KR20240047746A - Upcycling method of waste cathode active material - Google Patents

Abstract

The present invention includes i) a chlorination step of reacting a waste cathode active material containing lithium transition metal oxide with a chlorine-containing gas; ii) separating lithium chloride and transition metal oxide formed in the chlorination step; iii) mixing a compound containing lithium and a transition metal compound with the separated transition metal oxide; iv) first heating the mixture obtained in step iii) at 100 to 600°C; and v) secondary heating the result obtained in step iv) at 600 to 1000°C. It relates to a method of upcycling a waste cathode active material.

Description

Upcycling method of waste cathode active material}

The present invention relates to a method for upcycling waste cathode active material, a cathode active material upcycled through the method, and a lithium secondary battery containing the same.

Lithium secondary batteries are widely used for storing electrochemical energy due to their many advantages such as high energy density, long lifespan, and low self-discharge rate. The lithium secondary battery market is rapidly expanding from electronic devices to electric vehicles and power storage fields, and the global lithium secondary battery market is expected to continue to grow.

As the demand for lithium secondary batteries increases significantly, lithium resources are expected to suffer from a supply shortage within several decades. In addition, used lithium secondary batteries contain toxic substances such as heavy metals and organic electrolytes that have a harmful effect on the environment, so the problem of environmental pollution from waste lithium secondary batteries is also a problem that must be solved.

Meanwhile, waste lithium secondary batteries contain many precious metals such as cobalt, nickel, manganese, and lithium that can solve resource shortage problems, and methods for recycling waste cathode active materials have been proposed. To date, pyrometallurgy and Waste cathode active materials have been mainly recycled through hydrometallurgy.

Dry smelting is a method of high-temperature smelting at over 1000°C to remove organic materials such as polymer binders and separators and form an alloy containing nickel, cobalt, copper, etc. through carbon reduction. Precious metals can be recovered with high efficiency through dry smelting, but the amount of energy consumed in dry smelting is significant and can cause large amounts of carbon dioxide emissions, and it is excessively expensive to reproduce the cathode active material through the recovered metal. There is a problem of low economic feasibility due to this requirement.

Meanwhile, hydrometallurgy is carried out at relatively low temperatures and uses various chemical processes including leaching, extraction, ion exchange, chemical precipitation, etc. to recover metals such as nickel, cobalt, aluminum, copper, and lithium. Hydrometallurgical smelting uses a large amount of highly concentrated acid solution and reducing agent, and not only causes problems such as secondary environmental pollution and equipment corrosion due to wastewater and harmful gas emissions, but is also somewhat disadvantageous in terms of economic feasibility as it consists of complex process steps. There is a downside to this.

Accordingly, direct recycling of waste cathode active material is attracting attention in consideration of economic feasibility and environmental issues. There is also a technology to resynthesize waste cathode active material into existing cathode active material by adding only lithium to waste cathode active material. If it is simply recycled when its performance has deteriorated, its useful value may be greatly reduced.

In addition, it is difficult to quantify the amount of residual lithium in the recycling process of waste cathode active material, so it is necessary to synthesize it by adding a large amount of lithium and remove impurities formed by the excess lithium, but there is a risk of performance deterioration in this process.

In addition, recycled positive electrode active materials generally take the form of secondary particles, and microcracks occur between particles due to contraction and expansion of particles during the charging and discharging process, which causes deterioration of life characteristics.

Therefore, there is a need to develop technology for an upcycling method for waste cathode active materials that can not only recycle waste cathode active materials in an economical and eco-friendly way, but also manufacture high value-added cathode active materials with improved performance from waste cathode active materials. This is the situation.

The present invention is intended to solve the above-mentioned problem, enabling the quantification of lithium through chlorination treatment of waste cathode active material, and mixing lithium and transition metal after the chlorination treatment and heat treatment in a specific temperature range to form a single crystal. The aim is to provide a method of upcycling waste cathode active materials that can manufacture cathode active materials in the form of cathode active materials and provide cathode active materials with improved performance without consuming enormous costs or emitting pollutants.

According to one embodiment of the present invention, i) a chlorination step of reacting a waste cathode active material containing lithium transition metal oxide with a chlorine-containing gas; ii) separating lithium chloride and transition metal oxide formed in the chlorination step; iii) mixing a compound containing lithium and a transition metal compound with the separated transition metal oxide; iv) first heating the mixture obtained in step iii) at 100 to 600°C; and v) secondary heating the result obtained in step iv) at 600 to 1000°C.

In addition, according to another embodiment of the present invention, a cathode active material manufactured by upcycling according to the upcycling method of a spent cathode active material of the present invention is provided, and the cathode active material has a single crystal structure.

