Study On Cu,Al And Fe Co-doped Li[Ni_1/3Co_1/3Mn_1/3]O₂ Cathode Materials Based On New Methods For Recycling Spent Lithium-ion Batteries

With continuous expansion of lithium-ion batteris?LIBs?service derived from the rapid development of mobile electronic devices and the electric vehicle industry,how to efficiently recycle the spent LIBs has become focus of research in the field of environmental science and resource recycling.The regeneration of Li[Ni Co Mn]_1/3O₂from waste lithium-ion batteries based on wet chemical method has the advantages of short flow and good sustainability.It is one of the most promising methods for the recycling of waste lithium-ion batteries proposed in recent years.Although this method can be used for simultaneous materialization of Ni,Co and Mn in the active materials of spent LIBs,the main impurity elements Cu,Al and Fe in the regeneration system need to be deeply removed,having drawbacks of high cost and secondary pollutions.If Cu,Al,and Fe can be used as useful dopants of Li[Ni Co Mn]_1/3O₂,we can not only further reduce costs and pollutions,but also make this route more in line with the requirements of resource recycling and sustainable development.To this end,it is necessary to evaluate the influence of Cu,Al and Fe co-doping on the structure and electrochemical properties of Li[Ni Co Mn]_1/3O₂.In the present work,the effects of Cu,Al and Fe co-doping on the structure and electrochemical properties of Li[Ni Co Mn]_1/3O₂ were systematic studied by using chemical reagents as raw materials.A series of Ni Co Mn carbonates were prepared by carbonate coprecipitation method,and the precursors were obtained by addition of Li and doping elements according to a certain stoichiometric ratio.The samples of Li[Ni Co Mn]_1/3O₂,Li[Ni Cu_x/3Al_2x/3Co_?1-x?Mn]_1/3O₂?x=0.02,0.04,0.05,0.06,0.07,0.08?,Li[Ni Cu_x/2Fe_x/2Co_?1-x?Mn_1/3]O₂?x=0.04,0.05,0.06,0.07,0.08?,Li[Ni Fe_x/3Al_2x/3Co_?1-x?Mn]_1/3O₂?x=0.04,0.05,0.06,0.07,0.08?and Li[Ni Cu_x/4Fe_x/4Al_x/2Co_?1-x?Mn]_1/3O₂?x=0.02,0.04,0.06,0.08?were synthesized by roasting the precursors at 500°C×5 h+900°C×12 h.The structure and electrochemical properties of samples were tested and analyzed by powder X-ray diffraction?XRD?,scanning electron microscope?SEM?,X-ray energy dispersive spectroscopy?EDS?,cyclic voltammetry?CV?and electrochemical impedance spectroscopy?EIS?,respectively.The XRD patterns indicated that the prepared cathode materials exhibit well crystalline structures.The characteristic diffraction peaks of all samples are well consistent with those of?-Na Fe O₂ reported in the literatures,and there are no obvious impurity peaks,meaning that the doping elements are doped into the matrix lattice.The co-doping of Cu,Al,Fe can reduce the mixed degree of Li/Ni of the samples,and the materials has a good layered structure.The calculation results by‘Scherrer'Equation showed that the primary grain sizes of samples increase first and then decrease with the increase of the doping amount,which indicates that a small amount doping can accelerate the growth of grain,but the excess doping would hinder the crystal growth.SEM images suggested that the powder samples are sphere-like particles,and the size of the particles increases with the increase of the doping amount,and the variation trend agree with that of the average grain size calculated by the XRD data.Micro-doping has a certain inhibitory effect on the agglomeration of the particles,but when the doping amount is excessive,the degree of agglomeration of the particles is increased again.EDS and elemental mapping results showed that the distributions of all elements of samples are uniform.The electrochemical performances of the samplesLi[Ni Cu_x/3Al_2x/3Co_?1-x?Mn]_1/3O₂,Li[Ni Cu_x/2Fe_x/2Co_?1-x?Mn_1/3]O₂,Li[Ni Fe_x/3Al_2x/3Co_?1-x?Mn]_1/3O₂ and Li[Ni Cu_x/4Fe_x/4Al_x/2Co_?1-x?Mn]_1/3O₂ were tested,and found that the best electrochemical performances were obtained at x=0.04,0.05,0.05and 0.04,respectively.At a current density of 0.1 C,the first discharge capacity of the tested samples was 162.1,160.3,161.9,162.3 m Ah·g^-1,respectively.The first discharge capacity of the tested samples was 150.1,150.67,151.52,151.17 m Ah·g^-1at 1 C,wtih capacity retention rate of 91.69%,91.54%,92.79%and 94.28%after 50cycles,respectively.CV and EIS results revealed that such improvements in rate capacity and cycling behaviors are ascribed to the lower charge-transfer resistance,higher Li⁺diffusion coefficient and exchange current density derived from Cu,Al and Fe co-doping.The results suggest that appropriate Cu,Al and Fe co-doping can effectively improve the structural stability and electrochemical properties of Li[Ni Co Mn]_1/3O₂,and the best total amount of Cu,Al and Fe co-doped is 4%of Co.It demonstrates the feasibility of reusing Cu,Al and Fe as the beneficial dopingelements for regenerating cathode materials from spent LIBs,providing an experimental basis and support to simultaneous materialization of the valuable elements in spent LIBs in more sustainable manner.