Holistic Design Consideration of Metal–Organic Framework-Based Composite Membranes for Lithium–Sulfur Batteries

Abstract

Metal−organic framework (MOF)-based membranes have received significant attention as separators for lithium−sulfur (Li−S) batteries because of their high porosities, well-defined and tailored structures, and other tunable features that are desirable for preventing the "shuttle effect" of soluble polysulfides. Because of the insulating nature of most MOFs, composite membranes are generally constructed by a combination of MOFs and electron-conductive materials. In this work, we examine the property−performance relation between MOF-based separators and Li−S batteries by systematically adjusting the electrical conductivity, thickness, and mass loading of the MOF-based composite. Beyond the commonly referenced trapping or blocking ability of MOFs toward polysulfides, we find that by fixing the thickness of the MOF-based composite coating layer (∼40 μm) on a Celgard membrane, the electrical conductivity of the MOF composite layer is of paramount importance compared with the physical/ chemical trapping ability of polysulfides. However, the trapping ability of MOFs becomes indispensable when the thickness of the composite layer is small (e.g., ∼20 μm), indicating the synergetic effects of the adsorption and conversion capabilities of the thin composite layer. This work suggests the importance of a holistic design consideration for a MOF-based membrane for long-life and high-energy-density Li−S batteries.

Advances of Electroactive Metal–Organic Frameworks

“…Pristine MOFs and hybrid MOFs have been also extensively studied as separators [82,93,310,[419][420][421][422] or coating layers integrated separators [94,95,311,[423][424][425][426][427][428][429][430][431][432][433][434][435][436] in LSBs. For instance, a Cu MOF (HKUST-1) constructed by H 3 BTC, L8, and Cu(NO 3 ) 2 •3H 2 O was well connected by binder PVDF-HFP as separators in LSBs to show blocking polysulfides diffusion (Figure 16a,b).…”

Metal–Organic Frameworks for the Enhancement of Lithium‐Based Batteries: A Mini Review on Emerging Functional Designs

“…[3] To overcome these challenges, lithiummetal batteries (LMBs) demonstrate even higher capacities and have recently been referred to as the "holy grail" for next-generation energy systems. [4][5][6][7] Currently, both LIBs and LMBs continue to face countless restrictions to their electrochemical performances, notably, due to their capacity fading during repeated electrochemical cycling. [8] A major factor of this loss is due to corrosive hydrogen fluoride (HF) that is generated through the hydrolysis of electrolytes.…”

“…[ 3 ] To overcome these challenges, lithium–metal batteries (LMBs) demonstrate even higher capacities and have recently been referred to as the “holy grail” for next‐generation energy systems. [ 4 , 5 , 6 , 7 ]…”