According to the upcycling method of the waste cathode active material of the present invention, lithium can be quantified by completely removing lithium from the waste cathode active material through chlorination treatment, and therefore, ancillary lithium removal process as in the prior art is not required. It's economical.

In addition, the cathode active material manufactured through the upcycling method of waste cathode active material according to the present invention is free of impurities and has a single crystal form, making it possible to implement a high value-added cathode active material with improved performance.

1 is a schematic diagram showing a method for upcycling a waste cathode active material according to an embodiment of the present invention.
Figure 2 is a diagram showing the results of XRD analysis of the positive electrode active material immediately after going through the chlorination step in Example 1.
Figures 3a to 3d show the results of X-ray diffraction analysis of the positive electrode active materials prepared according to Examples 1 to 4.
Figure 4a is a diagram showing the results of charge and discharge experiments for lithium secondary batteries according to Examples 8 to 11.
Figure 4b is a diagram showing the change in capacity of lithium secondary batteries according to Examples 8 to 11 as the cycle progresses.
Figures 5a to 5d show SEM images of positive electrode active materials according to Examples 1 to 4.
Figure 6 is a diagram showing the results of X-ray diffraction analysis of the positive electrode active material prepared according to Example 5.
Figure 7a is a diagram showing the results of a charge/discharge test for a lithium secondary battery according to Example 12.
Figure 7b is a diagram showing the change in capacity of the lithium secondary battery according to Example 12 as the cycle progresses.
Figures 8a and 8b show the results of XRD analysis of the positive electrode active material according to Example 6 and Example 7, respectively.
Figure 9a is a diagram showing the results of charge and discharge experiments for lithium secondary batteries according to Examples 13 and 14.
Figure 9b is a diagram showing the capacity change according to the cycle of the lithium secondary battery according to Example 13 and Example 14.
Figures 10a and 10b show SEM images of positive electrode active materials according to Examples 6 and 7.
Figures 11a and 11b show the results of particle size distribution analysis for the positive electrode active materials according to Examples 6 and 7.

Hereinafter, with reference to the attached drawings, the upcycling method of the waste cathode active material of the present invention will be described in detail so that it can be easily performed by those skilled in the art.

A method for upcycling a waste cathode active material according to an embodiment of the present invention includes: i) a chlorination step of reacting a waste cathode active material containing lithium transition metal oxide with a chlorine-containing gas; ii) separating lithium chloride and transition metal oxide formed in the chlorination step; iii) mixing a compound containing lithium and a transition metal compound with the separated transition metal oxide; iv) first heating the mixture obtained in step iii) at 100 to 600°C; and v) secondary heating of the result obtained in step iv) at 600 to 1000°C.

In step i), the lithium transition metal oxide contained in the waste cathode active material has the same composition as LiMOx, where Li is lithium, M is a transition metal, and X may be an integer from 1 to 5.

The transition metal may include at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), and magnesium (Mg).

Specifically, the lithium transition metal oxide may have, for example, an average composition represented by the following Chemical Formula 1.

[Formula 1]

Li _x [Ni _y Co _z Mn _1-yz ]O ₂

In Formula 1,

0≤x≤1, 0≤y≤1, 0≤z≤1.

In step i), lithium chloride and transition metal oxide may be formed by reacting the waste cathode active material containing lithium transition metal oxide with a chlorine-containing gas. Specifically, the lithium chloride may be in the form of LiCl, and the transition metal oxide may be in the form of MOx. Additionally, transition metal chlorides may also be formed, and may be formed in the form of MCl _x .

The reaction with the chlorine-containing gas in step i) may be carried out at 400 to 800°C, preferably 450 to 700°C, and more preferably 500 to 600°C. If the reaction temperature in step i) exceeds the upper limit of the numerical range, the excessively high temperature may accelerate chlorination of the transition metal instead of lithium, which may cause a problem of lowering the recovery rate of the transition metal. If it is insufficient, there may be a problem that the separation efficiency of the waste cathode active material is reduced because lithium chloride is not sufficiently formed.

Additionally, the reaction with the chlorine-containing gas in step i) may be carried out for 1 to 10 hours, preferably 2 to 8 hours, and more preferably 3 to 5 hours.

The chlorine-containing gas in step i) is an inert gas and chlorine gas (Cl ₂ ) in a ratio of 1:0.01 to 1:0.1, preferably 1:0.02 to 1:0.08, more preferably 1:0.04 to 1:0.06. It may be included in a volume ratio of . If the volume ratio of the inert gas and chlorine gas in the chlorine-containing gas exceeds the upper limit of the above numerical range, excess chlorine gas may not react and there may be a problem of reduced process efficiency, and if it falls below the lower limit of the above numerical range, chlorination may occur. There may be a problem in which the efficiency of the reaction is reduced and the waste cathode active material is not sufficiently separated.

