3D Pathways Enabling Highly-Efficient Lithium Reservoir for Fast-Charging Batteries.

Enhancing the mobility of lithium-ions (Li+ ) through surface engineering is one of major challenges facing fast-charging lithium-ion batteries (LIBs). In case of demanding charging conditions, the use of a conventional artificial graphite (AG) anode leads to an increase in operating temperature and the formation of lithium dendrites on the anode surface. In this study, a biphasic zeolitic imidazolate framework (ZIF)-AG anode, designed strategically and coated with a mesoporous material, is verified to improve the pathways of Li+ and electrons under a high charging current density. In particular, the graphite surface is treated with a coating of a ZIF-8-derived carbon nanoparticles, which addresses sufficient surface porosity, enabling this material to serve as an electrolyte reservoir and facilitate Li+ intercalation. Moreover, the augmentation in specific surface area proves advantageous in reducing the overpotential for interfacial charge transfer reactions. In practical terms, employing a full-cell with the biphasic ZIF-AG anode results in a shorter charging time and improved cycling performance, demonstrating no evidence of Li plating during 300 cycles under 3.0 C-charging and 1.0 C-discharging. The research endeavors to contribute to the progress of anode materials by enhancing their charging capability, aligning with the increasing requirements of the electric vehicle applications.

Dry-Electrode All-Solid-State Batteries Fortified with a Moisture Absorbent.

For realizing all-solid-state batteries (ASSBs), it is highly desirable to develop a robust solid electrolyte (SE) that has exceptional ionic conductivity and electrochemical stability at room temperature. While argyrodite-type Li6PS5Cl (LPSCl) SE has garnered attention for its relatively high ionic conductivity (∼3.19 × 10-3 S cm-1), it tends to emit hydrogen sulfide (H2S) in the presence of moisture, which can hinder the performance of ASSBs. To address this issue, researchers are exploring approaches that promote structural stability and moisture resistance through elemental doping or substitution. Herein, we suggest using zeolite imidazolate framework-8 as a moisture absorbent in LPSCl without modifying the structure of the SE or the electrode configuration. By incorporating highly ordered porous materials, we demonstrate that ASSBs configured with LPSCl SE display stable cyclability due to effective and long-lasting moisture absorption. This approach not only improves the overall quality of ASSBs but also lays the foundation for developing a moisture-resistant sulfide electrolyte.

Bi-Morphological Form of SiO2 on a Separator for Modulating Li-Ion Solvation and Self-Scavenging of Li Dendrites in Li Metal Batteries.

The lithium (Li) metal anode is highly desirable for high-energy density batteries. During prolonged Li plating-stripping, however, dendritic Li formation and growth are probabilistically high, allowing physical contact between the two electrodes, which results in a cell short-circuit. Engineering the separator is a promising and facile way to suppress dendritic growth. When a conventional coating approach is applied, it usually sacrifices the bare separator structure and severely increases the thickness, ultimately decreasing the volumetric density. Herein, we introduce dielectric silicon oxide with the feature of bi-morphological form, i.e., backbone-covered and backbone-anchored, onto the conventional polyethylene separator without any volumetric change. These functionally vary the Li+ transference number and the ionic conductivity so as to modulate Li-ion solvation and self-scavenging of Li dendrites. The proposed separator paves the way to maximizing the full cell performance of Li/NCM622 toward practical application.

Nanoarchitectonics of the cathode to improve the reversibility of Li-O2 batteries.

The strategic design of the cathode is a critical feature for high-performance and long-lasting reversibility of an energy storage system. In particular, the round-trip efficiency and cycling performance of nonaqueous lithium-oxygen batteries are governed by minimizing the discharge products, such as Li2O and Li2O2. Recently, a metal-organic framework has been directly pyrolyzed into a carbon frame with controllable pore volume and size. Furthermore, selective metallic catalysts can also be obtained by adjusting metal ions for outstanding electrochemical reactions. In this study, various bimetallic zeolitic imidazolate framework (ZIF)-derived carbons were designed by varying the ratio of Zn to Co ions. Moreover, carbon nanotubes (CNTs) are added to improve the electrical conductivity further, ultimately leading to better electrochemical stability in the cathode. As a result, the optimized bimetallic ZIF-carbon/CNT composite exhibits a high discharge capacity of 16,000 mAh·g-1, with a stable cycling performance of up to 137 cycles. This feature is also beneficial for lowering the overpotential of the cathode during cycling, even at the high current density of 2,000 mA·g-1.

