Constructing oxygen-deficient V_(2)O_(3)@C nanospheres for high performance potassium ion batteries

Potassium ion batteries(PIBs) have been regarded as promising alternatives to lithium ion batteries(LIBs)on account of their abundant resource and low cost in large scale energy storage applications. However,it still remains great challenges to explore suitable electrode materials that can reversibly accommodate large size of potassium ions. Here, we construct oxygen-deficient V_(2)O_(3)nanoparticles encapsulated in amorphous carbon shell(Od-V_(2)O_(3)@C) as anode materials for PIBs by subtly combining the strategies of morphology and deficiency engineering. The MOF derived nanostructure along with uniform carbon coating layer can not only enables fast K+migration and charge transfer kinetics, but also accommodate volume change and maintain structural stability. Besides, the introduction of oxygen deficiency intrinsically tunes the electronic structure of materials according to DFT calculation, and thus lead to improved electrochemical performance. When utilized as anode for PIBs, Od-V_(2)O_(3)@C electrode exhibits superior rate capability(reversible capacities of 262.8, 227.8, 201.5, 179.8, 156.9 mAh/g at 100, 200, 500, 1000 and2000 mA/g, respectively), and ultralong cycle life(127.4 mAh/g after 1000 cycles at 2 A/g). This study demonstrates a feasible way to realize high performance PIBs through morphology and deficiency engineering.

Asymmetric nonlinear-mode-conversion in an optical waveguide with PT symmetry

Asymmetric mode transformation in waveguide is of great significance for on-chip integrated devices with one-way effect,while it is challenging to achieve asymmetric nonlinear-mode-conversion(NMC)due to the limitations imposed by phase-matching.In this work,we theoretically proposed a new scheme for realizing asymmetric NMC by combining frequencydoubling process and periodic PT symmetric modulation in an optical waveguide.By engineering the one-way momentum from PT symmetric modulation,we have demonstrated the unidirectional conversion from pump to second harmonic with desired guided modes.Our findings offer new opportunities for manipulating nonlinear optical fields with PT symmetry,which could further boost more exploration on on-chip nonlinear devices assisted by non-Hermitian optics.