Patent Publication Number: US-11394048-B2

Title: Regenerated lithium-ion cathode materials having modified surfaces

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. application patent Ser. No. 16/177,040, filed Oct. 31, 2018, the entire disclosure of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to regenerated lithium-ion cathode materials having modified surfaces enabling reuse of the cathode material. 
     BACKGROUND 
     Due to increasing demand of lithium-ion batteries for electric vehicles (EVs) and hybrid electric vehicles (HEV), the lithium-ion battery market is expected to grow rapidly in the next decade. Valuable metals are used in the cathode active materials of these batteries. The price of cathode active materials has been increasing due to the depletion of resources like cobalt, nickel and lithium. 
     The increased demand of EVs and HEVs will lead to a significant increase in end-of-life (EOL) batteries. Therefore, there is interest in recycling the material in these EOL batteries. Traditional recycling techniques (such as pyro-metallurgy and hydro-metallurgy) use smelting or leaching processes which eventually result in recovering valuable metals and materials and the recovered metals can be potentially used for resynthesizing new cathode active materials or for other purposes. However, these traditional recycling techniques are neither environmentally friendly nor cost-effective. 
     SUMMARY 
     Disclosed herein are embodiments of a regenerated cathode active material for use in a lithium-ion battery. The regenerated cathode active material comprises a core material comprising lithium and a transition metal oxide, the core material having a surface, wherein the core material is a recycled cathode active material that has been re-lithiated. At least two different lithium-ion conducting species are on the surface of the core material. The at least two different lithium-ion conducting species are selected from AlF 3 , Li 3 PO 4 , and a lithium metal oxide. 
     Another embodiment of a regenerated cathode active material for use in a lithium-ion battery comprises a core material comprising a transition metal oxide and lithium, the core material having a surface, and multiple lithium-ion conducting species on the surface, wherein the core material is a recycled cathode active material that has been re-lithiated. 
     Also disclosed are methods of producing a regenerated cathode active material for a lithium ion battery. An exemplary method comprises using a cathode active material removed from an end-of-life lithium-ion battery, recycled with a direct recycling process, and re-lithiated. The cathode active material is comprised of a core material having a surface on which organic species and inorganic species exist, the inorganic species selected from LiOH, Li 2 CO 3 , Li 2 O and LiF. The cathode active material is rinsed with a solvent to remove the organic species from the surface of the cathode active material. After removing the organic species, either the cathode active material is heated to a temperature of ≥700° C. and ≤1000° C. in a hydrogen atmosphere to convert LiOH to Li 2 O and reacted with carbon dioxide at a temperature of ≥400° C. and ≤700° C. to convert Li 2 O to Li 2 CO 3 , resulting in the cathode active material having Li 2 CO 3  and LiF as most or all remaining inorganic species, or the LiOH and Li 2 O are removed from the surface by dissolving in water, resulting in the cathode active material having Li 2 CO 3  and LiF as most or all remaining inorganic species. The Li 2 CO 3  and LiF are converted to lithium-ion conducting species by reacting with one or more of aluminum, a metal oxide and a phosphate using a solid-state reaction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
         FIG. 1  is a flow diagram of a method of recycling cathode active material. 
         FIG. 2  is a flow diagram of a method of regenerating recycled cathode active material as disclosed herein. 
         FIG. 3  is a cross-sectional schematic of a regenerated cathode active material as disclosed herein. 
         FIG. 4  is a cross-sectional schematic of another regenerated cathode active material as disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     Due to the increasing demand of lithium-ion batteries for HEVs, EVs, consumer electronics, and renewable energy storage systems, it is estimated that more than 340,000 ton/year of spent lithium-ion batteries needs to be recycled or properly disposed. Traditional metal recycling processes may produce recycled elemental metals, but such conventional processes are not economical and not environmentally friendly. Because EOL batteries from EVs still retain about 80% of their initial capacity, recycling of these materials should be prioritized. 
     A recycling technique, known as a direct recycling process, offers the potential for greater environmental and economic savings. Direct recycling produces recycled electrode active materials rather than the elemental metals that are produced by hydro-metallurgy and pyro-metallurgy processes. These recycled electrode materials must be further processed (i.e., re-lithiated) to reinstate the electrochemical activity to produce ready-to-use electrode active materials. A short annealing process may precede the re-lithiation process to improve the crystallinity and structural defects of the recycled EOL electrode active material. 
