Polyethylenimine Expanded Graphite Oxide Enables High Sulfur Loading and Long-Term Stability of Lithium-Sulfur Batteries

Enhanced Yield of Large-Sized Ti3C2Tx MXene Polymers Nanosheets via Cyclic Ultrasonic-Centrifugal Separation

Water pollution has spurred the development of membrane separation technology as a potential means of solving the issue. In contrast to the irregular and asymmetric holes that are easily made during the fabrication of organic polymer membranes, forming regular transport channels is essential. This necessitates the use of large-size, two-dimensional materials that can enhance membrane separation performance. However, some limitations regarding yield are associated with preparing large-sized MXene polymer-based nanosheets, which restrict their large-scale application. Here, we propose a combination of wet etching and cyclic ultrasonic-centrifugal separation to meet the needs of the large-scale production of MXene polymers nanosheets. It was found that the yield of large-sized Ti3C2Tx MXene polymers nanosheets reached 71.37%, which was 2.14 times and 1.77 times higher than that prepared with continuous ultrasonication for 10 min and 60 min, respectively. The size of the Ti3C2Tx MXene polymers nanosheets was maintained at the micron level with the help of the cyclic ultrasonic-centrifugal separation technology. In addition, certain advantages of water purification were evident due to the possibility of attaining the pure water flux of 36.5 kg m−2 h−1 bar−1 for the Ti3C2Tx MXene membrane prepared with cyclic ultrasonic-centrifugal separation. This simple method provided a convenient way for the scale-up production of Ti3C2Tx MXene polymers nanosheets.

Blocking chemical warfare agent simulants by graphene oxide/polymer multilayer membrane based on hydrogen bonding and size sieving effect

Chemical warfare agents (CWAs) are toxic materials that cause death by contact with the skin or by respiration. Although studies on detoxification of CWAs have been intensively conducted, studies that block CWAs permeation are rare. In this study, for blocking CWAs, a multilayer thin film composed of linear polyethylenimine (LPEI) and graphene oxide (GO) is simply prepared through a spray-assisted Layer-by-Layer (LbL) assembly process. LPEI could change its morphology dependent on pH, which is known as a representative hydrogen donor and acceptor. By controlling the shape of the polymer chain, a heterogenous film could have a loose or dense inner structure. CWAs mainly move through diffusion and have hydrogen bonding sites. Therefore, the heterogeneous film can limit CWAs movement based on controlling pathways and hydrogen bonds within the film. The protective effect of this membrane is investigated using dimethyl methylphosphonate (DMMP), a nerve gas simulant. DMMP vapor transmittance rate (DVTR) and N₂ permeance of LPEI/GO are 67.91 g/m² day and 34,293.04 GPU. It means that the protection efficiency is 72.65%. Although this membrane has a thin thickness (100 nm), it shows a high protective effect with good breathability. And water/DMMP selectivity of the membrane is 66.63. Since this multilayer membrane shows efficient protection performance with a simple preparation method, it has a high potential for applications such as protective suits and masks.

Metastable marcasite NiSe2 nanodendrites on carbon fiber clothes to suppress polysulfide shuttling for high-performance lithium-sulfur batteries

The incorporation of catalytic components is a promising strategy to promote redox reaction kinetics and suppress polysulfide shuttling for high-performance lithium-sulfur batteries (LSBs). In this work, metastable marcasite NiSe₂ nanodendrites grown on carbon fiber clothes (m-NiSe₂/CFC) were synthesized to improve chemical adsorption and electrocatalytic activity towards lithium polysulfides. The multifunctional m-NiSe₂/CFC film was utilized as both the interlayer and the three-dimensional (3D) current collector in LSBs. In comparison with the stable pyrite NiSe₂ nanodendrite-covered CFC (p-NiSe₂/CFC) counterpart, the m-NiSe₂/CFC film exhibits even stronger chemisorption, higher catalytic activity and faster reaction kinetics, thereby resulting in significantly improved lithium storage performance. The Al@S/rGO@m-NiSe₂/CFC cell has a high reversible capacity of 1646 mA h g^-1 at 0.2C, a high Q_L/Q_H ratio of 3.00 at 0.2C, a high rate capability of 900 mA h g^-1 at 4C, and an outstanding cyclic stability exhibiting a low capacity decay of 0.028% per cycle for 600 cycles at 4C. Moreover, a symmetrically sandwiched cathode of m-NiSe₂/CFC@S/rGO@m-NiSe₂/CFC was designed for high sulfur loading LSBs (4.5 mg cm^-2) with superior electrochemical performance of 3.73 mA h cm^-2 after 100 cycles at 1C rate. Our work opens up a new opportunity to enhance the electrochemical performance of LSBs by phase engineering of NiSe₂ catalysts in sandwiched structural cathodes.

