Chemical pressure-stabilized post spinel-NaMnSnO4 as potential cathode for sodium-ion batteries

Spinel LiMn2O4 is a popular cathode material in lithium-ion batteries due to its high operating voltage and reversible specific capacity. Synthesizing analogous NaMn2O4 in the spinel structure, for sodium-ion batteries, is challenging due to the thermodynamic instability of the compound, mostly arising due to Jahn–Teller distortion of the Mn3+ centre. However, post-spinel NaMn2O4 (named as such because the compounds were initially achieved by subjecting a spinel phase to high pressure) could be synthesized at a high temperature and pressure (1373 K and 4.5 GPa, respectively) and is found to be stable at standard conditions. Also, these compounds have a lower ion diffusion barrier than their respective spinels. In this work, an attempt has been made to induce chemical pressure within the system by the use of a heavy cation, i.e., Sn4+ in the framework, to synthesize post-spinel NaMnSnO4 at ambient pressure conditions. The as-prepared NaMnSnO4 samples are characterized with scanning electron microscopy, X-ray diffraction, inductively coupled plasma-atomic emission spectroscopy and galvanostatic cycling with potential limitation measurements.