Characterization of NaxLi0.67+yNi0.33Mn0.67O2 as a positive electrode material for lithium-ion batteries†
Abstract
The relationship between the charge–discharge properties and crystal structure of NaxLi0.67+yNi0.33Mn0.67O2 (0.010 ≤ x ≤ 0.013, 0.16 ≤ y ≤ 0.20) has been investigated. Li/NaxLi0.67+yNi0.33Mn0.67O2 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 Na0.15Li0.51Ni0.33Mn0.67O2 to 226 mA h g−1 for Na0.010Li0.83Ni0.33Mn0.67O2 with an increase in the Li content. The initial maximum discharge capacity was 252 mA h g−1 in the case of Na0.010Li0.83Ni0.33Mn0.67O2 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 Na0.010Li0.83Ni0.33Mn0.67O2. This study shows that chemical lithiation using LiI is effective to improve the electrochemical properties.