Direct Growth of Binder-Free CNTs on a Nickel Foam Substrate for Highly Efficient Symmetric Supercapacitors

In the modern civilized world, energy scarcity and associated environmental pollution are the center of focus in the search for reliable energy storage and harvesting devices. The need to develop cheaper and more competent binder-free electrodes for high-performance supercapacitors has attracted considerable research attention. In this study, two different procedures are followed to enhance the growth of carbon nanotubes (CNT-E and CNT-NF) directly coated on a Ni-foam substrate by a well-functioning chemical vapor deposition (CVD) method. Thus, directly grown optimized CNT electrodes are used as electrodes for electrochemical devices. Furthermore, solid-state symmetric supercapacitors are fabricated using CNT-NF//CNT-NF, and fruitful results are obtained with maximum specific capacitance (250.51 F/g), energy density (68.19 Wh/kg), and power density (2799.77 W/kg) at 1 A/g current density. The device exhibited good cyclic stability, with 92.42% capacitive retention and 99.68% Coulombic efficiency at 10 000 cycles, indicating the suitability of the electrodes for practical applications. This study emphasizes the importance of studying the direct growth of binder-free CNT electrodes to understand the actual behavior of electrodes and the proper storage mechanism.

Synthesis and Applications of Dimensional SnS2 and SnS2/Carbon Nanomaterials

Dimensional nanomaterials can offer enhanced application properties benefiting from their sizes and morphological orientations. Tin disulfide (SnS₂) and carbon are typical sources of dimensional nanomaterials. SnS₂ is a semiconductor with visible light adsorption properties and has shown high energy density and long cycle life in energy storage processes. The integration of SnS₂ and carbon materials has shown enhanced visible light absorption and electron transmission efficiency. This helps to alleviate the volume expansion of SnS₂ which is a limitation during energy storage processes and provides a favorable bandgap in photocatalytic degradation. Several innovative approaches have been geared toward controlling the size, shape, and hybridization of SnS₂/Carbon composite nanostructures. However, dimensional nanomaterials of SnS₂ and SnS₂/Carbon have rarely been discussed. This review summarizes the synthesis methods of zero-, one-, two-, and three-dimensional SnS₂ and SnS₂/Carbon composite nanomaterials through wet and solid-state synthesis strategies. Moreover, the unique properties that promote their advances in photocatalysis and energy conversion and storage are discussed. Finally, some remarks and perspectives on the challenges and opportunities for exploring advanced SnS₂/Carbon nanomaterials are presented.

Dual Network Sponge for Compressible Lithium-Ion Batteries

Compressible energy devices have received increasing attention with the rapid development of flexible electronics and wearable devices due to their size adaptability and functional stability. However, it is hard to simultaneously achieve satisfactory energy density and mechanical stability for electrodes. Here an open-porous dual network sponge (DNS) with two networks of highly conductive carbon nanotubes and Li⁺ -intercalating TiO₂ -B nanowires is synthesized and employed as compressible lithium ion battery electrodes. All 1D components inside the DNS mutually penetrate with each other to form two physically distinct but functionally coupling networks, endowing DNS excellent compressibility and stability. A prototype compressible lithium-ion battery (C-LIB) is also demonstrated, in which the DNS exhibits a specific capacity of >238 mAh g^-1 under static 50% strain, and further in situ measurements show that under 1000 times of cyclic strains, DNS can charge and discharge normally maintaining a high capacity of 240 mAh g^-1 and exhibits robustness to fast strain rates up to 500% min^-1 . The dual network structure can be extended to design high-performance compliant electrodes that are promising to serve in future compressible and deformable electronics and energy systems.

Application-Driven Carbon Nanotube Functional Materials

Carbon nanotube functional materials (CNTFMs) represent an important research field in transforming nanoscience and nanotechnology into practical applications, with potential impact in a wide realm of science, technology, and engineering. In this review, we combine the state-of-the-art research activities of CNTFMs with the application prospect, to highlight critical issues and identify future challenges. We focus on macroscopic long fibers, thin films, and bulk sponges which are typical CNTFMs in different dimensions with distinct characteristics, and also cover a variety of derived composite/hierarchical materials. Critical issues related to their structures, properties, and applications as robust conductive skeletons or high-performance flexible electrodes in mechanical and electronic devices, advanced energy conversion and storage systems, and environmental areas have been discussed specifically. Finally, possible solutions and directions are proposed for overcoming current obstacles and promoting future efforts in the field.

