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van der Waals (vdW) superlattices, comprising different 2D materials aligned alternately by weak interlayer interactions, offer versatile structures for the fabrication of novel semiconductor devices. Despite their potential, the precise control of optoelectronic properties with interlayer interactions remains challenging. Here, we investigate the discrepancies between the SnS/TiS 2 superlattice (SnTiS 3 ) and its subsystems by comprehensive characterization and DFT calculations. The disappearance of certain Raman modes suggests that the interactions alter the SnS subsystem structure. Specifically, such structural changes transform the band structure from indirect to direct band gap, causing a strong PL emission (∼2.18 eV) in SnTiS 3 . In addition, the modulation of the optoelectronic properties ultimately leads to the unique phenomenon of thermally activated photoluminescence. This phenomenon is attributed to the inhibition of charge transfer induced by tunable intralayer strains. Our findings extend the understanding of the mechanism of interlayer interactions in van der Waals superlattices and provide insights into the design of high-temperature optoelectronic devices.

The continuous advancements in studying two-dimensional (2D) materials pave the way for groundbreaking innovations across various industries. In this study, by employing density functional theory calculations, we comprehensively elucidate the electronic structures of MZX (M = Ga and In; Z = Si, Ge, and Sn; X = S, Se, and Te) monolayers for their applications in photocatalytic, thermoelectric, and spintronic fields. Interestingly, GaSiS, GaSiSe, InSiS, and InSiSe monolayers are identified to be efficient photocatalysts for overall water splitting with band gaps close to 2.0 eV, suitable band edge positions, and excellent optical harvest ability. In addition, the InSiTe monolayer exhibits a ZT value of 1.87 at 700 K, making it highly appealing for applications in thermoelectric devices. It is further highlighted that GaSnTe, InSnS, and InSnSe monolayers are predicted to be 2D topological insulators (TIs) with bulk band gaps of 115, 54, and 152 meV, respectively. Current research expands the family of 2D GaGeTe materials and establishes a path toward the practical utilization of MZX monolayers in energy conversion and spintronic devices.

Although two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit attractive prospects for gas-sensing applications, the rapid and precise sensing of TMDs at low loss remains challenging. Herein, a NO 2 sensor based on an expanded VS 2 (VS 2 - E )/carbon nanofibers (CNFs) composite (abbreviated as VS 2 -E-C ) with ultrafast response/recovery at a low-loss state is reported. In particular, the impact of the CNF content on the NO 2 -sensing performance of VS 2 -E-C was thoroughly explored. Expanded VS 2 nanosheets were grafted onto the surface of hollow CNFs, and the combination boosted the charge transport, exposing abundant active edges of VS 2 , which enhanced the adsorption of NO 2 efficiently. The activity of the VS 2 edge is further confirmed by stronger NO 2 adsorption with a more negative adsorption energy (-3.42 eV) and greater than the basal VS 2 surface (-1.26 eV). Moreover, the exposure of rich edges induced the emergence of the expanded interlayers, which promoted the adsorption/desorption of NO 2 and the interaction of gas molecules within VS 2 -E-C . The synergism of edge effect and interlayer engineering confers the VS 2 -E-C3 sensor with ultrafast response/recovery speed (9/10 s) at 60 °C, high sensitivity (∼2.50 to 15 ppm NO 2 ), good selectivity/stability, and a low detection limit of 23 ppb. The excellent "4S" functions indicate the promising prospect of the VS 2 -E-C3 sensor for fast and precise NO 2 detection at low-loss condition.

