Study on Na2V0.67Mn0.33Ti(PO4)3 electrodes with ultralow voltage hysteresis for high performance sodium-ion batteries.

This study highlights Na+ ion storage mechanism in a Na 2 Mn 0.33 V 0.67 Ti(PO 4) 3 electrode material with ultralow voltage hysteresis for Na-ion batteries. The electrochemical phase transition and Na+ ion transfer processes are studied by in situ methods during the 1st/2nd cycles. It is found that the fast (de)sodiation process are facilitated by the reversible volume variation in this electrode without structural collapse. [Display omitted] • Mn integration into a Na 2 VTi(PO 4) 3 cathode enlarges Na+ migration pathway. • Mn substitution decreases the voltage hysteresis of redox couples in the NMVTP. • Monophasic + biphasic Na+ storage is discovered by synchrotron radiation diffraction. • Low Na+ migration energy in the NMVTP is proved via DFT and real-time EIS. 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 (Na 2 VTi(PO 4) 3) decreases the voltage hysteresis of the redox couples due to the enlarged migration pathway for mobile Na+ ions. When using Na 2 V 0.67 Mn 0.33 Ti(PO 4) 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 Na 2 V 0.67 Mn 0.33 Ti(PO 4) 3 is a promising material for sodium-ion batteries. [ABSTRACT FROM AUTHOR]