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 affinity. 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 separators 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 (∼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.