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Octahedral molecular sieves (OMSs) based on MnO

GeP5, as the most representative phosphorus-based material in two-dimensional layered phosphorous compounds, has shown a fairly bright application prospect in the field of energy storage because of its ultrahigh electrical conductivity. However, high-yield exfoliation methods and effective structure construction strategies for GeP5 nanosheets are still missing, which completely restricts the further application of GeP5-based nanocomposites. Here, we not only improved the yield of GeP5 nanosheets by a liquid nitrogen-assisted liquid-phase exfoliation technique but also constructed the GeP5@RuO2 nanocomposites with the 0D/2D heterostructure by in situ introduction of ultrafine RuO2 nanoparticles on highly conductive GeP5 nanosheets using a simple hydrothermal synthesis method, and then applying it to micro-supercapacitors (MSCs) as electrode materials through a mask-assisted vacuum filtration technique. It is precisely because of the synergy of the electrical double-layer material, GeP5 nanosheets and the pseudocapacitance material RuO2 nanoparticles that endows the GeP5@RuO2 electrode with outstanding electrochemical performance in micro-supercapacitors with a large specific capacitance of 129.5 mF cm-2/107.9 F cm-3, high energy density of 17.98 μWh cm-2, remarkable long-term cycling stability with 98.4% capacitance retention after 10 000 cycles, the exceptional mechanical stability, outstanding environmental stability, and excellent integration features. This work opens up a new avenue to construct GeP5-based nanocomposites as a most promising novel electrode material for practical application in flexible portable/wearable micro-nanoelectronic devices.

2D functional materials, such as 2D magnet and superconductor, spark massive interests from synthesis, manipulation to application. Especially, FeTex with multi-phases provides an ideal platform to explore the possible superconducting, ferromagnetic or antiferromagnetic properties and even their functional heterostructures. Herein, we report a facile chemical vapor deposition (CVD) approach to synthesize ultrathin tetragonal FeTe (down to monolayer), hexagonal FeTe (down to 2.3 nm), and Fe-rich hexagonal FeTe with superlattice by tuning the growth temperature according to the phase diagram. Scanning transmission electron microscopy (STEM) is further performed to confirm the difference among these various FeTe phases. Magneto-transport illustrates that the tetragonal device displays a high linear magnetoresistance (LMR) up to 10.5% at 1.9 K, and the LMR of hexagonal FeTe reaches 5.8% at 1.9 K. Interestingly, O doped tetragonal thick FeTe displays a superconducting transition at 9 K, which can persist even at 16 T. In summary, this study illustrates a phase-selective synthesis of FeTex ultrathin crystals, providing promising opportunities to construct complicated devices such as ferromagnet/antiferromagnet, magnet/superconductor heterostructures.

The development of stable and low-cost catalysts with high reactivity to replace Pt-based ones is the central focus but challenging for hydrogen evolution reaction (HER). The incorporation of single atoms into two-dimensional (2D) supports has been demonstrated as an effective strategy because of the highly active single atomic sites and extremely large surface area of two-dimensional materials. However, the doping of single atoms is normally performed on the surface suffering from low stability, especially in acidic media. Moreover, it is experimentally challenging to produce monolayered 2D materials with atomic doping. Here, we propose a strategy to incorporate single foreign Fe atoms to substitute W atoms in sandwiched two-dimensional WS2. Because of the charge transfer between the doped Fe atom and its neighboring S atoms on the surface, the proximate S atoms become active for HER. Our theoretical prediction is later verified experimentally, showing an enhanced catalytic reactivity of Fe-doped WS2 in HER with the Volmer-Heyrovsky mechanism involved. We refer to this strategy as proximity catalysis, which is expected to be extendable to more sandwiched two-dimensional materials as substrates and transition metals as dopants.