For lithium metal batteries (LMBs), the elevated operating temperature results in severe capacity fading and safety issues due to unstable electrode-electrolyte interphases and electrolyte solvation structures. Therefore, it is crucial to construct advanced electrolytes capable of tolerating harsh environments to ensure stable LMBs. Here, we proposed a stable localized high-concentration electrolyte (LHCE) by introducing the highly solvating power solvent diethylene glycol dimethyl ether (DGDME). Computational and experimental evidence discloses that the original DGDME-LHCE shows favorable features for high-temperature LMBs, including high Li + -binding stability, electro-oxidation resistance, thermal stability, and nonflammability. The tailored solvated sheath structure achieves the preferred decomposition of anions, inducing the stable (cathode and Li anode)/interphases simultaneously, which enables a homogeneous Li plating-stripping behavior on the anode side and a high-voltage tolerance on the cathode side. For the Li||Li cells coupled with DGDME-LHCE, they showcase outstanding reversibility (a long lifespan of exceeding 1900 h). We demonstrate exceptional cyclic stability (∼95.59%, 250 cycles), high Coulombic efficiency (>99.88%), and impressive high-voltage (4.5 V) and high-temperature (60 °C) performances in Li||NCM523 cells using DGDME-LHCE. Our advances shed light on an encouraging ether electrolyte tactic for the Li-metal batteries confronted with stringent high-temperature challenges.

Ti, Cr dual-element-doped LiMn 1.5 Ni 0.5 O 4 (LNMO) cathode materials (LTNMCO) were synthesized by a simple high-temperature solid-phase method. The obtained LTNMCO shows the standard structure of the Fd 3 ®m space group, and the Ti and Cr doped ions may replace the Ni and Mn sites in LNMO, respectively. The effect of Ti-Cr doping and single-element doping on the structure of LNMO was studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) characteristics. The LTNMCO exhibited excellent electrochemical properties with a specific capacity of 135.1 mAh·g -1 for the first discharge cycle and a capacity retention rate of 88.47% at 1C after 300 cycles. The LTNMCO also has high rate performance with a discharge capacity of 125.4 mAh·g -1 at a 10C rate, 93.55% of that at 0.1C. In addition, the CIV and EIS results show that the LTNMCO showed the lowest charge transfer resistance and the highest diffusion coefficient of lithium ions. The enhanced electrochemical properties may be due to a more stable structure and an optimized Mn 3+ content in LTNMCO through TiCr doping., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The problems of lithium-ion battery (LIB) failure have attracted growing attention since flammable and explosive electrolyte leakage might lead to serious consequences. However, due to the redox-neutral and volatile nature of main electrolyte components, such as dimethyl carbonate (DMC), trace leakages are difficult to detect. Therefore, research on LIB electrolyte sensors is urgent and lacking. Herein, sensors based on rare-earth Nd-doped SnO 2 nanofibers are reported for detecting DMC vapor in LIB. The excellent sensitivity (distinct response to 20 ppb DMC), high response (∼38.13-50 ppm DMC), and superior selectivity and stability of 3%Nd-SnO 2 suggest that it should be a promising candidate for LIB safety monitors. Meanwhile, it also shows clear and rapid response during the LIB-leakage real-time detection experiment. The doping of Nd endows SnO 2 with more oxygen vacancy defects. In addition, the highly active Nd sites greatly enhanced the adsorption energy of DMC on SnO 2 . All of these features contribute to the improvement of DMC-sensing performances.

Triggered by the expanding demands of semiconductor devices, strain engineering of two-dimensional transition metal dichalcogenides (TMDs) has garnered considerable research interest. Through steady-state measurements, strain has been proved in terms of its modulation of electronic energy bands and optoelectronic properties in TMDs. However, the influence of strain on the spin-orbit coupling as well as its related valley excitonic dynamics remains elusive. Here, we demonstrate the effect of strain on the excitonic dynamics of monolayer WS 2 via steady-state fluorescence and transient absorption spectroscopy. Combined with theoretical calculations, we found that tensile strain can reduce the spin-splitting value of the conduction band and lead to transitions between different exciton states via spin-flip mechanism. Our findings suggest that the spin-flip process is strain-dependent, provides a reference for application of valleytronic devices, where tensile strain is usually existing during their design and fabrication.

