Phase-inversion Induced Co-assembly of Poly(ether imide)/Aramid Nanofibrillar Composite Separators for High-speed Lithium-metal Batteries

Li-metal batteries with high energy capacities and charging rates remain far from practical implementation, mainly due to uncontrollable Li dendrite growth. Herein, we report poly(ether imide)/aramid nanofibrillar (PEI/ANF) composite separators fabricated using the phase-inversion induced co-assembly method, which can effectively suppress dendrite growth. Phase-inversion processes facilitated the co-assembly of PEI agglomerates and self-assembled ANFs into composite nanofibrillar network structures to achieve ultrahigh bulk porosity (>95%) with controlled surface porous structures. Additionally, the unique shapes of the undulated PEI sheaths over the ANF nanofibrils promoted a high surface area of the exposed ether (C−O−C) and carbonyl (C=O) functionality with high affinity to carbonate electrolytes and Li+ and PF6− ions. The resultant films presented enhanced ionic conductivities of up to 3.30 mS cm−1, and a maximum Li+ ion transference number of 0.84. These characteristics promote the formation of compact and stable fluorine-rich solid-electrolyte interphase (SEI) layers on the Li-metal anodes and effectively suppressed Li dendrite growth under extremely high charge/discharge conditions. The Li/Li symmetric cells exhibited stable operation up to 1500 cycles with a high current density of 10 mA cm–2. Moreover, LiFePO4/Li full cells with a high cathode mass loading (6–7 mg cm–2) exhibited a capacity retention of 74.3% after 500 cycles at 10 C-rate (12.0 mA cm−2). The suggested fabrication method would serve as a novel and promising approach for separators in next-generation batteries with high energy density and high C-rate capability.