The inert gas may include at least one selected from the group consisting of Ar, N ₂ , He, and Ne.

The reaction in step i) may be performed by mixing 200 to 800 parts by weight of the chlorine-containing gas based on 100 parts by weight of the waste cathode active material. When the content of the reacting chlorine-containing gas satisfies the above numerical range, the chlorination reaction proceeds sufficiently even with an appropriate amount of chlorine-containing gas, thereby reducing process costs and efficiently separating transition metal oxides.

Through the above chlorination step, the present invention enables the separation of lithium without a separate auxiliary process using strong acids, etc., and allows for the simple and selective recovery of lithium chloride without generating contaminants such as acid waste. Process efficiency can be maximized.

Next, the method for upcycling waste cathode active material according to the present invention includes step ii) of separating lithium chloride and transition metal oxide formed in the chlorination step.

Separation in step ii) may be performed through washing with a solvent. A solvent that can dissolve lithium chloride and transition metal chloride without dissolving the transition metal oxide formed through step i) may be used.

The solvent may be water or alcohol, preferably water, but any solvent that can dissolve lithium chloride without dissolving transition metal oxide can be applied without limitation.

Thereafter, a step of mixing a compound containing lithium and a transition metal compound with the separated transition metal oxide is performed. The lithium-containing compound may have the form of Li(OH) ₂ , Li(OH)·H ₂ O, Li ₂ CO ₃ , etc., but is not necessarily limited thereto, and reacts with the transition metal compound to form a positive electrode active material. It can be applied without restrictions as long as it can be played. In addition, the transition metal compound may also have a form such as Ni(OH) ₂ , but as long as it can regenerate the positive electrode active material by reacting with the lithium compound, it is not limited to the form and can be applied in any form.

In step iii), lithium and transition metal may be mixed at a molar ratio of 1:0.9 to 1:1, preferably 1:0.94 to 1:1, and more preferably 1:0.97 to 1:1. If the molar ratio of lithium and transition metal mixed exceeds the upper limit of the above numerical range, impurities may be formed due to excessive lithium, which may cause a problem in that the electrochemical properties of the manufactured lithium secondary battery deteriorate, and the lower limit of the above numerical range may occur. If it is less than lithium, the synthesized positive electrode may have an electrochemically inactive structure.

Next, step iv) is performed, in which the mixture obtained in step iii) is first heated. The first heating may be performed at 100 to 600°C, preferably 150 to 550°C, and more preferably 200 to 500°C.

Lithium can be uniformly dispersed in the mixture through the primary heating in step iv). That is, when the primary heating temperature satisfies the above numerical range, it is possible to manufacture a positive electrode active material with a more uniform structure by maintaining the temperature at which the lithium-containing compound begins to decompose for a certain period of time.

Thereafter, step v) of secondary heating of the result obtained in step iv) is performed. The secondary heating may be performed at 600 to 1000°C, preferably 650 to 950°C, and more preferably 700 to 900°C.

The positive electrode active material may be re-synthesized through secondary heating in step v). If the secondary heating exceeds the upper limit of the above numerical range, deterioration from the layered structure to the electrochemically inactive spinel or rock salt structure occurs, thereby reducing the performance of the manufactured lithium secondary battery. There may be a problem of deterioration, and if it falls below the lower limit of the above numerical range, the resynthesis reaction may not proceed, and there may be a problem that the synthesis of the layered structure proceeds incompletely.

Meanwhile, between step ii) and step iii), heat treatment is performed at 400 to 900°C, preferably 450 to 850°C, more preferably 500 to 800°C in an inert gas atmosphere. It may be. When the heat treatment temperature satisfies the above numerical range, the particle size of the transition metal oxide separated in step ii) may have the effect of becoming uniform. Accordingly, future mixing with lithium and transition metals can be facilitated, and a single crystal cathode active material can be formed as a result of a synthesis reaction at high temperature.

The heat treatment between step ii) and step iii) may be performed for 2 to 10 hours, preferably 4 to 8 hours. When the heat treatment time satisfies the above numerical range, the particle size of the separated transition metal oxide can be uniformly dispersed without deterioration problems.

The inert gas may include at least one selected from the group consisting of Ar, N ₂ , He, and Ne.

In addition, after step v), the step of performing heat treatment at 500 to 900°C, preferably 550 to 850°C, and more preferably 600 to 800°C may be further included.

