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. R 3̄ m ). 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.