A Polysulfides-Confined All-in-One Porous Microcapsule Lithium-Sulfur Battery Cathode

Developing emerging materials for high energy-density lithium-sulfur (Li-S) batteries is of great significance to suppress the shuttle effect of polysulfides and to accommodate the volumetric change of sulfur. Here, a novel porous microcapsule system containing a carbon nanotubes/tin dioxide quantum dots/S (CNTs/QDs/S) composite core and a porous shell prepared through a liquid-driven coaxial microfluidic method as Li-S battery cathode is developed. The encapsulated CNTs in the microcapsules provide pathways for electron transport; SnO₂ QDs on CNTs immobilize the polysulfides by strong adsorption, which is verified by using density functional theory calculations on binding energies. The porous shell of the microcapsule is beneficial for ion diffusion and electrolyte penetration. The void inside the microcapsule accommodates the volumetric change of sulfur. The Li-S battery based on the porous CNTs/QDs/S microcapsules displays a high capacity of 1025 mAh g^-1 after 100 cycles at 0.1 C. When the sulfur loading is 2.03 mg cm^-2 , the battery shows a stable cycling life of 700 cycles, a Coulombic efficiency exceeding 99.9%, a recoverable rate-performance during repeated tests, and a good temperature tolerance at both -5 and 45 °C, which indicates a potential for applications at different conditions.

Intercalation Strategy in 2D Materials for Electronics and Optoelectronics

Intercalation is an effective approach to tune the physical and chemical properties of 2D materials due to their abundant van der Waals gaps that can host high-density intercalated guest matters. This approach has been widely employed to modulate the optical, electrical, and photoelectrical properties of 2D materials for their applications in electronic and optoelectronic devices. Thus it is necessary to review the recent progress of the intercalation strategy in 2D materials and their applications in devices. Herein, various intercalation strategies and the novel properties of the intercalated 2D materials as well as their applications in electronics and optoelectronics are summarized. In the end, the development tendency of this promising approach for 2D materials is also outlined.

Sandwiched Cathodes Assembled from CoS2 -Modified Carbon Clothes for High-Performance Lithium-Sulfur Batteries

Structural design of advanced cathodes is a promising strategy to suppress the shuttle effect for lithium-sulfur batteries (LSBs). In this work, the carbon cloth covered with CoS2 nanoparticles (CC-CoS2 ) is prepared to function as both three-dimensional (3D) current collector and physicochemical barrier to retard migration of soluble lithium polysulfides. On the one hand, the CC-CoS2 film works as a robust 3D current collector and host with high conductivity, high sulfur loading, and high capability of capturing polysulfides. On the other hand, the 3D porous CC-CoS2 film serves as a multifunctional interlayer that exhibits efficient physical blocking, strong chemisorption, and fast catalytic redox reaction kinetics toward soluble polysulfides. Consequently, the Al@S/AB@CC-CoS2 cell with a sulfur loading of 1.2 mg cm-2 exhibits a high rate capability (≈823 mAh g-1 at 4 C) and delivers excellent capacity retention (a decay of ≈0.021% per cycle for 1000 cycles at 4 C). Moreover, the sandwiched cathode of CC-CoS2 @S/AB@CC-CoS2 is designed for high sulfur loading LSBs. The CC-CoS2 @S/AB@CC-CoS2 cells with sulfur loadings of 4.2 and 6.1 mg cm-2 deliver high reversible capacities of 1106 and 885 mAh g-1 , respectively, after 100 cycles at 0.2 C. The outstanding electrochemical performance is attributed to the sandwiched structure with active catalytic component.

ZIF-8 derived hollow carbon to trap polysulfides for high performance lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have a high theoretical energy density and are low cost. However, the undesirable shuttle effect with the solid discharge product, Li2S, greatly impedes their market penetration. Conductive carbon materials with functional elements are beneficial in controlling the shuttle effect and can reactivate the Li2S, leading to improved long term cycling performance of LSBs. Herein, we report zinc (Zn) and nitrogen (N) co-doped ZIF-8 derived hollow carbon (ZHC) as a promising separator coating for LSBs to control the shuttle effect. The hollow area in the ZHC is identified to be around 250 nm with a carbonized outer surface thickness of approximately 50 nm. The presence of Zn and N in the nanohollow carbon structure helps to mitigate polysulfide (PS) diffusion in LSBs. Furthermore, the hollow interior of the carbon acts as a PS pocket to physically capture the PS and in addition Zn and N chemically attract the PS through polar-polar and metal sulfide interactions. The ZHC with its unique architecture and functional groups shows a promising performance with an initial specific capacity (S.cap) of 842 mA h g-1 at 4.80 mg cm-2 and cycling stability until 400 cycles, which is considerably higher in comparison with the cycling performance of parent ZIF-8.

