Li-based layered nickel–tin oxide obtained through electrochemically-driven cation exchange

The Li-based layered nickel-tin oxide Li(0.35)Na(0.07)Ni(0.5)Sn(0.5)O(2) has been synthesized via electrochemically-driven Li(+) for Na(+) exchange in O3-NaNi(0.5)Sn(0.5)O(2). The crystal structure of Li(0.35)Na(0.07)Ni(0.5)Sn(0.5)O(2) was Rietveld-refined from powder X-ray diffraction data (a = 3.03431(7) Å, c = 14.7491(8) Å, S. G. R3̄m). It preserves the O3 stacking sequence of the parent compound, but with ∼13% lower unit cell volume. Electron diffraction and atomic-resolution scanning transmission electron microscopy imaging revealed short-range Ni/Sn ordering in both the pristine and Li-exchanged materials that is similar to the “honeycomb” Li/M ordering in Li(2)MO(3) oxides. As supported by bond-valence sum and density functional theory calculations, this ordering is driven by charge difference between Ni(2+) and Sn(4+) and the necessity to maintain balanced bonding for the oxygen anions. Li(0.35)Na(0.07)Ni(0.5)Sn(0.5)O(2) demonstrates reversible electrochemical (de)intercalation of ∼0.21 Li(+) in the 2.8–4.3 V vs. Li/Li(+) potential range. Limited electrochemical activity is attributed to a formation of the surface Li/Ni disordered rock-salt barrier layer as the Li(+) for Na(+) exchange drastically reduces the energy barrier for the Li/Ni antisite disorder.