Effects of scandium doping on the electrochemical performance of cathode materials Na3MnTi(PO4)3 for sodium-ion batteries

A lately proposed NASICON-structured Na3MnTi(PO4)3 (NMTP) provides a promising solution that enables a large theoretical specific capacity and a high voltage discharge platform. However, it encounters a difficulty in electronic conductivity which obstructs its further implements. Herein, in this work we propose the Sodium-ion battery cathode materials Na3Mn1−xScxTi(PO4)3/C with different Sc contents (x = 0, 0.01, 0.03, 0.05, 0.07, 0.1), a potential cathode material for sodium-ion batteries with typical three-dimensional NASICON structure were synthesized by sol-gel method aiming to address the problem. Doping of Sc3+ in the NMTP structure was proved by powder X-ray diffraction and energy dispersive X-ray spectroscopy techniques. Impedance spectroscopy and galvanostatic intermittent titration technique results suggest that appropriate-proportion doping has dramatically enhanced the electrical conductivity and Na ion migration of the NMTP matrix. Na3Mn0.95Sc0.05Ti(PO4)3 exhibited a higher initial discharge specific capacity (123 mA h /g at 0.2 C, 111 mA h /g at 1 C) and the highest cycling stability (capacity retention of 93% after 250cycles at 0.2 C, capacity retention of 88% after 500 cycles at 1 C). In addition, Electrochemical Impedance Spectroscopy and X-ray diffraction tests revealed the reasons for the improved cycling stability of the materials due to doping. Furthermore, Na3Mn0.95Sc0.05Ti(PO4)3//hard carbon full cells also demonstrates ideal electrochemical properties.