Two-dimensional (2D) magnetic CrI3 has received considerable research attention because of its intrinsic features, including insulation, Ising ferromagnetism, and stacking-order-dependent magnetism, as well as potential in spintronic applications. However, the current strategy for the production of ambient-unstable CrI3 thin layer is limited to mechanical exfoliation, which normally suffers from uncontrollable layer thickness, small size, and low yet unpredictable yield. Here, via a confined vapor epitaxy (CVE) method, we demonstrate the mass production of flower-like CrI3 monolayers on mica. Interestingly, we discovered the crucial role of K ions on the mica surface in determining the morphology of monolayer CrI3, reacting with precursors to form a KIx buffer layer. Meanwhile, the transport agent affects the thickness and size of the as-grown CrI3. Moreover, the Curie temperature of CrI3 is greatly affected by the interaction between CrI3 and the substrate. The monolayer CrI3 on mica could act as a magnetic substrate for valley Zeeman splitting enhancement of WSe2. We reckon our work represents a major advancement in the mass production of monolayer 2D CrI3 and anticipate that our growth strategy may be extended to other transition metal halides.

As an emerging ultrathin semiconductor material, Bi2O2Se exhibits prominent performances in electronics, optoelectronics, ultrafast optics, etc. However, until now, the in-plane growth of Bi2O2Se thin films is mostly fulfilled on atomically flat mica substrates with interfacial electrostatic forces setting obstacles for Bi2O2Se transfer to fabricate functional van der Waals heterostructures. In this work, controlled growth of inclined Bi2O2Se ultrathin films is realized with apparently reduced interfacial contact areas upon mica flakes. Consequently, the transfer of Bi2O2Se could be facile by overcoming weaker electrostatic interactions. From cross-sectional characterizations at the Bi2O2Se/mica interfaces, it is found that there are no oxide buffer layers in existence for both in-plane and inclined growths, while the un-neutralized charge density is apparently decreased for inclined films. By mechanical pressing, inclined Bi2O2Se could be transferred onto SiO2/Si substrates, and back-gated Bi2O2Se field effect transistors are fabricated, outperforming previously reported in-plane Bi2O2Se devices transferred with the assistance of corrosive acids and adhesive polymers. Furthermore, Bi2O2Se/graphene heterostructures are fulfilled by a probe tip to fabricate hybrid phototransistors with pristine interfaces, exhibiting highly efficient photoresponses. The results in this work demonstrate the potential of inclined Bi2O2Se to act as a building block for prospective van der Waals heterostructures.

In spite of extremely high strength and hardness, the property of brittleness is tightly linked to diamond. In the deformation of diamond at room temperature, the plasticity of the diamond is normally considered hard to occur because of the domination of catastrophic brittle fracture. Herein, we employed in-situ transmission electron microscopy to reveal the diamond room-temperature plastic behavior, and compared it with a recent report (Adv. Mater. 2020, 1906458) on transformation-induced room-temperature plasticity of diamond nanopillars. Our present in-situ uniaxial compression tests in sub-micron-sized diamond pillars indicate that the plasticity in diamond is carried out by dislocations slipping instead of phase transformation and the initiation of plasticity highly depends on the stress state. On the other hand, we noted that a high proportion of amorphous surface layer in the diamond pillars with a diameter of less than 20 nm may be a significant factor leading to the plasticity.

In-situ transmission electron microscopy (TEM) has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects. To take advantage of the atomic resolution of advanced TEMs, a compact five-degree-of-freedom nanomanipulator was integrated with an indenter that was made of nanotwinned diamonds, for both the in-situ mechanical testing and double tilting of TEM samples. As a demonstration, in-situ bending tests were performed on the (111), (110) and (100) single-crystal diamond needles. The tests revealed the {111} cleavage to be the dominant failure mode. The in-situ indentation on a diamond nanoplate led to curved cracks consisting of nanometer-scale steps, which were identified to be atomic flat {111} facets. The atomic-scale observation of the deformation and failure of diamonds demonstrated the stability of the entire system and the durability of the indenter. We expect that more delicate research can be carried out by means of this holder in the near future, including in-situ stimulation, atomic characterization, and tomography.