Porous carbon architectures with different dimensionalities for lithium metal storage.

Lithium metal batteries have recently gained tremendous attention owing to their high energy capacity compared to other rechargeable batteries. Nevertheless, lithium (Li) dendritic growth causes low Coulombic efficiency, thermal runaway, and safety issues, all of which hinder the practical application of Li metal as an anodic material. In this review, the failure mechanisms of Li metal anode are described according to its infinite volume changes, unstable solid electrolyte interphase, and Li dendritic growth. The fundamental models that describe the Li deposition and dendritic growth, such as the thermodynamic, electrodeposition kinetics, and internal stress models are summarized. From these considerations, porous carbon-based frameworks have emerged as a promising strategy to resolve these issues. Thus, the main principles of utilizing these materials as a Li metal host are discussed. Finally, we also focus on the recent progress on utilizing one-, two-, and three-dimensional carbon-based frameworks and their composites to highlight the future outlook of these materials.

Strategic Approaches to the Dendritic Growth and Interfacial Reaction of Lithium Metal Anode.

Utilization of lithium (Li) metal anode is highly desirable for achieving high energy density batteries. Even so, the unavoidable features of Li dendritic growth and inactive Li are still the main factors that hinder its practical application. During plating and stripping, the solid electrolyte interphase (SEI) layer can provide passivation, playing an important role in preventing direct contact between the electrolyte and the electrode in Li metal batteries. Because of complexities of the electrolyte chemical and electrochemical reactions, the various formation mechanisms for the SEI are still not well understood. What we do know is that a strategic artificial SEI achieved through additives electrolyte can suppress the Li dendrites. Otherwise, the dendrites keep generating an abundance of irreversible Li, resulting in severe capacity loss, internal short-circuiting, and cell failure. In this minireview, we focus on the phenomenon of dendritic Li-growth and provide a brief overview of SEI formation. We finally provide some clear insights and perspectives toward practical application of Li metal batteries.

Patchable and Implantable 2D Nanogenerator.

With the development of technology, electronic devices are becoming more miniaturized and multifunctional. With the development of small electronic devices, they are changing from the conventional accessory type, which is portable, to the patchable type, which can be attached to a person's apparel or body, and the eatable/implantable type, which can be directly implanted into the human body. In this regard, it is necessary to address various technical issues, such as high-capacity/high-efficiency small-sized battery technology, component miniaturization, low power technology, flexible technology, and smart sensing technology. In addition, there is a demand for self-powered wireless systems in particular devices. A piezoelectric/triboelectric nanogenerator (PENG/TENG) can generate electric energy from small amounts of mechanical energy such as from blood flow and heartbeats in the human body as well as human movement, so it is expected that it will enable the development of self-powered wireless systems. Due to their unique properties, such as flexibility, transparency, mechanical stability, and nontoxicity, 2D materials are optimal materials for the development of implantable and patchable self-powered nanodevices in the human body. In this Review, the studies related to patchable and implantable devices for the human body using PENGs/TENGs based on 2D materials are discussed.

Biomolecular Piezoelectric Materials: From Amino Acids to Living Tissues.

Biomolecular piezoelectric materials are considered a strong candidate material for biomedical applications due to their robust piezoelectricity, biocompatibility, and low dielectric property. The electric field has been found to affect tissue development and regeneration, and the piezoelectric properties of biological materials in the human body are known to provide electric fields by pressure. Therefore, great attention has been paid to the understanding of piezoelectricity in biological tissues and its building blocks. The aim herein is to describe the principle of piezoelectricity in biological materials from the very basic building blocks (i.e., amino acids, peptides, proteins, etc.) to highly organized tissues (i.e., bones, skin, etc.). Research progress on the piezoelectricity within various biological materials is summarized, including amino acids, peptides, proteins, and tissues. The mechanisms and origin of piezoelectricity within various biological materials are also covered.

Everlasting Living and Breathing Gyroid 3D Network in Si@SiOx/C Nanoarchitecture for Lithium Ion Battery.

