Study on Na₂V_0.67Mn_0.33Ti(PO₄)₃ electrodes with ultralow voltage hysteresis for high performance sodium-ion batteries

The Na superionic conductor (NASICON) is one of the promising electrode materials used in advanced Na-based secondary batteries, but designing a low-overpotential structure is crucial for developing NASICON-type electrodes to repress voltage hysteresis and reduce energy loss. In this study, the integration of Mn³⁺ into a NASICON-type material (Na₂VTi(PO₄)₃) decreases the voltage hysteresis of the redox couples due to the enlarged migration pathway for mobile Na⁺ ions. When using Na₂V_0.67Mn_0.33Ti(PO₄)₃ as cathode material, two Na⁺ ions can be extracted from the structure, leading to the specific capacity of 110 mAh g⁻¹ at the current density of 0.1 C. In operando synchrotron radiation diffraction elucidates that there is a combination of mono- and biphasic mechanisms for reversible Na⁺ insertion/extraction within initial two cycles. Moreover, fast sodium diffusion in the NMVTP electrode has been measured and analysed via first-principles calculation and real-time impedance spectroscopy. The results of this work indicate that Na₂V_0.67Mn_0.33Ti(PO₄)₃ is a promising material for sodium-ion batteries.