Stable high energy density in orthogonal layered cathode achieved by trace-substitution strategy

Abstract

P′2-type Na0.67MnO2 is considered as one of the most promising cathode materials due to its high theoretical capacities and the low cost of sodium-ion batteries (SIBs). However, the multiple phase transitions and distortion of MnO6 octahedron during Na+ extraction/insertion cause poor structural stability and electrochemical properties. Here, a trace-substitution strategy of electronegative Zn2+ and Ti4+ was applied to balance the high capacity and structural stability. The obtained Na0.67Zn0.04Ti0.06Mn0.9O2 (NZTM4) maintains a high capacity of up to 204.3 and 109 mAh g−1 at 0.1 and 10 C rate, respectively, simultaneously achieving excellent capacity retention of 90.6% after 300 cycles. The Mn-O-Zn-O-Ti local structure formed after Zn incorporation inhibits the distortion of MnO6 octahedron and provides lower activation barrier for Na+ diffusion. With the addition of sodium supplements, this enables a high energy density of 241 Wh kg−1 and satisfactory cycle performance in full cells. These findings provide a promising strategy for designing high-capacity layered cathodes of SIBs.