Separator modified by Co-porphyrin based Zr-MOF@CNT composite enabling efficient polysulfides catalytic conversion for advanced lithium-sulfur batteries

Porous crystalline conjugated macrocyclic materials and their energy storage applications

Porous crystalline conjugated macrocyclic materials (CMMs) possess high porosity, tunable structure/function and efficient charge transport ability owing to their planar macrocyclic conjugated π-electron system, which make them promising candidates for applications in energy storage. In this review, we thoroughly summarize the timely development of porous crystalline CMMs in energy storage related fields. Specifically, we summarize and discuss their structures and properties. In addition, their energy storage applications, such as lithium ion batteries, lithium sulfur batteries, sodium ion batteries, potassium ion batteries, Li-CO2 batteries, Li-O2 batteries, Zn-air batteries, supercapacitors and triboelectric nanogenerators, are also discussed. Finally, we present the existing challenges and future prospects. We hope this review will inspire the development of advanced energy storage materials based on porous crystalline CMMs.

Polysulfides in Magnesium-Sulfur Batteries

Mg-S batteries hold great promise as a potential alternative to Li-based technologies. Their further development hinges on solving a few key challenges, including the lower capacity and poorer cycling performance when compared to Li counterparts. At the heart of the issues is the lack of knowledge on polysulfide chemical behaviors in the Mg-S battery environment. In this Review, a comprehensive overview of the current understanding of polysulfide behaviors in Mg-S batteries is provided. First, a systematic summary of experimental and computational techniques for polysulfide characterization is provided. Next, conversion pathways for Mg polysulfide species within the battery environment are discussed, highlighting the important role of polysulfide solubility in determining reaction kinetics and overall battery performance. The focus then shifts to the negative effects of polysulfide shuttling on Mg-S batteries. The authors outline various strategies for achieving an optimal balance between polysulfide solubility and shuttling, including the use of electrolyte additives, polysulfide-trapping materials, and dual-functional catalysts. Based on the current understanding, the directions for further advancing knowledge of Mg polysulfide chemistry are identified, emphasizing the integration of experiment with computation as a powerful approach to accelerate the development of Mg-S battery technology.

Breaking the Barrier: Strategies for Mitigating Shuttle Effect in Lithium-Sulfur Batteries Using Advanced Separators

Lithium-sulfur (Li-S) batteries are considered one of the most promising energy storage systems due to their high theoretical capacity, high theoretical capacity density, and low cost. However, challenges such as poor conductivity of sulfur (S) elements in active materials, the "shuttle effect" caused by lithium polysulfide, and the growth of lithium dendrites impede the commercial development of Li-S batteries. As a crucial component of the battery, the separator plays a vital role in mitigating the shuttle effect caused by polysulfide. Traditional polypropylene, polyethylene, and polyimide separators are constrained by their inherent limitations, rendering them unsuitable for direct application in lithium-sulfur batteries. Therefore, there is an urgent need for the development of novel separators. This review summarizes the applications of different separator preparation methods and separator modification methods in lithium-sulfur batteries and analyzes their electrochemical performance.

Donor-Acceptor Conjugated Microporous Polymer toward Enhanced Redox Kinetics in Lithium-Sulfur Batteries

Conjugated microporous polymers (CMPs) with porous structure and rich polar units are favorable for high-performance lithium-sulfur (Li-S) batteries. However, understanding the role of building blocks in polysulfide catalytic conversion is still limited. In this work, two triazine-based CMPs are constructed by electron-accepting triazine with electron-donating triphenylbenzene (CMP-B) or electron-accepting triphenyltriazine (CMP-T), which can grow on a conductive carbon nanotube (CNT) to serve as separator modifiers for Li-S batteries. CMP-B@CNT features faster ion transportation than the counterpart of CMP-T@CNT. More importantly, compared with acceptor-acceptor (A-A) CMP-T, donor-acceptor (D-A) CMP-B possesses a higher degree of conjugation and a narrower band gap, which are conducive to the electron transfer along the polymer skeleton, thus accelerating the sulfur redox kinetics. Consequently, the CMP-B@CNT functional separator endows Li-S cells with an outstanding initial capacity of 1371 mAh g^-1 at 0.1 C and favorable cycling stability with a capacity degradation rate of 0.048% per cycle at 1 C for 800 cycles. This work provides insight into the rational design of efficient catalysts for advanced Li-S batteries.

