solvents and without the risk of toxic gas generation or explosion.

In addition, an object of the present invention is to provide a positive electrode active material having excellent electrochemical performance, resistance characteristics, and capacity characteristics.

The above and other objects of the present invention can all be achieved by the present invention described below.

In order to achieve the above object, the present invention provides (a) recovering a cathode active material by heat-treating a waste cathode including a current collector and a cathode active material layer coated thereon at 300 to 650 ° C. in air; (b) washing the recovered cathode active material with a washing solution at 40 to 100 °C; and (c) adding a lithium precursor to the washed cathode active material and annealing it in air at 400 to 1000 °C.

The waste cathode in step (a) may be a cathode separated from a lithium secondary battery discarded after use, a defective cathode sheet generated in a lithium secondary battery manufacturing process, or cathode scrap remaining after a cathode plate is punched out from a cathode sheet. .

The cathode active material is preferably a lithium cobalt oxide such as LiCoO ₂ ; lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ ; lithium iron phosphate compounds such as LiFePO ₄ and the like; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO ₂ and the like; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; and NCM-based lithium composite transition metal oxides in which a portion of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co).

The washing liquid in step (b) may preferably be water or a basic aqueous solution of a lithium compound.

The washing solution of step (b) may be preferably used in an amount of 8 to 22 times the weight of the recovered cathode active material.

The washing of the step (b) may preferably include stirring the recovered cathode active material and the washing solution.

The stirring can be preferably carried out within one week.

Step (b) may preferably include a process of drying the washed cathode active material.

The lithium precursor in step (c) may be at least one selected from the group consisting of LiOH, Li ₂ CO ₃ , LiNO ₃ and Li ₂ O.

Preferably, the amount of the lithium precursor in step (c) is reduced by at least the molar ratio of lithium in the cathode active material in step (a) based on the amount of lithium in the washed cathode active material.

The annealing temperature in step (c) may preferably be a temperature exceeding the melting point of the lithium precursor.

The method of regenerating the cathode active material may preferably include (d) coating the annealed cathode active material with a coating material containing metal or carbon, and then heat-treating the annealed cathode active material at 100 to 1200 °C.

In addition, the present invention provides a regenerated cathode active material produced by the regeneration method of the cathode active material.

In addition, the present invention is a lithium cobalt oxide such as LCO; lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ ; lithium iron phosphate compounds such as LiFePO ₄ and the like; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO ₂ and the like; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; And at least one selected from the group consisting of NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and fluorine (F) Provided is a recycled cathode active material having a content of 600 ppm or less.

Preferably, the surface of the recycled cathode active material may be coated with a coating material containing metal or carbon.

According to the present invention, the F component remaining on the surface of the regenerated cathode active material is cleanly removed with a small amount of washing solution, thereby greatly reducing the generation of wastewater, greatly improving the rate performance of the battery, and being eco-friendly and , It does not require neutralization and wastewater treatment, so process costs are reduced, and there are no wasted metal elements by reproducing the cathode active material as it is without disassembling it, and it is possible to recover it because it does not dissolve the current collector. Provides a method for regenerating a cathode active material suitable for mass production using a process that is easy to manage, such as heat treatment or sedimentation, without the risk of gas generation or explosion, and a cathode active material that is regenerated from the method and has excellent electrochemical performance, resistance characteristics, and capacity characteristics has the effect of

The following drawings attached to this specification illustrate embodiments of the present invention, and together with the detailed description below serve to further understand the technical idea of the present invention, the present invention is limited to the matters described in these drawings should not be interpreted
1 is a view showing cathode scrap discarded after cutting an electrode plate from a cathode sheet.
2 is a graph showing the rate performance according to the number of cycles as a result of cell evaluation of the regenerated cathode active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 and the cathode active material of Reference Example (Reference NCM65). am.
FIG. 3 is a graph showing the rate performance according to the number of cycles as a result of cell evaluation of the regenerated cathode active materials prepared in Comparative Examples 1 to 4 and the cathode active material of Reference Example (Reference NCM65).
4 is a flow chart of a process for regenerating a cathode active material according to one embodiment of the present invention.

While researching a direct recycled method (direct recycled method) of recycling the cathode active material from the waste cathode without disassembling it, the present inventors recovered the cathode active material from cathode scrap generated in the lithium secondary battery manufacturing process by a firing method, and then When the positive electrode active material recovered in the reforming process is washed with a washing solution warmed to a predetermined temperature range, it is confirmed that the battery characteristics of the regenerated positive active material are improved, and based on this, further research has been conducted to complete the present invention.

Hereinafter, a method for regenerating the cathode active material of the present disclosure and a cathode active material regenerated therefrom will be described in detail.

However, the terms or words used in this specification and claims cannot be construed as being limited to ordinary or dictionary meanings, and the inventor may properly define the concept of terms in order to best explain his or her application. It should be interpreted as a meaning and concept consistent with the technical spirit of the present invention based on the principle that it can be. Therefore, the embodiments described in this specification and the configurations shown in the drawings are only one embodiment of the present invention and do not represent all of the technical spirit of the present invention, so various equivalents and modifications that can replace them It should be understood that there may be, and may be arranged, substituted, combined, separated or designed in a variety of different configurations.

