An ultrathin phase-inversion induced co-assembly separator for high-performance lithium-metal batteries

Lithium metal batteries (LMBs) have been regarded as promising electrochemical energy storage systems due to the high theoretical specific capacity of metallic lithium. However, the uncontrolled growth of lithium dendrites, stemming from uneven lithium deposition, poses a significant challenge to their practical implementation. To tackle this issue, an ultra-thin composite separator, consisting of octamethacryloyloxy sesquioxane (MA-POSS), methacryloyloxy trimethoxysilane grafted holey graphene oxide (MPS-HGO), and aramid nanofibers (ANF), was prepared through a combination of phase transition-induced co-assembly and in situ polymerization techniques. Experiments indicate that the composite separator, with a thickness of only 3.8 μm, exhibits exceptional mechanical properties, specifically a tensile strength of 104 ± 5.1 MPa and a modulus of 3.23 ± 0.2 GPa, due to extensive hydrogen bonding and π-π interactions between the HGO sheets and ANF. Furthermore, benefiting from the synergistic effect of the abundant pores in MPS-HGO and the inhibition of stacking through the copolymerization of MPS-HGO and MA-POSS, the composite separator also demonstrates good electrolyte infiltration and a high lithium-ion transport number (t_Li⁺ = 0.87), which not only acts as a physical obstacle but also efficiently regulates Li-ion transport to hinder irregular dendritic growth. The simultaneous regulation of Li-ion transport and mitigation of dendrite growth resulted in a long cycle life for Li|Li cells without dendrite deposition after 1500 cycles at a high current density of 5 mA cm⁻². Moreover, the LiFePO₄ (LFP)|Li battery with the composite separator displayed a capacity of 154 mA h g⁻¹, a coulombic efficiency of 99%, and a high capacity retention of 99.6% after 250 cycles at 0.5C (85.7% after 1000 cycles at 2C). This work provides a promising new approach to fabricating high-performance lithium battery separators.