| LiNi0.83Co0.11Mn0.06O2(NCM83),a high-nickel layered cathode material for lithium-ion batteries,is one of the most promising cathode materials for power lithium-ion batteries due to its high energy density,high voltage platform,and good rate performance.However,during the charge-discharge cycle,its widespread commercial application has been severely hampered by the inherent issues of rapid capacity decay brought on by the collapse of the cathode material structure,phase transformation,and interface side reactions.In this study,the structural stability and electrochemical performance of the NCM83 cathode materials were improved from the preparation and synthesis process,element bulk phase doping,and surface modification strategies,with the goal of addressing the issue of the high-nickel layered cathode material’s rapid capacity decay during the cycling process.Mechanical ball milling was used to mix the precursor and lithium source uniformly.The differences in structure,morphology and electrochemical properties of NCM83 cathode materials prepared under different initial Li/TM ratio and sintering temperature were investigated.Structure analysis and electrochemical testing were used to identify the NCM83 cathode materials’ ideal synthesis parameters.The NCM83 cathode materials have the best stable layered crystal structure and the lowest lithium nickel mixed ratio.It was created at a sintering temperature of 800℃ and an initial Li/TM ratio of 1.05.At 0.2 C rate,the initial discharge specific capacity can increase to 195.48 mAh g-1,and the medium voltage drop during the discharge process from 0.2 C to 5.0 C is only 0.125 V.By using a straightforward solid phase method,the nano-nobium source was added to the structure of the NCM83 cathode materials,yielding a niobium-modified version of the material with a Li3NbO4 surface coating and Nb5+bulk phase doping.Both before and after the modification,the materials’ structure and surface morphology remained largely unchanged.The degree of electrode polarization and the disorder of Li+/Ni2+cations are both significantly decreased by the addition of Nb5+.The NCM83 cathode materials with 1.0 mol%niobium modification have the lowest 1%miscibility of lithium and nickel.At 0.2 C rate,the first discharge has a specific capacity of 211.83 mAh g-1 and a coulomb efficiency of 84.91%.The Nb-O bond has a higher dissociation energy than the chemical bond formed by the transition metal and oxygen,demonstrating that the niobium modification has contributed to the stabilization of the lattice and greatly enhancing cycle stability of the NCM83 cathode materials,which has the highest capacity retention rate of 86.55%after 100 cycles at 1.0 C.Based on the modification of niobium,the surface of the cathode materials were coated with conductive polyaniline using a wet chemical process.As a result,the NCM83 cathode materials with niobium doping and polyaniline coating were produced.When niobium and polyaniline are modified in the amounts of 1.0 mol%and 1.0 wt%,respectively,the modified sample has a first discharge specific capacity of 236 mAh g-1 at 0.2 C rate in the voltage range of 2.7-4.4 V,a capacity retention rate of 84.44%after 100 cycles at 2.0 C rate,and a lithium ion diffusion coefficient that ranges from 2.70 ×10-11 cm2 s-1 to 1.42 ×10-10 cm2 s-1.The polyaniline coating’s good chemical stability and conductivity,which can simultaneously improve the cycle stability and rate discharge capacity,are the basis for achieving the effect of niobium modification.The first discharge capacity can still reach 155 mAh g-1 even under the test conditions of 2.7-4.5 V and 10.0 C,and can maintain 77.06%of the initial capacity when the cycle reaches the 100th cycle.The surface polyaniline coating can minimize the irreversible capacity loss of the NCM83 cathode materials in the long cycle by preventing direct contact between the material and the electrolyte,effectively inhibiting the interface side reaction,and the surface phase transformation process. |
PDF Full Text Request