Electrophilic fluoroalkyl radical-intermediates enabled organic sulfinate electrolyte additives for sodium-ion supply

Na-ion batteries face a critical 10–20% initial capacity loss due to the low initial Coulombic efficiency of hard carbon anodes. While Na-ion supply additives can replenish these losses, their design demands precise optimization of electrochemical potential, decomposition pathways, and residue-free integration, which are unmet by current molecules. Here, we utilized substituent-driven molecular engineering of sodium sulfinates to develop sodium trifluoromethanesulfinate (NaSO 2 CF 3 ) as an electrolyte additive for effective Na-ion supply. The strong electron-withdrawing trifluoromethyl (–CF 3 ) group reduces the binding energy between Na ions and anions, thereby enhancing solubility and enabling oxidative decomposition at 3.65 V via CF 3 SO 2 · intermediates. The electrophilic cleavage of these intermediates released Na ions and gaseous byproducts, SO 2 and C 2 F 6 , which are harmlessly expelled during cell formation. Successful Na-ion supply was demonstrated in hard carbon|NVP-Na 3 V 2 (PO 4 ) 3 pouch cells, where the initial Coulombic efficiency improved from 82.6% to 96.0% and extended cycle life beyond 600 cycles. This strategy extends to various cathode materials, including P2-Na 2/3 Ni 1/3 Mn 1/3 Ti 1/3 O 2 , O3-NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , and PW-Na 2 Mn[Fe(CN) 6 ], thereby establishing a universal molecular design paradigm to mitigate Na ions loss. • Substituent-driven molecular engineering and DFT calculations were employed to develop NaSO 2 CF 3 as an electrolyte additive for effective Na-ion supply. • The electron-withdrawing effect of the trifluoromethyl group enhances the solubility of sodium sulfinate and imparts suitable oxidation potential along with favorable decomposition products. • This Na-ion supply method enhances the initial Coulombic efficiency of Na-ion batteries, leaves no residue in the battery system, and demonstrates broad applicability.