Impact of Electrolyte Composition on the Performance of Na3(VOPO4)2F Cathodes: A Comprehensive Case Study

The performance of rechargeable batteries relies primarily on the formation of a solid electrolyte interface (CEI/SEI) via electrode–electrolyte interactions. Na-ion technology is no exception in this regard. Hence, a major focus of battery research is to identify the most appropriate electrolyte formulation to minimize unwanted interfacial reactions while enhancing cell performance, stability over multiple cycles, and safety. A suitable gold standard for Na-ion battery (NIB) electrolytes is yet to be identified. This investigation presents our effort to identify appropriate electrolyte composition sans additives for pairing with sodium vanadium fluorophosphate (Na3(VO1–xPO4)2F1+2x; 0 ≤ x ≤ 1), one of the most promising cathode materials for NIBs. A series of electrolyte formulations were prepared, and comprehensive physicochemical and electrochemical characterizations were carried out to determine the key parameters, i.e., the ion solvation in the electrolyte, specific conductivity and ion transport behavior, dominant ionic species, electrochemical stability, etc., prior to being tested for their performance against electrodes fabricated using synthesized Na3(VOPO4)2F (NVOPF). The impact of all six select electrolyte compositions on the specific capacity, reversibility, charge retention, stability and C-rate capability were investigated in detail. The comparative appraisal of electrode–electrolyte pairs on performance, the key inferences drawn, influence on the CEI/SEI layer, operational feasibility and cyclability of the NVOPF electrodes against each electrolyte composition were rationalized with the end-of-life cycle analysis that provided key insights to preserve the structural integrity of electrodes over multiple cycles.