Coordinated self-assembly of ultraporous 3D aramid nanofibrous separators with a poly(vinyl alcohol) sheath for lithium-metal batteries

Li-metal batteries with a low negative/positive electrode capacity ratio require significant improvement to ensure their practical implementation as high-energy-density batteries. In the present study, ultraporous aramid nanofiber (ANF) separators with a poly(vinyl alcohol) (PVA) sheath were fabricated using a coordinated self-assembly process to produce an ultrahigh bulk (>95 %) and surface (>48.6 %) porosity and a high ion affin-ity. In this process, sol films consisting of an optimized mixture of aramid nanoseed sols and PVA were sequentially immersed in ethanol and water to induce the formation of a 3D aramid network and the phase separation of PVA by their rate differences, followed by swelling-induced pore formation. The resulting sepa-rators exhibited an excellent ion conductivity and Li+ ion transference number of up to 2.73 mS cm(-1) and 0.78, respectively, with the effective suppression of Li dendritic growth and the formation of a stable fluorine-rich solid electrolyte interphase (SEI) layer on the Li-metal surface. Li/Li half cells exhibited stable operation for up to 1500 cycles with a high current density of 10 mA cm(-2) and an areal capacity of 1 mAh cm(-2), with Li/Cu half cells operating for over 244 cycles even with a lithiophobic Cu current collector. LFP/Li full cells with a low N/P ratio (similar to 2.03) exhibited stable operation for 172 cycles with an average Coulombic efficiency of 99.6 %. NCM/Li full cell with extremely low N/P ratio (0.96) and lean electrolyte condition (4 g Ah(-1)) stably operated for 55 cycles with projected energy density of 350.7 Wh kg(-1).