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The investigation of the lithiation−delithiation kinetics of anodes comprising carbon-coated ZnFe 2 O 4 nanoparticles is reported in here. The study confirmed that, as occurring with other conversion electrodes, lithiation of ZnFe 2 O 4 nanoparticles is a multistep process involving the presence of intermediate Li−Zn−Fe−O phases as precursors for the formation of amorphous Li 2 O. A detailed knowledge on the reaction kinetics of the involved electrochemical mechanisms has been achieved by using impedance spectroscopy. It has been observed that lithiation reactions introduce a long delay that limits the electrode charging, not related to diffusion mechanisms. The sloping curve following the conversion plateau of the galvanostatic discharge is connected to a retardation effect in the reaction kinetics. This limitation is seen as an additional resistive process originated by the specific lithiation microscopic features. It is concluded that capacitance spectra allow distinguishing two separate processes: formation of kinetically favored intermediate Li−Zn−Fe−O phases and subsequent reaction to produce highly dispersed LiZn and Fe 0 in an amorphous Li 2 O matrix. A detailed electrical model is provided accounting for the overall electrode lithiation process. ■ INTRODUCTIONLi-ion batteries have become core devices for the consumer electronics industry. Materials for commercial battery electrodes are mostly chosen from a set of intercalation compounds that reversibly accommodate lithium ions in host sites in the lattice without severely distorting the structure. In most transition metal compounds such as LiCoO 2 , LiNi 1−y−z Mn y Co z O 2 , LiFePO 4 , and Li 4 Ti 5 O 12, redox activity is restricted to a few exchanged electrons. Therefore, intercalation materials exhibit intrinsic limitations that make them unviable when high capacity requirements have to be fulfilled as in the case of large scale or automotive applications.1−3 During the past decades a new family of electrode materials operating under the so-called conversion reaction has been intensely studied.4 For these compounds lithiation occurs through the reaction that involves a complete metal reduction as M a X b + (bn)Li ↔ aM + bLi n X, where M = transition metal, X = anion (O, S, N, P, and F), and n = anion formal oxidation state. Conversion reaction is able to accommodate larger amount of Li atoms into the lithium binary compound Li n X, which explains specific capacities exceeding 1000 mAh g −1 as reported for many compounds. Interestingly, conversion materials usually show good reversibility because of the formation of a nanostructured matrix that comprises metallic nanoparticles surrounded by amorphous Li n X phases. Intimate phase contact facilitates reactivity as evidenced by the observation of remaining metallic nanoparticles after extended oxidation/ reduction cycling. 4 Despite their potentialities, conversion compounds present a series of performance limitations that hinders their straightforward application in commercial devices. There...

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This work addressed to investigate the use of fructose as an ingredient in the feedstock suspension of a Y-TZP/Al2O3/SiC multicomponent coating manufactured by SPS. The effect on suspension rheology and resulting coatings microstructure and thermal conductivity was assessed. It was observed that addition of fructose hardly affected the rheological behaviour of the suspensions while a strong decrease in the surface tension of water occurred. Drastic changes of coating microstructures were attributed to this effect in liquid surface tension i.e. fructose favoured the growth of columnar structure in the coatings. XRD patterns showed that fructose increased the crystallinity of the tetragonal Y-TZP phase of the coatings. The determination of thermal conductivity showed that the formation of a controlled columnar structure along with porosity is beneficial for thermal insulation. The results show, for the first time, the designing of coatings with columnar microstructure by SPS from water-based suspension feedstocks.

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.

Thermoelectric materials can directly convert waste heat into electricity. Due to the vast amount of energy available as waste heat in our society, these materials could contribute to reduce our dependence on fossil fuels and their associated environmental problems. However, the heat to electricity conversion efficiency of thermoelectric materials is still a limiting factor, and extensive efforts are being undertaken to improve their performance. The search for more efficient materials is focused on the optimization of three properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Typically, these are determined as function of temperature through