High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications

All battery technologies are known to suffer from kinetic problems linked to the solid-state diffusion of Li in intercalation electrodes, the conductivity of the electrolyte in some cases and the quality of interfaces. For Li-ion technology the latter effect is especially acute when conversion rather than intercalation electrodes are used. Nano-architectured electrodes are usually suggested to enhance kinetics, although their realization is cumbersome. To tackle this issue for the conversion electrode material Fe3O4, we have used a two-step electrode design consisting of the electrochemically assisted template growth of Cu nanorods onto a current collector followed by electrochemical plating of Fe3O4. Using such electrodes, we demonstrate a factor of six improvement in power density over planar electrodes while maintaining the same total discharge time. The capacity at the 8C rate was 80% of the total capacity and was sustained over 100 cycles. The origin of the large hysteresis between charge and discharge, intrinsic to conversion reactions, is discussed and approaches to reduce it are proposed. We hope that such findings will help pave the way for the use of conversion reaction electrodes in future-generation Li-ion batteries

A controlled copper-coating method for the preparation of ZnS:MnZnS:Mn DC electroluminescent powder phosphors

A new wet-chemical method is described for the deposition of electrically conducting copper sulfide coating on $ZnS: Mn$ powder phosphors for the electroluminescent (EL) devices working in the direct current (DC) mode. The nature of the coated layers and the changes undergone by them in the DCEL devices are investigated by X-ray photoelectron and Auger spectroscopy. The as-coated layers of <150 nm have dominant $Cu^+$ character. The $Cu_xS/ZnS$ interface acquires sharper concentration profile on heating, accompanied by the interaction with oxygen from the ambient atmosphere. This leads to increased resistivity of the coating through the incorporation of O^2^- and the out-diffusion of $Cu$-ions to upper regions. Heat treatment alters charge state of copper to Cu^2^+ at deeper regions towards $ZnS$. Similar changes are noticed for the phosphor recovered from the electrically ‘formed’ EL display panels

Behaviour of acceptor states in semiconducting BaTiO3 and SrTiO3

The semiconductivity inMTiO3 (M=Ba, Sr) in the temperature range of practical applications is greatly influenced by the electronic charge redistribution among the acceptor states, arising from the frozen cation vacancies as well as the transition metal ion impurities. The conductivity measurements and defect chemistry investigations above 800 K indicate that the predominant lattice defects areM− and oxygen vacancies. There is dominantp-type conduction at higherP O 2 values in acceptor doped materials at high temperatures. However, they are insulating solids around room temperature due to the redistribution of electrons between the neutral, singly-or doubly-ionised acceptor states. Results fromepr and resistivity measurements show that the above charge redistribution is dependent on crystal structure changes. Hence the electron or hole loss by the acceptor states is influenced by the soft modes which also accounts for the differences in electrical properties of BaTiO3 and SrTiO3. The results are also useful in explaining the positive temperature coefficient in resistance and some photo-electrochemcial properties of these solids

Luminescence of Ce3+-sensitized and Dy3+-activated aluminoborates, M3Al6B8O24 (M = Ca, Ba)

The near white emission of Dy^3^+ is remarkably sensitized by Ce^3^+ when present together in the recently reported aluminoborates, M_3Al_6B_8O_2_4 $(M = Ca, Ba)$. Energy transfer from Ce^3^+ to Dy^3^+ at 300K has been examined. The multiplicity of the Ce^3^+ excitation band of Ce^3^+ + Dy^3^+ containing phosphors and its concentration dependance point to the prevalence of rare earth (RE^3^+) ion pairs. More efficient energy migration to Dy^3^+ takes place from Ce^3^+ - Ce^3^+ pair than from isolated Ce^3^+ . The results indicate the role of borate group in the interaction between RE^3^+ ions

Luminescence of Ce3+Ce^{3+} -doped aluminoborates, M3Al6B8O24M_3Al_6B_8O_{24} (M = Mg, Ca, Sr, Ba)

Newer dielectric materials doped with appropriate impurities are often sought for tunable blue laser applications. Thus, the luminescence properties of $Ce^{3+}$ in the novel ternary borates, $M_3Al_6B_8O_{24}$ (M = Mg, Ca, Sr, Ba) have been investigated. The single excitation band centred around 310 nm and the broad emission band maximising around 400 nm are devoid of the characteristic $Ce^{3+}$ doublet and the vibrational fine structures, even at low temperatures. These luminescence features are due to the extensive crystal-field splitting of the 4f ground state. The large Stokes shift of $\sim7000cm^{-1}$ and the half-band-widths are influenced by $M^{2+}$ ions