A molecule-confined two-dimensional (2D) hybrid superlattice is emerging for uncovering the chemical properties as well as distinctive physical phenomenon arising from the interface electronic stat...

Encapsulation is critical for devices to guarantee their stability and reliability. It becomes an even more essential requirement for devices based on 2D materials with atomic thinness and far inferior stability compared to their bulk counterparts. Here a general van der Waals (vdW) encapsulation method for 2D materials using Sb

The observation of fracture behaviors in perfect and twinned B

Pressure, as an independent thermodynamic parameter, is an effective tool to obtain novel material system and exotic physical phenomena not accessible at ambient conditions, because it profoundly modifies the charge, orbital and spin state by reducing the interatomic distance in crystal structure. However, the studies of magnetoelectricity and multiferroicity are rarely extended to high pressure dimension due to properties measured inside the high pressure vessel being a challenge. Here we reported the temperature-magnetic field-pressure magnetoelectric (ME) phase diagram of Y type hexaferrite Ba0.4Sr1.6Mg2Fe12O22 derived from static pyroelectric current measurement and dynamic magnetodielectric in diamond anvil cell and piston cylinder cell. We found that a new spin-driven ferroelectric phase emerged at P = 0.7 GPa and sequentially ME effect disappeared around P = 4.3 GPa. The external pressure may enhance easy plane anisotropy to destabilize the longitudinal conical magnetic structure with the suppression of ME coefficient. These results offer essential clues for the correlation between ME effect and magnetic structure evolution under high pressure.

With the rapid development of wearable electronic and smart electronic devices, the flexible supercapacitors have attracted special attention in energy storage and conversion. Indium selenide (InSe) as a novel two-dimensional layered material has been widely investigated in photodetector, solar cell, and so on due to high electron mobility, anomalous optical response and tuning the bandgap. InSe nanoflakes are obtained from bulk layered InSe materials via a liquid-exfoliation technique and used as electrodes materials of supercapacitors. Flexible all-solid-state supercapacitors (ASSPs) with sandwich structure using InSe nanoflakes have a volumetric capacitance of 3.48 F cm−3 at a scan rate of 0.005 V s−1. For improving the performance of ASSPs based on InSe, highly conductive carbon nanotubes (CNTs) are added into InSe nanoflakes to enhance the conductivity of InSe/CNTs composites used as electrodes of ASSPs. InSe/CNTs (mass ratio 6:1) ASSPs deliver high volumetric capacitance of 25.1 F cm−3 at a scan rate of 0.005 V s−1, good mechanical properties (93.2% capacitance at 180° bending) and long cycle stability (88.3% capacitance after 10000 cycles). In addition, ASSPs based on InSe/CNTs composites exhibit a high power density of 410.15 W cm−3 and a superior energy density of 3.48 mWh cm−3. The InSe/CNTs composite is expected to have a potential candidate in high-performance electrochemical energy storage devices.

Since the discovery of graphene, van der Waals (vdW) two-dimensional (2D) materials have attracted considerable attention for various potential applications. Recently, a Se-terminated bismuth oxychalcogenide, Bi2O2Se, has been fabricated using the vapor deposition method. Bi2O2Se is not a vdW 2D material, but the as-grown substance shows 2D characteristics. For example, Bi2O2Se exhibits layer number-dependent absorption spectra in experiments, but until now, there has been no reasonable explanation as to why. Here, we propose a 50% Se-passivation surface model, which elucidates the production of such spectra. Our model is also consistent with recent observations using scanning tunneling microscopy. Moreover, high-resolution transmission electron microcopy observations show a broken zipper-like structure in Bi2O2Se. We ascribe Bi2O2Se as a zipper 2D material, and we summarize the characteristics of zipper 2D materials while proposing the development of others. Zipper 2D materials not only are an important subset of 2D materials but also bridge the gap between vdW 2D materials and traditional 3D materials. Because they are a big family, including insulators, semiconductors, and magnetic metals, zipper 2D materials lend themselves to a plethora of applications.

