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Research Topic:
  Novel nanostructured carbons for electrochemical energy conversion and storage
Kathleen Nimmrich

Since its first introduction into the market, in the 90´s by Sony, graphite anode for lithium ion batteries are still being used due to their outstanding electrochemical stability. Today, efforts are being made to design anodes material based on silicon as this element reversibly alloy lithium at low potential (vs Li/Li+) with a specific charge capacity exceeding carbonaceous material by one order of magnitude. However, silicon based materials have a poor cycling stability which is conjectured to be related to two distinct degradation mechanisms which are the mechanical fragmentation of the silicon upon charging and discharging and to the formation of a poor quality passivation layer, namely the solid electrolyte interface. In order to guarantee the reproducibility and purity of the Si-based anode material, in comparison to alternative preparation routes such as precursor calcination or electro-deposition of silicon, a versatile low pressure chemical vapor deposition (LP-CVD) technique was specifically designed, by our group, for the deposition of silicon on particulate carbonaceous material. The Figure shows several SEM images of a selection of carbonaceous material prior (left) and after (right) Si deposition. More specifically, the images shows various loading of Si-nanodroplets on (b) graphite, (d) hydrothermal carbon and (f) multiwall carbon nanotubes (MWCNT) which have been prepared in a join work with the CEC Mülheim (group of Dr. Sylvia Reiche). Preliminary results, established that the stability of Si deposited by LP-CVD is superior to the “classical” graphite/Si-nanoparticles composite route. It has also been demonstrated that the interfacial chemistry significantly affects the electrochemical stability of the electrode. Currently, the nature of the adhesion of the Si-nanodroplets to the carbonaceous materials is investigated by varying both the deposition conditions and by surface functionalization of the carbonaceous material in the perspective to further develop the correlation between surface chemical activity and electrochemical stability and dynamic performance.

Several SEM images of a selection
of carbonaceous material
prior (left) and after (right) Si deposition.

(to see full size, click on the image)
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