Xiuling Zhang

New insights into designing high-rate performance cathode materials for sodium ion batteries by enlarging the slab-spacing of the Na-ion diffusion layer

Recently, the design and synthesis of high performance cathode materials for sodium ion batteries have attracted great interest. In this study, we propose a novel strategy to design high-rate performance cathode materials for sodium ion batteries through enlarging the d-spacing of the Na-ion diffusion layer. More importantly, some new insights into the expansion mechanism of the interplanar spacing for Na0.67Mn0.8Ni0.1Mg0.1O2 induced by Ni and Mg co-doping and the resulting high-rate capability have been presented for the first time. We find that Mg and Ni co-doping leads to the shortening of the TM–O (TM = transition metal) bond lengths and the shrinkage of the TMO6 octahedrons, which might be largely responsible for the expansion of the interplanar spacing of the Na-ion diffusion layer. In comparison with Na0.67Mn0.8Ni0.2O2 and Na0.67Mn0.8Mg0.2O2, Mg and Ni co-doped Na0.67Mn0.8Ni0.1Mg0.1O2 has a higher Na-ion diffusion coefficient and can deliver around 160, 145, 133 and 124 mA h g−1 at 24, 48, 120 and 240 mA g−1, respectively. In particular, at the high current densities of 480 (2C), 1200 (5C) and 1920 mA g−1 (8C), MMN can still offer reversible capacities of 110, 66 and 37 mA h g−1, respectively. In addition, the cycling stability has also been enhanced via Mg and Ni co-doping at the same time, which means that Mg and Ni co-doping also has a positive effect on the stability of the layered structure.

Fe3O4@porous carbon hybrid as the anode material for a lithium-ion battery: performance optimization by composition and microstructure tailoring

Confining Fe3O4 into nanoporous carbon frameworks has been achieved through self-assembly and the use of a subsequent syn-carbonization strategy, where Fe3O4 and carbon frameworks are generated simultaneously and Fe3O4 particles are confined into porous carbon frameworks (Fe3O4@C). Both the composition and microstructure have a significant effect on the electrochemical performances. In comparison with bulk Fe3O4, Fe3O4@C-2 with optimal void pore volume and oxide content shows a significant enhancement in both cycling stability and high-rate capacity. The reversible capacity of Fe3O4@C-2 is retained at 932 mA h g−1 after 100 cycles compared to only 410 mA h g−1 for bulk Fe3O4. The capacity of Fe3O4@C-2 at the current density of 2 A g−1 has been significantly improved to 478 mA h g−1 from only 26 mA h g−1 for bulk Fe3O4. The considerable enhancement of both the cyclability and high-rate capability can be attributed to the synergic effect of nanoconfinement as well as the optimized composition and microstructure: the good dispersion of oxide particles, and the efficient volume change alleviation during the discharge–charge process.

Triboelectric‐Based Transparent Secret Code

Abstract Private and security information for personal identification requires an encrypted tool to extend communication channels between human and machine through a convenient and secure method. Here, a triboelectric‐based transparent secret code (TSC) that enables self‐powered sensing and information identification simultaneously in a rapid process method is reported. The transparent and hydrophobic TSC can be conformed to any cambered surface due to its high flexibility, which extends the application scenarios greatly. Independent of the power source, the TSC can induce obvious electric signals only by surface contact. This TSC is velocity‐dependent and capable of achieving a peak voltage of ≈4 V at a resistance load of 10 MΩ and a sliding speed of 0.1 m s−1, according to a 2 mm × 20 mm rectangular stripe. The fabricated TSC can maintain its performance after reciprocating rolling for about 5000 times. The applications of TSC as a self‐powered code device are demonstrated, and the ordered signals can be recognized through the height of the electric peaks, which can be further transferred into specific information by the processing program. The designed TSC has great potential in personal identification, commodity circulation, valuables management, and security defense applications.