“…[8] Several different categories of compounds have been investigated as potential cathode materials. These include layered oxides, [9][10][11][12] polyanionic compounds, [13][14][15][16] Prussian blue analogs, [17,18] and some organics. [19,20] Among them, layered transition-metal (TM) oxides Na x TMO 2 (TM, TM ═ Fe, Mn, Ni, Co, Cr, Ti, V, Cu, and their combinations, 0 < x ≤ 1, the most common structures of Na x TMO 2 are P2, P3, and O3) have been extensively exploited due to their high capacities, good stability, and simple synthesis procedures, and are thus extensively being exploited.…”