An ingenious double-modified strategy to prepare a “hexagonal warrior” separator for lithium metal batteries†

Abstract

Lithium metal batteries (LMBs) represent a favorable option for the new-generation high-energy-density batteries. Nevertheless, LMBs utilizing the current commercial separators consistently encounter some issues, including the irregular development of lithium dendrites, bulk fluctuation of the lithium anode, and excessive electrolyte consumption. In this study, we innovatively coated the double-sides of a commercial polypropylene (PP) separator with an electrostatically assembled composite of CoMo-layered double-hydroxide (CoMo-LDH) hollow polyhedra and high-crystallinity graphitic carbon nitride to enhance the electrochemical properties of the separator. The CoMo-LDH exhibited a certain effect on accommodating the bulk variation throughout the Li deposition/stripping procedure. Additionally, the triazine-based structure of graphitic carbon nitride synthesized by the molten-salt-assisted approach introduced Cl⁻ to regulate the ion selectivity in the separator and promoted the uniform plating of Li⁺. Satisfactorily, it was demonstrated that the double-modified PP (DMP) separator exhibited a significantly improved ionic conductivity (1.11 mS cm⁻¹) and Li⁺ transference number (0.75) compared to the conventional PP separator. In-situ puncture experiments for lithium dendrites revealed that the DMP separator could withstand a lithium deposition capacity of 17 mAh cm⁻². Furthermore, the DMP-equipped Li//LFP full-cell delivered a primary discharge capacity of 149 mAh g⁻¹ and maintained 96.6% capacity retention after 100 cycles at 0.2 C. Even, after 500 cycles at 1 C, a retention rate of 94.1% was still achieved. Additionally, the Li//NCM523 full-cell assembled with the DMP separator exhibited a good electrochemical performance at 0.2 C. This work exhibited the universality and practicality of the DMP separator as a dependable solution for restraining the development of lithium dendrites on LMBs. Furthermore, this solution could be applied to other alkali metal anodes.