Method for recovering active metals from lithium secondary batteries

Abstract

In a method for recovering active metals from a lithium secondary battery, positive electrode active material particles containing lithium-transition metal oxide are prepared. The positive electrode active material particles are reduced. The reduced positive electrode active material particles are ultrasonically dispersed and hydrated. The hydrated transition metal slurry is recovered. The recovery rate of lithium and transition metals can be increased by deagglomeration using ultrasonic dispersion.

Description

Technical Field

[0001] The present invention relates to a method for recovering active metals of a lithium secondary battery. More specifically, it relates to a method for recovering active metals from the positive electrode of a lithium secondary battery.

Background Art

[0002] In recent years, secondary batteries have been widely applied and developed as power sources for portable electronic communication devices such as camcorders, mobile phones, and notebook computers, as well as for vehicles such as hybrid automobiles and electric vehicles. As secondary batteries, lithium secondary batteries have been actively developed and applied because of their high operating voltage and energy density per unit weight, and their advantages in charging speed and weight reduction.

[0003] As the active material for the positive electrode of the lithium secondary battery, a lithium metal oxide can be used. The lithium metal oxide can further contain transition metals such as nickel, cobalt, and manganese.

[0004] Since the above-mentioned high-cost valuable metals are used in the active material for the positive electrode, more than 20% of the manufacturing cost is spent on the manufacture of the positive electrode material. Also, recently, due to the increasing interest in environmental protection, research on recycling methods for the active material for the positive electrode has been advanced.

[0005] For example, by subjecting the waste positive electrode active material to a reduction reaction, lithium and transition metals can be separated and recovered. However, if the conditions of the reduction reaction are not properly controlled, aggregation and agglomeration of the active material particles may occur. In this case, the proportion of lithium and transition metals that cannot be recovered may increase, and the purity of the recovered active metals may also decrease.

[0006] For example, Korean Patent No. 10-0709268 discloses a recycling apparatus and method for waste manganese batteries and alkaline batteries, but does not show a dry-based method for regenerating valuable metals with high selectivity and high yield.

Summary of the Invention

[0007] The object of this invention is to provide a method for recovering active metals from lithium secondary batteries with high efficiency and high purity. [Means for solving the problem]

[0008] In an exemplary embodiment of a method for recovering active metals from a lithium secondary battery, positive electrode active material particles containing a lithium-transition metal oxide are prepared. The positive electrode active material particles are subjected to a reduction treatment. The reduced positive electrode active material particles are ultrasonically dispersed and hydrated. The hydrated transition metal slurry is recovered.

[0009] In some embodiments, the reduction treatment can form lithium precursor particles, transition metal oxide particles, and transition metal particles from the positive electrode active material particles.

[0010] In some embodiments, the reduction treatment can form aggregates of the lithium precursor particles, the transition metal oxide particles, and the transition metal particles.

[0011] In some embodiments, the aggregates can be decomposed by ultrasonic dispersion hydration.

[0012] In some embodiments, the aggregate can be broken down into particles with a particle size of 300 μm or less by ultrasonic dispersion hydration.

[0013] In some embodiments, the ultrasonic dispersion hydration may include a solid-liquid two-phase process.

[0014] In some embodiments, ultrasonic waves with a power of 50 to 110 W can be applied in the ultrasonic dispersion hydration.

[0015] In some embodiments, the ultrasonic dispersion hydration can be performed by applying ultrasonic waves with a power of 2.5 to 5.5 W / g based on 1 g of aggregate.

[0016] In some embodiments, the ultrasonic dispersion hydration can be performed by applying ultrasonic waves with a power of 0.6 to 1.4 W / g based on 1 g of the recovered transition metal slurry.

[0017] In some embodiments, the reduction treatment of the positive electrode active material particles can be carried out in a fluidized bed reactor using a reducing gas.

[0018] In some embodiments, the recovered transition metal slurry can be rehydrated.

[0019] In some embodiments, the positive electrode active material particles can be heat-treated at a temperature of 500°C or lower before being subjected to reduction treatment. [Effects of the Invention]

[0020] According to the exemplary embodiment described above, for example, lithium precursors can be recovered from waste cathode active material by a dry-based process utilizing a dry reduction process. This makes it possible to obtain lithium precursors of high purity without the complex leaching and addition processes required in wet-based processes using acid solutions.

[0021] According to an exemplary embodiment, aggregates generated due to excessive progress in the dry reduction step or an excessive increase in the heat of the reduction reaction can be eliminated by ultrasonic dispersion. This improves the recovery rate of the slurry containing transition metals in the hydration step and reduces the amount of aggregates that are not recovered.