By performing heat treatment in the above temperature range after step v), it can be recovered from the displacement phenomenon and structural deterioration of lithium and transition metal in the crystal structure formed in step v), and the synthesized positive electrode active material can have structural stability. In addition, it is possible to prevent deterioration in capacity, lifespan, and high rate characteristics.

According to another embodiment of the present invention, a positive electrode active material is provided, which is manufactured according to the upcycling method of the waste positive electrode active material and has a single crystal structure.

If the positive electrode active material is polycrystalline, when charging and discharging are repeated, cracks occur within the particle structure as the particles repeat contraction and expansion, and due to the small particle size and large surface area, side reactions with the electrolyte become active, thereby damaging the positive electrode active material. There is a problem that the efficiency of the lithium secondary battery included is reduced. On the other hand, when the particles of the positive electrode active material have the form of a single crystal, the surface reaction of the positive electrode active material is reduced compared to the case of polycrystalline, and the strength is strong enough to prevent cracks from occurring even after frequent charging and discharging, thereby improving electrochemical stability and lithium secondary batteries. performance can be improved.

In addition, the cathode active material prepared according to the upcycling method of the waste cathode active material contains 1 to 50% by weight of transition metal, preferably 10 to 50% by weight, more preferably 30 to 30% by weight, compared to the waste cathode active material before upcycling. It may contain an additional 50% by weight. In this way, as the content of transition metals contained in the cathode active material after upcycling becomes higher than the content of transition metals contained in the spent cathode active material before upcycling, the energy density and performance of the cathode active material can be improved.

According to another embodiment of the present invention, a positive electrode comprising a positive electrode active material manufactured according to the upcycling method of the waste positive electrode active material; and a negative electrode containing lithium metal.

The positive electrode included in the lithium secondary battery may be manufactured by coating a positive electrode slurry containing the positive electrode active material, a binder, a conductive material, and a solvent on a positive electrode current collector, followed by drying and rolling.

The positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface treated with carbon, nickel, titanium, silver, etc., and may be used chemically in the lithium secondary battery. There is no particular limitation as long as it is challenging without causing change.

The binder is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and is composed of polyvinylidene fluoride (PVDF), poly(ethylene glycol) dimethyl ether, and polyhexamethylene fluoride. Copolymer of fluoropropylene and polyvinylidene fluoride (poly(vinylidene fluoride-co-hexafluoropropylene)), poly(vinyl acetate), polyvinyl alcohol, polyethylene oxide, poly Polyvinyl pyrrolidone, polyvinyl ether, poly(methyl methacrylate), poly(ethyl acrylate), polytetrafluoro Ethylene (polytetrafluoroethylene, PTFE), polyvinyl chloride, polyacrylonitrile, poly(vinyl pyridine), styrene butadiene rubber (SBR) and acrylonitrile- It may include at least one selected from the group consisting of butadiene rubber (acrylonitrile-butadiene rubber).

The conductive materials include carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, natural graphite, artificial graphite, graphite, carbon fiber, metal fiber, fluorinated carbon, aluminum, nickel powder, zinc oxide, and titanic acid. It may contain at least one selected from the group consisting of potassium, titanium oxide, and polyphenylene derivatives, and is not particularly limited as long as it has conductivity without causing chemical changes in the lithium secondary battery.

The solvent is N-methyl-2-pyrrolidone (NMP), acetone, ethanol, tetrahydrofuran (THF), dimethyl acetamide, It may be one or more selected from the group consisting of DMAc) and toluene.

Like the positive electrode, the negative electrode included in the lithium secondary battery can be manufactured by coating a negative electrode slurry containing a negative electrode active material, a binder, a conductive material, and a solvent on a negative electrode current collector, followed by drying and rolling.

Copper, stainless steel, titanium, nickel, etc. may be used as the negative electrode current collector, and lithium metal, etc. may be used as the negative electrode active material.

The binder, conductive material, and solvent are the same as previously described for the positive electrode.

The capacity of the lithium secondary battery may be improved by 5 to 35% compared to a lithium ion battery containing a waste cathode active material before upcycling.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only intended to aid understanding of the present invention, and the scope of the present invention is not limited to these examples in any way.