     Electrode active materials recovered by the direct recycling process contain inorganic and organic chemical species on the surface due to battery cycling under various conditions and electrolyte decomposition, which are not removed during the direct recycling process. Organic and inorganic chemical species can also be formed due to chemical reactions that occur during the recycling process. The current direct recycling process is illustrated in  FIG. 1  and involves physical separation of the battery cell materials in step  10 , liberation and sieving of the cathode and anode materials in step  20 , and two stage froth flotation in step  30  to separate the cathode material from the anode material. The separated cathode material is re-lithiated in step  40  for reuse as active cathode material. Further, a sintering step  50  may be performed to improve the physical structure of the material. 
     The surface impurities or impure surface layers on the electrode active material cannot be removed or purified by the current direct recycling process. EOL cathode active material is primarily covered by inorganic species such as LiOH, Li 2 O, Li 2 CO 3 , and LiF and organic species such as alkoxides (ROLi), carboxylates (LiO—C═O), alcohols (R—OH), and semi-organic carbonates (RC(═O)OLi). Typically, inorganic species have very resistive characteristics, thereby significantly contributing to cell resistance. Organic species can be dissolved or removed by soaking or rinsing with dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), 1,2-dimeth-oxyethane (DME), etc. However, inorganic species cannot be dissolved or removed easily during the recycling process. 
     These surface impurities or impure surface layers lead to limited electrochemical performance compared with a virgin electrode active material. The battery cell made by the recycled electrode active material shows a very high cell resistance and electrode polarization, thereby diminishing the overall efficiency of the battery when compared with a virgin (unused) electrode active material. This makes the use of recycled electrode material unappealing. 
     Proposed herein are recycled electrode active materials having modified surfaces so that battery performance is not a disadvantage when compared with virgin electrode active material. In particular, the materials and processes herein focus on recycled cathode active material for lithium-ion batteries. 
     The processes and materials herein convert the inorganic species to species that enhance the electrochemical performance of the cathode active material. The recycled cathode active material is regenerated or re-functionalized with lithium-conducting species. The regenerated cathode active material, when used in a battery, compared to recycled cathode active material, reduces cell resistance, has better rate capability, and has longer-term durability (i.e., cyclability). When the regenerated cathode active material is used in a solid-state battery, interfacial resistance between cathode particles and solid electrolyte particles is reduced due to the layer of multiple lithium-ion conductors on the regenerated cathode active material. The regenerated cathode active material has better surface structure stability due to the surrounding multiple lithium-ion conductors. The multiple lithium-ion conductors protect the core of the regenerated cathode active material from severe etching/corrosion by the acidic species in the electrolyte, as well as reducing oxidation of the electrolyte at high voltage. Thus, the regenerated cathode active material can be adopted for use in high-voltage battery cells. The method of regeneration proposed herein is environmentally friendly and cost-effective, compared to traditional recycling techniques. 
     As disclosed herein, a regenerated cathode active material for use in a lithium-ion battery comprises a core material comprising a transition metal oxide and lithium, the core material having a surface, and multiple lithium-ion conducting species on the surface, wherein the core material is a recycled cathode active material that has been re-lithiated. The core material can be any cathode active material known to those skilled in the art for use in a lithium-ion battery, such as LiCoO 2 , LiMn 2 O 4 , LiMnO 2 , LiNiO 2 , LiFePO 4 , LiNiCoMnO 2 , LiNiCoAlO 2 , and LiNi 0.5 Mn 1.5 O 4  as non-limiting examples. 
     An exemplary method of making the regenerated cathode active materials disclosed herein is illustrated in  FIG. 2 . The method  100  is performed on a cathode active material removed from an end-of-life lithium-ion battery, recycled with a direct recycling process, and re-lithiated, as illustrated in  FIG. 1 . The cathode active material provided in step  110  is comprised of a core material having a surface on which organic species and inorganic species exist, the inorganic species selected from LiOH, Li 2 CO 3 , Li 2 O and LiF. The cathode active material is rinsed with a solvent in step  120  to remove the organic species from the surface of the cathode active material. 
     After removing the organic species, the inorganic species LiOH and Li 2 O are either converted to Li 2 CO 3  and LiF in step  130  or removed in step  140 , leaving only Li 2 CO 3  and LiF. Step  130  can be performed by heating the cathode active material in step  132  to a temperature of ≥700° C. and ≤1000° C. in a hydrogen atmosphere to convert LiOH to Li 2 O and then reacting with carbon dioxide in step  134  at a temperature of ≥400° C. and ≤700° C. to convert Li 2 O to Li 2 CO 3 , resulting in the cathode active material having Li 2 CO 3  and LiF as most or all remaining inorganic species. In step  140 , the LiOH and Li 2 O can be removed from the surface by dissolving in water in step  142 , resulting in the cathode active material having Li 2 CO 3  and LiF as most or all remaining inorganic species. The Li 2 CO 3  and LiF are converted to lithium-ion conducting species in step  150  by reacting with one or more of aluminum, a metal oxide and a phosphate using a solid-state reaction. Step  150  is performed by selecting one or more of aluminum, the metal oxide and the phosphate as the converting material, forming a mixture by mixing the converting material with the cathode active material, wherein an amount of the converting material is 1.0 wt % to 5.0 wt % of the cathode active material and has a diameter of between 1.0 nm and 100 nm, inclusive and calcining the mixture at a temperature of between ≥600° C. and ≤1100° C. for a period of time. 
