A Li+-flux-homogenizing separator for long-term cycling of Li metal anodes

Abstract

Uneven arrangement of pores and the poor electrolyte affinity of separators made from polyolefins or poly(vinylidene difluoride) result in disordered Li⁺ flux and rugged deposition layers, triggering continuous consumption of lithium salt and premature expiration of lithium metal batteries (LMBs). Although adjusting the pore structure or modifying the surface of these separators is effective, it is space-occupied and not economically or industrially viable. Herein, we incorporate antistatic agent SN (SN), namely, octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate, into PVDF-HFP matrix to prepare a homogeneous composite separator (PVDF-HFP/SN) for LMBs through a feasible method. The ammonium head of the SN provides numerous anion-friendly sites that absorb PF₆⁻ in the electrolyte. This forms the Li-affinity matrix of SN⋯PF₆⁻, which allows for the uniform distribution and deposition of Li⁺ in the SN⋯PF₆⁻⋯Li⁺ structure, and further, reduces the consumption of lithium salt and ensures the formation of a dendrite-free Li anode. Hence, using the PVDF-HFP/SN separator, we achieve exceptional stability of Li‖Li symmetric cells for 1000 hours at 0.5 mA cm⁻² with a capacity of 1 mA h cm⁻², and the Li‖LiFePO₄ cell demonstrates a capacity of 120.4 mA h g⁻¹ with an unparalleled capacity retention of 93.4% after 1000 cycles at 2C (1C = 170 mA g⁻¹).