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 Sb2O3, 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–LiNi0.8Co0.1Mn0.1O2 (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.