Modification And Lithium Storage Performance Of Ni-rich LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials

Based on the resource utilization of nickel-cobalt slag in Xinjiang,the thesis studied the“optimized treatment of impurity elements”.Because the slag contained many impurity elements,the thesis took Li Ni_0.8Co_0.1Mn_0.1O₂（NCM811）as the research object,and adopted the traditional“additive”doping method to explore the effect of dual-element doping on the lithium storage performance of Ni-rich cathode materials.The researches provide data supporting for the“differential purification”of impurity elements in slag.The specific research contents are as follows:（1）Li Ni_0.8Co_0.1Mn_0.08Mg_0.01Al_0.01O₂（NCM-MA）cathode material was synthesized by co-precipitation method in the work.The research results showed that Mg²⁺/Al³⁺co-doping could effectively inhibit the Li⁺/Ni²⁺mixing,stabilize the lattice oxygen,and maintain a well-ordered layer structure.After 200 cycles at 1 C,the capacity retention rates of NCM and NCM-MA were 61.23%and 72.23%,respectively.Even after450 cycles,the capacity retention of NCM-MA was improved by 12.5%,indicating that Mg²⁺/Al³⁺co-doping improved the structural stability of the material.This could be attributed to the strong Al-O bond suppressing the overflow of lattice oxygen,and the“pillar”effect of Mg²⁺at the Li⁺sites.At the same time,NCM-MA showed good rate capability,which was due to the suppression of the side reaction between the lattice oxygen and the electrolyte.The side-products on the particle surface was reduced,which improved the transfer rate of ions and electrons on the interface,thereby improving its rate capability.（2）Ni_0.8Co_0.1Mn_0.09Mg_0.01（OH）₂ precursor was prepared by co-precipitation method.The precursor was grounded with NH₄H₂PO₄（1%）and an appropriate amount of lithium salt,and then calcined to obtain Mg²⁺/PO₄^3-co-doped cathode material（NCM-PM）.Since the bond energy of Niⁿ⁺-PO₄^3-was greater than that of Niⁿ⁺-O^2-,and the steric hindrance of Mg²⁺in the lithium layer was relatively large,the co-doping of Mg²⁺/PO₄^3-greatly inhibited the migration of transition mental ions.Atomic occupancy refinement showed that the degree of Li⁺/Ni²⁺mixing in NCM-PM was reduced by 69%,which was beneficial to improve the structural stability of the material.Therefore,after 100 cycles at 1 C,the capacity retention of NCM was improved from 71.6%to 84%,and the voltage decay was suppressed.At the same time,due to the stabilizing effect of PO₄^3-on lattice oxygen,the content of residual alkali on the surface of the material was reduced.That improves the transport rate of ions and electrons on the interface.Therefore,even at 5 C,the discharge specific capacity of NCM-PA was still as high as 148.3 m Ah/g,which was 44.6 m Ah/g higher than that of the pristine material.（3）Al³⁺/PO₄^3-co-doped cathode material（NCM-PA）was prepared by co-precipitation and calcination method.The atomic occupancy refinement showed that the Li⁺/Ni²⁺mixing in NCM and NCM-PA were9.08%and 4.06%,respectively,which proved that Al³⁺and PO₄^3-co-doping could effectively suppress the Li⁺/Ni²⁺mixing,and maintain the well-ordered layered structure of cathode materials.Therefore,the capacity retention rate of NCM-PA was improved by 14.1%after 100cycles at 1 C,and its voltage decay was only 1/7 of the pristine material.XPS test showed that Al³⁺and PO₄^3-co-doping could inhibit the release of lattice oxygen,and reduced the residual alkali on the surface of the material.The less by-product on the surface could reduce the transfer resistance of ions and electrons,thus the rate capability was improved.