A combination of transparency and photochromic (PC) properties in ferroelectrics has promising application potential in smart windows and optical storage/imaging. Nonetheless, limited by understanding the underlying PC mechanism, a splendid PC performance is rarely achieved in transparent ferroelectrics. Here, a strategy to construct deep-lying traps by ion-doping induced defect engineering in (K 0.5 Na 0.5 )NbO 3 -based ferroelectric ceramics is proposed. Based on the improved density functional theory simulations, a high concentration of vacancy defects can be realized by codoping 1 mol % Pr and 4 mol % Ba in (K 0.5 Na 0.5 )NbO 3 , which helps achieving deep-lying traps and then superior PC performance. Through traditional pressureless sintering, highly transparent ceramics with designed optimal composition have been fabricated in a wide sintering temperature range (1170-1210 °C), exhibiting an ultrafast PC feature, i.e., 0.1 s response time (by illumination of 400 nm light), along with high PC efficiency (5.8 cm 2 ·W -1 ) and PC rate (7.1 s -1 ), preeminent among reported inorganic PC transparent materials. Additionally, the ceramics have been utilized for real-time optical recording, displaying unambiguous patterning with long-time preservation (21 days). This research supplies a paradigm for designing high-performance PC transparent materials in optical applications and helps deepen the comprehensive understanding of the PC mechanism.

Lithium (Li) metal batteries with high energy density are of great promise for next-generation energy storage; however, they suffer from severe Li dendritic growth and an unstable solid electrolyte interphase. In this study, a mixed ionic and electronic conductive (MIEC) interphase layer with an adjustable ratio assembled by ZnO and Zn nanoparticles is developed. During the initial cycle, the in situ formed Li 2 O with high ionic conductivity and a lithiophilic LiZn alloy with high electronic conductivity enable fast Li + transportation in the interlayer and charge transfer at the ion/electron conductive junction, respectively. The optimized interface kinetics is achieved by balancing the ion migration and charge transfer in the MIEC Li 2 O-LiZn interphase. As a result, the symmetric cell with MIEC interphase delivers superior cycling stability of over 1200 h. Also, Li||Zn-ZnO@PP||LFP (LFP = LiFePO 4 ) full cells exhibit long cyclic life for 2000 cycles with a very high capacity retention of 91.5% at a high rate of 5 C and stable cycling for 350 cycles at a high LFP loading mass of 13.27 mg cm -2 .

Recently, nonclassical fullerene derivatives C 66 H 4 and C 70 Cl 6 , which both contain two negatively curved moieties of heptagons, have been successfully synthesized. Inspired by these experimental achievements, the structural and electronic properties of C 66 H 4 , C 70 Cl 6 , Li@C 66 H 4 , F@C 66 H 4 , Li@C 70 Cl 6 , and F@C 70 Cl 6 were systematical studied through density functional theory calculations in this work. Our results show that the reduction of the front molecular orbital gap of fullerene derivatives occurs with the introduction of Li and F atoms. After quantitative analysis of back-donations of charge between an encapsulated atom and an external carbon cage, it is found that C 66 H 4 and C 70 Cl 6 prefer to act as electron acceptors. It is interesting to note that the strong covalent nature of the interactions between a F atom and a carbon cage is observed, whereas the weak covalent and strong ionic interactions occur between a Li atom and a carbon cage. On the other hand, according to the first hyperpolarizability results, the encapsulation of the Li atom enhances the nonlinear optical response of fullerene derivatives. This work provides a strategy to improve nonlinear optical properties of C 66 H 4 and C 70 Cl 6 , reveals the internal mechanism of the contribution from Li and F atoms to endohedral fullerene derivatives, and will contribute to the designation of endohedral fullerene derivative devices., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Lithium-rich manganese-based (LRM) layered oxides are considered as one of the most promising cathode materials for next-generation high-energy-density lithium-ion batteries (LIBs) because of their high specific capacity (>250 mAh g -1 ). However, they also go through severe capacity decay, serious voltage fading, and poor rate capability during cycling. Herein, a multiscale deficiency integration, including surface coating, subsurface defect construction, and bulk doping, is realized in a Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2 cathode material by facile Na-rich engineering through a sol-gel method. This multiscale design can significantly improve the bulk and surface structural stability and diffusion rate of Li + ions of electrode materials. Specifically, an outstanding specific capacity of 201 mAh g -1 is delivered at 1C of the designed cathode material after 400 cycles, relating to a large capacity retention of 89.0%. Meanwhile, the average voltage is retained up to 3.13 V with a large voltage retention of 89.6% and the energy density is maintained at 627.4 Wh kg -1 . In situ X-ray diffraction (XRD), ex situ transmission electron microscopy (TEM) investigations, and density functional theory (DFT) calculations are conducted to explain the greatly enhanced electrochemical properties of a LRM cathode. We believe that this strategy would be a meaningful reference of LRM cathode materials for the research in the future.

