Covalently anchoring silsesquioxanes layer onto fiber separator for high-rate-charging and long-cycling lithium metal battery

Abstract

The practical application of lithium metal batteries (LMBs) is impeded by the uncontrolled growth of lithium dendrites and the infinite volume expansion of the lithium anode during cycling, which results in low coulombic efficiency and premature failure. Designing a multifunctional separator with abundant ion migration pathways and robust mechanical properties is essential for optimizing ion transport in LMBs. Herein, a mechanically stable hybrid fiber separator is developed by introducing functional octasilsesquioxane (CSQ) layer onto nano/microfibrous polymer separators (EHMs). The lithiophilic –NH and CF groups from the obtained separator increase the electrolyte wettability of the separator and decrease the diffusion barrier for lithium ions. Furthermore, the anchoring CSQ layer established an intimate interfacial mechanical interlock between fibers significantly enhancing the mechanical strength and electrochemical stability of the obtained separator, thereby suppressing lithium dendrites growth to delay the time penetrating through the separator. As a result, the EHM-10 separator exhibits a remarkable Li⁺ transference number (0.84) and ultrawide electrochemical window (5.4 V), as well as a long-term stable reversible Li plating/striping in Li||Li cells (over 2000 h). In addition, the Li||LiFePO₄ cell with EHM-10 separator exhibits superior rate and cycle performance (high discharge specific capacity of 104.2 mAh g⁻¹ after 200 cycles each at 8 C and 10 C). This work demonstrates a feasible and scalable approach towards the advancement of long-life and high-rate lithium metal batteries.