Liquid Exfoliation Few-Layer SnSe Nanosheets with Tunable Band Gap

Two-dimensional (2D) materials have recently drawn tremendous attention because of their novel properties and potential applications in high-speed transistors, solar cells, and catalysts. Few-layer SnSe is a new member of the 2D family with excellent performance in optoelectronic and thermoelectric devices. It is necessary to synthesize few-layer SnSe nanosheets in large scale for various applications. In this work, we develop a scalable liquid-phase exfoliation method to synthesize high-quality crystalline SnSe nanosheets. The morphology and microstructure of SnSe nanosheets are systematically investigated with high-resolution transmission electron microscopy, atomic force microscopy, and Raman spectroscopy. The thinnest nanosheets are bilayered. The optical absorption properties of SnSe nanosheets from near-infrared to ultraviolet light are studied. It is worth noting that the band gap of the nanosheets monotonically increases with the reduction of the nanosheet thickness. The electronic structure of SnSe nanosheets with various thicknesses is calculated by first-principles calculations, the evolution of the band gap as a function of the nanosheet thickness is confirmed, and the mechanism of the band gap evolution is discussed. Our work paves the way for the scalable synthesis of 2D SnSe with tunable optical absorption and band gap, which has potential for use in photoelectronic and photocatalytic applications

Achieving High Energy Density in PVDF-Based Polymer Blends: Suppression of Early Polarization Saturation and Enhancement of Breakdown Strength

Polymers with high dielectric strength and favorable flexibility have been considered promising materials for dielectrics and energy storage applications, while the achievable energy density (<i>U</i>_e) of polymer is rather limited by the intrinsic low dielectric constant and ferroelectric hysteresis. Polyvinylidene fluoride-trifluoroethylene-chlorofluoroethylene (P­(VDF-TrFE-CFE)) with ultrahigh ε_r of >50 is considered promising in achieving high <i>U</i>_e of polymer dielectrics. However, P­(VDF-TrFE-CFE) only exhibits moderate <i>U</i>_e due to the early saturation of electrical polarization at low electric field. In this contribution, we show that, by blending P­(VDF-TrFE-CFE) with polyvinylidene fluoride (PVDF), the early saturation of P­(VDF-TrFE-CFE) is substantially suppressed, giving rise to concomitant enhancement of dielectric permittivity and breakdown strength. An ultrahigh energy density of 19.6 J/cm³ is thus achieved at ∼640 kV/mm, which is 1600% greater than <i>U</i>_e of the benchmark biaxially oriented polypropylene (BOPP, 1.2 J/cm³ at 640 kV/mm). Results of phase field simulations reveal that the interfaces between PVDF and P­(VDF-TrFE-CFE) play a critical role by not only suppressing early saturation of electrical polarization in P­(VDF-TrFE-CFE) but also inducing additional interfacial polarization. Binary phase diagram of P­(VDF-TrFE-CFE)/PVDF blends is also systematically explored with their dielectric and energy storage behavior studied

Oxygen Vacancy Dynamics at Room Temperature in Oxide Heterostructures

Oxygen vacancy dynamic behavior at room temperature in complex oxides was carefully explored by using a combined approach of ion liquid gating technique and resistance measurements. Heterostructures of PrBaCo₂O_5+δ/Gd₂O₃-doped CeO₂ epitaxial thin films were fabricated on (001) Y₂O₃-stabilized ZrO₂ single crystal substrates for systematically investigating the oxygen redox dynamics. The oxygen dynamic changes as response to the gating voltage and duration were precisely detected by in situ resistance measurements. A reversible and nonvolatile resistive switching dynamics was detected at room temperature under the gating voltage >13.5 V with pulse duration >1 s

Oxygen Vacancy Dynamics at Room Temperature in Oxide Heterostructures

Oxygen vacancy dynamic behavior at room temperature in complex oxides was carefully explored by using a combined approach of ion liquid gating technique and resistance measurements. Heterostructures of PrBaCo₂O_5+δ/Gd₂O₃-doped CeO₂ epitaxial thin films were fabricated on (001) Y₂O₃-stabilized ZrO₂ single crystal substrates for systematically investigating the oxygen redox dynamics. The oxygen dynamic changes as response to the gating voltage and duration were precisely detected by in situ resistance measurements. A reversible and nonvolatile resistive switching dynamics was detected at room temperature under the gating voltage >13.5 V with pulse duration >1 s

