Diagnostics of sealed coal mine fires /

Bibliography: p. 25.Mode of access: Internet

Origin of the Voltage Hysteresis in the CoP Conversion Material for Li-Ion Batteries

The electrochemical activity of the CoP conversion electrode was investigated through the combination of computational and experimental techniques. The carbon-free CoP electrode shows better performances than the carbon-coated electrode, in sharp contrast with the beneficial role of carbon coating reported in many insertion materials. A two-step insertion/conversion process associated with the exchange of 3Li is predicted for this system from the <i>T</i> = 0 K phase stability diagram performed on bulk structures within the DFT framework. The voltage hystereses measured for these two processes through a seven-day relaxation procedure (GITT) are 1 order of magnitude higher for the conversion process (Δ<i>V</i>_conv^exp = 0.44 V) than for the insertion process (Δ<i>V</i>_ins^exp = 0.04 V). The various elementary reactions susceptible to occur at the surface of the electrode were investigated by means of surface DFT calculations. This mechanistic study shows that the insertion mechanism is not significantly affected by the electrode nanosizing (Δ<i>V</i>_ins^th = 0.04 V), while the conversion reaction does. Asymmetric responses are expected upon charge and discharge for this system, due to the growth of different interfaces. This induces different electrochemical equilibriums and then different voltages in charge and discharge. The hysteresis voltage computed for the conversion of LiCoP into Li₃P + Co⁰ is again in very good agreement with experiments (Δ<i>V</i>_conv^th = 0.41 V). Such results are very encouraging and open new routes to the rationalization of the microscopic mechanisms acting as limiting reactions in electrode materials for Li-ion batteries

The role of structure and interface in the performance of TiSnSb as an electrode for Li-ion batteries

The lithium-ion battery electrode material TiSnSb shows excellent electrochemical performance related to its high capacity (550 mA h g−1) and rate capability over 210 cycles. To discriminate between the role of active material and the role of the electrode formulation in the good electrochemical features of the TiSnSb electrodes, a full study comparing the electrochemical mechanisms of TiSnSb and a Ti/ Sn/Sb composite vs Li is undertaken by combining X-ray diffraction (XRD), 121Sb, 119Sn Mössbauer and 7Li NMR spectroscopic in situ measurements. During the first discharge, TiSnSb undergoes a direct conversion reaction while Ti/Sn/Sb composites proceed by a stepwise alloying process, both leading to a mixture of lithium antimonide, lithium stannides, and titanium. More surprisingly the charge occurs differently with a reformation of the "TiSnSb" phase in the first case and the formation of Sn and Sb in the second case. The key role of the interfaces in conversion type reactions is discussed. The nature of the interfaces is linked to the long-range order of elements in the starting material. Furthermore, the length scales of the interfaces between Li3Sb, LixSn and Ti appear to control the reactions that occur on charge.Advanced lithium energy storage systems based on the use of nano-powders and nano-composite electrodes/electrolytes (ALISTORE