Development of stable electrode-electrolyte interfaces with multifunctional flame-retardant microspheres for safe, high-voltage, and high-energy-density lithium batteries

Polyethylene oxide (PEO) organic solid electrolyte is regarded as one of the important research directions of next-generation battery technology due to its good electrode interface compatibility, mechanical flexibility, and economic processability. However, the low ionic conductivity, limited electrochemical stability, and flammability of PEO have restricted its large-scale application. This work reports the synthesis of multifunctional flame-retardant microspheres (HCCP-THEIC, HT) using hexachlorocyclotriphosphazene (HCCP) and 1,3,5-tris(2-hydroxyethyl) isocyanurate (THEIC), and subsequently incorporation into PEO. It has been demonstrated that the crystallinity of PEO is reduced under the synergistic effect of physical hindrance from HT and the weak intermolecular hydrogen-bond interactions between HT and PEO. This promotes the dissociation of lithium salts, leading to an increase in the mobility and concentration of free Li + , thereby expanding the electrochemical window to 4.7 V. More importantly, HT stabilizes the electrode-electrolyte interface, promotes the formation of stabilized constituents in both the SEI (solid electrolyte interphase) and CEI (cathode electrolyte interphase) layers, and effectively suppresses lithium dendrites growth. The LiNi₀.₈Mn₀.₁Co₀.₁O₂ (NCM811)//Li cell retains 77.4 % of its capacity after 100 cycles at 4.3 V and 0.5C. Additionally, HT enhances fire safety through free radical scavenging and condensed-phase carbonization, reducing the heat release of pouch batteries by approximately 10 %. This simple and scalable HT synthesis offers a promising approach for producing safe, high-performance, and stable all-solid-state lithium metal batteries.