[0022] In some embodiments, the ultrasonic dispersion is carried out in a two-phase state of solid and liquid, which can improve the slurry recovery rate. [Brief explanation of the drawing]

[0023] [Figure 1]FIG. 1 is a schematic flowchart for explaining a method of recovering an active metal of a lithium secondary battery according to an exemplary embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the particle flow and phase change in the reduction step and the hydration step. [Figure 3] FIG. 3 is a schematic diagram showing the particle flow and phase change in the reduction step and the hydration step. [Figure 4] FIG. 4 is a schematic diagram showing the particle flow and phase change in the reduction step and the hydration step. MODE FOR CARRYING OUT THE INVENTION

[0024] Embodiments of the present invention provide a method for recovering an active metal from a lithium secondary battery with high purity and high yield by a reduction reaction.

[0025] Hereinafter, embodiments of the present invention will be described more specifically with reference to the accompanying drawings. However, these embodiments are merely illustrative of the present invention and do not limit the present invention.

[0026] As used herein, the term "precursor" is used to comprehensively refer to a compound containing a specific metal in order to provide the specific metal contained in the electrode active material.

[0027] FIG. 1 is a schematic flowchart for explaining a method of recovering an active metal of a lithium secondary battery according to an exemplary embodiment. FIGS. 2 to 4 are schematic diagrams showing the particle flow and phase change in the reduction step and the hydration step.

[0028] Referring to FIG. 1, for example, in step S 10, a positive electrode active material mixture can be prepared.

[0029] According to an exemplary embodiment, active material particles (e.g., waste positive electrode active material particles) can be prepared from a waste positive electrode of a lithium secondary battery.

[0030] The lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator membrane interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode may each include a positive electrode current collector and a positive electrode active material layer and a negative electrode active material layer coated on the negative electrode current collector, respectively.

[0031] For example, the positive electrode active material contained in the positive electrode active material layer may include an oxide containing lithium and a transition metal.

[0032] In some embodiments, the positive electrode active material may include a compound represented by the following chemical formula 1.

[0033] [Chemical formula 1] Li x M1 a M2 b M3 c O y

[0034] In chemical formula 1, M1, M2 and M3 may be transition metals selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B. <x≦1.1、2≦y≦2.02、0<a<1、0<b<1、0<c<1、0<a+b+c≦1であってもよい。

[0035] In some embodiments, the positive electrode active material may be an NCM-based lithium oxide containing nickel, cobalt, and manganese.

[0036] The positive electrode can be separated from the waste lithium secondary battery and recovered. The waste positive electrode includes a positive electrode current collector (e.g., aluminum (Al)) and a positive electrode active material layer, as described above, and the positive electrode active material layer may include a conductive material and a binder in addition to the positive electrode active material.

[0037] The conductive material may include, for example, carbon-based materials such as graphite, carbon black, graphene, and carbon nanotubes. The binder may include, for example, resin materials such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate.

[0038] In some embodiments, the positive electrode active material layer can be peeled off from the positive electrode current collector, and the separated positive electrode active material layer can be pulverized to produce positive electrode active material particles. These positive electrode active material particles can then be manufactured in powder form and collected, for example, in the form of black powder.

[0039] The positive electrode active material particles include, as described above, a lithium-transition metal oxide powder, and may include, for example, NCM-based lithium oxide powder (e.g., Li(NCM)O2). In this case, M1, M2, and M3 in the chemical formula 1 may be Ni, Co, and Mn, respectively.

[0040] As used in this application, the term "positive electrode active material particles" may refer to the raw material material that is introduced into the reducing reaction treatment described later after the positive electrode current collector has been substantially removed from the waste positive electrode. In one embodiment, the positive electrode active material particles may include the NCM-based lithium oxide. In one embodiment, the positive electrode active material particles may partially contain components derived from the binder or the conductive material.

[0041] In some embodiments, the average particle size (D50) (average particle size in the volume cumulative distribution) of the positive electrode active material particles may be 5 to 100 μm. Within this range, the reducing reaction using a fluidized bed reactor, as described later, can be easily carried out.

[0042] For example, in step S20, the positive electrode active material particles can be subjected to a reduction reaction in the reducing reactor 100.

[0043] Referring to Figures 2 and 3, the aforementioned positive electrode active material particles 50 can be introduced into the reducing reactor 100 (for example, in step S21).

