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Light weight carbon nanofibers (CNF) fabricated by a simple electrospinning method and used as a 3D structured current collector for a sulfur cathode. Along with a light weight, this 3D current collector allowed us to accommodate a higher amount of sulfur composite, which led to a remarkable increase of the electrode capacity from 200 to 500 mAh per 1 g of the electrode including the mass of the current collector. Varying the electrospinning solution concentration enabled obtaining carbonized nanofibers of uniform structure and controllable diameter from several hundred nanometers to several micrometers. The electrochemical performance of the cathode deposited on carbonized PAN nanofibers at 800 °C was investigated. An initial specific capacity of 1620 mAh g−1 was achieved with a carbonized PAN nanofiber (cPAN) current collector. It exhibited stable cycling over 100 cycles maintaining a reversible capacity of 1104 mAh g−1 at the 100th cycle, while the same composite on the Al foil delivered only 872 mAh g−1. At the same time, 3D structured CNFs with a highly developed surface have a very low areal density of 0.85 mg cm−2 (thickness of ~25 µm), which is lower for almost ten times than the commercial Al current collector with the same thickness (7.33 mg cm−2).

Significant research efforts have been dedicated to progressing Li/S batteries owing to the active material’s superior capacity and abundancy. Yet, one of the major drawbacks of the Li/S battery relates to the separator part since it is a crucial component that directly influences its electrochemical performance. The reversible capacity, Coulombic efficiency, and cycling stability of Li/S batteries can all be increased by rationally constructing and improving commercially available separators. To date, various modifications on the separator surface have been proposed to enhance the electrochemical performance of Li/S batteries. Thus, this review mainly focuses on major problems of Li/S batteries and their resolving methods by advancing these separators. Enhancement of separators are categorized as physical and chemical based on modification technique types. In the physical modification section, different types of coatings using carbon, polymer, inorganic, and metal–organic framework (MOF) were comprehensively discussed. In contrast, relatively less work on chemical modification has been reported, yet a critical summary has been provided. The perspectives and challenges of separator modification for Li/S battery has been also proposed.

A novel crosslinked electrospun nanofibrous membrane with maleated lignin (ML) and poly(acrylonitrile) (PAN) is presented as a separator for lithium-ion batteries (LIBs). Alkali lignin was treated with an esterification agent of maleic anhydride, resulting in a substantial hydroxyl group conversion to enhance the reactivity and mechanical properties of the final nanofiber membranes. The maleated lignin (ML) was subsequently mixed with UV-curable formulations (up to 30% wt) containing polyethylene glycol diacrylate (PEGDA), hydrolyzed 3-(Trimethoxysilyl)propyl methacrylate (HMEMO) as crosslinkers, and poly(acrylonitrile) (PAN) as a precursor polymer. UV-electrospinning was used to fabricate PAN/ML/HMEMO/PEGDA (PMHP) crosslinked membranes. PMHP membranes made of electrospun nanofibers feature a three-dimensional (3D) porous structure with interconnected voids between the fibers. The mechanical strength of PMHP membranes with a thickness of 25 µm was enhanced by the variation of the cross-linkable formulations. The cell assembled with PMHP2 membrane (20 wt% of ML) showed the maximum ionic conductivity value of 2.79*10−3 S cm−1, which is significantly higher than that of the same cell with the liquid electrolyte and commercial Celgard 2400 (6.5*10−4 S cm−1). The enhanced LIB efficiency with PMHP2 membrane can be attributed to its high porosity, which allows better electrolyte uptake and demonstrates higher ionic conductivity. As a result, the cell assembled with LiFePO4 cathode, Li metal anode, and PMHP2 membrane had a high initial discharge specific capacity of 147 mAh g−1 at 0.1 C and exhibited outstanding rate performance. Also, it effectively limits the formation of Li dendrites over 1000 h. PMHP separators have improved chemical and physical properties, including porosity, thermal, mechanical, and electrochemical characteristics, compared with the commercial ones.