All technical and scientific terms used in this description have meanings as commonly understood by those of ordinary skill in the art to which the present invention belongs unless otherwise defined.

Regeneration method of cathode active material

The method of regenerating a cathode active material of the present invention includes (a) recovering a cathode active material by heat-treating a waste anode including a current collector and a cathode active material layer coated thereon in air at 300 to 650 ° C; (b) washing the recovered cathode active material with a neutral or basic washing solution at 40 to 100 °C; and (c) adding a lithium precursor to the washed cathode active material and annealing it in air at 400 to 1000 ° C. In this case, the F component remaining on the surface of the regenerated cathode active material is cleaned with a small amount of washing solution. It greatly reduces the generation of wastewater and greatly improves the rate performance of the battery, and is environmentally friendly because it does not use acid. There is no wasted metal element by regeneration as it is, and it is possible to recover it because it does not dissolve the current collector. It does not use organic solvents, so there is no risk of toxic gas or explosion. It has advantages suitable for mass production.

(a) recovering the cathode active material from the waste anode

The step of (a) recovering the cathode active material from the waste cathode according to the present invention preferably comprises the steps of recovering the cathode active material by heat-treating the waste cathode including a current collector and a cathode active material layer coated thereon at 300 to 650 ° C. in air. In this case, while the process is simple, there is an effect of cleanly removing the binder, the conductive material, and the current collector.

The waste cathode may preferably be a cathode separated from a lithium secondary battery discarded after use, a defective cathode sheet or cathode scrap generated in a lithium secondary battery manufacturing process, and more preferably, a cathode remaining after a cathode plate is punched out from a cathode sheet. could be scrap.

The cathode active material layer of step (a) may preferably include a cathode active material, a binder, and a conductive material.

The cathode active material is preferably lithium cobalt oxide such as LiCoO ₂ (hereinafter referred to as 'LCO'); lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ ; lithium iron phosphate compounds such as LiFePO ₄ and the like; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO ₂ and the like; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; and NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and more preferably nickel-manganese-based. It is lithium composite metal oxide, NCM-based lithium composite transition metal oxide, or a mixture thereof, and in this case, there is an effect of excellent reversible capacity and thermal stability.

As another specific example, the cathode active material is represented by Chemical Formula 1

[Formula 1]

Li _a Ni _x Mn _y Co _z M _w O _{2 +δ}

(In Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 1<a≤1.1, 0<x<0.95, 0<y<0.8, 0< z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1).

The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT, or a mixture thereof.

The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, more preferably polyvinylidene It may be fluoride.

The heat treatment temperature may be preferably 400 to 600 °C, more preferably 500 to 600 °C, and still more preferably 530 to 580 °C, and within this range, the current collector does not melt and only the binder is removed from the current collector. There is an advantage in that the cathode active material is easily separated.

The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, still more preferably 30 minutes to 2 hours, even more preferably 30 minutes to 1 hour, and within this range In this method, the current collector is not melted and only the binder is removed, so that the cathode active material is easily separated from the current collector.

In the present description, the heat treatment time is the time to be treated at the corresponding heat treatment temperature, and the time to reach the corresponding heat treatment temperature is not calculated.

1 shows cathode scrap discarded after cutting a cathode plate from a cathode sheet.

Referring to FIG. 1, a cathode active material layer 20 including a cathode active material, a conductive material, a binder, etc. is coated on an aluminum foil 10, which is a long sheet-shaped cathode current collector, to prepare a cathode sheet 30, and then a cathode sheet 30 is prepared. The positive electrode plate 40 is produced by punching to size, and then the positive electrode scrap 50 is generated as the remaining portion. The punching is one means of cutting the cathode sheet.

In addition, the positive electrode active material layer 20 is formed by coating aluminum foil 10 with a slurry in which a positive electrode active material, a conductive material, a binder, and a solvent are mixed, and the slurry is very sensitive to the environment such as temperature. Since it is not very difficult, waste cathode sheets are generated until a condition for manufacturing a cathode sheet 30 of desired quality is found through a predetermined test.

For reference, in the following examples, anode scrap was used as a waste anode.

(b) washing the cathode active material (surface modification step)

Step (b) washing the cathode active material according to the present invention may preferably be a step of washing the recovered cathode active material with a washing solution at 40 to 100 ° C. In this case, a small amount of the F component remaining on the surface of the regenerated cathode active material It has the effect of significantly reducing the generation of wastewater and greatly improving the output performance of the battery.

The washing liquid may be preferably 40 to 90 °C, more preferably 50 to 90 °C, even more preferably 60 to 80 °C, even more preferably 65 to 75 °C, and regeneration within this range By removing the F component remaining on the surface of the positive electrode active material with a small amount of cleaning solution, wastewater generation is greatly reduced and at the same time, the output performance of the battery is greatly improved.

The washing solution of step (b) may be preferably used in an amount of 3 to 22 times the weight of the recovered active material, more preferably 5 to 20 times the weight, and even more preferably 8 to 20 times the weight. It is used, more preferably 10 to 15 times the weight, and within this range, the F component remaining on the surface of the regenerated cathode active material is clearly removed with a small amount of washing solution, greatly reducing wastewater generation and at the same time output performance of the battery has a significant improvement effect.

