Antimony Ethoxide as a Flame-Retardant Synergist for Enhancing the Safety of Lithium-Ion Batteries

The flammability of organic electrolytes remains a critical safety challenge for lithium-ion batteries (LIBs), often addressed by adding large amounts of fluorinated flame retardants. However, excessive fluorides compromise ionic conductivity and raise environmental concerns. Herein, we report antimony ethoxide (Sb(OEt) 3 ), a liquid organoantimony compound, as an effective flame-retardant synergist. Only 0.5 vol % Sb(OEt) 3, combined with 5 vol % fluoroethylene carbonate (FEC), enhances electrolyte flame resistance without compromising electrochemical performance. Thermal decomposition of Sb(OEt) 3 yields Sb 2 O 3, which catalyzes the defluorination of FEC by reducing the energy barrier for fluorine radical (F • ) generation, thereby disrupting combustion chain reactions and suppressing flame propagation. Moreover, the addition of Sb(OEt) 3 improves the cycling stability and rate performance of Li–graphite (Gr) and Li–LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cells. A practical 3 Ah Gr–NCM811 pouch cell using this electrolyte demonstrates capacity retention of 85.6% after 500 cycles. Nail penetration and accelerating rate calorimetry (ARC) tests further confirm the flame-retardant synergistic effect of Sb(OEt) 3 .