Carbonaceous photonic crystals (CPCs) were prepared from peacock feather fibers (PFF) via high-temperature carbonization (HTC) and hydrothermal carbonization (HC), and by comparing the optical reflection microphotographs, the CPCs-HTC and CPCs-HC still owned the structural coloration as the natural PFF. Raman results showed that the ID/IG value of CPCs-HTC was higher than the one of CPCs-HC, demonstrating more defects and higher graphitization degree of CPCs-HTC. Due to the presence of defects and the different degrees of graphitization, complex permittivity of CPCs can be controlled. The microwave absorption performance of 30 wt% CPCs-HTC was better than the CPCs-HC. The minimum reflection loss (RL) of CPCs-HTC was − 57.9 dB when the frequency was 7.3 GHz and the thickness was 2.5 mm. The frequency range, in which the RL values were less than − 10 dB, was 6.4–8.5 GHz. Compared with other biomass-derived materials, the CPCs-HTC shows several advantages, such as the specific photonic structure, simple preparation process and excellent microwave absorption performances. Thus, CPCs-HTC has the potential to be a lightweight microwave absorption material.

Phase transformation in emerging two-dimensional (2D) materials is crucial for understanding and controlling the interplay between structure and electronic properties. In this work, we investigate ...

Alloying is an effective way to modulate material’s properties. In particular, graded alloying within a single domain of two-dimensional transition-metal chalcogenide (2D-TMC) is of great technolog...

Nanotwinned cubic boron nitride (nt-cBN) with remarkable hardness, toughness, and stability has attracted widespread attention due to its distinct scientific and industrial importance. The key for nt-cBN synthesis is to adopt an onion-like BN (oBN) nano-precursor and induce phase transition under high pressure. Here, we found that the size change of oBN used greatly affected the mechanical performance of products. With the precursor size decreasing from ~320 to 90 nm, the Vickers hardness of nanostructured products improved from 61 to 108 GPa, due to the fact that large oBN nanoparticles possessed more flattened, orderly and graphite-like shell layers, in sharp contrast to the highly wrinkled and imperfect layers in small-diameter nanoparticles, thus resulting in the apparent reduction of ultrafine-twin substructure in the synthetic products. This study reveals that only small oBN precursor could produce complete ultrafine nt-cBN with outstanding performance. A practical route was proposed to further improve the performance of this important material.

High energy storage capacity of tin oxide (SnO2) makes it a promising anode material for high capacity lithium (Li)-ion batteries. Previous experiments reported by Nie et al. (2013) and Huang et al. (2010) have shown that SnO2 lithiation occurs in two stages. First, Li diffuses rapidly through distinct narrow stripes along the electrode axis. This is followed by a second stage where the diffusion/amorphization of the nanowire occurs. In order to understand and possibly predict this complex chemo-mechanical phenomenon, a finite element (FE) model is developed in this work. The model captures the formation of the striped diffusion regime and the corresponding expansion of the nanowire during the lithiation of SnO2. The effect of the stress on the Li diffusion is modeled at the macroscopic level by implementing a stress-dependent expression for the diffusion coefficient. The modeling results clearly show the formation of the striped diffusion regime due to the induced stresses, at low concentrations of Li. This results in a small strain of 0.017 within the nanowire followed by a bulk diffusion and expansion at higher Li concentrations. Thus, the model allows for the spatiotemporally resolved analysis of Li diffusion/intercalation and helps predicting its influence on the mechanical performance of the electrode under the realistic operational conditions.

Two-dimensional (2D) layered magnetic materials have attracted great attention in recent years because of the discovery of long-range order of magnetism down to the monolayer and its expected appli...