Review on carbonaceous materials and metal composites in deformable electrodes for flexible lithium-ion batteries

With the rapid propagation of flexible electronic devices, flexible lithium-ion batteries (FLIBs) are emerging as the most promising energy supplier among all of the energy storage devices owing to their high energy and power densities with good cycling stability. As a key component of FLIBs, to date, researchers have tried to develop newly designed high-performance electrochemically and mechanically stable pliable electrodes. To synthesize better quality flexible electrodes, based on high conductivity and mechanical strength of carbonaceous materials and metals, several research studies have been conducted. Despite both materials-based electrodes demonstrating excellent electrochemical and mechanical performances in the laboratory experimental process, they cannot meet the expected demands of stable flexible electrodes with high energy density. After all, various significant issues associated with them need to be overcome, for instance, poor electrochemical performance, the rapid decay of the electrode architecture during deformation, and complicated as well as costly production processes thus limiting their expansive applications. Herein, the recent progression in the exploration of carbonaceous materials and metals based flexible electrode materials are summarized and discussed, with special focus on determining their relative electrochemical performance and structural stability based on recent advancement. Major factors for the future advancement of FLIBs in this field are also discussed.

A Dual Protection System for Heterostructured 3D CNT/CoSe2/C as High Areal Capacity Anode for Sodium Storage

3D electrode design is normally opted for multiple advantages, however, instability/detachment of active material causes the pulverization and degradation of the structure, and ultimately poor cyclic stability. Here, a dually protected, highly compressible, and freestanding anode is presented for sodium-ion batteries, where 3D carbon nanotube (CNT) sponge is decorated with homogeneously dispersed CoSe2 nanoparticles (NPs) which are protected under carbon overcoat (CNT/CoSe2/C). The 3D CNT sponge delivers enough space for high mass loading while providing high mechanical strength and faster conduction pathway among the NPs. The outer amorphous carbon overcoat controls the formation of solid electrolyte interphase film by avoiding direct contact of CoSe2 with electrolyte, accommodates large volume changes, and ultimately enhances the overall conductivity of cell and assists in transmitting electron to an external circuit. Moreover, the hybrid can be densified up to 11-fold without affecting its microstructure that results in ultrahigh areal mass loading of 17.4 mg cm-2 and an areal capacity of 7.03 mAh cm-2 along with a high gravimetric capacity of 531 mAh g-1 at 100 mA g-1. Thus, compact and smart devices can be realized by this new electrode design for heavy-duty commercial applications.

Two-phase interface hydrothermal synthesis of binder-free SnS2/graphene flexible paper electrodes for high-performance Li-ion batteries

Binder-free SnS₂/graphene flexible paper produced from a two-phase interface hydrothermal reaction with excellent electrochemical performance for lithium-ion batteries.

Laser-etch patterning of metal oxide coated carbon nanotube 3D architectures

This paper describes a way to fabricate novel hybrid low density nanostructures containing both carbon nanotubes (CNTs) and ceramic nanotubes. Using atomic layer deposition, a thin film of aluminum oxide was conformally deposited on aligned multiwall CNT foams in which the CNTs make porous, three-dimensional interconnected networks. A CO₂ laser was used to etch pure alumina nanotube structures by burning out the underlying CNT substrate in discrete locations via the printed laser pattern. Structural and morphological transitions during the calcination process of aluminum oxide coated CNTs were investigated through in situ transmission electron microscopy and high-resolution scanning electron microscopy. Laser parameters were optimized to etch the CNT away (i.e. etching speed, power and focal length) while minimizing damage to the alumina nanotubes due to overheating. This study opens a new route for fabricating very low density three dimensionally patterned materials with areas of dissimilar materials and properties. To demonstrate the attributes of these structures, the etched areas were used toward anisotropic microfluidic liquid flow. The demonstration used the full thickness of the material to make complex pathways for the liquid flow in the structure. Through tuning of processing conditions, the alumina nanotube (etched) regions became hydrophilic while the bulk material remained hydrophobic and electrically conductive.

