Hydrides as high capacity anodes in lithium cells: an Italian “Futuro in Ricerca di Base FIRB-2010” project

Automotive and stationary energy storage are among the most recently-proposed and still unfulfilled applications for lithium ion devices. Higher energy, power and superior safety standards, well beyond the present state of the art, are actually required to extend the Li-ion battery market to these challenging fields, but such a goal can only be achieved by the development of new materials with improved performances. Focusing on the negative electrode materials, alloying and conversion chemistries have been widely explored in the last decade to circumvent the main weakness of the intercalation processes: the limitation in capacity to one or at most two lithium atoms per host formula unit. Among all of the many proposed conversion chemistries, hydrides have been proposed and investigated since 2008. In lithium cells, these materials undergo a conversion reaction that gives metallic nanoparticles surrounded by an amorphous matrix of LiH. Among all of the reported conversion materials, hydrides have outstanding theoretical properties and have been only marginally explored, thus making this class of materials an interesting playground for both fundamental and applied research. In this review, we illustrate the most relevant results achieved in the frame of the Italian National Research Project FIRB 2010 Futuro in Ricerca “Hydrides as high capacity anodes in lithium cells” and possible future perspectives of research for this class of materials in electrochemical energy storage devices

Silicon-based nanocomposite for advanced thin film anodes in lithium-ion batteries

This work describes the preparation and the characterization of Si-based nano-composite anodes. The samples are prepared by a unique combination of two techniques: Laser Assisted Chemical Vapor Pyrolysis and Electrospray Deposition. The former is used to synthesize the active material, while the latter is employed for the deposition of thin electrode layers onto stainless steel supports. The silicon nano-particles characterization indicates a well-defined crystalline structure and a homogeneous, spherical-like morphology. The electrochemical measurements performed using the silicon-based electrode in the lithium cell show a maximum specific capacity of the order of 1200 mA h g(-1) and a good rate capability. The initial irreversible capacity associated with this class of materials is strongly reduced by preliminary surface treatment. The morphology changes upon cycling are minimal and no extended fractures are observed for the cycled electrodes, thus finally indicating the validity of our silicon based electrode as an anode for advanced lithium-ion batteries

Silicon nanoparticles produced by spark discharge

On the example of silicon, the production of nanoparticles using spark discharge is shown to be feasible for semiconductors. The discharge circuit is modelled as a damped oscillator circuit. This analysis reveals that the electrode resistance should be kept low enough to limit energy loss by Joule heating and to enable effective nanoparticle production. The use of doped electrodes results in a thousand-fold increase in the mass production rate as compared to intrinsic silicon. Pure and oxidised uniformly sized silicon nanoparticles with a primary particle diameter of 3–5 nm are produced. It is shown that the colour of the particles can be used as a good indicator of the oxidation state. If oxygen and water are banned from the spark generation system by (a) gas purification, (b) outgassing and (c) by initially using the particles produced as getters, unoxidised Si particles are obtained. They exhibit pyrophoric behaviour. This continuous nanoparticle preparation method can be combined with other processing techniques, including surface functionalization or the immediate impaction of freshly prepared nanoparticles onto a substrate for applications in the field of batteries, hydrogen storage or sensors.Chemical EngineeringApplied Science