LAUSR

There are many interfaces in conventional nanostructured silicon anodes for LIBs including: 1) the solid-electrolyte interface (SEI), 2) interfaces between Si nanoparticles (NPs) and binders, and 3) interface between the current collector and active materials (CCAMI). Interfacial layers (e.g., graphene, activated carbon) coated on conventional Cu foil current collectors are often used to improve charge transfer and reduce CCAMI resistance. Indeed, our detailed studies show that the introduction of interfacial graphene layers results in ~20-60% increase in capacity after 500 cycles at 0.1C. While the capacity is enhanced by inclusion of interfacial layers or conductive additives, they do not resolve problems associated with the diffusion of Li+ ions in the anode because the current collector remains mostly impermeable to Li+ ions. Such electrodes that cannot accommodate the fast diffusion of Li+ ions are prone to plating. Here, we show that the use of freestanding and scalably produced carbon nanotube Bucky paper or Bucky sandwich electrodes containing Si NPs (dia. ~100nm) exhibit up to ~1200% and 1900% increase in the gravimetric capacity after 500 cycles at 0.1C, respectively when discharged to 0.1V. Using detailed electrochemical impedance spectroscopy, we show that the diffusion impedance in the Bucky paper and Bucky sandwich electrodes is reduced by two orders of magnitude compared to the bare Cu foil. Furthermore, we demonstrate that the Bucky paper and Bucky sandwich electrodes can withstand high rates up to 4C, and show long cycle life up to ~500 cycles at 0.1 C. Lastly, we show that the Bucky sandwich electrode architecture with smaller diameter SiNPs (~30nm) leads to capacities as high as ~1490mAh/g (~1635 mAh/g) at 0.1C up to 100 cycles when discharged to 0.1V (0.01V).