Patent Publication Number: US-2022212942-A1

Title: Method for isolating lithium precursor and system for isolating lithium precursor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     This application claims benefit under 35 U.S.C. 119(e), 120, 121, or 365(c), and is a National Stage entry from International Application No. PCT/KR2020/004296, filed Mar. 30, 2020, which claims priority to the benefit of Korean Patent Application No. 10-2019-0058661 filed in the Korean Intellectual Property Office on May 20, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a method for isolating lithium precursor and a system for isolating a lithium precursor. More particularly, the present invention relates to a method and a system for isolating a lithium precursor from a preliminary precursor mixture. 
     2. Background Art of the Invention 
     A secondary battery which can be charged and discharged repeatedly has been widely employed as a power source of a mobile electronic device such as a camcorder, a mobile phone, a laptop computer, etc., according to developments of information and display technologies. The secondary battery includes, e.g., a lithium secondary battery, a nickel-cadmium battery, a nickel-hydrogen battery, etc. The lithium secondary battery is actively developed and applied due to high operational voltage and energy density per unit weight, a high charging rate, a compact dimension, etc. 
     The lithium secondary battery may include an electrode assembly including a cathode, an anode and a separation layer (a separator), and an electrolyte immersing the electrode assembly. The lithium secondary battery may further include an outer case having, e.g., a pouch shape for accommodating the electrode assembly and the electrolyte. 
     A lithium metal oxide may be used as a cathode active material of the lithium secondary battery. The lithium metal oxide may additionally contain a transition metal such as nickel, cobalt and manganese. 
     The lithium metal oxide as the cathode active material may be prepared by reacting a lithium precursor and a nickel-cobalt-manganese (NCM) precursor containing nickel, cobalt and manganese. 
     As the above-described high-cost valuable metals are used in the cathode active material, an excessive cost is required in a manufacture of the cathode active material. Additionally, as environmental protection issues have been recently highlighted, a recycling method of the cathode active material has been researched. For the recycle of the cathode active material, a regeneration of the lithium precursor is needed from a used cathode with high efficiency and high yield. 
     For example, Korean Published Patent Application No. 2015-0002963 discloses a method for recovering lithium using a wet method. However, lithium is recovered by wet extraction from a waste liquid remaining after extracting cobalt, nickel, etc., and thus a recovery ratio may be excessively reduced, and a large number of impurities may be generated from the waste liquid. 
     SUMMARY 
     According to an aspect of the present invention, there is provided a method for isolating a lithium precursor with high efficiency and high purity. 
     According to an aspect of the present invention, there is provided a system for isolating a lithium precursor with high efficiency and high purity. 
     In a method for isolating a lithium precursor according to exemplary embodiments, a preliminary precursor mixture including a preliminary lithium precursor and a preliminary transition metal precursor is prepared. The preliminary precursor mixture and a precipitation liquid are mixed in a reactor to form a precursor mixture. A non-reactive gas is injected into the precursor mixture. 
     In some embodiments, the reactor may be a fluidized bed reactor. 
     In some embodiments, the preliminary precursor mixture may be prepared by performing a reductive reaction of a cathode active material collected from a lithium secondary battery. 
     In some embodiments, the reductive reaction may be performed before forming the precursor mixture in the reactor. 
     In some embodiments, the preliminary lithium precursor may include lithium hydroxide. 
     In some embodiments, the preliminary lithium precursor may further include lithium oxide or lithium carbonate. 
     In some embodiments, the precursor mixture may be formed by selectively dissolving lithium hydroxide in the precipitation liquid. 
     In some embodiments, the precipitation liquid may include water. 
     In some embodiments, the precipitation liquid may further include dimethyl carbonate or diethyl carbonate. 
     In some embodiments, a mass of the precipitation liquid in the precursor mixture may be 2 to 20 times a mass of the preliminary lithium precursor. 
     In some embodiments, the precursor mixture may include a slurry or a solution containing the preliminary precursor mixture. 
     In some embodiments, injecting the non-reactive gas into the precursor mixture may include a pulse injection of the non-reactive gas. 
     In some embodiments, a solubility of the non-reactive gas in the precipitation liquid may be 1.5 g/L or less. 
     In some embodiments, the non-reactive gas may include at least one selected from the group consisting of nitrogen, neon, argon, krypton and xenon. 
     In some embodiments, the non-reactive gas may be injected into a lower portion of the reactor. 
     In some embodiments, injecting the non-reactive gas may include reducing a linear velocity of the non-reactive gas at an upper portion top of the reactor. 