       FIG. 3  is an example schematic of a regenerated cathode active material for use in a lithium-ion battery. The regenerated cathode active material  200  comprises a core material  210 , shown in cross section, comprising lithium and a transition metal oxide. The core material is a recycled cathode active material that has been re-lithiated, such as the core of the material resulting from the process in  FIG. 1 , without the surface impurities. The core material has a surface  220  on which are at least two different lithium-ion conducting species  230 ,  240 . The at least two different lithium-ion conducting species are selected from AlF 3 , Li 3 PO 4 , and a lithium metal oxide. 
     The lithium-ion conducting species  230 ,  240  may cover any portion of the surface  220  of the core material  210 . For example, the lithium-ion conducting species  230 ,  240  may cover a majority or the surface  210 , or may cover nearly the entire surface  220 , creating a so-called coating on the surface  220 . The lithium-ion conducting species  230 ,  240  can be non-uniformly positioned on the core material  210  such that a portion of the surface  220  of the core material  210  is exposed. 
     The regenerated cathode active material  200  in  FIG. 3  is provided for illustrative purposes and is not drawn to scale. The core material  210  can have a particle size ranging between 5.0 and 25.0 micron, inclusive, and the lithium-ion conducting species  230 ,  240  can have a particle size ranging between 1.0 nm and 100 nm, inclusive. 
     To produce a regenerated cathode active material  200  having lithium-ion conducting species of AlF 3  and a lithium metal oxide, in step  150 , the LiF is reacted with aluminum to produce AlF 3  and the Li 2 CO 3  is reacted with a metal oxide to produce a lithium metal oxide. Examples of metal oxides include SiO 2 , Al 2 O 3 , ZrO 2 , or TiO 2  with the respective lithium metal oxide being Li 4 SiO 4 , LiAlO 2 , Li 2 ZrO 3 , or Li 2 TiO 3 . 
     To produce a regenerated cathode active material  200  having lithium-ion conducting species of AlF 3  and Li 3 PO 4  and a lithium metal oxide, in step  150 , the LiF can be reacted with AlPO 4  to produce AlF 3  and Li 3 PO 4  and the Li 2 CO 3  is reacted with a metal oxide to produce a lithium metal oxide. Examples of metal oxides include SiO 2 , Al 2 O 3 , ZrO 2 , or TiO 2  with the respective lithium metal oxide being Li 4 SiO 4 , LiAlO 2 , Li 2 ZrO 3 , or Li 2 TiO 3 . 
     To produce a regenerated cathode active material  200  having lithium-ion conducting species of AlF 3  and Li 3 PO 4 , in step  150 , the LiF and the Li 2 CO 3  can be reacted with AlPO 4  to produce AlF 3  and Li 3 PO 4 . 
     When removing LiOH and Li 2 O from the surface by dissolving in water, as in step  140 , rather than converting LiOH and Li 2 O to additional LiF and Li 2 CO 3  as in step  130 , additional surface  220  of the core material  210  is exposed. Depending on the amount of LiOH and Li 2 O removed, the amount of exposed surface area will vary. To further increase the lithium-ion conduction, the exposed portions of the surface  220  can be coated with a lithium-ion conducting material. The additional coating can be a material that is the same or different from the lithium-ion conducting species. As non-limiting examples, the coating can be Li 4 SiO 4 , LiAlO 2 , Li 2 ZrO 3 , Li 2 TiO 3 , AlF 3  and Li 3 PO 4 . 
       FIG. 4  is an example schematic of another regenerated cathode active material for use in a lithium-ion battery. The regenerated cathode active material  300  comprises a core material  310 , shown in cross section, comprising lithium and a transition metal oxide. The core material is a recycled cathode active material that has been re-lithiated, such as the core of the material resulting from the process in  FIG. 1 , without the surface impurities. The core material has a surface  320  on which are at least two different lithium-ion conducting species  330 ,  340 . The at least two different lithium-ion conducting species are selected from AlF 3 , Li 3 PO 4 , and a lithium metal oxide. A lithium-ion conducting coating  350  is deposited on the surface  320  where there are no lithium-ion conducting species  330 ,  340 . 
     While the disclosure has been described in connection with certain embodiments, it is to be understood that the disclosure is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.