Two-Dimensional Material-Functionalized Separators for High-Energy-Density Metal-Sulfur and Metal-Based Batteries

Prussian blue analogue/KB-derived Ni/Co/KB composite as a superior adsorption-catalysis separator modification material for Li-S batteries

Lithium‑sulfur batteries (LSBs) are gradually replacing conventional lithium-ion batteries (LIBs), credited to their high theoretical capacity, low cost, and non-toxicity. Nevertheless, the substantial capacity degradation caused by the polysulfide shuttling during charging and discharging has seriously hindered the commercialization of LSBs. Separator modification with functionalized carbon materials has been found to catalyze the breakdown of polysulfides, thereby improving the efficiency of LSBs. Herein, we synthesized Ni/Co-PBAs with KB structures to subsequently derive Ni/Co/KB composites by a carbonization process, which were later used as a modifier layer on the barrier in LSBs in order to effectively alleviate the shuttle problem. The capacity of the Ni/Co/KB composite decorated separator is found to be 1032 mAh/g at 0.5 C with a coulombic efficiency closer to 100%. In the long-term cycling capability evaluation, the initial cycle is approximately 802.9 mAh/g at 1 C, while capacity retention after 400 cycles is also 678.8 mAh/g, with a high-capacity retention rate of 84.5%. The potential of these composites as modifying materials for superior LSBs separators is verified by experimental and theoretical methods.

Two-dimensional materials towards separator functionalization in advanced Li-S batteries

Functional separators have played important roles in improving the electrochemical performance of lithium-sulfur (Li-S) batteries by addressing the key issues of both the sulfur cathode and lithium anode. Compared with other materials that are used for separator functionalization, two-dimensional (2D) materials with atomic layer thickness and infinite lateral dimensions feature several advantages of ultra-thin laminate structure, remarkable physical properties and tunable surface chemistry, which show potential applications in separator functionalization towards addressing the issues of both the shuttle effect and formation of Li dendrites in Li-S batteries. In this review, the unique advantages of 2D materials for separator functionalization in Li-S batteries and their common construction methods are introduced. Then, recent progress and advances in the construction of 2D materials functional separators are summarized in detail towards inhibiting the shuttle effect of polysulfides and suppressing Li dendrite growth in Li-S batteries. Finally, some opportunities and challenges of 2D materials for constructing high-performance functional separators are proposed. We anticipate that this review will provide new insights into separator functionalization for developing advanced Li-S batteries.

Recent Progress in High-Performance Lithium Sulfur Batteries: The Emerging Strategies for Advanced Separators/Electrolytes Based on Nanomaterials and Corresponding Interfaces

Lithium-sulfur (Li-S) batteries, possessing excellent theoretical capacities, low cost and nontoxicity, are one of the most promising energy storage battery systems. However, poor conductivity of elemental S and the "shuttle effect" of lithium polysulfides hinder the commercialization of Li-S batteries. These problems are closely related to the interface problems between the cathodes, separators/electrolytes and anodes. The review focuses on interface issues for advanced separators/electrolytes based on nanomaterials in Li-S batteries. In the liquid electrolyte systems, electrolytes/separators and electrodes system can be decorated by nano materials coating for separators and electrospinning nanofiber separators. And, interface of anodes and electrolytes/separators can be modified by nano surface coating, nano composite metal lithium and lithium nano alloy, while the interface between cathodes and electrolytes/separators is designed by nano metal sulfide, nanocarbon-based and other nano materials. In all solid-state electrolyte systems, the focus is to increase the ionic conductivity of the solid electrolytes and reduce the resistance in the cathode/polymer electrolyte and Li/electrolyte interfaces through using nanomaterials. The basic mechanism of these interface problems and the corresponding electrochemical performance are discussed. Based on the most critical factors of the interfaces, we provide some insights on nanomaterials in high-performance liquid or state Li-S batteries in the future.

Designing conductive networks of hybrid carbon enables stable and long-lifespan cotton-fiber-based lithium–sulfur batteries

In modern society, flexible rechargeable batteries have become a burgeoning apodictic choice for wearable devices. Conventional lithium–sulfur batteries lack sufficient flexibility because their electrode materials are too rigid to bend. Along with the inherent high theoretical capacity of sulfur, lithium–sulfur batteries have some issues, such as dissolution and shuttle effect of polysulfides, which restricts their efficiency and practicability. Here, a flexible and “dead-weight”-free lithium–sulfur battery substrate with a three-dimensional structure was prepared by a simple strategy. With the cooperative assistance of carbon nanotubes and graphene attached to cotton fibers, the lithium–sulfur battery with 2.0 mg cm⁻² sulfur provided a high initial discharge capacity of 1098.7 mA h g⁻¹ at 1C, and the decay rate after 300 cycles was only 0.046% per cycle. The initial discharge capacity at 2C was 872.4 mA h g⁻¹ and the capacity was maintained 734.4 mA h g⁻¹ after 200 cycles with only a 0.079% per cycle decay rate.

A flexible, “dead weight”-free lithium–sulfur battery substrate was prepared, and batteries using these substrates showed great electrochemical performance.