     In some embodiments, the linear velocity of the non-reactive gas may be reduced to 0.1 to 3 cm/s. 
     In some embodiments, the upper portion of the reactor may include an expansion unit having an expanded diameter or width. 
     In some embodiments, forming the precursor mixture and injecting the non-reactive gas may be repeatedly performed in a plurality of cycles. 
     A system for isolating a lithium precursor according to exemplary embodiments includes a reactor body into which a lithium precursor is introduced, a precipitation liquid injection unit for injecting a precipitation liquid into the reactor body, and a gas injection unit for injecting a non-reactive gas into a lower portion of the reactor body, and an expansion unit extending from an upper portion of the reactor body and having an expanded diameter or width. 
     According to the above-described exemplary embodiments, a preliminary precursor mixture including a preliminary lithium precursor and a preliminary transition metal precursor, and a precipitation liquid may be mixed in a reactor to form a precursor mixture, and a non-reactive gas may be injected into the precursor mixture to separate a lithium precursor with high purity and high efficiency. 
     The non-reactive gas may disperse the preliminary precursor mixture in the precipitation liquid, thereby selectively dissolving the lithium precursor including lithium hydroxide in the precipitation liquid. Additionally, the preliminary transition metal precursor not dissolved in the precipitation liquid may be precipitated. 
     Accordingly, the lithium precursor may be only isolated selectively from the preliminary precursor mixture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a process flow diagram illustrating a method of isolating a lithium precursor in accordance with exemplary embodiments. 
         FIG. 2  is a schematic diagram for describing a system for isolating a lithium precursor in accordance with exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     According to exemplary embodiments of the present invention, there is provided a method and a system for isolating a lithium precursor where a preliminary precursor mixture and a precipitation liquid are mixed in a reactor to form a precursor mixture, and injecting a non-reactive gas into the precursor mixture to separate the lithium precursor with high efficiency and high purity. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments are provided as exemplary examples, and the spirit of the present invention are not limited to those specific embodiments. 
     The term “precursor” in the present specification is used to generically refer to a compound containing a specific metal to provide the specific metal included in an electrode active material. 
       FIG. 1  is a process flow diagram illustrating a method of isolating a lithium precursor in accordance with exemplary embodiments.  FIG. 2  is a schematic diagram for describing a system for isolating a lithium precursor in accordance with exemplary embodiments. 
     Hereinafter, a method and a system for isolating a lithium precursor are described together with reference to  FIGS. 1 and 2 . 
     Referring to  FIG. 1 , a preliminary precursor mixture including a preliminary lithium precursor and a preliminary transition metal precursor may be prepared (e.g., in a step of S 10 ). 
     In exemplary embodiments, the preliminary precursor mixture including the preliminary lithium precursor and the preliminary transition metal precursor may be obtained from a cathode active material mixture collected from a lithium secondary battery. For example, the cathode active material mixture may be obtained from a lithium-containing compound obtained from the lithium secondary battery. 
     The lithium secondary battery may include an electrode assembly including a cathode, an anode and a separation layer interposed between the cathode and the anode. The cathode and the anode may include a cathode active material layer and an anode active material layer coated on a cathode current collector and an anode current collector, respectively. 
     For example, a cathode active material included in the cathode active material layer may include an oxide containing lithium and a transition metal. 
     In some embodiments, the cathode active material may include a compound represented by Chemical Formula 1 below. 
       Li x M1 a M2 b M3 c O y   [Chemical Formula 1]
 
     In Chemical Formula 1, M1, M2 and M3 may each be a transition metal selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga or B. In Chemical Formula 1, 0≤x≤1.1, 2≤y≤2.02, 0&lt;a&lt;1, 0&lt;b&lt;1, 0&lt;c&lt;1, and 0&lt;a+b+c≤1. 
     In some embodiments, the cathode active material may be an NCM-based lithium oxide containing nickel, cobalt and manganese. The NCM-based lithium oxide as the cathode active material may be prepared by reacting the lithium precursor and an NCM precursor (e.g., an NCM oxide) with each other through, e.g., a co-precipitation reaction. 
     However, embodiments of the present invention may be commonly applied not only to the cathode material including the NCM-based lithium oxide, but also to a lithium-containing electrode material. 
     The lithium precursor may include lithium hydroxide (LiOH), lithium oxide (Li 2 O) or lithium carbonate (Li 2 CO 3 ). Lithium hydroxide may be advantageous as the lithium precursor in an aspect of a charge/discharge property, a life-span property, a high temperature stability, etc., of the lithium secondary battery. For example, lithium carbonate may cause an immersion reaction on the separation layer, thereby reducing life-span stability. 
