Final Report Summary - NANOSOUND (Wet deposition of silicon for electrochemical devices)
In this research proposal, we propose to synthesise and study the electrochemical behaviour of silicon nanomaterials. Apart from the technological aspects discussed above, the nanoscale brings very challenging aspects in terms of controlling such a high surface area out of thermodynamic equilibrium at very low potential in an electrolyte, i.e. an electrode material. The challenge brings also a very nice opportunity of understanding the surface contribution of the materials due to high surface to volume ratio.
Si nanostructures elaborated by vapour deposition or etching are not cost effective and do not allow for the design of a complex material. In our research, Si nanoparticles are synthesised by a metal assisted mechano-synthesis approach using a high energy ball-miller in high boiling point solvents. This wet process allows decreasing the grain sise of the material down to 10 - 20 nm, where according to our preliminary results particle sise being critical for anodic stability. In the same step, metal nanoparticles are deposited on the Si through a galvanic displacement reaction yielding bi-metallic nanoparticles. Galvanic displacement can be applied to any metal with a higher redox potential than the couple Si(IV)/Si. The surface of Si NPs is partially coated with metallic nanoparticles (Ag, Cu, Ni) which mediate the electronic connectivity of the anode.
Application as anode material for electrochemistry
The present process displays a high yield of more than 80 % on the basis of a 500 mg of Si powder and can be easily scaled up to several grams. This process will be fully detailed while a provisional patent will be issued. TEM shows a narrow sise distribution and electron diffraction, the nanopowder consists of agglomerated 15 nm crystalline Si NPs. Micron scale silicon does not show any reversible cycling. The anode made from nano-Si shows a capacity of 1000 mAh.g-1 after 60 cycles.