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Highlights: The growth of high-quality single-crystalline Te nanobelts is reported by introducing atomically flat hexagonal boron nitride (h-BN) nanoflakes into the chemical vapor deposition system as the growth substrate. The field-effect transistor based on Te grown on h-BN exhibits an ultrahigh hole mobility up to 1370 cm2 V−1 s−1 at room temperature. The lack of stable p-type van der Waals (vdW) semiconductors with high hole mobility severely impedes the step of low-dimensional materials entering the industrial circle. Although p-type black phosphorus (bP) and tellurium (Te) have shown promising hole mobilities, the instability under ambient conditions of bP and relatively low hole mobility of Te remain as daunting issues. Here we report the growth of high-quality Te nanobelts on atomically flat hexagonal boron nitride (h-BN) for high-performance p-type field-effect transistors (FETs). Importantly, the Te-based FET exhibits an ultrahigh hole mobility up to 1370 cm2 V−1 s−1 at room temperature, that may lay the foundation for the future high-performance p-type 2D FET and metal–oxide–semiconductor (p-MOS) inverter. The vdW h-BN dielectric substrate not only provides an ultra-flat surface without dangling bonds for growth of high-quality Te nanobelts, but also reduces the scattering centers at the interface between the channel material and the dielectric layer, thus resulting in the ultrahigh hole mobility. [ABSTRACT FROM AUTHOR]

Subtle structural changes during electrochemical processes often relate to the degradation of electrode materials. Characterizing the minute-variations in complementary aspects such as crystal structure, chemical bonds, and electron/ion conductivity will give an in-depth understanding on the reaction mechanism of electrode materials, as well as revealing pathways for optimization. Here, vanadium pentoxide (V2O5), a typical cathode material suffering from severe capacity decay during cycling, is characterized by in-situ X-ray diffraction (XRD) and in-situ Raman spectroscopy combined with electrochemical tests. The phase transitions of V2O5 within the 0–1 Li/V ratio are characterized in detail. The V–O and V–V distances became more extended and shrank compared to the original ones after charge/discharge process, respectively. Combined with electrochemical tests, these variations are vital to the crystal structure cracking, which is linked with capacity fading. This work demonstrates that chemical bond changes between the transition metal and oxygen upon cycling serve as the origin of the capacity fading. [ABSTRACT FROM AUTHOR]

In situ X-ray diffraction (XRD), as a widely used tool in probing the structure evolution in electrochemical process as well as the energy storage and capacity fading mechanism, has shown great effects with optimizing and building better batteries. Based on the research progresses of in situ XRD in recent years, we give a review of the development and the utilization of this powerful tool in understanding the complex electrochemical mechanisms. The studies on in situ XRD are divided into three sections based on the reaction mechanisms: alloying, conversion, and intercalation reactions in lithium-ion batteries. The alloying reaction, in which lithium ions insert into Si, Sb, and Ge is firstly reviewed, followed by a discussion about the recent development of in situ XRD on conversion reaction materials (including metal oxides and metal sulfides) and intercalation reaction materials (including cathode materials and some structure-stable anode materials). As for sodium-ion batteries, we divide these researches on structure evolution into two categories: cathode and anode materials. Finally, the future development of in situ XRD is discussed. [ABSTRACT FROM AUTHOR]