The cleaning solution in step (b) may preferably be neutral water or a basic aqueous solution of a lithium compound. In this case, the F component remaining on the surface of the regenerated cathode active material is clearly removed with a small amount of the cleaning solution, greatly reducing the generation of wastewater and At the same time, there is an effect of greatly improving the output performance of the battery.

The basic lithium compound aqueous solution may preferably include more than 0% by weight and less than 15% by weight of a basic lithium compound, more preferably more than 0% by weight to 10% by weight of a basic lithium compound, , within this range, the surface modification effect of removing LiF and metal fluoride formed on the surface of the positive electrode active material in the preceding heat treatment process is excellent.

The step (b) may preferably be a step of washing the recovered cathode active material by stirring it in an aqueous solution of a basic lithium compound. In this case, it is a process of modifying the surface of the cathode active material. There is an effect of removing foreign substances such as LiF or metal fluoride generated.

The stirring is performed for example within a week, preferably within a day, more preferably for 1 hour or less, 40 minutes or less, 30 minutes or less or 20 minutes or less, or for example 5 minutes or more, preferably 10 minutes or more. , It may be 20 minutes or more or 30 minutes or more, and within this range, all foreign substances such as LiF or metal fluoride generated on the surface of the positive electrode active material are removed, and nonetheless, excessive elution of lithium does not occur, so the battery has excellent capacity characteristics. .

The washing liquid may preferably maintain the temperature range of the washing liquid by a heating means during the washing, stirring or mixing, and within this range, the F component remaining on the surface of the regenerated cathode active material is cleanly removed with a small amount of the washing liquid to generate wastewater There is an effect of greatly reducing the occurrence and at the same time greatly improving the output performance of the battery.

In the present description, the heating means is temperature controllable and is not particularly limited if it is a heating means commonly used in the art to which the present invention belongs.

The washing in the step (b) may preferably include a step of collecting the solid positive electrode active material by filtering or discarding the supernatant after the stirring or mixing is finished, and then drying. In this case, lithium There is an effect of optimizing the precursor addition process.

The drying may be preferably carried out at 70 to 200 ° C., more preferably at 20 to 130 ° C., until there is no change in weight, for example, for 1 to 24 hours. It has the effect of efficiently removing the contained moisture.

(c) After adding a lithium precursor to the cathode active material annealing step

The step of annealing after adding the lithium precursor to the cathode active material (c) according to the present invention may preferably be a step of adding the lithium precursor to the washed cathode active material and annealing at 400 to 1000 ° C. in air, in which case the crystal There is an effect of improving the battery characteristics of the regenerated cathode active material by improving the crystallinity, such as increasing the crystallinity or restoring the crystal structure.

The lithium precursor in step (c) may be at least one selected from the group consisting of LiOH, Li ₂ CO ₃ , LiNO ₃ and Li ₂ O.

The lithium precursor in step (c) may be added in a reduced amount, preferably at least in the molar ratio of lithium in the cathode active material in step (a) based on the amount of lithium in the washed cathode active material, and more preferably may be added in an amount such that the molar ratio of lithium is 0.0001 to 0.2 with respect to the molar ratio of lithium in the cathode active material in step (a), and within this range, insufficient lithium in the regenerated cathode active material is supplemented to increase crystallinity or crystal structure There is an advantage in that battery characteristics of the regenerated cathode active material are improved by improving crystallinity such as recovery.

The lithium precursor in step (c) is preferably added in an amount capable of providing 1 to 40 mol% of lithium based on 100 mol% of the total lithium in the cathode active material in step (a), More preferably, it may be added in an amount capable of providing lithium corresponding to 1 to 15 mol%, more preferably in an amount capable of providing lithium corresponding to 7 to 11 mol%, and within this range It is very useful for improving battery characteristics because there is no residual precursor that can increase the resistance of the regenerated cathode active material.

The annealing temperature in step (c) can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, in the case of LiCO ₃ , the melting point is 723 ° C, preferably 700 to 900 ° C, more preferably 710 to 900 ° C. It can be annealed at 780 ° C, and in the case of LiOH, the melting point is 462 ° C, preferably 400 to 600 ° C, more preferably 450 to 480 ° C, and within this range, the crystal structure is recovered and the output of the battery It has excellent performance effect.

The annealing temperature in step (c) may preferably exceed the melting point of the lithium precursor, but if it exceeds 1000 ° C., thermal decomposition of the positive electrode active material may occur, resulting in degradation of battery performance.

(d) heat treatment after coating with a coating agent

The step of heat treatment after coating with a coating agent (d) according to the present invention is an optional step, preferably, after coating the annealed cathode active material of step (c) with a coating agent containing metal or carbon, 100 to 1200 ° C. It may be a heat treatment step, and in this case, there is an effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

The coating agent containing the metal is preferably one or more selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V and Y. It is a coating agent containing, more preferably a coating agent containing at least one selected from the group consisting of B, W, Al, Ti and Mg. There is an effect of replenishing or restoring the lost metal or surface coating layer other than lithium.

