Symmetric Sodium-Ion Battery Based on Dual-Electron Reactions of NASICON-Structured NaMnTi(PO) Material.

Symmetric sodium-ion batteries possess promising features such as low cost, easy manufacturing process, and facile recycling post-process, which are suitable for the application of large-scale stationary energy storage. Herein, we proposed a symmetric sodium-ion battery based on dual-electron reactions of a NASICON-structured NaMnTi(PO) material. The NaMnTi(PO) electrode can deliver a stable capacity of up to 160 mAh g with a Coulombic efficiency of 97% at 0.1 C by utilizing the redox reactions of Ti, Mn, and Mn. This is the first time to investigate the symmetric sodium-ion full cell using NaMnTi(PO) as both cathode and anode in the organic electrolyte, demonstrating excellent reversibility and cycling performance with voltage plateaus of about 1.4 and 1.9 V. The full cell exhibits a reversible capacity of 75 mAh g at 0.1 C and an energy density of 52 Wh kg. In addition, both X-ray diffraction (XRD) analysis and first-principles calculations are employed to investigate the sodiation mechanism and structural evolution. The current research provides a feasible strategy for the symmetric sodium-ion batteries to achieve high energy density.