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.