<Example 1> Manufacturing 1 of upcycled cathode active material from waste cathode active material

Step i) (chlorination step)

First, a Li(Ni _0.6 Co _0.2 Mn _0.2 )O ₂ sample (Sungil Hitech) was used as a waste cathode active material, and 2 g of the sample was placed in a mixture of 190 mL/min argon and 10 mL/min chlorine gas (Cl ₂ ). It was reacted with gas at 550°C for 4 hours.

ii) Step (separation step)

The reaction mixture was immersed in water to dissolve lithium chloride, and transition metal oxide (Ni _0.6 Co _0.2 Mn _0.2 )O ₂ that was not dissolved in water was separated through a filter. Afterwards, the separated transition metal oxide was placed in an oven and dried at 120°C for 2 hours.

iii) Step (mixing step)

Next, 0.3 g of the solid state transition metal oxide (Ni _0.6 Co _0.2 Mn _0.2 O ₂ ) separated to proceed as shown in Scheme 1 below, and lithium hydroxide monohydrate (LiOH·H ₂ O) 0.29621 as a compound containing lithium. g and 0.26893 g of nickel hydroxide (Ni(OH) ₂ ) as a transition metal compound was added. That is, lithium was added at a molar ratio of 1.03 based on the total number of moles of nickel, cobalt, and manganese of nickel and separated transition metal oxides in the added nickel hydroxide.

[Scheme 1]

LiOHㆍH ₂ O + 0.375Ni(OH) ₂ + 0.625Ni _0.6 Co _0.2 Mn _0.2 O ₂ → Li(Ni _0.75 Co _0.125 Mn _0.125 )O ₂ + xH ₂ O + yO ₂

ⅳ) (First heat treatment step)

In order to uniformly disperse lithium within the mixture particles thus obtained, primary heat treatment was performed at 250°C for 6 hours.

Step v) (secondary heat treatment step)

Afterwards, high-temperature synthesis was performed by secondary heating at 800°C for 12 hours in an oxygen atmosphere.

<Example 2> Production of upcycled cathode active material from waste cathode active material 2

To proceed as shown in Scheme 2 below, 0.3 g of the solid transition metal oxide (Ni _0.6 Co _0.2 Mn _0.2 O ₂ ) separated in step iii) of Example 1 was mixed with lithium hydroxide monohydrate (LiOH) as a compound containing lithium. The positive electrode active material was upcycled under the same conditions as in Example 1, except that 0.58687 g of H ₂ O) and 0.78612 g of nickel hydroxide (Ni(OH) ₂ ) as a transition metal compound were added.

[Scheme 2]

LiOHㆍH ₂ O + 0.625Ni(OH) ₂ + 0.375Ni _0.6 Co _0.2 Mn _0.2 O ₂ → Li(Ni _0.85 Co _0.075 Mn _0.075 )O ₂ + xH ₂ O + yO ₂

<Example 3> Production of upcycled cathode active material from waste cathode active material 3

To proceed as shown in Scheme 3 below, 0.3 g of the solid transition metal oxide separated in step iii) of Example 1, 0.73452 g of lithium hydroxide monohydrate (LiOH·H ₂ O) as a compound containing lithium, and 0.73452 g of the transition metal The positive electrode active material was upcycled under the same conditions as in Example 1, except that 1.04472 g of nickel hydroxide (Ni(OH) ₂ ) was added as a compound.

[Scheme 3]

LiOHㆍH ₂ O + 0.7Ni(OH) ₂ + 0.3Ni _0.6 Co _0.2 Mn _0.2 O ₂ → Li(Ni _0.88 Co _0.06 Mn _0.06 )O ₂ + xH ₂ O + yO ₂

<Example 4> Production of upcycled cathode active material from waste cathode active material 4

To proceed as shown in Scheme 4 below, 0.3 g of the solid transition metal oxide separated in step iii) of Example 1, 0.9806 g of lithium hydroxide monohydrate (LiOH·H ₂ O) as a compound containing lithium, and 0.9806 g of the transition metal The positive electrode active material was upcycled under the same conditions as in Example 1, except that 1.47571 g of nickel hydroxide (Ni(OH) ₂ ) was added as a compound.

[Scheme 4]

LiOHㆍH ₂ O + 0.75Ni(OH) ₂ + 0.25Ni _0.6 Co _0.2 Mn _0.2 O ₂ → Li(Ni _0.9 Co _0.05 Mn _0.05 )O ₂ + xH ₂ O + yO ₂

<Example 5> Production of upcycled cathode active material from waste cathode active material 5

In order to make the overall particle size uniform, the chlorination treatment step, that is, step ii), was performed in the same manner as in Example 1, and then heat treatment was performed for 4 hours in an argon gas atmosphere at 600°C. After heat treatment, steps iii) to v) of Example 1 were performed in the same manner.

