Characterization of Na x Li 0.67+ y Ni 0.33 Mn 0.67 O 2 as a positive electrode material for lithium-ion batteries.

The relationship between the charge-discharge properties and crystal structure of Na x Li 0.67+ y Ni 0.33 Mn 0.67 O 2 (0.010 ≤ x ≤ 0.013, 0.16 ≤ y ≤ 0.20) has been investigated. Li/Na x Li 0.67+ y Ni 0.33 Mn 0.67 O 2 cells exhibit gradually sloping initial charge and discharge voltage-capacity curves. The initial charge capacity increased from 171 mA h g -1 for thermally-treated Na 0.15 Li 0.51 Ni 0.33 Mn 0.67 O 2 to 226 mA h g -1 for Na 0.010 Li 0.83 Ni 0.33 Mn 0.67 O 2 with an increase in the Li content. The initial maximum discharge capacity was 252 mA h g -1 in the case of Na 0.010 Li 0.83 Ni 0.33 Mn 0.67 O 2 between 4.8 and 2.0 V at a fixed current density of 15 mA g -1 (0.06C) at 25 °C. The predominance of the spinel phase leads to the high initial discharge capacity of Na 0.010 Li 0.83 Ni 0.33 Mn 0.67 O 2 . This study shows that chemical lithiation using LiI is effective to improve the electrochemical properties.