[0044] In some embodiments, the positive electrode active material particles 50 can be heat-treated before reduction treatment. This heat treatment removes or reduces impurities such as the conductive material and binder contained in the positive electrode active material particles 50, allowing the lithium-transition metal oxide to be reduced to a high purity.

[0045] The temperature of the heat treatment may be, for example, about 500°C or less, in one embodiment about 100 to 500°C, preferably about 350 to 450°C. Within this range, the impurities can be substantially removed, and the decomposition and damage of the lithium-transition metal oxide can be prevented.

[0046] In one embodiment, the heat treatment can be carried out in a reducing reactor 100. In this case, a carrier gas such as nitrogen (N2), helium (He), or argon (Ar) can be injected through a gas injection unit 110 located at the bottom of the reducing reactor 100, and fluidization heat treatment can be performed in the reducing reactor 100.

[0047] In one embodiment, the positive electrode active material particles 50 may be introduced into the reducing reactor 100 after being heat-treated.

[0048] For example, in step S23, the positive electrode active material particles 50 can be reduced. According to an exemplary embodiment, the reducing reactor 100 can be provided as a fluidized bed reactor. A reducing gas is injected from the bottom of the reducing reactor 100 via a gas injection section 110, and a fluidized bed of positive electrode active material particles 50 is formed within the reducing reactor 100, thereby inducing a reduction reaction.

[0049] The reducing gas may include hydrogen (H2). The reducing gas may further include a carrier gas such as nitrogen, helium, or argon (Ar).

[0050] Since the reducing gas is supplied from the bottom of the reducing reactor 100 and comes into contact with the positive electrode active material particles 50, the positive electrode active material particles 50 can either move to the top of the reducing reactor 100 or remain inside the reducing reactor 100 and react with the reducing reaction gas.

[0051] As described above, a fluidized bed can be formed by injecting the reducing gas. Within the fluidized bed, the positive electrode active material particles 50 come into contact with the reducing gas and repeatedly rise, remain, and descend, thereby increasing the reaction contact time and promoting the dispersion of the particles.

[0052] Furthermore, since the reducing gas is supplied from the bottom of the reducing reactor 100 and comes into contact with the positive electrode active material particles 50, the reaction region can be expanded as the positive electrode active material particles 50 move to the top of the reducing reactor 100.

[0053] However, the concept of the present invention is not necessarily limited to fluidized bed reactions. For example, a fixed reaction may be carried out by pre-loading a positive electrode active material mixture into a batch reactor or tubular reactor and then supplying a reducing reaction gas.

[0054] In some embodiments, a dispersion plate 120 can be placed at the bottom of the reducing reactor 100. The reducing gas can be facilitated to rise and be ejected through injection holes contained in the dispersion plate 120.

[0055] By initiating the reduction reaction, lithium precursor particles 60 can be generated from the positive electrode active material particles 50. For example, as the reduction process progresses, the crystalline structure of Li(NCM)O2 collapses, and Li is released from the crystalline structure, allowing reduction in the form of lithium hydroxide (LiOH), lithium oxide (e.g., Li2O), and / or lithium carbonate (Li2CO3). In a preferred embodiment, the lithium precursor particles 60 may include lithium hydroxide (LiOH).

[0056] On the other hand, the transition metal can be reduced from the crystal structure to produce transition metal oxide particles 70. For example, the transition metal oxide particles 70 may include transition metal oxides such as NiO and CoO.

[0057] Referring to Figure 3, for example, in step S25, the reduction reaction may proceed further to generate more transition metal particles 75. For example, the transition metal particles 75 may include nickel (Ni) or cobalt (Co). As the transition metal particles 75 are formed, the increasing heat of reaction may initiate the aggregation or aggregation of the particles.

[0058] If the reduction reaction proceeds excessively, for example in step S27, clumping or sintering of particles may occur, resulting in the formation of aggregates 80.

[0059] For example, the temperature of the reduction reaction can be adjusted to 500°C or below to prevent over-reduction. However, the heat of reaction generated during the reduction reaction can cause the temperature inside the reducing reactor 100 to rise above 500°C. As a result, the transition metal oxide particles 70 or the positive electrode active material particles 50 may be over-reduced, and transition metal particles 75 may be generated.

[0060] Furthermore, aggregates 80 may be generated by metallic bonding or sintering between transition metal particles 75, and lithium precursor particles 60 and transition metal oxide particles 70 may be attached to and contained within the aggregates 80.

