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Nanoporous Si was obtained by means of metal-assisted chemical etching. Li ion insertion-extraction was tested by voltammetric and galvanostatic electrochemical cycling in conventional 1 M LiPF ethylene carbonate/dimethyl carbonate EC/DMC and in 1 M LiTFSI 1-butyl-1-methyl-pyrrolidinium bis (trifluoromethyl) sulfonylimide [BMP] [TFSI] electrolytes. The nanoporous Si demonstrated high reversibility when cycled in 1 M LiPF EC/DMC electrolyte and showed superior activity compared to the non-structured sample. In contrast to the organic carbonate electrolyte, the material cycling in ionic liquid media showed reduced capacity and reversibility of the Li ion exchange. The latter results were discussed in terms of the high viscosity of the ionic liquid and ineffective cathodic passivation of the Si substrate in the ionic liquid-based electrolyte. Scanning electron microscopy imaging showed minor morphological changes due to the large volume change during Li insertion. No signs of crack formation and propagation were detected during the time span of the measurement. [ABSTRACT FROM AUTHOR]

In the present work, the electrochemical behaviour of LiFePO4/C electrode has been reported. Specially, the electrochemical impedance spectroscopies (EIS) have been studied in detail. The discharge capacity is more than 120 mAh/g. There are two semicircles being found in the Nyquist plot for the cycled electrode and one semicircle for the as-prepared electrode. It is found that the interface capacitance is in an order of magnitude of 10 μF/cm for the high-frequency semicircle, while for the second semicircle the interface capacitance is 5.3~45.4 × 10 μF/cm. It could be concluded that the high-frequency semicircle is to correspond to the charge transfer process. The function of the carbon layer is also briefly discussed. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Olivine LiFePO/C cathode materials for lithium ion batteries were synthesized using monodisperse polystyrene (PS) nano-spheres and other carbon sources. The structure, morphology, and electrochemical performance of LiFePO/C were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests, electrochemical impedance spectroscopy (EIS) measurements, and Raman spectroscopy measurements. The results demonstrated that LiFePO/C materials have an ordered olivine-type structure with small particle sizes. Electrochemical analyses showed that the LiFePO/C cathode material synthesized from 7 wt.% PS nano-spheres delivers an initial discharge capacity of 167 mAh g (very close to the theoretical capacity of 170 mAh g) at 0.1 C rate cycled between 2.5 and 4.1 V with excellent capacity retention after 50 cycles. According to Raman spectroscopy and EIS analysis, this composite had a lower I/ I, sp/ sp peak ratio, charge transfer resistance, and a higher exchange current density, indicating an improved electrochemical performance, due to the increased proportion of graphite-like carbon formed during pyrolysis of PS nano-spheres, containing functionalized aromatic groups. [ABSTRACT FROM AUTHOR]

A series of Cr-doped LiVCr(PO) ( x = 0, 0.1, 0.25, and 0.5) samples are prepared by a sol-gel method. The effects of Cr doping on the physical and chemical characteristics of LiV(PO) are investigated. Compared with the XRD pattern of the undoped sample, the XRD patterns of the Cr-doped samples have no extra reflections, which indicates that Cr enters the structure of LiV(PO). As indicated by the charge-discharge measurements, the Cr-doped LiVCr(PO) ( x = 0.1, 0.25, and 0.5) samples exhibit lower initial capacities than the undoped sample at the 0.2 C rate. However, both the discharge capacity and cycling performance at high rates (e.g., 1 and 2 C) are enhanced with proper amount of Cr doping ( x = 0.1). The highest discharge capacity and capacity retention at the rates of 1 and 2 C are obtained for LiVCr(PO). The improvement of the electrochemical performance can be attributed to the higher crystal stability and smaller particle size induced by Cr doping. [ABSTRACT FROM AUTHOR]