Over the last decade, sodium-ion batteries are widely pursued as an alternative to Li-ion batteries.  Similar to the Li-ion batteries, the development of sodium batteries rely on discovery and optimization of efficient insertion materials. In this pursuit, polyanionic materials are put on anvil to unravel novel  compounds with descent electrochemical properties and thermal/ chemical stability.  Guided by the inductive effect principle, the redox potential of polyanionic cathodes can be tuned  by playing with the electronegativity of constituent anion units. Here, electronegative SO₄-based materials can deliver the highest redox potential vis-a-vis other polyanionic materials. Based on this principle,  novel Na₂Fe₂(SO₄)₃ alluaudite cathode has been recently reported offering ~100 mAh/g capacity along with high rate kinetics and cycling reversibility [Nature Communications, 5, 4358, 2014]. It marks the highest Fe³⁺/Fe²⁺ redox potential (ca. 3.8 V vs. Na/Na+). We have pursued this high-voltage Na-M-S-O quaternary insertion material system employing low temperature solvothermal synthesis like (i) ionothermal method, (ii) spray drying route and (iii) Pechini synthesis. We will describe these new synthetic routes to obtain alluaudite high-voltage cathode material for sodium-ion batteries. Using these green synthesis routes, we have explored other 3d metal homologues in Na-M-S-O quaternary system. Using experimental and DFT calculations, we will summarise the structure and electrochemical performance of Na-M-S-O quaternary alluaudite cathode materials.