Storage technology of electrical energy with ultrafast charge/discharge rates is in high demand for future electronics and electric vehicles. Among them, sodium ion batteries (SIBs) have received much attention, however, the exploration of electrode materials with a high rate capacity and long cycle life still faces great challenges. In this work, we have fabricated coralloid NixCo1−xSe2 with a hierarchical architecture for the first time, and it presents specific capacities of 321 mA h g−1 after 2000 cycles at 2 A g−1, corresponding to a capacity decay rate of 0.011% per-cycle, and 277 mA h g−1 even at the high rate of 15 A g−1, which could be attributed to the enhanced conductivity by Co-doping, the hierarchical architecture preventing the structure from collapsing or crushing, the accelerated electron transmission and the shortened diffusion distance of Na+. The extremely fast electron and Na ion transfer kinetics could be associated with the capacitive contribution. We further reveal the ultrastable and ultrahigh rate Na-ion storage mechanism through systematic analysis including compositional/structure evolution studies and comprehensive electrochemical characterizations. The presented strategy for the design and synthesis of coralloid, Co doped NiSe2 with a hierarchical architecture could enlighten researchers on the development of electrodes with an ultralong cycle life and ultrahigh rate capability.

Lead-free Cs3Sb2Br9 perovskites demonstrate wide applications in photodetectors owing to their remarkable optical properties and nontoxicity. Herein, we utilized an inverse temperature crystallization strategy to synthesize submillimeter Cs3Sb2Br9 perovskite nanoflakes. The carrier relaxation dynamics was investigated. Moreover, the Cs3Sb2Br9 perovskite nanoflake device exhibits fast response speed, high responsivity and excellent detectivity.

Perovskite-like ABX3 metal-organic frameworks (MOFs) have gathered great interest due to their intriguing chemical and physical properties, including their magnetism, ferroelectricity, and multiferroicity. Pressure is an effective thermal parameter in tuning related properties in MOFs due to the adjustable organic framework. Though spectrum experiments have been made on the structural evolution during decompression, there is a lack of electrical studies on the order-disorder ferroelectric transition in the metal-organic frameworks under pressure. In this work, we use a static pyroelectric current measurement, a dynamic dielectric method combined with a Raman scattering technique with applying in situ pressure, to explore the order-disorder ferroelectric transition in [(CH3)2NH2]Co(HCOO)3. The ferroelectric transition vanishes around the external pressure of 1.6 GPa, emerging with a new paraelectric phase. Another phase transition was observed at 6.32 GPa, mainly associated with the distortive transition of DMA+ cations. A phenomenological theory of ferroelectricity vanishing at 1.6 GPa for [(CH3)2NH2]Co(HCOO)3 is also discussed. Our study gives a comprehensive understanding in the pressure tuning of ferroelectric properties in hybrid inorganic-organic materials.

Germanium monochalcogenides (GeSe and GeS) are promising materials for various optoelectronic applications because of their solar range bandgaps, high carrier mobilities, high stabilities, earth abundance, and anisotropic optical properties. Precise control of germanium monochalcogenide bandgaps is critical to applications in continuously tunable optoelectronics. In this paper, we combine first-principles calculations and experiments to predict and confirm that alloy engineering is a significant strategy for tailoring germanium monochalcogenide (${\mathrm{GeS}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x}$) optoelectronic properties. When the Se content $x$ increases from 0.0 to 1.0, the bandgap decreases from 1.23 to 0.89 eV. In addition, there is a direct-indirect bandgap transition when $x$ is approximately 0.3. Tunable ${\mathrm{GeS}}_{1\ensuremath{-}x}{\mathrm{Se}}_{x}$ bandgaps can open up exciting opportunities for the development of various electronic and optoelectronic devices.