The heat treatment temperature may be preferably 100 to 1000 °C, more preferably 200 to 1000 °C, and even more preferably 200 to 500 °C, and within this range, while maintaining the properties of the positive electrode active material itself, structural stability and electrical It has the effect of improving chemical performance.

As a specific example, when the coating agent contains B, B-W, B-Ti or B-W-Ti, the heat treatment temperature may be preferably 200 to 500 °C.

The coating agent may be preferably 0.01 to 10 parts by weight, more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the total amount of the positive electrode active material, and within this range, while maintaining the properties of the positive electrode active material itself, structural stability and electrochemical It has the effect of improving performance.

The heat treatment time may be preferably 1 to 16 hours, more preferably 3 to 7 hours, and within this range, the effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself. there is

The coating method is not particularly limited in the case of a coating method commonly used in the technical field to which the present invention belongs, and as an example, a liquid phase method of preparing a liquid coating agent and mixing it with a cathode active material, a mechanochemical method using high mechanical energy of ball milling, It may be a fluidized bed coating method, a spray drying method, a precipitation method in which a coating agent is precipitated on the surface of a cathode active material in an aqueous solution, a method utilizing a reaction between a coating agent in a gaseous phase and a cathode active material, or a sputtering method.

The coating agent may be, for example, spherical, plate-shaped, prismatic, or needle-shaped, and such a shape may be adjusted by changing process conditions, etc., in the manufacturing process thereof, for example, and the specificity of each shape is conventional in the art to which the present invention belongs. It is not particularly limited as long as it follows the definition recognized as The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of 10 to 100 m 2 / g, more preferably an average diameter of 10 to 100 nm and a specific surface area of 20 to 100 m 2 / g It can be uniformly attached to the surface of the positive electrode active material within this range to impart structural stability to the positive electrode active material, thereby improving lifespan characteristics and electrochemical performance degradation due to lattice deformation or collapse of the crystal structure of the positive electrode active material. there is.

In the present disclosure, the average diameter can be measured by a measurement method commonly used in the technical field to which the present invention belongs, and can be measured using, for example, a laser diffraction method. Specifically, the particles of the positive electrode active material After dispersing in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz are irradiated with an output of 60 W, and the average particle diameter on the basis of 50% of the particle diameter distribution in the measuring device ( D50) can be calculated.

In the present description, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention belongs, and can be measured by, for example, the Brunauer-Emmett-Teller (BET) method, specifically, BELSORP, manufactured by BEL Japan. It can be calculated from the nitrogen gas adsorption amount under liquid nitrogen temperature (77K) using mino II.

4 is a flow chart of a process for regenerating a cathode active material according to an embodiment of the present invention.

Referring to FIG. 4 , first, cathode scrap is prepared (step S10). For example, a slurry prepared by adding NMP (N-methyl pyrrolidone) to NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride is coated on aluminum foil, and then heated in a vacuum oven at about 120 ° C. dried to prepare a positive electrode sheet. After a positive electrode plate of a certain size is punched out therefrom, the remaining positive electrode scrap may be prepared.

The cathode scrap has a cathode active material layer on an aluminum foil, and the cathode active material layer has a structure in which a binder binds the cathode active material and the conductive material after solvent volatilization. Therefore, when the binder is removed, the positive electrode active material is separated from the aluminum foil.

Next, the prepared anode scrap is crushed into an appropriate size (step S20). Here, the shredding includes cutting or shredding the anode scrap into a size that is easy to handle. As a specific example, the shredded anode scrap may have a size of 1 cm x 1 cm. The crushing may use various dry grinding equipment such as, for example, a hand-mill, a pin-mill, a disk-mill, a cutting-mill, and a hammer-mill, or may use a high-speed cutter to increase productivity.

The shredding may be carried out or the size of the pieces may be determined in consideration of characteristics required by equipment used in handling of anode scrap and subsequent processes. For example, in the case of using equipment capable of continuous processing, fluidity is It has to be good, so the anode scrap needs to be shredded into smaller pieces.

Next, the anode scrap is heat-treated in air (step S30). Here, the heat treatment is performed to thermally decompose the binder in the active material layer.

Through the above heat treatment in air, the binder and conductive material in the active material layer are thermally decomposed into CO ₂ and H ₂ O and removed. Since the binder is removed, the positive active material is separated from the current collector, and the separated positive active material is easily sorted into a powder form. Therefore, only step S30 can separate the active material layer from the current collector, and further recover the positive electrode active material in the active material layer in the form of powder.

It is important that the heat treatment is performed in air. When the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and the conductive material are carbonized without thermal decomposition. When carbonized, carbon components remain on the surface of the positive electrode active material, and the performance of the reused positive electrode active material deteriorates. However, when heat treatment is performed in air, both the binder and the conductive material are removed because the carbon component in the binder and the conductive material reacts with oxygen and disappears as a gas such as CO or CO ₂ .

The heat treatment is preferably performed at 300 to 650 ° C., and as a specific example, at 550 ° C., below 300 ° C., it is difficult to remove the binder and the current collector cannot be separated, and above 650 ° C. the current collector melts. A problem arises that cannot be separated.

