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.