Active Organic Salts Enabling Non-Intrusive Electrolyte Presodiation Strategy.

Abstract

Na-ion batteries show great promise, but their practical utilization is hindered by irreversible Na-ion loss during cell formation, resulting in initial coulombic efficiencies typically below 80%. Conventional presodiation methods, which involve solid additives in the cathode, can compromise electrode integrity and leave deteriorated residues, especially with high Na ion compensation (20%). An electrolyte presodiation approach is introduced that utilizes sodium thiocyanate (NaSCN) as an electrolyte additive, discovered through cheminformatics and machine learning. This organic salt decomposes at 3.3-4.0 V, releasing active Na ions and forming a cosolvent without damaging the electrode and the cell, as confirmed by spectroscopic and microscopic analyses. The method improves the initial coulombic efficiency of a hard carbon|P2-Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂ pouch cell from 80.8% to 95.2%, with a capacity retention of 84.5% over 400 cycles. These findings present a practical and non-intrusive way to address Na-ion deficiency challenges in Na-ion batteries.