<Example 6> Production of upcycled cathode active material from waste cathode active material 6

To proceed as shown in Scheme 5 below, 0.3 g of the solid transition metal oxide separated in step iii) is mixed with 0.3001708 g of lithium hydroxide monohydrate (LiOH·H ₂ O) as a compound containing lithium and nickel hydroxide as a transition metal compound. (Ni(OH) ₂ ) 0.2689381 g was added (i.e., lithium was added to have a molar ratio of 1.06 based on the total number of moles of nickel, cobalt, and manganese of nickel and separated transition metal oxides in the added nickel hydroxide. ) and v) were carried out in the same manner as in Example 1, except that the high-temperature synthesis conditions in steps were carried out in an oxygen atmosphere at 900°C for 4 hours, and then at a relatively low temperature to stabilize the structure of the positive electrode active material particles. Heat treatment was performed at 750°C for 10 hours.

[Scheme 5]

LiOHㆍH ₂ O + 0.375Ni(OH) ₂ + 0.625Ni _0.6 Co _0.2 Mn _0.2 O ₂ → Li(Ni _0.75 Co _0.125 Mn _0.125 )O ₂ + xH ₂ O + yO ₂

<Example 7> Production of upcycled cathode active material from waste cathode active material 7

In order to determine the difference depending on the atmosphere for synthesizing the cathode active material, a cathode active material was manufactured in the same manner as in Example 6, except that step v) was performed in a general air atmosphere rather than an oxygen atmosphere.

<Example 8> Manufacture of a lithium secondary battery using the cathode active material according to Example 1

First, to manufacture a positive electrode, the upcycled positive electrode active material according to Example 1, polyvinylidene fluoride (PVDF) as a binder, and carbon black as a conductive material were added to N-methyl-2-pyrrolidone (NMP) solvent. A slurry was prepared by mixing at a mass ratio of 8:1:1. Then, the slurry was coated on aluminum foil and dried in a vacuum oven to remove the solvent, thereby completing the production of the positive electrode.

A CR2032 coin cell was made using the above electrode as an anode, lithium metal as a cathode, 1M LiPF ₆ in EC/EMC (ethylene carbonate/ethylmethyl carbonate) with 2wt% VC (vinylene carbonate) as an electrolyte, and a glass fiber membrane as a separator. Manufactured.

<Example 9> Manufacture of a lithium secondary battery using the cathode active material according to Example 2

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 2 was used instead of the cathode active material according to Example 1.

<Example 10> Manufacturing a lithium secondary battery using the cathode active material according to Example 3

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 3 was used instead of the cathode active material according to Example 1.

<Example 11> Manufacture of a lithium secondary battery using the cathode active material according to Example 4

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 4 was used instead of the cathode active material according to Example 1.

<Example 12> Manufacture of a lithium secondary battery using the cathode active material according to Example 5

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 5 was used instead of the cathode active material according to Example 1.

<Example 13> Manufacture of a lithium secondary battery using the cathode active material according to Example 6

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 6 was used instead of the cathode active material according to Example 1.

<Example 14> Manufacture of a lithium secondary battery using the cathode active material according to Example 7

A lithium secondary battery was manufactured under the same conditions as Example 8, except that the cathode active material according to Example 7 was used instead of the cathode active material according to Example 1.

<Experimental Example 1> X-ray diffraction analysis of the positive electrode active materials according to Examples 1 to 4

First, X-ray diffraction analysis (XRD) was performed on the positive electrode active material immediately after going through step i) (chlorination step) in Example 1, and the results are shown in FIG. 2.

The positive electrode active material before going through the chlorination step has a trigonal crystal structure with a space group of R-3m. Through the chlorination step, lithium is removed from the trigonal crystal structure in the form of lithium chloride, and the space group is Fd-3m (66.6%). ) It was confirmed that the cubic spinel crystal structure and space group changed to a rock salt structure of Fm-3m (33.4%).

Next, the results of X-ray diffraction analysis of the positive electrode active materials prepared according to Examples 1 to 4 in which upcycling was completed are shown in FIGS. 3A to 3D. 3A to 3D, it was confirmed that the structures of Fd-3m and Fm-3m formed after the chlorination step were restored to the single crystal R-3m structure. In addition, no pattern related to impurities due to excessive lithium was seen, and it was confirmed that an appropriate amount of lithium was added to form a positive electrode active material with a uniform structure and to manufacture a secondary battery with stable electrochemical properties.

<Experimental Example 2> Analysis of electrochemical properties of lithium secondary batteries according to Examples 8 to 11

Charge and discharge experiments were performed on lithium secondary batteries according to Examples 8 to 11 manufactured using the upcycled cathode active materials according to Examples 1 to 4.

A charge/discharge experiment was conducted using a cycler in CCCV (constant current-constant voltage) mode under a constant current of 40 mA/g in a voltage range of 2.5-4.3 V, and the results are shown in Figure 4a.

