Enhanced\nElectrochemical Performance of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode for Lithium-Ion Batteries by Precursor\nPreoxidation

Abstract

Nickel-rich layered\noxide LiNi_0.8Co_0.1­Mn_0.1O₂ suffers from severe structural instability, causing inferior\nelectrochemical performance. For a solution to this problem, a Na₂S₂O₈ preoxidation method is employed\nto modify the surface structure of precursor Ni_0.8Co_0.1­Mn_0.1(OH)₂. Transmission electron\nmicroscopy images show that the lattice orientations of the precursor\nare well-ordered, and the resulted product LiNi_0.8Co_0.1­Mn_0.1O₂ with this precursor\nexhibits a well-defined layered structure without a cation-mixing\nlayer on the surface. X-ray photoelectron spectroscopy and Rietveld\nrefinement results indicate that the contents of Ni²⁺,\nCo²⁺, and Li⁺/Ni²⁺ disordering ratio\nare significantly reduced at the same time. ICP-AES and titration\nresults suggest that the average oxidation state of Ni is enhanced\nafter Na₂S₂O₈ preoxidation. A further\nelectrochemical kinetic analysis using electrochemical impedance spectroscopy\nand a potentiostatic intermittent titration technique reveals that\nthe LiNi_0.8Co_0.1­Mn_0.1O₂ sample after precursor preoxidation possesses a fast charge\ntransfer and Li⁺ diffusion process. It also performs excellent\ncycling stability and rate capability. Remarkably, the sample with\nan optimum oxidation time of 30 min (S-NCM-30min) delivers a high\ndischarge capacity of 203.5 mA h g^–1 and retains\n99.0% capacity after 100 cycles in the voltage range 3.0–4.3\nV. The superior electrochemical performance is attributed to the well-ordered\nsurface structure with Na₂S₂O₈ preoxidation,\nwhich can suppress the anisotropic shrinkage/expansion and meanwhile\nstabilize the original layered structure of LiNi_0.8Co_0.1­Mn_0.1O₂ material during repeated\ncharge–discharge cycling.