Layered germanium phosphide (GeP), a recently developed two-dimensional material, promises highly attractive theoretical capacity for use as a lithium-ion battery anode. Here, we comprehensively investigate its electrochemical performance and the modification mechanism. GeP flakes demonstrate large initial discharge/charge capacity and high initial Coulombic efficiency. However, the cycling performance is disappointing in the potential window of 0.001-3 V in which capacity retention is only ∼18% after 100 cycles. In situ transmission electron microscopy reveals that the poor cycling behavior results in the unexpected large volume change induced by complex reaction processes in cycles. Serious cracking and fracture appear clearly on the electrode surface after cycling. Narrowing the working voltage window to 0.001-0.85 V, cycling stability will be greatly enhanced, with 75% capacity retaining after 100 cycles and ∼50% left after 350 cycles due to the absence of the dealloying of Li

It is well known that diamond does not deform plastically at room temperature and usually fails in catastrophic brittle fracture. Here we demonstrate room-temperature dislocation plasticity in sub-micrometer sized diamond pillars by in-situ mechanical testing in the transmission electron microscope. We document in unprecedented details of spatio-temporal features of the dislocations introduced by the confinement-free compression, including dislocation generation and propagation. Atom-resolved observations with tomographic reconstructions show unequivocally that mixed-type dislocations with Burgers vectors of 1/2 are activated in the non-close-packed {001} planes of diamond under uniaxial compression of and directions, respectively, while being activated in the {111} planes under the directional loading, indicating orientation-dependent dislocation plasticity. These results provide new insights into the mechanical behavior of diamond and stimulate reconsideration of the basic deformation mechanism in diamond as well as in other brittle covalent crystals at low temperatures.

In the modern construction industry, large gypsum (CaSO4·2H2O) boards are manufactured through a two-step procedure, which features the heating of fine gypsum powders to form the intermediate plast...

Although various cathode materials have been explored to improve the energy density of lithium-ion batteries, LiCoO2 is still the first choice for 3C consumer electronics due to the high tap density and high volumetric energy density. However, only 0.5 mol of lithium ions can be extracted from LiCoO2 to avoid side reactions and irreversible structure change, which typically occur at high voltage (>4.2 V). To improve the electrochemical performances of the LiCoO2 cathode material at high cut-off voltage and elevated temperature for higher energy density, an in situ formed spinel interfacial coating layer of LiCoxMn2–xO4 is achieved by the reaction of the surface region of the LiCoO2 host. The capacity retention of the modified LiCoO2 cycled at a high voltage of 4.5 V is significantly increased from 15.5 to 82.0% after 300 cycles at room temperature, due to the stable spinel interfacial inhibiting interfacial reactions between LiCoO2 and the electrolyte as confirmed by impedance spectroscopy. We further dem...

In this study, high quality GeP5 crystals with two-dimensional (2D) layered structures and novel electrical conductivity of 2.4 × 106 S m−1 have been prepared under high-temperature high-pressure oriented growth technique (HTHP-OGT). The as-synthesized GeP5 nanoflakes, after liquid phase exfoliation, show promising potential for application as electrode materials in all-solid-state supercapacitors (ASSPs). The as-prepared GeP5-ASSP exhibits excellent electrochemical performances, including an ultrahigh scan rate of 1000 V s−1, a high specific capacitance of up to 35.86 F cm−3 at 5 mV s−1, a great power density of 397.24 W cm−3 and an energy density of 4.98 mW h cm−3. Moreover, the device can retain 83.7% and 88% of the initial capacitance retention at 180° bending and after 10 000 cycles, respectively, showing outstanding flexibility and superior cycling stability. These properties indicate the promising application of the metallic layered GeP5 for flexible energy storage devices.