The heat treatment preferably has a temperature rise rate of 1 to 20 °C/min, more preferably a temperature rise rate of 3 to 10 °C/min, and a specific example is 5 °C/min. It can be implemented without going, and there is an advantage of not generating thermal shock or the like to the anode scrap.

The heat treatment may be performed, for example, for a time sufficient to sufficiently thermally decompose the binder, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specific examples are around 30 minutes. Within the range, the binder is sufficiently thermally decomposed, and there is an effect of excellent thermal decomposition efficiency.

The heat treatment is performed using, for example, various types of furnaces, for example, a box-type furnace, and considering productivity, it is performed using a rotary kiln capable of continuous processing.

After the heat treatment, it may be slowly cooled or rapidly cooled in air.

Next, as a surface modification step, the recovered cathode active material is washed with a high-temperature cleaning solution (step S40).

The high-temperature washing effectively removes foreign substances that may be generated on the surface of the positive electrode active material during the heat treatment step (S30) with a small amount of washing liquid so that foreign substances do not remain on the surface of the regenerated positive electrode active material.

As a specific example, the high-temperature washing may be performed using a washing solution heated to about 70 ° C. In this case, there is an advantage in that foreign substances formed on the surface of the positive electrode active material are effectively removed while greatly reducing the amount of the washing solution.

It is also important to use neutral water or basic lithium compound aqueous solution as the cleaning solution. If sulfuric acid or hydrochloric acid aqueous solution is used, foreign substances such as fluorine (F) compounds on the surface of the positive electrode active material can be washed, but Co , transition metals such as Mg are eluted, thereby degrading the performance of the regenerated cathode active material.

However, the neutral water or basic lithium compound aqueous solution is safe and inexpensive, and can remove binders that may remain in trace amounts even after thermal decomposition in step S30 without loss of other elements, as well as transition metals present in the positive electrode active material. It is preferable because it does not elute, and in the case of a basic lithium compound aqueous solution, it can also play a role in supplementing the amount of lithium that can be eluted in the washing process.

The basic lithium compound aqueous solution contains, for example, more than 0% to 15% or less of the basic lithium compound, and a high concentration of the lithium compound aqueous solution exceeding this may leave an excess of lithium compound on the surface of the active material after washing, so that future annealing processes adversely affect

For the washing, as a specific example, a washing solution of 5 to 15 times the weight of the positive electrode active material to be washed may be used.

The lithium compound is preferably LiOH.

In this description, % means weight% unless otherwise defined.

The washing is carried out, for example, by stirring and mixing the recovered cathode active material and the washing solution. The agitation here is not particularly limited, but may be mechanical agitation or ultrasonic agitation.

The washing is carried out for 10 to 20 minutes as a specific example, and within this range, there is an effect of preventing capacity degradation of the battery due to excessive elution of lithium.

The reason for washing the positive electrode active material recovered in the present description with neutral water or basic lithium compound aqueous solution is to modify the surface to remove LiF and metal fluoride that may be present on the surface of the recovered positive electrode active material. . During the heat treatment in step S30, the binder and conductive material in the active material layer are vaporized and removed as CO ₂ and H ₂ O. In this process, CO ₂ and H ₂ O react with lithium on the surface of the positive electrode active material to form Li ₂ CO ₃ and LiOH. LiF or metal fluoride may be formed by reacting F present in a binder such as PVdF with lithium or other metal elements constituting the positive electrode active material. If such LiF or metal fluoride remains on the surface of the cathode active material, battery characteristics deteriorate when reused.

After stirring or mixing of the recovered cathode active material and neutral water or basic lithium compound aqueous solution is completed, the cathode active material slurry formed therefrom is filtered or the supernatant is drained off to obtain a solid cathode active material.

It is preferable to dry the obtained cathode active material, and as a specific example, it may be dried in the air using an oven (convection type).

Next, a lithium precursor is added to the washed cathode active material and annealed (step S50).

Since lithium in the cathode active material is lost during the previous steps S30 and S40, the loss of lithium is compensated for in step S50. In addition, since a deformed structure (eg, Co ₃ O ₄ in the case of LCO active material) may appear on the surface of the cathode active material during the previous step, in step S50, the crystal structure of the cathode active material is recovered through annealing to regenerate the cathode active material. to improve the properties or restore them to the level of the new cathode active material. Here, 'new birth' is a concept opposite to 'regeneration', and means something made for the first time, and the same word as 'raw material' used in the examples.

As the lithium precursor, LiOH is used as a specific example.

The lithium precursor is preferably added in an amount equal to the molar ratio of lithium lost in comparison with the molar ratio of lithium and other metals in the new cathode active material used in the cathode active material layer. Addition of a lithium precursor in excess of the amount of lost lithium leaves an unreacted lithium precursor in the regenerated cathode active material, which serves to increase resistance, and therefore, an appropriate amount of the lithium precursor is required. For example, when the molar ratio of lithium to other metals in the new cathode active material is 1, a lithium precursor may be added in an amount of 0.001 to 0.4 molar ratio of lithium, preferably a lithium precursor of 0.01 to 0.2 molar ratio of lithium. can be added.

