Na‐ion batteries (SIB) are considered promising systems for energy storage devices, however diversity of available cathode materials is lower compared to lithium ion batteries. Recently, Na3V2(PO4)2F3 (NVPF) has been demonstrated as promising cathode material for SIB owing to high specific capacity and electrochemical reversibility. However, most of reports demonstrates capacities lower than theoretical value and optimization of electrochemical performances by controlled morphology and crystal structure was not demonstrated yet. Here, we demonstrate a scalable synthesis strategy to tailor the crystal structure and morphology of NVPF and showed that our approach enables to optimize the Na+ ion accommodation, diffusion and stability. A flower morphology (NVPF‐F) crystalizes in tetragonal structure, demonstrates discharge capacity of 109.5 mA.h.g−1 and 98.1 % columbic efficiency whereas a hollow spherical morphology (NVPF‐S) with orthorhombic structure exhibits discharge capacity of 124.8 mA.h.g−1 (very close to theoretical value) and 99.5 % columbic efficiency. The observed discharge capacity for NVPF‐S is highest reported value which is ascribed due to stable crystal structure and monodispersed morphology. Long term stability with negligible capacity loss is demonstrated over 550 cycles. Our findings shed light on importance of crystal structure and morphology of NVPF on electrochemical response, and realization as cathode material for SIB.

Opto-mechanical interactions in planar photonic integrated circuits draw great interest in basic research and applications. However, opto-mechanics is practically absent in the most technologically significant photonics platform: silicon on insulator. Previous demonstrations required the under-etching and suspension of silicon structures. Here we present surface acoustic wave-photonic devices in silicon on insulator, up to 8 GHz frequency. Surface waves are launched through absorption of modulated pump light in metallic gratings and thermo-elastic expansion. The surface waves are detected through photo-elastic modulation of an optical probe in standard race-track resonators. Devices do not involve piezo-electric actuation, suspension of waveguides or hybrid material integration. Wavelength conversion of incident microwave signals and acoustic true time delays up to 40 ns are demonstrated on-chip. Lastly, discrete-time microwave-photonic filters with up to six taps and 20 MHz-wide passbands are realized using acoustic delays. The concept is suitable for integrated microwave-photonics signal processing.

Surface modification of electrode materials using chemical treatments and atomic layer deposition is documented as an efficient method to stabilize the lattice structure as well as to reinforce the electrode/electrolyte interface. Nevertheless, expensive instrumentation and intrinsic deterioration of the material under high-temperature conditions and aggressive chemical treatments limit their practical application. Here, we report enhanced electrochemical stability and performances by simple atomic surface reduction (ASR) treatment of Li- and Mn-rich 0.35Li2MnO3·0.65LiNi0.35Mn0.45Co0.20O2 (HE-NMC). We provide mechanistic indications showing that ASR altered the electronic structure of surface Mn and Ni, leading to higher stability and reduced parasitic reactions. We demonstrate significant improvement in the battery performance with the proposed surface reduction, which is reflected by the enhanced capacity (290 mA h g–1), rate capabilities (∼15% enhancement at rates of 1 and 2 C), 50–60 mV narrow voltage hysteresis, and  faster (twice) Li+ diffusion. Utilizing online electrochemical mass spectrometry (OEMS), we show in-operando that the reduced surface layer results in suppressed side reactions. We further characterized the surface coating with high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and solid-state NMR before and after cycling. The results presented herein address all the critical challenges associated with the complex HE-NMC material and thus provide a promising research direction for choosing relevant methodology for surface treatment.

NVPF) is a promising cathode material for sodium ion batteries, owing to its high voltage and promising cycling profile. Nevertheless, most previous reports demonstrated only approximately 100 mAh g À 1 at limited operating voltage. Using a solvothermal synthesis route, we synthesized the NVPF cathode with a controlled architecture and spherical morphology. We used this electrode as the cathode for a sodium-ion battery and managed to intercalate/deintercalate the third Na + ion from the structure, demonstrating a high specific capacity (197 mAh g À 1 ). Long-term stability challenges of these electrodes under a wide potential regime are also presented here in.Recent advances and the large-scale implementation of renewable energy systems pose a challenge to developing large energy storage technology. The most fascinating energy storage technology in mobile application are secondary batteries, of which the lithium ion batteries (LIBs) are recognized as excellent viable energy storage devices (ESD). [1][2][3][4][5][6][7] Due to the superior performances of LIB, and their projected utilization of batteries in electric vehicles, and due limited abundancy of lithium, alternatives to LIB technology are required for stationary large energy storage units. Hence, the search of efficient alternatives converges at sodium (Na) which is the 4 th most abundance element and much lower in cost than lithium. The sodium ion batteries (SIB) demonstrates similar electrochemical intercalation behavior as Li, and considered as the most promising candidate for ESD. [8][9][10][11] However, the larger ionic radius of Na requires the development of suitable electrode material of large tunnel structure for facile intercalation/deintercalation and faster kinetics. Over the various materials, such as metal oxides, [12][13][14] sulfides, [15][16][17] phosphates, [18][19][20] ferrocyanides, [21,22] the NSIOCON structure shown its prominence as the most suitable candidate than others. [15,23,24] Considering the extensive research on Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) over the past few decades, [25][26][27][28] it has been observed that NVPF a promising positive electrode material for SIB which can deliver reversible capacity of 128 mAh.g À 1 for the extraction of two Na + ions per formula unit via two redox plateaus at nearly 3.7 V and 4.1 V vs. Na/Na + with excellent stability and columbic efficiency. [8,29] In order to boost up the electrode capacity, Bianchini et al. [30] attempted to intercalate/ deintercalate the third Na ion at potential window of 1.6-4.5 V (vs. Na/Na + ) which deliver specific extra capacity of 65 mAh.g À 1 . Very Recently, Yan et. al. [31] demonstrated the feasibility to increase the charging voltage up to 4.8 vs Na/Na + and discharging down to 1 V vs Na/Na + and observed a structural phase transformation in NVPF from orthorhombic to tetragonal. They observed a sodium-driven structural/charge compensation mechanism along with a new phase which remains disordered upon cycling with varying average vanadium oxidation state from ...

MXenes are a large class of 2D materials that consist of few‐atoms‐thick layers of transition metal carbides, nitrides, or carbonitrides. The surface functionalization of MXenes has immense implications for their physical, chemical, and electronic properties. However, solution‐phase surface functionalization often leads to structural degradation of the MXene electrodes. Here, a non‐conventional, single‐step atomic surface reduction (ASR) technique is adopted for the surface functionalization of MXene (Ti3C2Tx) in an atomic layer deposition reactor using trimethyl aluminum as a volatile reducing precursor. The chemical nature of the modified surface is characterized by X‐ray photoelectron spectroscopy and nuclear magnetic resonance techniques. The electrochemical properties of the surface‐modified MXene are evaluated in acidic and neutral aqueous electrolyte solutions, as well as in conventional Li‐ion and Na‐ion organic electrolytes. A considerable improvement in electrochemical performance is obtained for the treated electrodes in all the examined electrolyte solutions, expressed in superior rate capability and cycling stability compared to those of the non‐treated MXene films. This improved electrochemical performance is attributed to the increased interlayer spacing and modified surface terminations after the ASR process.