The layered transition metal dichalcogenides (TMDs) exhibit the intriguing physical properties and potential application in novel electronic devices. However, controllable growth of multilayer TMDs remains challenging. Herein, large-scale and high-quality multilayer prototype TMDs of W(Mo)Se2 were synthesized via chemical vapor deposition. For Raman and photoluminescence measurements, 2H and 3R multilayer WSe2 crystals displayed significant layer-dependent peak position and intensity feature. Besides, different from the oscillatory relationship of second harmonic generation (SHG) intensity for odd–even layer numbers in 2H-stacked multilayer WSe2, the SHG intensity of 3R-stacked ones parabolically increased with the thickness due to the absence of inversion symmetry. For device application, photodetectors based on WSe2 with increasing thickness exhibited p-type (bilayer), ambipolar (trilayer), and n-type (four layers) semiconductor behaviors, respectively. Furthermore, photodetectors based on the as-synthesized 3R-stacked WSe2 flakes displayed an excellent responsivity of 7.8 × 103 mA W−1, high specific detectivity (Da*) of 1.7 × 1014 Jones, outstanding external quantum efficiency of 8.6 × 102%, and fast response time (τ Rise = 57 ms and τ Fall = 53 ms) under 532 nm illumination with bias voltage of V ds = 5 V. Similar results have also been achieved in multilayer MoSe2 crystals. All these findings indicate great potential of 3R-stacked TMDs in two-dimensional optoelectronic applications.

Tensile strain is intrinsic to monolayer crystals of transition metal disulfides such as Mo(W)S2 grown on oxidized silicon substrates by chemical vapor deposition (CVD) owing to the much larger thermal expansion coefficient of Mo(W)S2 than that of silica. Here we report fascinating fluorescent variation in intensity with aging time in CVD-grown triangular monolayer WS2 crystals on SiO2 (300 nm)/Si substrates and formation of interesting concentric triangular fluorescence patterns in monolayer crystals of large size. The novel fluorescence aging behavior is recognized to be induced by the partial release of intrinsic tensile strain after CVD growth and the induced localized variations or gradients of strain in the monolayer crystals. The results demonstrate that strain has a dramatic impact on the fluorescence and photoluminescence of monolayer WS2 crystals and thus could potentially be utilized to tune electronic and optoelectronic properties of monolayer transition metal disulfides.

Thermal runaways triggered by the oxygen release from oxide cathode materials pose a major safety concern for widespread application of lithium ion batteries. Utilizing in situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at high temperatures, we show that oxygen release from LixCoO2 cathode crystals is occurring at the surface of particles. We correlated this local oxygen evolution from the LixCoO2 structure with local phase transitions spanning from layered to spinel and then to rock salt structure upon exposure to elevated temperatures. Ab initio molecular dynamics simulations (AIMD) results show that oxygen release is highly dependent on LixCoO2 facet orientation. While the [001] facets are stable at 300 °C, oxygen release is observed from the [012] and [104] facets, where under-coordinated oxygen atoms from the delithiated structures can combine and eventually evolve as O2. The novel understanding that emerges from the present stud...

Ultrathin dual phase nanosheets consisting of alternating spinel Li4Ti5O12 (LTO) and rutile TiO2 (RT) lamellas are synthesized through a facile and scalable hydrothermal method, and the formation mechanism is explored. The thickness of constituent lamellas can be controlled exactly by adjusting the mole ratio of Li:Ti in the original reactants. Alternating insertion of the RT lamellas significantly improves the electrochemical performance of LTO nanosheets, especially at high charge/discharge rates. As anodes in lithium-ion batteries (LIBs), the dual phase nanosheet electrode with the optimized phase ratio can deliver stable discharge capacities of 178.5, 154.9, 148.4, 142.3, 138.2, and 131.4 mA h g–1 at current densities of 1, 10, 20, 30, 40, and 50 C, respectively. Meanwhile, they inherit the excellent cyclic stability of pure spinel LTO and exhibit a capacity retention of 93.1% even after 500 cycles at 50 C. Our results indicate that the alternating nanoscaled lamella structure is a good alternative to...

