Search

The influence of partial substitution of manganese by nickel or magnesium in Na0.44MnO2on cathode performance in sodium ion batteries has been investigated. Partial substitution changes the structure of parent Na0.44MnO2 from tunnel into layered P2-type, or a mixture of P2- and P3-type materials. Substitution smoothes the charge/discharge curves and may significantly improve capacity, albeit with a lower capacity retention relative to pristine Na0.44MnO2. In particular, high discharge capacities are found in the voltage range 2.0–4.2 V at 0.1 C rate for Na0.44Mn0.89Ni0.11O2 (193 mAh g−1) and Na0.44Mn0.89Mg0.11O2 (188 mAh g−1), with a capacity retention of 74% and 81%, respectively, after 70 cycles. [ABSTRACT FROM AUTHOR]

LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g−1 and 95% coulombic efficiency under 0.1 C (1 C = 120 mA g−1) current rate between 1.5-4.1 V. It also shows excellent rate capability that reaches 92 mAh g−1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage. [ABSTRACT FROM AUTHOR]

Layer-structured O3 type cathode materials Na1−xCr1−xTixO2 (x=0, 0.03, 0.05) are fabricated by a thermo-polymerization method. The structures and morphologies are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. It has been found that the appropriate Ti doping effectively leads to the formation of uniform morphology. As a cathode, the x=0.03 sample delivers a quite high discharge capacity of 110 mAh/g at 32 C in the voltage range from 2.0 V to 3.6 V (vs. Na/Na+) and with a capacity retention of 96% after 100 cycles at 0.2 C. The Na//Na0.97Cr0.97Ti0.03O2 cell exhibits very high coulombic efficiency (above 96%). All these results suggest that Na0.97Cr0.97Ti0.03O2 is very promising for high-rate sodium ion batteries. [ABSTRACT FROM AUTHOR]

We report, for the first time, that a nanocrystalline layered TiP2O7 as a cathode material for Li-, Na- and K-alkali metal batteries is prepared by a solvothermal process followed by a heat treatment at 600 °C. For comparison, a crystalline cubic TiP2O7 is also synthesized at 800 °C. It is clarified that the layered TiP2O7 is slightly poorer for lithium storage but much better for sodium and potassium storages than the cubic phase. The detailed electrochemical processes are investigated by means of ex situ XRD analyses. Different from the two-phase co-existence mechanism for the cubic phase, a solid-solution mechanism is identified for the layered phase to follow in the Li/Na/K intercalation reactions based on electrochemical and structural studies. To overcome the poor electronic conductivity limit for high rate applications, carbon coating is employed on the TiP2O7 samples. The carbon-coated layered phase TiP2O7 (600 °C) displays fairly reversible capacity close to 100 mA h g−1 in both Li and Na rechargeable alkali metal batteries. It is a promising electrode material for large energy storage systems. [ABSTRACT FROM AUTHOR]

A solid-state reaction process with poly(vinyl alcohol) as the carbon source is developed to synthesize LiFePO4-based active powders with or without modification assistance of a small amount of Li3V2(PO4)3. The samples are analyzed by X-ray diffraction, scanning/transmission electron microscopy, and Raman spectroscopy. It is found that, in addition to the minor effect of a lattice doping in LiFePO4 by substituting a tiny fraction of Fe2+ ions with V3+ ions, the change in the form of carbon coating on the surface of LiFePO4 plays a more important role to improve the electrochemical properties. The carbon changes partially from sp3 to sp2 hybridization and thus causes the significant rise in electronic conductivity in the Li3V2(PO4)3-modified LiFePO4 samples. Compared with the carbon-coated baseline LiFePO4, the composite material 0.9LiFePO4·0.1Li3V2(PO4)3 shows totally different carbon morphology and much better electrochemical properties. It delivers specific capacities of 143.6 mAh g−1 at 10 C rate and 119.2 mAh g−1 at 20 C rate, respectively. Even at the low temperature of −20 °C, it delivers a specific capacity of 118.4 mAh g−1 at 0.2 C. [ABSTRACT FROM AUTHOR]

Terahertz (THz) is the frequency region ranging from 0.1 to 2.0 THz, which lies in the far-infrared region. Compared to Fourier transform infrared spectra (FTIR), terahertz time-domain spectra (THz-TDS) has low energy, high signal-to-noise ratio (SNR) and is non-ionizing radiation. Low-frequency vibrational modes of some amino acids, such as torsional and collective vibrational modes and hydrogen-bond modes, exist in the THz region. Amino acids are important organic compounds and are the fundamental components of proteins. Amino acids can exist with a highly ordered crystal structure linked by hydrogen intermolecular bonds in the solid phase. The absorption spectra of amino acids in the THz region show marked differences while mid-infrared absorption spectra usually show very little difference. Up to now, absorption spectra of twenty kinds of amino acids have been studied by many researchers using THz technique; the quantitative analysis of amino acids by THZ-TDS is also included. Investigation of THz spectra of amino acids are of fundamental interests, and will lead to further understanding of low-frequency vibrations of protein/DNA and relevant biological reactions and activities. In the present paper, the latest progress in absorption spectra of amino acids determined by THz spectroscopy is reviewed and a database is built. Some brief remarks on future developments in and prospects for THz application in amino acids are also provided.