     Accordingly, according to embodiments of the present invention, a method of isolating lithium hydroxide as the lithium precursor with high selectivity may be provided. 
     For example, the cathode may be separated and recovered from the lithium secondary battery. The cathode may include the cathode current collector (e.g., aluminum (Al)) and the cathode active material layer, and the cathode active material layer may include a conductive material and a binder together with the above-described cathode active material. 
     The conductive material may include, e.g., a carbon-based material such as graphite, carbon black, graphene, carbon nanotube, etc. The binder may include a resin material such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, etc. 
     A cathode active material mixture may be prepared from the recovered cathode. In some embodiments, the cathode active material mixture may be prepared in a powder form through a physical method such as a grinding treatment. The cathode active material mixture may include a powder of a lithium-transition metal oxide, and may include, e.g., an NCM-based lithium oxide powder (e.g., Li(NCM)O 2 ). 
     In some embodiments, the cathode active material mixture may be heat-treated before the grinding treatment. In this case, the cathode current collector may be more easily detached from the cathode before the grinding treatment, and the binder and the conductive material may be removed. For example, a temperature of the heat treatment may be in a range from about 100° C. to about 500° C., preferably in a range from about 350° C. to about 450° C. 
     In some embodiments, the cathode active material mixture may be obtained after immersing the recovered cathode in an organic solvent. For example, the recovered cathode may be immersed in the organic solvent to separate and remove the cathode current collector, and the cathode active material may be selectively extracted by a centrifugation. 
     By the above-described processes, the cathode current collector component such as aluminum may be substantially completely separated and removed, and the cathode active material mixture from which a content of carbon-based components derived from the conductive material and the binder may be removed or reduced may be obtained. 
     In some embodiments, the preliminary precursor mixture may be generated by reducing the cathode active material mixture (e.g., the cathode active material). For example, the preliminary precursor mixture may be formed by reducing the cathode active material mixture with hydrogen. 
     The hydrogen reductive reaction may be performed at a temperature from about 350 to about 700° C., preferably from about 400 to about 550° C. 
     The preliminary precursor mixture may include the preliminary lithium precursor and the preliminary transition metal precursor that may be products from the hydrogen reductive reaction of the lithium-transition metal oxide included in the cathode active material mixture. 
     The preliminary lithium precursor may include lithium hydroxide, lithium oxide and/or lithium carbonate. In exemplary embodiments, the preliminary lithium precursor may be obtained through the hydrogen reductive reaction, so that a mixed content of lithium carbonate may be decreased. 
     The preliminary transition metal precursor may include Ni, Co, NiO, CoO, MnO, or the like. 
     For example, the preliminary precursor mixture formed from the above-described reductive reaction may be transferred to a reactor  100  as will be described later. 
     In some embodiments, the reductive reaction may be performed in the reactor  100  in which a reaction for forming a precursor mixture of a preliminary precursor mixture  50  and a precipitation liquid  80  may be performed as described later. In this case, the precursor mixture forming reaction may be performed without transferring the preliminary precursor mixture. Accordingly, the yield reduction caused while transferring the preliminary precursor mixture may be prevented. 
     Referring to  FIGS. 1 and 2  together, the preliminary precursor mixture  50  and the precipitation liquid  80  may be mixed in the reactor  100  to form the precursor mixture (e.g., in a step of S 20 ). 
     For example, the precursor mixture may refer to a composition including a lithium precursor formed by reacting a preliminary lithium precursor  60  with the precipitation liquid  80  and a preliminary transition metal precursor  70  precipitated in the precipitation liquid  80 . 
     In some embodiments, the reactor  100  may be a fluidized bed reactor. For example, the fluidized bed reactor may refer to a reactor in which a fluid (gas or liquid) flows through the injected preliminary precursor mixture  50  to induce a fluidization. For example, the fluid may be a non-reactive gas as will be described later. 
     For example, the preliminary precursor mixture  50  may be fluidized in the fluidized bed reactor so that a contact area with the precipitation liquid  80  may be increased. Accordingly, the reaction between the preliminary lithium precursor  60  and the precipitation liquid  80  may be more promoted. 
     Additionally, the preliminary transition metal precursor  70  precipitated in the precipitation liquid  80  may be formed in a state of a slurry to be easily transferred to a subsequent reactor. 