[0061] Referring to Figures 1 and 4, the particles produced by the reduction reaction can be hydrated along with ultrasonic dispersion (e.g., in step S30).

[0062] For example, the aggregates 80 produced by the reduction treatment described above can be hydrated by supplying water. This hydration can be carried out together with ultrasonic dispersion. This hydration can be carried out by introducing water into the reducing reactor 100, or by introducing the aggregates 80 and water together into a separate storage container.

[0063] For example, after immersing the ultrasonic probe 150 in the aqueous solution containing the aggregate 80, power can be applied by the power supply unit P.

[0064] For example, as shown in step S34, ultrasonic dispersion hydration eliminates the sintering of the aggregate 80, allowing the lithium precursor particles 60 to be substantially dissolved in the aqueous solution. Furthermore, the transition metal oxide particles 70 and transition metal particles 75 contained in the aggregate 80 can be individually separated and dispersed in the solid phase in the aqueous solution.

[0065] As mentioned above, by performing ultrasonic dispersion along with hydration of lithium precursor particles 60 to decompose the aggregates 80, the recovery rate of transition metals can be significantly increased.

[0066] Returning to Figure 1, for example, the transition metal-containing slurry can be recovered by a filtration process (e.g., step S40).

[0067] As described above, the ultrasonic dispersion process can substantially break down the aggregates 80 into individual particles or into fine particles. This allows for the substantial removal of fractions that remain as aggregates 80 and are not recovered, and the transition metal components to be recovered substantially completely in the slurry.

[0068] In some embodiments, the ultrasonic dispersion step can substantially decompose and remove aggregates having a particle size of 1,000 μm or larger. For example, the ultrasonic dispersion step can decompose the aggregates 80 into particles, each having a particle size of 300 μm or less.

[0069] The transition metal components contained in the transition metal slurry can be recovered as transition metal precursors by acid treatment. For example, NiSO4, CoSO4, and MnSO4 can be recovered as transition metal precursors using a sulfuric acid solution.

[0070] The lithium precursor particles 60 dissolved in the aqueous solution can be recovered as a lithium precursor in the form of lithium hydroxide, for example, by a crystallization step. In some embodiments, a rehydration step (for example, a washing step) can be performed on the transition metal slurry. Rehydration can redissolve any lithium components remaining in the transition metal slurry, thereby increasing the recovery rate of the lithium precursor.

[0071] As described above, according to exemplary embodiments, the hydration and dispersion steps can be carried out in a solid-liquid two-phase process substantially utilizing ultrasound. This shortens the decoction time and ensures a transition metal recovery rate of substantially close to 100%.

[0072] In the comparative example, after adding water to the reducing reactor 100 to decompose the aggregate 80, a carrier gas can be supplied via the gas injection unit 110 to perform fluid hydration.

[0073] In this case, since the dispersion process is carried out in a three-phase process of solid-liquid-gas phases, the de-aggregation time may increase too much, and the recovery rate of lithium and transition metals may decrease significantly.

[0074] In contrast, according to the exemplary embodiment described above, the de-aggregation time can be significantly reduced by a two-phase dispersion process using ultrasound, thereby preventing the re-aggregation of particles and significantly increasing the recovery rate of lithium and transition metals.

[0075] In some embodiments, the power W applied during ultrasonic dispersion may be 50W or more. In this case, the dispersion time can be shortened, and substantially improved recovery rates for transition metals and lithium can be obtained.

[0076] Preferably, the power W applied during ultrasonic dispersion may be 50 to 110 W. For example, if the applied power exceeds 110 W, a further increase in recovery rate cannot be obtained, which is economically undesirable.

[0077] In some embodiments, the power applied per gram of aggregate 80 may be 2.5 W / g or more, preferably 2.5 to 5.5 W / g.

[0078] In some embodiments, the power applied per gram of recovered transition metal slurry may be 0.6 W / g or more, preferably 0.6 to 1.4 W / g or more.

[0079] The following are specific examples to aid in understanding the present invention, but these examples are merely illustrative and do not limit the scope of the appended claims. It will be obvious to those skilled in the art that various changes and modifications can be made to these examples within the scope of the present invention and the technical concept, and it is also obvious that these variations and modifications fall within the scope of the appended claims.

[0080] Examples One kilogram of positive electrode material separated from a waste lithium secondary battery was heat-treated at 450°C for one hour. The heat-treated positive electrode material was cut into small units and pulverized by milling to obtain a sample of Li-Ni-Co-Mn oxide positive electrode active material. Two hundred grams of the positive electrode active material sample was placed in a fluidized bed reactor, and while maintaining the internal temperature of the reactor at 480°C, 100% nitrogen gas was injected from the bottom of the reactor at a flow rate of 5.5 L / min to perform fluidization heat treatment for three hours.

