Characterization of Na Li_0.67+ Ni_0.33Mn_0.67O₂ as a positive electrode material for lithium-ion batteries

The relationship between the charge-discharge properties and crystal structure of Na Li_0.67+ Ni_0.33Mn_0.67O₂ (0.010 ≤ x ≤ 0.013, 0.16 ≤ y ≤ 0.20) has been investigated. Li/Na Li_0.67+ Ni_0.33Mn_0.67O₂ 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_0.15Li_0.51Ni_0.33Mn_0.67O₂ to 226 mA h g^-1 for Na_0.010Li_0.83Ni_0.33Mn_0.67O₂ with an increase in the Li content. The initial maximum discharge capacity was 252 mA h g^-1 in the case of Na_0.010Li_0.83Ni_0.33Mn_0.67O₂ 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_0.010Li_0.83Ni_0.33Mn_0.67O₂. This study shows that chemical lithiation using LiI is effective to improve the electrochemical properties.