Direct Ink Writing of Low-Concentration MXene/Aramid Nanofiber Inks for Tunable Electromagnetic Shielding and Infrared Anticounterfeiting Applications

MXene inks offer a promising avenue for the scalable production and customization of printing electronics. However, simultaneously achieving a low solid content and printability of MXene inks, as well as mechanical flexibility and environmental stability of printed objects, remains a challenge. In this study, we overcame these challenges by employing high-viscosity aramid nanofibers (ANFs) to optimize the rheology of low-concentration MXene inks. The abundant entangled networks and hydrogen bonds formed between MXene and ANF significantly increase the viscosity and yield stress up to 103 Pa·s and 200 Pa, respectively. This optimization allows the use of MXene/ANF (MA) inks at low concentrations in direct ink writing and other high-viscosity processing techniques. The printable MXene/ANF inks with a high conductivity of 883.5 S/cm were used to print shields with customized structures, achieving a tunable electromagnetic interference shielding effectiveness (EMI SE) in the 0.2–48.2 dB range. Furthermore, the MA inks exhibited adjustable infrared (IR) emissivity by changing the ANF ratio combined with printing design, demonstrating the application for infrared anticounterfeiting. Notably, the printed MXene/ANF objects possess outstanding mechanical flexibility and environmental stability, which are attributed to the reinforcement and protection of ANF. Therefore, these findings have significant practical implications as versatile MXene/ANF inks can be used for customizable, scalable, and cost-effective production of flexible printed electronics

Tuning Phase Composition of Polymer Nanocomposites toward High Energy Density and High Discharge Efficiency by Nonequilibrium Processing

Polymer nanocomposite dielectrics with high energy density and low loss are major enablers for a number of applications in modern electronic and electrical industry. Conventional fabrication of nanocomposites by solution routes involves equilibrium process, which is slow and results in structural imperfections, hence high leakage current and compromised reliability of the nanocomposites. We propose and demonstrate that a nonequilibrium process, which synergistically integrates electrospinning, hot-pressing and thermal quenching, is capable of yielding nanocomposites of very high quality. In the nonequilibrium nanocomposites of poly­(vinylidene fluoride-<i>co</i>-hexafluoropropylene) (P­(VDF-HFP)) and BaTiO₃ nanoparticles (BTO_nps), an ultrahigh Weibull modulus β of ∼30 is achieved, which is comparable to the quality of the bench-mark biaxially oriented polypropylene (BOPP) fabricated with melt-extrusion process by much more sophisticated and expensive industrial apparatus. Favorable phase composition and small crystalline size are also induced by the nonequilibrium process, which leads to concomitant enhancement of electric displacement and breakdown strength of the nanocomposite hence a high energy density of ∼21 J/cm³. Study on the polarization behavior and phase transformation at high electric field indicates that BTO_nps could facilitate the phase transformation from α- to β-polymorph at low electric field

Lithium-Salt-Rich PEO/Li_0.3La_0.557TiO₃ Interpenetrating Composite Electrolyte with Three-Dimensional Ceramic Nano-Backbone for All-Solid-State Lithium-Ion Batteries

Solid electrolytes with high ionic conductivity and good mechanical properties are required for solid-state lithium-ion batteries. In this work, we synthesized composite polymer electrolytes (CPEs) with a three-dimensional (3D) Li_0.33La_0.557TiO₃ (LLTO) network as a nano-backbone in poly­(ethylene oxide) matrix by hot-pressing and quenching. Self-standing 3D-CPE membranes were obtained with the support of the LLTO nano-backbone. These membranes had much better thermal stability and enhanced mechanical strength in comparison with solid polymer electrolytes. The influence of lithium (Li) salt concentration on the conductivity of 3D-CPEs was systematically studied, and an ionic conductivity as high as 1.8 × 10^–4 S·cm^–1 was achieved at room temperature. The electrochemical window of the 3D-CPEs was 4.5 V vs Li/Li⁺. More importantly, the 3D-CPE membranes could suppress the growth of Li dendrite and reduce polarization; therefore, a symmetric Li|3D-CPE|Li cell with these membranes was cycled at a current density of 0.1 mA·cm^–2 for over 800 h. All of the superior properties above made the 3D-CPEs with the LLTO nano-backbone a promising electrolyte candidate for flexible solid-state lithium-ion batteries