As a specific example, when a lithium precursor is added at a molar ratio of 0.09 to 0.1 (based on lithium metal), which is a loss ratio relative to the lithium content in the new positive electrode active material based on the results of ICP analysis, the effect of improving capacity is equivalent to that of the new positive electrode active material. Here, the ICP analysis result has an error value of about ±0.02.

The annealing is carried out in air under a condition of, for example, 400 to 1000 ° C, preferably 600 to 900 ° C, and this temperature should vary within a limited range depending on the type of lithium precursor.

The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, since thermal decomposition of the positive electrode active material occurs at a temperature exceeding 1000 ° C., performance degradation occurs, so that the temperature does not exceed 1000 ° C. Accordingly, when Li ₂ CO ₃ is used as the lithium precursor, the annealing temperature may be 700 to 900 °C, more preferably 710 to 780 °C, and most preferably 750 to 780 °C. In addition, when LiOH is used as the lithium precursor, the annealing temperature may be 400 to 600 °C, more preferably 450 to 480 °C, and most preferably 470 to 480 °C.

The annealing time is, for example, preferably 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. If the annealing time is long, the crystal structure can be sufficiently recovered, but even if the annealing is performed for a long time, the performance is not significantly affected. At this time, the same or similar equipment as in the heat treatment step S30 may be used as the annealing equipment.

The annealing step recovers the battery characteristics of the regenerated cathode active material by improving crystal structure recovery, that is, crystallinity, while being safe and inexpensive.

The regenerated cathode active material obtained through the cathode active material regeneration step as described above has a particle size distribution similar to that of the new cathode active material, and no carbon component resulting from carbonization of the binder or conductive material remains on the surface, so that it can be 100% intact or regenerated without additional treatment. It can be mixed with an active material and used for cathode manufacturing.

Next, as an optional step, surface coating may be further performed on the annealed cathode active material (S60).

The surface coating is, for example, after coating a coating agent containing metal or carbon on the surface in a solid or liquid manner and then heat treatment at 100 to 1200 ° C. When the heat treatment temperature is less than 100 ° C. Surface protection by a different metal through surface coating When the layer is not formed and the temperature exceeds 1200° C., the performance of the battery deteriorates due to thermal decomposition of the cathode active material.

Specifically, when a metal oxide such as B, W, B-W, etc. is coated on a cathode active material and heat treated, a lithium borooxide layer can be formed on the surface of the active material, which serves as a surface protective layer.

The solid-state or liquid-state method of the surface coating is performed by a method such as mixing, milling, spray drying, or grinding, for example.

For reference, when the molar ratio of lithium: other metals in the cathode active material is 1: 1 in the annealing step S50, lithium in the cathode active material reacts with the coating agent to reduce the molar ratio of lithium: other metals in the cathode active material to less than 1: 1. In this case, the capacity expression of the battery cannot be 100%. Therefore, by adding lithium, which was insufficient in the previous step S50, so that the molar ratio of lithium: other metals in the cathode active material is 1: 1, as well as 0.0001 to 0.1 molar ratio of lithium to other metals in the cathode active material. will be. Then, at the time of surface coating in step S60, the molar ratio of lithium to other metals in the positive electrode active material becomes 1: 1, and furthermore, a surface protective layer is formed.

Specifically, in step S50, lithium added in an excessive amount of about 0.0001 to 0.1 molar ratio reacts with metal oxides such as B, W, B-W, etc. in step S60, and the lithium: other metal molar ratio in the positive electrode active material does not decrease to less than 1: 1, resulting in a decrease in capacity does not occur

Regenerated Cathode Active Material

The regenerated cathode active material of the present invention is characterized in that it is produced by the above-described regeneration method of the cathode active material. There is an effect of greatly improving rate performance and the like.

In addition, the recycled cathode active material of the present invention is preferably a lithium cobalt oxide such as LCO; lithium manganese oxides such as LiMnO ₂ or LiMn ₂ O ₄ ; lithium iron phosphate compounds such as LiFePO ₄ and the like; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO ₂ and the like; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; And at least one selected from the group consisting of NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and fluorine (F) It is characterized in that the content is 600 ppm or less, and in this case, there are excellent effects such as electrochemical performance, resistance characteristics and capacity characteristics.

As a more specific example, the regenerated cathode active material is represented by Chemical Formula 1

[Formula 1]

Li _a Ni _x Mn _y Co _z M _w O _{2 +δ}

(In Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 1<a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1), and contains 1 to 10,000 ppm of Al ₂ O ₃ ; It is characterized in that the surface is coated with a coating agent containing metal or carbon, and in this case, excellent effects such as electrochemical performance, resistance characteristics and capacity characteristics are obtained.

The fluorine (F) content may be preferably 200 ppm or less, more preferably 100 ppm or less, still more preferably 50 ppm or less, and even more preferably 30 ppm, within this range excellent resistance properties and There is an effect that capacity characteristics are implemented.

The regenerated cathode active material may be preferably coated with a coating agent containing metal or carbon, and in this case, the structural stability of the cathode active material is improved without chemical or physical change of the cathode active material itself, thereby improving electrical performance such as output performance, life characteristics, and capacity. Chemical properties are improved, and physicochemical properties are also improved due to the effect of reducing the amount of residual lithium and reducing pH by being substituted with a heterogeneous element on the surface of the cathode active material.