Binder-free and high-loading sulfurized polyacrylonitrile cathode for lithium/sulfur batteries

Sulfurized polyacrylonitrile (SPAN) is a promising active material for Li/S batteries owing to its high sulfur utilization and long-term cyclability. However, because SPAN electrodes are synthesized using powder, they require large amounts of electrolyte, conducting agents, and binder, which reduces the practical energy density. Herein, to improve the practical energy density, we fabricated bulk-type SPAN disk cathodes from pressed sulfur and polyacrylonitrile powders using a simple heating process. The SPAN disks could be used directly as cathode materials because their π–π structures provide molecular-level electrical connectivity. In addition, the electrodes had interconnected pores, which improved the mobility of Li⁺ ions by allowing homogeneous adsorption of the electrolyte. The specific capacity of the optimal electrode was very high (517 mA h g_electrode⁻¹). Furthermore, considering the weights of the anode, separator, cathode, and electrolyte, the Li/S cell exhibited a high practical energy density of 250 W h kg⁻¹. The areal capacity was also high (8.5 mA h cm⁻²) owing to the high SPAN loading of 16.37 mg cm⁻². After the introduction of 10 wt% multi-walled carbon nanotubes as a conducting agent, the SPAN disk electrode exhibited excellent cyclability while maintaining a high energy density. This strategy offers a potential candidate for Li/S batteries with high practical energy densities.

A simple synthesis procedure to prepare bulk-type SPAN electrodes toward the realization of Li/S batteries with enhanced practical energy densities.

Immobilizing Polysulfide by In Situ Topochemical Oxidation Derivative TiC@Carbon-Included TiO2 Core-Shell Sulfur Hosts for Advanced Lithium-Sulfur Batteries

The performance of lithium-sulfur (Li-S) batteries is greatly hindered by the notorious shuttle effect of lithium polysulfides (LiPSs). To address this issue, in situ topochemical oxidation derivative TiC@carbon-included TiO₂ (TiC@C-TiO₂ ) core-shell composite is designed and proposed as a multifunctional sulfur host, which integrates the merits of conductive TiC core to facilitate the redox reaction kinetics of sulfur species, and porous C-TiO₂ shell to suppress the dissolution and shuttling of LiPSs through chemisorption. A unique dual chemical mediation mechanism is demonstrated for the proposed TiC@C-TiO₂ composite that synergistically entraps LiPSs through thiosulfate/polythionate conversion coupled with strong polar-polar interaction. The morphological characterization reveals that the TiC@C-TiO₂ -based cathode can well regulate the distribution of electrode materials to retard their accumulation inside the electrode, ensuring effective contact between the active materials and electrolyte. Based on its unique function and structure, the cathode delivers an improved capacity of 1256 mAh g^-1 at 0.2C, a remarkable rate capability of 643 mAh g^-1 , and an ultralow capacity decay rate of 0.065% per cycle at 2C over 900 cycles. This work not only demonstrates a dual chemical mediation mechanism to immobilize LiPSs, but also provides a universal strategy to construct multifunctional sulfur hosts for advanced Li-S batteries.

Cationic Covalent-Organic Framework as Efficient Redox Motor for High-Performance Lithium-Sulfur Batteries

The shuttle effect of soluble lithium polysulfides (LiPSs) leads to the rapid decay of sulfur cathode, severely hindering the practical applications of lithium-sulfur (Li-S) batteries. To this point, a covalent-organic framework (COF) with proper cationic sites, which can be utilized as the cathode host of high-performance Li-S batteries, is reported. The chemical sulfur anchoring within micropores effectively suppresses the dissolution of LiPSs into the electrolyte. During the discharge step, the cationic sites can accept electrons from anode and deliver them to polysulfides to facilitate the polysulfides' disintegration. Meanwhile, the cationic sites can receive electrons from polysulfides and then send them to the anode during the charge process, which promotes the polysulfides oxidation. Thus, both experiments and computational modeling show that the cationic COF can effectively inhibit the shuttle effect of LiPSs and improve the batteries' performances. Compared with electrically neutral COFs, the cationic COF-based batteries show much better cycling stability even at high current density, for instance, a high specific capacity of 468 mA h g^-1 is retained after 300 cycles at a current density of 4.0 C.

A green strategy for the preparation of a honeycomb-like silicon composite with enhanced lithium storage properties

The high-performance silicon (Si) composite electrodes are being widely developed due to their considerable theoretical capacity. Coating with carbon-based materials is an efficient way to solve the common issues of Si-based materials. Currently, most of the reported strategies are complicated, pollutive, or uneconomic, which hamper their practical applications. Herein, a honeycomb-like Si-based composite was prepared to address these issues via a facile and green reduction approach at room temperature. The pre-anchored Si nanoparticles could be packed and interconnected through a three-dimensional graphene network to further enhance the electrochemical properties of the active materials. As an electrode, this composite shows good rate capabilities upon lithium storage and cycling stability. The continued cycling measurement delivers a -0.049% capacity decay rate per cycle within 600 cycles. A direct comparison further exhibits the obviously improved performance between the as-designed Si-based composite and naked Si, suggesting a potential application of this convenient strategy for other high-performance electrode materials.