Synergistic Ni-Co Metal Nodes in a Conjugated MOF-Modified Separator for High-Performance Lithium-Sulfur Batteries.

Abstract

Lithium-sulfur batteries (LSBs) hold great potential as next-generation energy storage systems due to their high theoretical energy density and relatively low cost. However, their practical application is hindered by issues such as the shuttle phenomenon caused by soluble lithium polysulfides (LiPSs), slow redox reaction rates, and unsatisfactory cycling stability. In this study, novel conjugated metal-organic frameworks, M_xM″_3-x(HHTP)₂ (M, M″ = Ni²⁺, Co²⁺, Cu²⁺) is reported, as a functional coating on polypropylene (PP) separators. Leveraging the in-plane d-π conjugation, high porosity, and rich redox-active sites, the M_xM'_3-x(HHTP)₂-modified separators effectively suppress LiPSs' shuttling, facilitate Li⁺ transport, and accelerate LiPSs' redox conversion. Among the series, the bimetallic Ni_1.35Co_1.65(HHTP)₂/PP separator demonstrates superior electrochemical performance, owing to the synergistic interaction between Ni and Co metal centers. This synergism results in an optimized pore structure, enhances conductivity, and stronger polysulfide affinity compare to monometallic analogues. Consequently, the cell employing Ni_1.35Co_1.65(HHTP)₂/PP provides an initial discharge capacity of 1148 mAh g^-1 at 0.1 C and the capacity decay rate is 0.08% after 500 cycles at 1C. This work presents a scalable and environmentally friendly strategy for constructing multifunctional separators to fully realize the potential of high-energy-density LSBs.