Silicon-based materials are the most promising candidates to surpass the capacity limitation of conventional graphite anode for lithium ion batteries. Unfortunately, Si-based materials suffer from poor cycling performance and dimensional instability induced by the large volume changes during cycling. To resolve such problems, nanostructured silicon-based materials with delicately controlled microstructure and interfaces have been intensively investigated. Nevertheless, they still face problems related to their high synthetic cost and their limited electrochemical properties and thermal stability. To overcome these drawbacks, we demonstrate the strategic design and synthesis of a gyroid three-dimensional network in a Si@SiOx/C nanoarchitecture (3D-Si@SiOx/C) with synergetic interaction between the computational prediction and the synthetic optimization. This 3D-Si@SiOx/C exhibits not only excellent electrochemical performance due to its structural stability and superior ion/electron transport but also enhanced thermal stability due to the presence of carbon, which was formed by a cost-effective one-pot synthetic route. We believe that our rationally designed 3D-Si@SiOx/C will lead to the development of anode materials for the next-generation lithium ion batteries.

Two-Dimensional Materials Inserted at the Metal/Semiconductor Interface: Attractive Candidates for Semiconductor Device Contacts.

Metal-semiconductor junctions are indispensable in semiconductor devices, but they have recently become a major limiting factor precluding device performance improvement. Here, we report the modification of a metal/n-type Si Schottky contact barrier by the introduction of two-dimensional (2D) materials of either graphene or hexagonal boron nitride (h-BN) at the interface. We realized the lowest specific contact resistivities (ρc) of 3.30 nΩ cm2 (lightly doped n-type Si, ∼ 1015/cm3) and 1.47 nΩ cm2 (heavily doped n-type Si, ∼ 1021/cm3) via 2D material insertion are approaching the theoretical limit of 1.3 nΩ cm2. We demonstrated the role of the 2D materials at the interface in achieving a low ρc value by the following mechanisms: (a) 2D materials effectively form dipoles at the metal-2D material (M/2D) interface, thereby reducing the metal work function and changing the pinning point, and (b) the fully metalized M/2D system shifts the pinning point toward the Si conduction band, thus decreasing the Schottky barrier. As a result, the fully metalized M/2D system using atomically thin and well-defined 2D materials shows a significantly reduced ρc. The proposed 2D material insertion technique can be used to obtain extremely low contact resistivities in metal/n-type Si systems and will help to achieve major performance improvements in semiconductor technologies.

Point-Defect-Passivated MoS2 Nanosheet-Based High Performance Piezoelectric Nanogenerator.

In this work, a sulfur (S) vacancy passivated monolayer MoS2 piezoelectric nanogenerator (PNG) is demonstrated, and its properties before and after S treatment are compared to investigate the effect of passivating S vacancy. The S vacancies are effectively passivated by using the S treatment process on the pristine MoS2 surface. The S vacancy site has a tendency to covalently bond with S functional groups; therefore, by capturing free electrons, a S atom will form a chemisorbed bond with the S vacancy site of MoS2 . S treatment reduces the charge-carrier density of the monolayer MoS2 surface, thus the screening effect of piezoelectric polarization charges by free carrier is significantly prevented. As a result, the output peak current and voltage of the S-treated monolayer MoS2 nanosheet PNG are increased by more than 3 times (100 pA) and 2 times (22 mV), respectively. Further, the S treatment increases the maximum power by almost 10 times. The results suggest that S treatment can reduce free-charge carrier by sulfur S passivation and efficiently prevent the screening effect. Thus, the piezoelectric output peaks of current, voltage, and maximum power are dramatically increased, as compared with the pristine MoS2 .

Reliable Piezoelectricity in Bilayer WSe2 for Piezoelectric Nanogenerators.

