Study On Modification And Electrochemical Properties Of Nickel-Rich Layered Cathode Materials For Lithium-Ion Batteries

Nickel-rich layered transition metal oxides are considered to be one of the most promising cathode materials for Li-ion batteries due to their relatively high energy density and low cost.However,the poor rate capability and cycling stability,as well as safety issues stemming from the degradation of its interface and bulk structure seriously hinder its large-scale application.Therefore,in this paper,various modification strategies are used to improve the electrochemical performance of Nickel-rich layered cathode material Li Ni_0.83Co_0.12Mn_0.05O₂.The main research contents are as follows:1.Improving the electrochemical performance of Ni-rich layered cathodes through Mg²⁺uniform doping.A uniform PVP-Mg complex coating layer was constructed on the surface of the precursor,and then the high-temperature lithiation process was carried out to realize uniform doping of Mg²⁺in the Nickel-rich layered cathode materials.The study found that electrochemically inert Mg²⁺occupies the Li layer and acts as a"pillar",which can effectively suppress Li⁺/Ni²⁺cation mixing and lattice distortion,and the NCM-Mg2 sample with Mg doping content of 2 mol%has the best electrochemical performance.At the cut-off potential of 4.3 V,the capacity retention of NCM-Mg2 at 1 C after 100 cycles was 84.6%,which was much higher than 67.9%of the undoped material.when the cut-off potential was increased to 4.5 V,it still had a capacity retention of 73.9%,while the undoped material was only 49.7%.In addition,NCM-Mg2 can still provide a specific discharge capacity of 152.1 m Ah g^-1at a high rate of 10 C.2.Improveing the structural stability and electrochemical performance of Ni-rich layered oxide cathodes via one-step dual modification strategy.The Li Nb O₃ coating layer can regulate the interface and promote the diffusion of Li-ions,and the stronger Nb-O bond can effectively supress Li⁺/Ni²⁺cation mixing amd improve the stability of the crystal structure,thereby inhibiting the generation of microcracks.The research shows that the Ni-rich layered cathode material with dual modification of Nb⁵⁺bulk doping and Li Nb O₃ surface coating exhibits excellent structural stability and electrochemical performance.Among them,the modified material NCM-Nb2 with Nb addition of 1.4 mol%has the best comprehensive electrochemical performance,and still has a capacity retention of 90.8%after 100 cycles at 1 C in the voltage range of2.7-4.3 V,while the unmodified material is only 67.9%.In addition,NCM-Nb2 still exhibits an excellent rate capacibility of 149.1 m Ah g^-1 at a high rate of 10 C.3.Enabling high-rate capacibility and stable cycling of Ni-rich layered cathodes by multi-functional modification strategy.Based on the principle that a dopant with certain characteristics can selectively enter specific lattice site of the material,a multi-functional synergistic modification strategy integrating dual-site Mg/Nb co-doping and in-situ derived Li Nb O₃coating layer is proposed.Studies have shown that the co-modification strategy has more significant advantages than single-element modification in stabilizing the crystal structure and improving the electrochemical and safety performance.The Ni-rich cathode material co-modified with 2.0 mol%Mg and1.4 mol%Nb still exhibits a capacity retention of 84.1%after 200 cycles at 1 C at the cut-off potential of 4.3 V,and the discharge specific capacity is as high as 132.9 m Ah g^-1 at the ultra-high rate of 30 C.Furthermore,the multi-functional modification strategy can also effectively alleviate the grain-level intergranular cracks and structural degradation during long-term cycling.