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

Abstract

The Li-based layered nickel-tin oxide Li0.35Na0.07Ni0.5Sn0.5O2has been synthesizedviaelectrochemically-driven Li+for Na+exchange in O3-NaNi0.5Sn0.5O2. The crystal structure of Li0.35Na0.07Ni0.5Sn0.5O2was 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 Li2MO3oxides. As supported by bond-valence sum and density functional theory calculations, this ordering is driven by charge difference between Ni2+and Sn4+and the necessity to maintain balanced bonding for the oxygen anions. Li0.35Na0.07Ni0.5Sn0.5O2demonstrates reversible electrochemical (de)intercalation of ∼0.21 Li+in the 2.8-4.3 Vvs.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.