The regenerated cathode active material of the present invention may include all of the contents of the above-described regeneration method of the cathode active material. Therefore, redundant description thereof is omitted here.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are merely illustrative of the present invention, and various changes and modifications are possible within the scope and spirit of the present invention. It is obvious to those skilled in the art, It goes without saying that these variations and modifications fall within the scope of the appended claims.

[Example]

Example One

After punching out the positive electrode, the discarded positive electrode scraps (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide) are shredded, and heat treated in air at 550 ° C for 30 minutes to remove the binder and conductive material, and the current collector and positive electrode After separating the active material, the cathode active material was recovered. Here, the temperature rise rate until reaching the heat treatment temperature was 5 °C/min.

15 g of the recovered cathode active material was added to 150 g of water heated to 70 ° C (10 times the weight of the cathode active material) to remove foreign substances such as LiF and metal fluorine present on the surface and maintained at 70 ° C while stirring for 10 minutes. After the stirring was completed, the cathode active material slurry was filtered using a Buchner funnel to collect solids of the cathode active material. The collected cathode active material was dried at 100 °C for 12 hours.

LiOH, a lithium precursor, was added to the dried cathode active material in an amount of 0.11 molar ratio of lithium based on the molar ratio of lithium and other metals in the raw cathode active material, and annealed at 750 ° C. for 5 hours in air.

The annealed cathode active material was coated with boric acid and then heated at 300° C. for 5 hours to prepare a regenerated cathode active material. Here, the molar ratio of lithium and other metals in the cathode active material was measured through ICP analysis.

Example 2 to 3

A recycled cathode active material was prepared in the same manner as in Example 1, except that 5 times and 15 times the weight of the recovered cathode active material were used for water heated to 70 °C in Example 1, respectively.

Example 4

A regenerated cathode active material was prepared in the same manner as in Example 2, except that water heated to 40 °C was used in Example 2.

Example 5

A recycled positive electrode active material was prepared in the same manner as in Example 1, except that a 1 wt% LiOH aqueous solution was used instead of water as a washing solution in Example 1.

comparative example 1 to 4

The same method as in Example 1, except that 2 times, 5 times, 10 times, and 30 times the weight of the recovered positive electrode active material were used instead of the LiOH aqueous solution heated to 70 ℃ in Example 1. A recycled cathode active material was prepared.

reference example

A fresh NCM-based lithium composite transition metal oxide (NCM651520), not a reusable active material, was used.

[Test Example]

The characteristics of the regenerated cathode active materials obtained in Examples 1 to 5, Comparative Examples 1 to 4, and Reference Example were measured by the following method, and the results are shown in Table 1 and FIGS. 2 and 3 below.

* ICP analysis: The amount of LiF remaining, the ratio of lithium and other metals in the active material, and the content of specific elements such as F (mg/kg) were measured using an ICP analyzer. At this time, it can be measured with a general ICP analyzer widely used in laboratories, but there is no deviation depending on the measuring device or method.

* Cell evaluation: 96% by weight of a recycled or new cathode active material, 2% by weight of carbon black as a conductive material, and 2% by weight of PVdF as a binder were weighed, and mixed with NMP to prepare a slurry. After coating this on aluminum foil to prepare a positive electrode, a cell (Coin Half Cell, CHC) was prepared, and electrochemical performance was evaluated under a voltage of 3 to 4.5V.

division type of cleaning fluid Water volume (unit: times) wash temperature F content (mg/kg) Example 1 water 10 70℃ ND Example 2 water 15 70℃ ND Example 3 water 5 70℃ 580 Example 4 water 15 40℃ 70 Example 5 LiOH aqueous solution 10 70℃ ND Comparative Example 1 water 2 room temperature 5620 Comparative Example 2 water 5 room temperature 3750 Comparative Example 3 water 10 room temperature 2155 Comparative Example 4 water 30 room temperature ND

* ND means less than 30 ppm measured.

As shown in Table 1, the regenerated cathode active materials (Examples 1 to 5) according to the present invention, compared to Comparative Examples 1 to 4 not subjected to the high-temperature washing process according to the present invention, even with a very small amount of washing liquid, F It was confirmed that the content of impurities such as the content was significantly low. Looking at this in detail, in Examples 1 and 2, the F content, that is, the residual amount of the F component was ND with a small amount of washing liquid through warm washing at 70 ° C., and in Example 3, the residual amount of the F component was only 580 ppm I was able to confirm that it was ok. However, Comparative Example 4 has a problem that the residual amount of F component is ND by washing at room temperature, but the amount of washing liquid is 30 times too large. In particular, the paper 'Journal of Chemical and Engineering Data, Vol. 17, no. 4, 1972 491 ', looking at the experimental results in which the solubility of LiF or the like does not increase even in high temperature water, the results of the present invention shown in Table 1 can be simply explained by the solubility of LiF or the like in hot water. It is not possible, and it is presumed that the high temperature water affects the surface structure or environment of the positive electrode active material, and this effect directly or indirectly affects the desorption or dissolution of LiF or the like.