Recently, piezoelectricity has been observed in 2D atomically thin materials, such as hexagonal-boron nitride, graphene, and transition metal dichalcogenides (TMDs). Specifically, exfoliated monolayer MoS2 exhibits a high piezoelectricity that is comparable to that of traditional piezoelectric materials. However, monolayer TMD materials are not regarded as suitable for actual piezoelectric devices due to their insufficient mechanical durability for sustained operation while Bernal-stacked bilayer TMD materials lose noncentrosymmetry and consequently piezoelectricity. Here, it is shown that WSe2 bilayers fabricated via turbostratic stacking have reliable piezoelectric properties that cannot be obtained from a mechanically exfoliated WSe2 bilayer with Bernal stacking. Turbostratic stacking refers to the transfer of each chemical vapor deposition (CVD)-grown WSe2 monolayer to allow for an increase in degrees of freedom in the bilayer symmetry, leading to noncentrosymmetry in the bilayers. In contrast, CVD-grown WSe2 bilayers exhibit very weak piezoelectricity because of the energetics and crystallographic orientation. The flexible piezoelectric WSe2 bilayers exhibit a prominent mechanical durability of up to 0.95% of strain as well as reliable energy harvesting performance, which is adequate to drive a small liquid crystal display without external energy sources, in contrast to monolayer WSe2 for which the device performance becomes degraded above a strain of 0.63%.

Noise and sensitivity characteristics of solid-state nanopores with a boron nitride 2-D membrane on a pyrex substrate.

We have fabricated highly sensitive and low noise solid-state nanopores with multiple layers of boron nitride (BN) membranes transferred onto a pyrex substrate. Both the dielectric and flicker noise of the device, which have been described as one of the bottlenecks to making highly sensitive 2-D membrane nanopore devices, have been reduced as follows. Firstly, a pyrex substrate with a low dielectric constant (εr = 4.7-5.1) and low dielectric loss (D < 0.001) is used instead of a Si substrate to reduce the dielectric noise of the device. Secondly, flicker noise is minimized by employing a 100 nm thick SiNx supporting layer with a small opening (less than 100 nm) for BN membrane transfer to enhance the mechanical stability. The flicker noise is further reduced by transferring multiple layers of BN instead of a single layer of BN. The resulting multi-layered BN device shows significant reduction of dielectric and 1/f noise as compared to the devices with a single layer of the BN and Si substrate. Furthermore, we demonstrate dsDNA translocations with a high signal to noise ratio around 50 at 100 and 10 kHz bandwidths.

Surface energy and wettability of van der Waals structures.

The wetting behaviour of surfaces is believed to be affected by van der Waals (vdW) forces; however, there is no clear demonstration of this. With the isolation of two-dimensional vdW layered materials it is possible to test this hypothesis. In this paper, we report the wetting behaviour of vdW heterostructures which include chemical vapor deposition (CVD) grown graphene, molybdenum disulfide (MoS2) and tungsten disulfide (WS2) on few layers of hexagon boron nitride (h-BN) and SiO2/Si. Our study clearly shows that while this class of two-dimensional materials are not completely wetting transparent, there seems to be a significant amount of influence on their wetting properties by the underlying substrate due to dominant vdW forces. Contact angle measurements indicate that graphene and graphene-like layered transitional metal dichalcogenides invariably have intrinsically dispersive surfaces with a dominating London-vdW force-mediated wettability.

Formation of hexagonal boron nitride by metal atomic vacancy-assisted B-N molecular diffusion.

Because of the low solubility of N atoms in metals, hexagonal boron nitride (h-BN) growth has explained by surface reaction on metal rather than by penetration/precipitation of B and N atoms in metal. Here, we present an impressive pathway of h-BN formation at the interface between Ni and oxide substrate based on B-N molecular diffusion into Ni through individual atomic vacancies. First-principles calculations confirmed the formation energies of the h-BN layers on and under the metal and the probability of B-N molecular diffusion in metal. The interface growth behavior depends on the species of metal catalysts, and these simulation results well support experimental results.

Ridge formation and removal via annealing in exfoliated graphene.

It is well known that graphene is a very promising material due to its excellent physical, chemical, and thermal properties. Previously, ridges in graphene on a substrate were found in epitaxial graphene on a SiC substrate. It was found in this study that ridges can be made on a graphene layer via mechanical exfoliation on a sapphire substrate, and that ridges can be created or removed through heating and cooling. Due to the difference of the thermal-expansion coefficients of the substrate and graphene, it can be said that thermal cycling causes compressive strain, which is released by forming ridges. Annealing was carried out in a vacuum chamber within the pressure range of 10(-3)-10(-6) Torr and at 900-1100 degrees C. To analyze the shapes and mechanical properties of the ridges, Raman spectroscopy and AFM measurement were performed. It was found that the ridges can be extended by defect as a nucleation center, and the graphene layer can be folded along the preexisting ridge during heating and cooling.