An in-depth understanding of (de)lithiation induced phase transition in electrode materials is crucial to grasp their structure–property relationships and provide guidance to the design of more desirable electrodes. By operando synchrotron XRD (SXRD) measurement and Density Functional Theory (DFT) based calculations, we discover a reversible first-order phase transition for the first time during (de)lithiation of CeO2 nanoparticles. The LixCeO2 compound phase is identified to possess the same fluorite crystal structure with FM3M space group as that of the pristine CeO2 nanoparticles. The SXRD determined lattice constant of the LixCeO2 compound phase is 0.551 nm, larger than that of 0.541 nm of the pristine CeO2 phase. The DFT calculations further reveal that the Li induced redistribution of electrons causes the increase in the Ce–O covalent bonding, the shuffling of Ce and O atoms, and the jump expansion of lattice constant, thereby resulting in the first-order phase transition. Discovering the new phase ...

Lithium metal is a highly desirable anode material for lithium batteries due to its extremely high theoretical capacity (3860 mA h g−1), low potential (−3.04 V versus standard hydrogen electrode), and low density (0.534 g cm−3). However, dendrite growth during cycling and low coulombic efficiency, resulting in safety hazards and fast battery fading, are huge barriers to commercialization. Herein, we used atomic layer deposition (ALD) to prepare conformal, ultrathin aluminum oxide coatings on lithium. We investigated the growth mechanism during Al2O3 ALD on lithium by in situ quartz crystal microbalance and found larger growth than expected during the initial cycles. We also discovered that the ALD Al2O3 enhances the wettability of the Li surface towards both carbonate and ether electrolytes, leading to uniform and dense SEI formation and reduced electrolyte consumption during battery operation. Scanning electron microscopy verified that the bare Li surfaces become rough and dendritic after electrochemical cycling, whereas the ALD Al2O3 coated Li surfaces remain smooth and uniform. Analysis of the Li surfaces after cycling using X-ray photoelectron spectroscopy and in situ transmission electron microscopy revealed that the ALD Al2O3 coating remains intact during electrochemical cycling, and that Li ions diffuse through the coating and deposit on the underlying Li. Coin cell testing demonstrated more than two times longer cycling life for the ALD Al2O3 protected Li, and a coulombic efficiency as high as ∼98% at a practical current rate of 1 mA cm−2. More significantly, when the electrolyte volume was reduced from 20 to 5 μL, the stabilizing effect of the ALD coating became even more pronounced and the cycling life was around four times longer. These results indicate that ALD Al2O3 coatings are a promising strategy to stabilize Li anodes for high performance energy storage devices such as Li–S batteries.

Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium-ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB-COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few-layered COF nanosheets (E-TFPB-COF), whose restacking is prevented by the in situ formed MnO2 nanoparticles. Compared with the bulk TFPB-COF, the exfoliated TFPB-COF exhibits new active Li-storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E-TFPB-COF/MnO2 and E-TFPB-COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g-1 after 300 cycles with good high-rate capability.

2D ternary materials exhibit great promise in the field of polarization-sensitive photodetectors due to the low-symmetry crystal structure. However, the realization of ternary material growth is still a huge challenge because of the complex reaction process. Here, for the first time, 2D ternary In2 SnS4 flakes are obtained via synergistic additive of salt and molecular sieve-assisted chemical vapor deposition. Raman vibration mode of In2 SnS4 flakes exhibits polarization-dependent properties. The polarization-resolved absorption spectroscopy and azimuth-dependent reflectance difference microscopy further confirm its anisotropy of in-plane optical absorption and reflection. Besides, the In2 SnS4 flake based device on mica shows ultrafast rising and decay rates of ≈20 and 20 µs. Impressively, In2 SnS4 flake based phototransistor demonstrates giant gate-tunable polarization-sensitive photoresponse: the dichroic ratio can be adjusted in the range of 1.13-1.70 with gate voltage varying from -35-35 V. This work provides an effective means for modulating the polarization-sensitive photoresponse, which may significantly promote the research progress of polarization-sensitive photodetectors.