Lithium-Ion Battery Anodes Based on Silicon Nitride Nanoparticles as Active Material and Vertically Aligned Carbon Nanotubes as Electrically Conductive Scaffolding

Abstract

As part of lithium-ion battery research, especially in the field of electromobility, the improvement in battery capacity and rate capability is increasingly important to, e.g., be able to travel further and charge faster. Silicon in the form of nanoparticles as anode active material is therefore heavily investigated due to its high gravimetric capacity and tolerance against pulverization. However, the low electrical conductivity of silicon nanoparticle-coated layers, as a consequence of numerous point contacts between particles with and without a native oxide shell, has a negative impact on the silicon anode’s rate capability. To achieve silicon anodes with a high rate performance, vertically aligned carbon nanotubes with their intrinsically beneficial electrical properties, grown via chemical vapor deposition on copper foil and structured by solvent spray treatment, are used as an electrically conductive scaffolding in conjunction with silicon nanoparticles. The aim of this approach is to expand the two-dimensional surface of copper current collectors. Compared to conventional anodes, the carbon nanotube concept offers a higher proportion of active material in good electrical contact with the current collector and hence superior performance at higher C-rates. In our case, instead of using pure silicon nanoparticles, silicon-rich silicon nitride nanoparticles are integrated into this carbon nanotube structure by ultrasonic spray coating due to their superior cycling stability. As proof of principle, the first cycling results of half-cells with the silicon nitride/carbon nanotube composite anode structure are discussed, which show a capacity retention of 52% at a current of 10C. This corresponds to an improvement of 20% over a copper/silicon nanoparticle reference anode without vertically aligned carbon nanotubes.