The essence of this work lies in the large-scale production of high-quality graphene sheets and simultaneous functionalization with new electrochemical route. A multifunctional flame retardant with phosphazene rings is well designed to simultaneously exfoliate and functionalize graphene. Due to the antioxidant function of flame retardant, the electrochemically-exfoliated graphene sheets exhibit high quality and low defect (C/O = 10.4). Furthermore, the obtained graphene is noncovalently modified to form flame retardant functionalized graphene sheets (FGNS). Subsequently, the FGNS is applied to improve fire safety and mechanical performance of thermoplastic polyurethane (TPU). Compared to pure sample, the peak heat release rate and total heat release of TPU composites with the addition of 4 wt% FGNS are significantly decreased by 463% and 20.2%, respectively. The elongation at break and tensile strength of TPU are enhanced by 11.6% and 59.9%, respectively, with the addition of 2.0 wt% FGNS. The significant enhancement in fire safety is due to conjunct effects of FGNS and the flame retardant. Lower defect of graphene provides more stable layer structure, thus FGNS plays a remarkable barrier action to confine the escape of degradation products. The coated flame retardant is conducive to form compact and robust char residue by reacting with degradation products. In addition, the flame retardant facilitates the load transfer to the robust graphene sheets with improved interface interaction. Through an electrochemical route, designing a multifunctional flame retardant to simultaneously exfoliate and modify graphene provides new possibility for the industrialized application of graphene. (C) 2017 Elsevier B.V. All rights reserved.