     Referring to  FIG. 2 , the precipitation liquid  80  may be injected into the reactor  100  through a precipitation liquid injection unit  120 . The precipitation liquid  80  may be injected into a reactor body  110  through the precipitation liquid injection unit  120 . 
     For example, the precipitation liquid injection unit  120  may be located at an upper portion of the reactor body  110 . The precipitation liquid injection unit  120  may be located at a lower portion or a middle portion of the reactor body  110 . 
     In some embodiments, the preliminary lithium precursor may include lithium hydroxide. In some embodiments, the preliminary lithium precursor may further include lithium oxide or lithium carbonate. 
     In some embodiments, the precursor mixture may be formed by dissolving the preliminary lithium precursor  60  in the precipitation liquid  80 . 
     For example, lithium hydroxide contained in the preliminary lithium precursor  60  may be selectively dissolved in the precipitation liquid  80  to form the precursor mixture. For example, lithium oxide may react with the precipitation liquid  80  to form lithium hydroxide, and then may be dissolved in the precipitation liquid  80 . For example, lithium carbonate may have low solubility in the precipitation liquid  80 . Accordingly, lithium carbonate may be precipitated and removed from the preliminary precursor mixture. 
     In some embodiments, the precipitation liquid  80  may include water. For example, the preliminary lithium precursor  60  may be hydrated with water to form the precursor mixture including an aqueous solution in which lithium hydroxide is dissolved. 
     In some exemplary embodiments, the precipitation liquid may further include dimethyl carbonate or diethyl carbonate. 
     For example, dimethyl carbonate or diethyl carbonate may promote the reaction between the preliminary lithium precursor  60  and water. Accordingly, an isolation efficiency of the lithium precursor may be improved. 
     In some embodiments, a mass of the precipitation liquid  80  in the precursor mixture may be about 2 to 20 times a mass of the preliminary lithium precursor  60 , preferably about 2 to 10 times a mass of the preliminary lithium precursor  60 . 
     For example, in the above range, mixing of the preliminary lithium precursor  60  and the precipitation liquid  80  by a non-reactive gas as will be described later may be easily performed. Accordingly, the lithium precursor may be separated with high purity and high efficiency without using an excessive amount of the precipitation liquid. 
     In some embodiments, the precursor mixture may include a slurry or a solution including the preliminary precursor mixture  50 . 
     For example, the preliminary transition metal precursor  70  that may not be soluble in the precipitation liquid  80  may be dispersed in the precipitation liquid  80  to form the slurry. For example, lithium hydroxide contained in the preliminary lithium precursor  60  may be dissolved in the precipitation liquid  80  to form the solution. Accordingly, the preliminary transition metal precursor  70  and the preliminary lithium precursor  60  may be separated from each other. 
     Referring to  FIGS. 1 and 2 , a non-reactive gas may be injected into the precursor mixture (e.g., in a step of S 30 ). For example, the non-reactive gas may be injected into the precursor mixture located at an inside of the reactor  100  through a gas injection unit  130 . 
     For example, the non-reactive gas may be injected into the precursor mixture to promote mixing of the preliminary precursor mixture  50  and the precipitation liquid  80 . 
     For example, the non-reactive gas may apply a physical impact to an agglomerated preliminary precursor mixture  50 , so that the preliminary precursor mixture  50  may be uniformly dispersed in the precipitation liquid  80 . 
     Accordingly, a contact area between the precipitation liquid  80  and the preliminary precursor mixture  50  may be increased, so that the precursor mixture may be more easily formed. 
     In some embodiments, a pulse of the non-reactive gas may be injected into the precursor mixture. The pulse of the non-reactive gas may include a change with a constant period of an injection rate or an injection amount of the non-reactive gas. For example, a type of the pulse may be appropriately selected according to capacity and shape of the reactor  100 . 
     In some exemplary embodiments, a solubility of the non-reactive gas in the precipitation liquid  80  may be 1.5 g/L or less. A low solubility of the non-reactive gas in the precipitation liquid may be advantageous, and a lower limit of the solubility is not particularly limited. 
     In some exemplary embodiments, the non-reactive gas may include at least one selected from the group consisting of nitrogen, neon, argon, krypton and xenon which may have low solubility and reactivity with respect to the precipitation liquid. 
     In this case, a loss of the non-reactive gas caused when the non-reactive gas is dissolved in the precipitation liquid may be prevented. Further, the non-reactive gas may not react with the precursor mixture, so that a yield reduction of the lithium precursor due to a side reaction may be prevented. 