Single-walled carbon nanotube gutter layer supported ultrathin zwitterionic microporous polymer membrane for high-performance lithium-sulfur battery

Development of efficient lithium-sulfur (Li-S) battery requires the need to develop an appropriate functional separator that allows strong facilitation and transport of lithium ions together with limited passage of polysulfides. In this work, a multifunctional separator (TB-BAA/SWCNT/PP) is developed through spin coating of a novel zwitterionic microporous polymer (TB-BAA) on the gutter layer constructed from single-walled carbon nanotubes (SWCNT), where commercially available polypropylene (PP) separator is used to act as the mechanical support. SWCNT in this study serves as the first modification layer to decrease the size of the macropores in the PP separator, while the ultrathin TB-BAA top barrier layer with the presence of zwitterionic side chains allows the creation of confined ionic channels with both lithiophilic and sulfophilic groups. Due to the presence of available chemical interactions with lithium polysulfides, selective ion transport can be foreseen through such separator. In this regard, shuttle effect that is frequently encountered in Li-S battery can be suppressed effectively via implementing the as-obtained functional separator, resulting in the creation of credible and stable sulfur electrochemistry. The TB-BAA/SWCNT/PP-based Li-S battery has been investigated to possess high cycling ability (capacity fading per cycle of 0.055% over 500 cycles at 1 C) together with decent rate capability (736.6 mAh g^-1 at 3 C). In addition, a high areal capacity retention of 5.03 mAh cm^-2 after 50 cycles can be also obtained under raised sulfur loading (5.4 mg cm^-2).

Metal-Organic Frameworks Functionalized Separators for Lithium-Sulfur Batteries

Lithium sulfur batteries (LSBs) have attracted tremendous attention owing to their high theoretical specific capacity and specific energy. However, their practical applications are hindered by poor cyclic life, mainly caused by polysulfide shuttling. The development of advanced materials to mitigate the polysulfide shuttling effect is urgently demanded. Metal-organic frameworks (MOFs) have been exploited as multifunctional materials for the decoration of separators owing to their high surface area, structural diversity, tunable pore size, and easy tailor ability. In this review, we aim to present the state-of-the-art MOF-based separators for LSBs. Particular attention is paid to the rational design (pore aperture, metal node, functionality, and dimension) of MOFs with enhanced ability for anchoring polysulfides and facilitating Li⁺ transportation. Finally, the challenges and perspectives are provided regarding to the future design MOF-based separators for high-performance LSBs.

Carbon Nanotube Based Metal-Organic Framework Hybrids From Fundamentals Toward Applications

Metal-organic frameworks (MOFs) materials constructed by the coordination chemistry of metal ions and organic ligands are important members of the crystalline materials family. Owing to their exceptional properties, for example, high porosity, tunable pore size, and large surface area, MOFs have been applied in several fields such as gas or liquid adsorbents, sensors, batteries, and supercapacitors. However, poor conductivity and low stability hamper their potential applications in several attractive fields such as energy and gas storage. The integration of MOFs with carbon nanotubes (CNTs), a well-established carbon allotrope that exhibits high conductivity and stability, has been proposed as an efficient strategy to overcome such limitations. By combining the advantages of MOFs and CNTs, a wide variety of composites can be prepared with properties superior to their parent materials. This review provides a comprehensive summary of the preparation of CNT@MOF composites and focuses on their recent applications in several important fields, such as water purification, gas storage and separation, sensing, electrocatalysis, and energy storage (supercapacitors and batteries). Future challenges and prospects for CNT@MOF composites are also discussed.