The lithium secondary batteries according to Examples 8 to 11 showed a higher capacity of 180 to 200 mAh/g than the generally known capacity of Li(Ni _0.6 Co _0.2 Mn _0.2 )O ₂ of 160 to 170 mAh/g, and the improved capacity was achieved by nickel. This is due to an increase in the nickel redox reaction section due to an increase in the content.

In addition, a phase change was confirmed around 4.1-4.2V in Figure 4a, and this phase change is H2 expressed in a layered positive electrode active material containing a large amount of nickel (the positive electrode active material has a lattice constant that is longer than the intrinsic lattice constant in the c-axis direction). It is known as a phase change from (crystal structure with nickel) to H3 (crystal structure with a lattice constant shorter than the intrinsic lattice constant of the cathode active material in the c-axis direction), and it is known that the crystal structure containing a high content of nickel from the waste cathode active material It can be confirmed that the positive electrode active material was manufactured.

Meanwhile, Figure 4b shows the capacity change according to the cycle of the lithium secondary battery according to Examples 8 to 11. In all cases, it can be seen that the capacity of about 75% or more is maintained even after 50 cycles.

<Experimental Example 3> Composition analysis of positive electrode active material

The compositions of Examples 1 to 4 were determined through inductively coupled plasma analysis (ICP-MS) and are shown in Table 1 below. It was confirmed that the cathode active material was synthesized with a high content of nickel in proportion to the amount of nickel added in the composition of the existing waste cathode active material.

% Ni Co Mn Waste cathode active material 0.600 0.202 0.196 Example 1 0.755 0.127 0.117 Example 2 0.865 0.070 0.064 Example 3 0.889 0.058 0.052 Example 4 0.905 0.048 0.045

<Experimental Example 4> Observation of the structure of the positive electrode active material according to Examples 1 to 4

To observe the structure of the positive electrode active materials according to Examples 1 to 4, SEM images were observed and are shown in FIGS. 5A to 5D.

As a result, it was confirmed that the structure of the positive electrode active material according to Examples 1 to 4 had a single crystal form rather than the existing secondary particle form. Existing cathode active materials have a secondary particle form in which particles of 200-300 nm gather to form particles of 10-15 ㎛. In the case of these secondary particle cathode active materials, fine cracks may form within the existing secondary particle structure as the nanoparticles repeat contraction/expansion during the charging and discharging process, which causes a side reaction with the electrolyte and reduces the diffusion of lithium ions. .

However, in the case of single particles, the mentioned phenomena are suppressed, and it is believed that long-term life characteristics can be improved compared to existing secondary particle type waste cathode active materials.

<Experimental Example 5> X-ray diffraction analysis of the positive electrode active material according to Example 5

X-ray diffraction analysis (XRD) was performed on the positive electrode active material according to Example 5 under the same conditions as in Experimental Example 1, and the results are shown in FIG. 6.

^First , in ^the Confirmed.

Next, after performing all steps ii), the subsequent heat treatment, and steps iii) to v), an It was confirmed that it was synthesized well on a daily basis, and no impurities were confirmed.

<Experimental Example 6> Analysis of electrochemical properties of lithium secondary battery according to Example 12

A charging and discharging experiment was performed under the same conditions as in Experimental Example 2, except that the lithium secondary battery according to Example 12 was used instead of the lithium secondary battery according to Examples 8 to 11, and the results are shown in FIG. 7A.

As a result, a phase change was confirmed around 4.1-4.2V, and through this, it was confirmed that a positive electrode active material containing a large amount of nickel was synthesized.

Meanwhile, Figure 7b shows the capacity change according to the cycle of the lithium secondary battery according to Example 12. In both cases, it can be seen that the capacity of about 90% or more is maintained even after 50 cycles.

<Experimental Example 7> X-ray diffraction analysis of positive electrode active materials according to Examples 6 and 7

X-ray diffraction analysis (XRD) was performed on the positive electrode active materials according to Examples 6 and 7 under the same conditions as in Experimental Example 1, and the results are shown in FIGS. 8A and 8B.

It was confirmed that all had a single-phase crystal structure of R-3m structure, and no impurities were confirmed.

<Experimental Example 8> Analysis of electrochemical properties of lithium secondary batteries according to Examples 13 and 14

A charging and discharging experiment was performed under the same conditions as in Experimental Example 2, except that the lithium secondary batteries according to Examples 13 and 14 were used instead of the lithium secondary batteries according to Examples 8 to 11, and the results are shown in Figure 9a. shown in

A phase change was confirmed around 4.1~4.2V, and through this, it was confirmed that a positive electrode active material containing a large amount of nickel was synthesized.