     In some embodiments, the non-reactive gas may not include carbon dioxide (CO 2 ). Accordingly, the reduction the yield reduction of the lithium precursor due to a reaction between carbon dioxide and lithium hydroxide may be prevented. 
     In some embodiments, the non-reactive gas may be injected into the lower portion of the reactor  100 . For example, the non-reactive gas may be injected into the precursor mixture through the gas injection unit  130  positioned at the lower portion of the reactor  100 . 
     The non-reactive gas injected into the lower portion of the reactor  100  may rise to the upper portion of the reactor  100  to promote mixing of the preliminary precursor mixture  50  and the precipitation liquid  80  throughout the reactor body  110 . 
     In some embodiments, a linear velocity (cm/s) of the non-reactive gas injected into the precursor mixture may be from about 5 to 30 cm/s. 
     In the above range, the non-reactive gas may provide sufficient physical impact on the aggregated preliminary precursor mixture  50 , so that the mixing of the preliminary precursor mixture  50  and the precipitation liquid  80  may be further promoted. 
     In some embodiments, the non-reactive gas may have a reduced linear velocity (cm/s) at the upper portion of the reactor  100 . For example, the linear velocity may refer to a flow rate of a gas passing through per unit area. 
     For example, a mass of each particle of the preliminary precursor mixture  50  included in the reactor  100  may be different from each other. In this case, the particles of the preliminary precursor mixture  50  having a relatively small mass may flow out of the reactor body  110  by the non-reactive gas or may be precipitated in the upper portion of the reactor  100 . 
     Therefore, the linear velocity (cm/s) of the non-reactive gas may be reduced at the upper portion of the reactor  100 , so that the preliminary precursor mixture  50  may be effectively prevented from flowing out of the reactor body  110  or from being precipitated on the upper portion of the reactor  100 . 
     In some embodiments, the linear velocity of the non-reactive gas at the upper portion of the reactor  100  may be reduced to about 0.1 to 3 cm/s. For example, the linear velocity of the non-reactive gas in an expansion unit  140  located at the upper portion of the reactor body  110  may be reduced to about 0.1 to 3 cm/s. 
     In the above range, the preliminary precursor mixture  50  may be prevented from flowing out of the reactor body  110 , while further promoting the mixing of the preliminary precursor mixture  50  and the precipitation liquid  80 . 
     For example, the reactor  100  may include the expansion unit  140  extending from the upper portion of the reactor body  110  and having a larger diameter than that of the reactor body  110 . 
     For example, the expansion unit  140  may have a larger cross-sectional area than that of the reactor body  110 , so that the linear velocity (cm/s) of the non-reactive gas moving from the reactor body  110  to the expansion unit  140  may be reduced. In this case, a ratio of a diameter of the expansion unit  140  to a diameter of the reactor body  110  may be adjusted, and thus a reduction ratio of the linear velocity (cm/s) may be easily adjusted. 
     In some embodiments, the ratio of the diameter of the expansion unit  140  to the diameter of the reactor body  110  may be from 2 to 10. 
     In the above diameter ratio range, the preliminary precursor mixture  50  may be more effectively prevented from flowing out of the reactor body  110 . 
     In some exemplary embodiments, the formation of the precursor mixture and the injection of the non-reactive gas may be repeatedly performed in a plurality of cycles. 
     For example, separation efficiency and yield of the lithium precursor may be improved by repeatedly forming the precursor mixture and injecting the non-reactive gas. 
     For example, the formation of the precursor mixture and the injection of the non-reactive gas may be repeatedly performed, so that a content of the lithium precursor remaining undissolved in the precipitation liquid  80  may be reduced. Accordingly, the yield of the lithium precursor may be further improved. 
     For example, while repeatedly forming the precursor mixture and injecting the non-reactive gas, an injected amount of the precipitation liquid  80  and the non-reactive gas may be properly adjusted based on the solubility of the preliminary lithium precursor in the precipitation liquid  80  and the capacity of the reactor  100 . 
     For example, the injected amount of the precipitation liquid  80  and the non-reactive gas may be constant, or may be constantly increased or decreased as a plurality of the cycles are repeated. 
     In an embodiment, the precipitated preliminary transition metal precursor  70  may be collected from the reactor  100  to form a transition metal precursor. For example, the preliminary transition metal precursor  70  may react with an acid solution to form the transition metal precursor. 
     In an embodiment, sulfuric acid may be used as the acid solution. In this case, the transition metal precursor may include a transition metal sulfate. For example, the transition metal sulfate may include NiSO 4 , MnSO 4 , CoSO 4 , etc.