The efficient nondestructive assessment of quality and homogeneity for two-dimensional (2D) MoS 2 is critically important to advance their practical applications. Here, we presented a rapid and large-area assessment method for visually evaluating the quality and uniformity of chemical vapor deposition (CVD)-grown MoS 2 monolayers simply with conventional optical microscopes. This was achieved through one-pot adsorbing abundant sulfur particles selectively onto as-grown poorer-quality MoS 2 monolayers in a CVD system without any additional treatment. We further revealed that this favorable adsorption of sulfur particles on MoS 2 originated from their intrinsic higher-density sulfur vacancies. Based on unadsorbed MoS 2 monolayers, superior performance field effect transistors with a mobility of ∼49 cm 2 V -1 s -1 were constructed. Importantly, the assessment approach was noninvasive due to the all-vapor-phase and moderate adsorption-desorption process. Our work offers a new route for the performance and yield optimization of devices by quality assessment of 2D semiconductors prior to device fabrication.

A new trend is emerging that flexible batteries will play an indispensable role in the progress of social science and technology. However, flexibility exists only in a single direction for the existing electrode material. Searching for flexible battery materials has attracted more and more attention from researchers. In this article, the lattice structural stability, electronic structure modulation, and the Li adsorption properties of the heterostructures designed by assembling GeP 3 and NbX 2 (X = S, Se) together were methodically explored based on van der Waals. We found that diffusion barrier of the GeP 3 /NbS 2 heterostructure with metallic properties is 0.21 eV for Li. It greatly improves the charge and discharge performance of the battery. The predicted heterostructure shows quite high theoretical specific capacity with 540.24 mA h/g, which is higher than the traditional graphite anode (372 mA h/g). It demonstrates superior isotropic flexibility with a considerable small Young's modulus (151.98-159.02 N/m), which has promising application as flexible electrodes for rechargeable battery equipment., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The lead-free 0.5(Ba 0.7 Ca 0.3 )TiO 3 -0.5Ba(Ti 0.8 Zr 0.2 )O 3 (BCTZ) ceramics with Er doping have shown good upconversion photoluminescence (PL) and desirable optical temperature sensing properties. To bridge a relationship between the structure/intrinsic defects and properties of rare-earth-doped ferroelectrics, we designed and fabricated a series of BCTZ ceramics doped with 1 mol % Er 3+ by combining the first-principles calculations and experimental measurements. Theoretically, we discovered that Er can occupy both A sites (i.e., replacing Ba or Ca) and B sites (i.e., replacing Ti or Zr) in the BCTZ lattice and highlighted that the Er-doping-induced vacancy concentration decreases for both the oxygen vacancies ( V o ) and cation vacancies ( V c ). Experimentally, the enhanced PL performance and the dielectric, ferroelectric, and piezoelectric properties of the Er-doped BCTZ ceramics have been observed. Finally, the physical origin of Er-induced property enhancement in BCTZ has been elaborated according to the charge density and chemical bonding analysis. These results open up a path to investigate the effects of site substitution and vacancies on optoelectronic properties of multifunctional rare-earth-doped ferroelectrics., Competing Interests: The authors declare no competing financial interest.