[0081] After the heat treatment process, the reactor temperature was lowered to 460°C, and a mixed gas of 20 vol% hydrogen and 80 vol% nitrogen was injected from the bottom of the reactor at a flow rate of 5.5 L / min for 4 hours to carry out the reduction reaction. During this time, the internal temperature of the fluidized bed reactor was maintained at 460°C. After the reduction reaction had progressed, the reactor temperature was reduced to 25°C, and 20 g of aggregate was collected.

[0082] 20 g of the aggregate was mixed with 60 g of water, and an ultrasonic probe was immersed in the aqueous solution. The deaggregation process was then performed under the power and dispersion time conditions shown in Table 1.

[0083] Comparative Example 20 g of aggregates collected by the reduction reaction, similar to the example, were added to 60 g of water, and dispersion was carried out for 300 minutes while supplying nitrogen (N2) gas to the aqueous solution instead of ultrasonic dispersion.

[0084] After collecting the transition metal-containing slurry from the dispersions obtained from the examples and comparative examples, a water washing step was performed. Subsequently, the slurry recovery rate and lithium recovery rate were measured as follows.

[0085] 1) Measurement of slurry recovery rate The weight of the aggregates generated after the reduction process (A) and the weight of the solid-phase aggregates remaining inside the reactor without being dispersed in slurry form after the dispersion process (B) were measured, and the slurry recovery rate (=(1-B / A)×100)(%) was calculated.

[0086] 2) Measurement of lithium recovery rate After adding 19 times (by weight) more water to the slurry dispersion and stirring, the lithium precursor, in which lithium hydroxide and lithium carbonite were dissolved in water, was recovered. The lithium recovery rate (%) was calculated by measuring the weight of the lithium dissolved in water relative to the weight of lithium in the initial cathode active material sample.

[0087] The evaluation results are summarized in Table 1 below.

[0088] [Table 1]

[0089] On the other hand, in the examples, the power was calculated based on 1 g of recovered slurry and 1 g of aggregate. This is shown in Table 2 below.

[0090] [Table 2]

[0091] As can be seen from Tables 1 and 2, in the examples where ultrasonic dispersion hydration was performed, an improved recovery rate was achieved with a shorter dispersion time compared to the comparative example where a three-phase dispersion process was performed.

[0092] For example, in Examples 3 to 6, when ultrasonic dispersion was performed using a power supply of, for example, 50W or more, a slurry recovery rate of 80% or more and a lithium recovery rate of 70% or more were ensured.

Claims

1. A step of preparing positive electrode active material particles containing lithium-transition metal oxide, A step of reducing the positive electrode active material particles, wherein the reduction treatment is carried out in a fluidized bed reactor using a reducing gas, thereby forming aggregates of lithium precursor particles, transition metal oxide particles, and transition metal particles from the positive electrode active material particles, The steps include ultrasonically dispersing and hydrating the aggregates, The steps include recovering the hydrated transition metal slurry, A method for recovering active metals from a lithium secondary battery, wherein the ultrasonic dispersion and hydration step includes applying ultrasonic waves with a power of 2.5 to 5.5 W / g based on 1 g of the aggregate, and applying ultrasonic waves with a power of 0.6 to 1.4 W / g based on 1 g of the recovered transition metal slurry.

2. The method for recovering active metals from a lithium secondary battery according to claim 1, wherein the ultrasonic dispersion and hydration step includes decomposing the aggregates.

3. The method for recovering active metals from a lithium secondary battery according to claim 2, wherein the aggregate is decomposed into particles with a particle size of 300 μm or less by the ultrasonic dispersion and hydration step.

4. The method for recovering active metals from a lithium secondary battery according to claim 1, wherein the ultrasonic dispersion and hydration step includes a solid-liquid two-phase step.

5. The method for recovering active metals from a lithium secondary battery according to claim 1, wherein the ultrasonic dispersion and hydration step includes applying ultrasonic waves with a power of 50 to 110 W.

6. A method for recovering active metals from a lithium secondary battery according to claim 1, further comprising the step of rehydrating the recovered transition metal slurry.

7. A method for recovering active metals from a lithium secondary battery according to claim 1, further comprising the step of heat-treating the positive electrode active material particles at a temperature of 500°C or less before the step of reducing the positive electrode active material particles.

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