Low Voltage Sodium Intercalation in Na_xNi_x/2Ti_1-x/2O₂(0.5 ≤ x ≤ 1.0)

The Na x Ni x/2 Ti 1-x/2 O 2 (0.5 ≤ x ≤ 1.0) series of layered oxides were found to be remarkably stable to 0 V vs. Na and have a reversible low intercalation voltage plateau at 0.7 V. In situ X-ray diffraction measurements confirmed the low voltage intercalation mechanism. The low voltage plateau increases in capacity as x is decreased with the x = 0.6 composition having a reversible capacity of 100 mAh/g or 394 Ah/L between 0.005 and 2 V. Higher capacities may be possible in materials which can tolerate more vacancies in the sodium layer. Such layered transition metal titanates may represent a new class of negative electrode materials for applications in Na-ion batteries.