Manganese-based NASICON structured Na1+2Mn Ti2-(PO4)3 as promising cathode in aqueous sodium ion battery

Herein, a series of manganese-based NASICON structured Na1+2xMnxTi2-x(PO4)3 (x = 1, 1.2, 1.4, denoted as NMTP, NM1.2T0.8P and NM1.4T0.6P) are obtained by sol-gel method and employed as cathodes for an aqueous sodium ion battery (ASIB). There is no obvious difference in structure among these samples, except for a small amount of impurity phase detected in NM1.4T0.6P. Three as-prepared samples exhibit impressive electrochemical performances, thereinto NM1.2T0.8P possesses the best electrochemical performance with the proper operating potential. NM1.2T0.8P delivers a discharge specific capacity of 68.2, 60.3, 52.2, 45.9 mAh g−1 at 1, 2, 5, 10 C, and still maintain 62.8 mAh g−1 when the current density returns to 1 C. Meanwhile, long-term cycling performance test shows that NM1.2T0.8P displays an initial discharge capacity of 46.4 mAh g−1 and still retains a reversible capacity of 39.1 mAh g−1 at 10 C rate after 300 cycles. Cyclic voltammetry demonstrates that both the diffusion and pseudocapacitance determine the sodium-ion (Na-ion) storage mechanism of NM1.2T0.8P and the pseudocapacitance dominates the charge/discharge processes. Besides, a cathode-limited full cell with NM1.2T0.8P cathode and NaTi2(PO4)3 anode was assembled and shows excellent long-term cycling performance with a capacity retention ratio of 81.9 % at 10 C after 200 cycles. This exploration of manganese-based NASICON structured Na1+2xMnxTi2-x(PO4)3 provides an option for cathode materials of ASIB.