Meanwhile, Figure 9b shows the capacity change according to the cycle of the lithium secondary battery according to Example 13 and Example 14. In both cases, it can be seen that the capacity of about 80% or more is maintained even after 50 cycles.

In addition, better results in life characteristics were confirmed when secondary heating was performed in an oxygen atmosphere than when secondary heating was performed in a normal air atmosphere. In other words, in the case of synthesis in an oxygen atmosphere, compared to the case of synthesis in a general air atmosphere, the oxidation atmosphere is well formed on the particle surface during the synthesis process, preventing the reduction of transition metals on the particle surface, and lithium and lithium in the crystal structure. It can be confirmed that the displacement phenomenon of nickel is suppressed, which can lead to improved lifespan performance of the manufactured lithium secondary battery.

<Experimental Example 9> Observation of the structure of the positive electrode active material according to Examples 6 and 7

SEM images were taken under the same conditions as in Experimental Example 4, except that the cathode active materials according to Examples 6 and 7 were used instead of the cathode active materials according to Examples 1 to 4.

Referring to FIGS. 10A and 10B, as in Experimental Example 4, the positive electrode active materials according to Examples 6 and 7 were confirmed to have the form of a single crystal rather than a secondary particle, and were upcycled through existing simple synthesis. It was confirmed that the particle size increased compared to Examples 1 to 4.

In addition, Figures 11a and 11b show the results of particle size distribution analysis of the positive electrode active material according to Example 6 and Example 7, which shows that when upcycling was performed in a normal air atmosphere, upcycling was performed in an oxygen atmosphere. It was confirmed that the particle size was larger than in the proceeding case.

In other words, when the positive electrode active material according to Examples 6 and 7, which has undergone both particle uniformization and structure stabilization compared to Examples 1 to 4, is applied, the size of the particles constituting the positive electrode active material increases, resulting in superior electrochemical properties. It can be expressed. In addition, in the case of synthesis in an oxygen atmosphere, compared to the case of synthesis in a general air atmosphere, the oxidation atmosphere is well formed on the particle surface during the synthesis process, preventing the reduction of transition metals on the particle surface, and lithium and lithium in the crystal structure. It can be confirmed that the displacement phenomenon of nickel is suppressed, which can lead to improved lifespan performance of the manufactured lithium secondary battery.

Claims (14)

i) a chlorination step of reacting a waste cathode active material containing lithium transition metal oxide with a chlorine-containing gas;
ii) separating lithium chloride and transition metal oxide formed in the chlorination step;
iii) mixing a compound containing lithium and a transition metal compound with the separated transition metal oxide;
iv) first heating the mixture obtained in step iii) at 100 to 600°C; and
v) secondary heating of the result obtained in step iv) at 600 to 1000°C;
A method of upcycling a waste cathode active material, comprising: In claim 1,
The transition metal is a method of upcycling a waste cathode active material, wherein the transition metal includes at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), aluminum (Al), and magnesium (Mg). . In claim 1,
A method for upcycling a waste cathode active material, wherein the reaction with the chlorine-containing gas in step i) is performed at 400 to 800°C. In claim 1,
The chlorine-containing gas in step i) includes an inert gas and chlorine gas (Cl ₂ ) in a volume ratio of 1:0.01 to 1:0.1. In claim 1,
A method of upcycling a waste cathode active material, wherein the separation in step ii) is performed through washing with a solvent. In claim 1,
In step iii), the lithium and transition metal are mixed at a molar ratio of 1:0.9 to 1:1. In claim 1,
A method of upcycling a waste cathode active material, wherein lithium is uniformly dispersed in the mixture through the first heating in step iv). In claim 1,
A method of upcycling a waste cathode active material, in which the cathode active material is resynthesized through secondary heating in step v). In claim 1,
Between step ii) and step iii), performing heat treatment at 400 to 900° C. in an inert gas atmosphere. In claim 1,
After step v), the method of upcycling a waste cathode active material further includes performing heat treatment at 500 to 900°C. Manufactured by upcycling according to any one of claims 1 to 10,
A positive electrode active material whose crystal structure is in the form of a single crystal. In claim 11,
The positive electrode active material contains 1 to 50% by weight more transition metal compared to the waste positive electrode active material before upcycling. A positive electrode containing the positive electrode active material according to claim 11; and
A cathode containing lithium metal;
A lithium secondary battery containing. In claim 13,
The capacity of the lithium secondary battery is improved by 5 to 35% compared to a lithium ion battery containing a waste cathode active material before upcycling.