High Capacity and Superior Cyclic Performances of All-Solid-State Lithium Batteries Enabled by a Glass–Ceramics Solo

By using highly Li-ion conductive 78Li₂S–22P₂S₅ glass–ceramic (7822gc) as both the electrolyte and active material in the composite cathode obtained via ball-milling the 7822gc with multiple carbons, a kind of monolithic all-solid-state batteries were prepared with a lithium–indium foil as the anode. Such 7822gc-based monolithic batteries present stable discharge capacity of 480.3 mA h g^–1 at 0.176 mA cm^–2 after 60 cycles, which is three times larger than that of the previous work, with the highest capacity obtained so far among all attempts of using sulfide electrolytes as the active materials. High capacity retention of 90.6% and Coulombic efficiency of higher than 99% with high active material loading of 7 mg cm^–2 were also obtained. X-ray photoelectron spectroscopy was used to reveal the electrochemical reaction mechanisms in the 7822gc cathode

Synergistic Coupling between Li_6.75La₃Zr_1.75Ta_0.25O₁₂ and Poly(vinylidene fluoride) Induces High Ionic Conductivity, Mechanical Strength, and Thermal Stability of Solid Composite Electrolytes

Easy processing and flexibility of polymer electrolytes make them very promising in developing all-solid-state lithium batteries. However, their low room-temperature conductivity and poor mechanical and thermal properties still hinder their applications. Here, we use Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO) ceramics to trigger structural modification of poly­(vinylidene fluoride) (PVDF) polymer electrolyte. By combining experiments and first-principle calculations, we find that La atom of LLZTO could complex with the N atom and CO group of solvent molecules such as <i>N</i>,<i>N</i>-dimethylformamide along with electrons enriching at the N atom, which behaves like a Lewis base and induces the chemical dehydrofluorination of the PVDF skeleton. Partially modified PVDF chains activate the interactions between the PVDF matrix, lithium salt, and LLZTO fillers, hence leading to significantly improved performance of the flexible electrolyte membrane (<i>e.g.</i>, a high ionic conductivity of about 5 × 10^–4 S cm^–1 at 25 °C, high mechanical strength, and good thermal stability). For further illustration, a solid-state lithium battery of LiCoO₂|PVDF-based membrane|Li is fabricated and delivers satisfactory rate capability and cycling stability at room temperature. Our study indicates that the LLZTO modifying PVDF membrane is a promising electrolyte used for all-solid-state lithium batteries

Lattice Dynamics and Thermal Conductivity in Cu₂Zn_1–<i>x</i>Co_<i>x</i>SnSe₄

The quaternary compound Cu₂ZnSnSe₄ (CZTSe), as a typical candidate for both solar cells and thermoelectrics, is of great interest for energy harvesting applications. Materials with a high thermoelectric efficiency have a relatively low thermal conductivity, which is closely related to their chemical bonding and lattice dynamics. Therefore, it is essential to investigate the lattice dynamics of materials to further improve their thermoelectric efficiency. Here we report a lattice dynamic study in a cobalt-substituted CZTSe system using temperature-dependent X-ray absorption fine structure spectroscopy (TXAFS). The lattice contribution to the thermal conductivity is dominant, and its reduction is mainly ascribed to the increment of point defects after cobalt substitution. Furthermore, a lattice dynamic study shows that the Einstein temperature of atomic pairs is reduced after cobalt substitution, revealing that increasing local structure disorder and weakened bonding for each of the atomic pairs are achieved, which gives us a new perspective for understanding the behavior of lattice thermal conductivity