Tunable Free-Standing Core-Shell CNT@MoSe2 Anode for Lithium Storage

Heterogeneous nanostructuring of MoSe₂ over a carbon nanotube (CNT) sponge as a free-standing electrode not only brings higher performance but also eliminates the need for dead elements such as a binder, conductive carbon, and supportive current collectors. Further, the porous CNT sponge can be easily compacted via an intense densification of the active material MoSe₂ to produce an electrode with a high mass loading for a significantly improved areal capacity. In this work, we present a tunable coating of MoSe₂ on a CNT sponge to fabricate a core-shell MoSe₂@CNT anode. The three-dimensional nanotubular sponge is synthesized via a solvothermal process, followed by thermal annealing to improve crystallization. Structural and morphological studies revealed that MoSe₂ grew as a layered structure ( d = 0.66 nm), where numbers of layers can be controlled to yield optimized results for Li⁺ storage. We showed that the 10-layer core-shell CNT@MoSe₂ hybrid sponge delivered a discharge capacity of 820.5 mAh g^-1 after 100 cycles at 100 mA g^-1 with a high cyclic stability and rate capability. Further, an ex situ structural and morphological analysis revealed that ionic storage causes a phase change in MoSe₂ from a crystalline to a partial amorphous state for a continuous increase in the capacity with extended cycling. We believe that the strategy developed here will assist users to tune the electrode materials for future energy-storage devices, especially how the materials are changing with the passage of time and their effects on the device performance.

Flexible Electrodes for Sodium-Ion Batteries: Recent Progress and Perspectives

Sodium-ion batteries (SIBs) are considered as promising alternatives to lithium-ion batteries (LIBs) for large-scale electrical-energy-storage applications due to the wide availability and the low cost of Na resources. Along with the avenues of research on flexible LIBs, flexible SIBs are now being actively developed as one of the most promising power sources for the emerging field of flexible and wearable electronic devices. Here, the recent progress on flexible electrodes based on metal substrates, carbonaceous substrates (i.e., graphene, carbon cloth, and carbon nanofibers), and other materials, as well as their applications in flexible SIBs, are summarized. Also, some future research directions for constructing flexible SIBs are proposed, with the aim of providing inspiration to the further development of advanced flexible SIBs.

Unlocking the potential of SnS2: Transition metal catalyzed utilization of reversible conversion and alloying reactions

The alloying-dealloying reactions of SnS₂ proceeds with the initial conversion reaction of SnS₂ with lithium that produces Li₂S. Unfortunately, due to the electrochemical inactivity of Li₂S, the conversion reaction of SnS₂ is irreversible, which significantly limit its potential applications in lithium-ion batteries. Herein, a systematic understanding of transition metal molybdenum (Mo) as a catalyst in SnS₂ anode is presented. It is found that Mo catalyst is able to efficiently promote the reversible conversion of Sn to SnS₂. This leads to the utilization of both conversion and alloying reactions in SnS₂ that greatly increases lithium storage capability of SnS₂. Mo catalyst is introduced in the form of MoS₂ grown directly onto self-assembled vertical SnS₂ nanosheets that anchors on three-dimensional graphene (3DG) creating a hierarchal nanostructured named as SnS₂/MoS₂/3DG. The catalytic effect results in a significantly enhanced electrochemical properties of SnS₂/MoS₂/3DG; a high initial Coulombic efficiency (81.5%) and high discharge capacities of 960.5 and 495.6 mA h g⁻¹ at current densities of 50 and 1000 mA g⁻¹, respectively. Post cycling investigations using ex situ TEM and XPS analysis verifies the successful conversion reaction of SnS₂ mediated by Mo. The successful integration of catalyst on alloying type metal sulfide anode creates a new avenue towards high energy density lithium anodes.

Simple Synthesis of Nanocrystalline Tin Sulfide/N-Doped Reduced Graphene Oxide Composites as Lithium Ion Battery Anodes

Composites of nitrogen-doped reduced graphene oxide (NRGO) and nanocrystalline tin sulfides were synthesized, and their performance as lithium ion battery anodes was evaluated. Following the first cycle the composite consisted of Li₂S/Li_xSn/NRGO. The conductive NRGO cushions the stress associated with the expansion of lithiation of Sn, and the noncycling Li₂S increases the residual Coulombic capacity of the cycled anode because (a) Sn domains in the composite formed of unsupported SnS₂ expand only by 63% while those in the composite formed of unsupported SnS expand by 91% and (b) Li percolates rapidly at the boundary between the Li₂S and Li_xSn nanodomains. The best cycling SnS₂/NRGO-derived composite retained a specific capacity of 562 mAh g^-1 at the 200th cycle at 0.2 A g^-1 rate.

Controlled Synthesis of Core-Shell Carbon@MoS2 Nanotube Sponges as High-Performance Battery Electrodes

Heterogeneous inorganic nanotube structures consisting of multiwalled carbon nanotubes coated by long, continuous MoS₂ sheets with tunable sheet number are synthesized using a carbon-nanotube sponge as a template. The resulting 3D porous hybrid sponges have potential applications as high-performance freestanding anodes for Li-ion batteries with excellent specific capacity and cycling stability.