The development of bimetallic transition-metal sulfide and nitrogen-doped carbon composites with unique hollow structure is highly desirable for energy storage applications but is also challenging. In the present work, we demonstrate a facile metal-organic framework engaged strategy for synthesizing bimetallic nickel cobalt sulfide and nitrogen-doped carbon composites with hollow spherical structure (denoted as hollow Ni-Co-S- n/NC composites) and a Ni/Co molar ratio ( n value) that can be easily controlled. When evaluated as electrode materials for both supercapacitors and lithium ion batteries, it is found that the hollow Ni-Co-S-0.5/NC composite with a Ni/Co molar ratio of 0.5 exhibits optimal electrochemical performance. The hollow Ni-Co-S-0.5/NC composite exhibits a high specific capacity of 543.9 C g -1 at 1 A g -1 and maintains a capacity retention of 67.3% when the current density is increased to 20 A g -1 . An asymmetric supercapacitor based on the hollow Ni-Co-S-0.5/NC composite is fabricated, which shows good electrochemical performance with a high energy density of 39.6 W h kg -1 at a power density of 808 W kg -1 . For lithium storage, the hollow Ni-Co-S-0.5/NC composite manifests a high reversible discharge capacity of 755.0 mA h g -1 at 200 mA g -1 for 200 cycles as well as good rate capability. The excellent electrochemical performance could be attributed to the desirable structural, compositional, and component advantages. This work could offer new insight into the rational design and synthesis of highly efficient electrode materials for both supercapacitors and lithium ion batteries.

Anisotropic two-dimensional materials with direction-dependent mechanical and optical properties have attracted significant attention in recent years. In this work, based on density functional theory calculations, unexpected elastic anisotropy and optical isotropy in van der Waals (vdW) heterostructures have been theoretically proposed by assembling the well-known anisotropic black phosphorene (BP) and transition-metal trisulfides MS 3 (M = Ti, Hf) together. It is interesting to see that the BP/MS 3 vdW heterostructures show anisotropic flexibility in different directions according to the elastic constants, Young's modulus, and Poisson's ratio. We have further unraveled their physical origin of the type-II band structure nature with their conduction band minimum and valence band maximum separated in different layers. In particular, our results on the optical response functions including the excitonic effects of the BP/MS 3 vdW heterostructures suggest their unexpected optical isotropies together with the enhancements of the solar energy conversion efficiency., Competing Interests: The authors declare no competing financial interest.

Tc-based oxides are of interest because of their complex crystalline structures. In this work, the phonon dispersions, lattice distortions, and elastic constants of TcO 2 at external pressures up to 120 GPa were comprehensively studied using first-principles calculations. It is found that the lattice dynamic stability of TcO 2 can be assessed by fitting the Γ-Z acoustical phonon branch. The applied external pressure can be divided into three ranges: the low-pressure stable range, the middle-pressure buckling range, and the high-pressure unstable range. Interestingly, the variation tendency of the low-pressure stable range is very close to that of the high-pressure unstable range. On the other hand, the TcO 2 lattice responds intensely to external pressure in the middle-pressure buckling range, which can be sustained under about 71 GPa pressure. More importantly, we have unraveled the pressure-induced lattice distortion in TcO 2 , which leads to anomalous behaviors for the lattice constants, Tc-O bond lengths, and elastic constants at 10 and 20 GPa external pressures.

The idea of forming van der Waals (vdW) heterostructures by integrating various two-dimensional materials breaks the limitation of the restricted properties of single material systems. In this work, the electronic structure modulation, stability, entire stress response and the Li adsorption properties of heterostructures by combining blue phosphorene (BlueP) and MS2 (M = Nb, Ta) together were systematically investigated using first-principles calculations based on vdW corrected density functional theory. We revealed that BlueP/MS2 vdW heterostructures possess good structural stability with negative formation energy, enhanced electrical conductivity, improved mechanical flexibility (ultimate strain >17%) and high-capacity (528.257 mAhg(-1) for BlueP/NbS2). The results suggest that BlueP/NbS2 and BlueP/TaS2 heterostructures are ideal candidates used as promising flexible electrode for high recycling rate and portable lithium-ion batteries, which satisfy the requirement of next-generation flexible energy storage and conversion devices.