Functionally Modified Polyolefin-Based Separators for Lithium-Sulfur Batteries: Progress and Prospects

Abstract

The ever-growing demand for portable devices and electric vehicles are drawing widespread attention to advanced energy storage systems. Over the past few decades, lithium-sulfur batteries (LSBs) have vast potential to act as the next-generation of rechargeable power source due to their high theoretical specific energy, cost-effectiveness, and environmental benignity. However, insufficient sulfur utilization, inferior cyclability, and rate capability originating from the intrinsic insulating features of the sulfur and notorious polysulfide shuttle are major obstacles to fulfilling the industrialization of LSBs. In this respect, the introduction of a functional barrier layer coating on a separator has been verified as an effective strategy to overcome the aforementioned intractable problems. In this review, we focus on summarizing the current progress of the modified polyolefin-based separators (known as functional separators), including functional separator facing cathodes and functional separator facing anodes. According to the working mechanism, functional separator facing cathodes are divided into physical adsorption separators, chemical adsorption separators, catalytic conversion separators, and multifunctional separators. Meanwhile, functional separator facing anodes are classified into physical barrier separators, induced lithium growth separators, regulated lithium nucleation separators, and hybrid mechanism separators. Finally, the future perspective coupled with the practical utilization of functional separators in LSBs is proposed.

A Multi‐Functional Separator for Li‐S Batteries: WS2@C Nanoflowers Catalyze the Rapid Recycling of Lithium Polysulfides by Polar Attraction

“…As an indispensable part of the battery, separators contact and interact with both electrodes, preventing internal short circuits while providing transport pathways for ions. [23][24][25] Initially, various carbon-based materials with controlled pore size are made as free-standing interlayer/ coating layer of separators. [2,26] Compared with conventional polypropylene (PP) and polyethylene (PE) separators, they can enhance the ionic conductivity and cover the bare mesoporous structure against lithium polysulfides (LiPSs) diffusion.…”

“…[2,26] Compared with conventional polypropylene (PP) and polyethylene (PE) separators, they can enhance the ionic conductivity and cover the bare mesoporous structure against lithium polysulfides (LiPSs) diffusion. [25] However, with the weak Van der Waals' forces, these materials could only provide feebly physical adsorption to polar LiPSs. In recent years, numerous works have researched the strong interaction of separators with LiPSs like electrostatic interaction [27] or chemical bonding [28,29,12] to alleviate shuttle effects.…”

“…[31] Because the doped-N in the carbon matrix could boost polysulfide-binding via chemisorption, the battery exhibited better electrochemical performance. However, due to the limited function of ionic sieve caused by the LiPSs' high concentration, and the weak chemical binding of doped atoms as well as the uneven distribution of them into the matrix, [25] there is still much room for improvement for the above methods.…”

“…Initially, various carbon‐based materials with controlled pore size are made as free‐standing interlayer/coating layer of separators [2,26] . Compared with conventional polypropylene (PP) and polyethylene (PE) separators, they can enhance the ionic conductivity and cover the bare mesoporous structure against lithium polysulfides (LiPSs) diffusion [25] . However, with the weak Van der Waals’ forces, these materials could only provide feebly physical adsorption to polar LiPSs.…”

Comparing Internal and Interparticle Space Effects of Metal–Organic Frameworks on Polysulfide Migration in Lithium–Sulfur Batteries

“…To mitigate the shuttle effect, many Nanomaterials 2021, 11, 2689 2 of 14 efforts have been devoted to blocking soluble polysulfide intermediates via physical and chemical confinement of separators by introducing various coating materials. [3][4][5][6][7][8]. As for physical confinement, porous materials such as porous carbon, graphene, and metal oxide were used to prevent the penetration of polysulfides from cathode to anode [5,[9][10][11].…”