FIG. 2 is a graph showing the rate performance according to the number of cycles as a result of cell evaluation of the regenerated cathode active material prepared in Example 1 and Comparative Example 3 and the cathode active material of Reference Example (Reference NCM65). This is to examine the rate performance by evaluating the capacity according to the number of cycle repetitions at different currents. For reference, in the graph of FIG. 2, the horizontal axis is the number of cycles, and the vertical axis is the capacity.

Referring to FIG. 2, the regenerated cathode active material prepared in Example 1 had higher output performance in all cycle regions tested compared to the regenerated cathode active material of Comparative Example 3 and the cathode active material of Reference Example (Reference NCM65), and the regenerated cathode active material of Comparative Example 3 The active material had lower output performance than the positive electrode active material (Reference NCM65) of the reference example until the fourth cycle, but had higher output performance than the positive electrode active material (Reference NCM65) of the reference example in the fifth cycle. This is inferred to be because foreign substances such as component F are effectively removed by the high-temperature washing process according to the present invention, and crystallinity is improved compared to the new cathode active material of the reference example only by the firing process and the annealing process according to the present invention.

3 shows the result of cell evaluation of the regenerated cathode active materials prepared in Comparative Examples 1 to 4 and the new cathode active material of Reference Example. The highest, and in Comparative Examples 1 to 3, in which the F component residual amount was high by reducing the amount of washing liquid, the output performance decreased in inverse proportion to the amount of washing liquid.

10: entire collector
20: active material layer
30: anode sheet
40: positive plate
50: anode scrap

Claims (16)

(a) heat-treating a waste anode including a current collector and a cathode active material layer coated thereon in air at 300 to 650° C. to recover the cathode active material;
(b) washing the recovered cathode active material with a washing solution at 40 to 100 °C; and
(c) adding a lithium precursor to the washed cathode active material and annealing it in air at 400 to 1000 ° C.
Regeneration method of cathode active material. According to claim 1,
The waste cathode in step (a) is a cathode separated from a lithium secondary battery discarded after use, a defective cathode sheet generated in the manufacturing process of a lithium secondary battery, or a cathode scrap remaining after punching out a cathode plate from a cathode sheet
Regeneration method of cathode active material. According to claim 1,
The cathode active material layer may include lithium cobalt oxide; lithium manganese oxide; iron phosphate compounds; lithium nickel cobalt aluminum oxide; lithium nickel oxide; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; And at least one selected from the group consisting of NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) is substituted with manganese (Mn) and cobalt (Co) in the lithium nickel oxide.
Regeneration method of cathode active material. According to claim 1,
Characterized in that the washing solution in step (b) is water or a basic aqueous solution of a lithium compound
Regeneration method of cathode active material. According to claim 1,
Characterized in that the washing solution of step (b) is used in 3 to 22 times the weight of the recovered positive electrode active material
Regeneration method of cathode active material. According to claim 1,
The washing in step (b) comprises stirring the recovered positive electrode active material and the washing solution.
Regeneration method of cathode active material. According to claim 6,
Characterized in that the stirring is carried out within one week
Regeneration method of cathode active material. According to claim 1,
Wherein step (b) includes a step of drying the washed cathode active material
Regeneration method of cathode active material. According to claim 1,
The lithium precursor in step (c) is at least one selected from the group consisting of LiOH, Li ₂ CO ₃ , LiNO ₃ and Li ₂ O
Regeneration method of cathode active material. According to claim 1,
The lithium precursor in step (c) is added at least in an amount reduced from the molar ratio of lithium in the cathode active material in step (a) based on the amount of lithium in the washed cathode active material.
Regeneration method of cathode active material. According to claim 1,
Characterized in that the annealing temperature in step (c) is a temperature exceeding the melting point of the lithium precursor
Regeneration method of cathode active material. According to claim 1,
The regeneration method of the cathode active material comprises the step of (d) coating the annealed cathode active material with a metal or carbon-containing coating and then heat-treating it at 100 to 1200 ° C.
Regeneration method of cathode active material. Characterized in that it is produced by the regeneration method of the cathode active material according to claims 1 to 12
Regenerated cathode active material. lithium cobalt oxide; lithium manganese oxide; iron phosphate compounds; lithium nickel cobalt aluminum oxide; lithium nickel oxide; a nickel-manganese-based lithium composite metal oxide in which a part of nickel (Ni) is substituted with manganese (Mn) in the lithium nickel oxide; And at least one selected from the group consisting of NCM-based lithium composite transition metal oxides in which a part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and fluorine (F) Characterized in that the content is less than 600 ppm
Regenerated cathode active material. According to claim 14,
The regenerated cathode active material is represented by Chemical Formula 1
[Formula 1]
Li _a Ni _x Mn _y Co _z M _w O _{2 +δ}
(In Formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 1<a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x + y + z + w = 1), characterized in that the content of fluorine (F) is 600 ppm or less to be
Regenerated cathode active material. The method of claim 14 or 15,
The regenerated cathode active material is characterized in that the surface is coated with a coating agent containing metal or carbon
Regenerated cathode active material.

Images