Bifunctional sodium tetrakis [3,5-bis(trifluoromethyl)phenyl] borate additive for long-lifespan sodium-ion batteries with NaNi0.33Fe0.33Mn0.33O2 cathode

Sodium-ion batteries (SIBs) are viable contenders for large-scale energy storage systems owing to the plentiful supply of sodium resources. However, the poor stability of electrolyte/ electrode interface severely limits the cycle life of SIBs. Herein, sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaTFPB), a boron-centered fluorinated organic sodium salt, is used as a bifunctional additive in the Base electrolyte (NaPF 6 in EC/DMC/FEC) for NaNi 0.33 Fe 0.33 Mn 0.33 O 2 ||hard carbon pouch cells. Theoretical simulations and experimental studies demonstrate that NaTFPB modulates the first solvation shell structure of Na + and undergoes preferential redox reactions at both electrodes simultaneously. This behaviour contributes to the formation of robust interfacial layers. As a result, uniform and stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) layers, enriched with NaF and boron compounds, are formed. The Ah-scale pouch cell with NaTFPB exhibits a high capacity retention of 79 % after 500 cycles at 1 C rate under room temperature. Remarkably, under harsh operational stress combining elevated temperature (45 °C) and an upper high cutoff voltage of 4.1 V, the cell retains 96 % capacity retention over 250 cycles. Additionally, it exhibits excellent low-temperature discharge capability at −20 °C. This innovative design of functional additive addresses interfacial stability challenges, advancing high-energy–density SIBs for practical applications.