Enhanced Electrochemical Performance of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode for Lithium-Ion Batteries by Precursor Preoxidation

Nickel-rich layered oxide LiNi0.8Co0.1Mn0.1O2 suffers from severe structural instability, causing inferior electrochemical performance. For a solution to this problem, a Na2S2O8 preoxidation method is employed to modify the surface structure of precursor Ni0.8Co0.1Mn0.1(OH)2. Transmission electron microscopy images show that the lattice orientations of the precursor are well-ordered, and the resulted product LiNi0.8Co0.1Mn0.1O2 with this precursor exhibits a well-defined layered structure without a cation-mixing layer on the surface. X-ray photoelectron spectroscopy and Rietveld refinement results indicate that the contents of Ni2+, Co2+, and Li+/Ni2+ disordering ratio are significantly reduced at the same time. ICP-AES and titration results suggest that the average oxidation state of Ni is enhanced after Na2S2O8 preoxidation. A further electrochemical kinetic analysis using electrochemical impedance spectroscopy and a potentiostatic intermittent titration technique reveals that the LiNi0.8Co0.1Mn0.1O2 sample after precursor preoxidation possesses a fast charge transfer and Li+ diffusion process. It also performs excellent cycling stability and rate capability. Remarkably, the sample with an optimum oxidation time of 30 min (S-NCM-30min) delivers a high discharge capacity of 203.5 mA h g–1 and retains 99.0% capacity after 100 cycles in the voltage range 3.0–4.3 V. The superior electrochemical performance is attributed to the well-ordered surface structure with Na2S2O8 preoxidation, which can suppress the anisotropic shrinkage/expansion and meanwhile stabilize the original layered structure of LiNi0.8Co0.1Mn0.1O2 material during repeated charge–discharge cycling.