Silicon and Carbon-Based Anode Materials for Lithium and Sodium-Ion Rechargeable Batteries

• Author / Creator

  Memarzadeh Lotfabad,Elmira

• This thesis is focused on the Si-based anode materials for lithium-ion batteries (LIBs) as well as biomass-derived carbons for LIBs and sodium-ion batteries (NIBs). In our first attempt we investigated the effect of the support growth substrate as well as of aluminum coating layers on the electrochemical performance of the silicon nanowires. We observed improved cycling performance in the Si nanowires coated with 3 and 8 wt.% aluminum, as compared to the uncoated nanowires. The aluminum shell helps maintain the mechanical integrity of the coated parts of the nanowires, thereby slowing down capacity degradation. A solid electrolyte interphase (SEI) that was stable under the beam in a transmission electron microscope (TEM) was observed only on bare parts of a nanowire. Nanowires grown on a TiN underlayer not only demonstrated a higher specific capacity during cycling but also significantly improved coulombic efficiency with respect to nanowires grown directly on stainless steel, which is attributed mainly to a difference in size distribution. In our second attempt, we conformally coated the Si nanowires with TiO2 using atomic layer deposition (ALD), in which it showed a remarkable performance improvement. The coulombic efficiency is increased to ~99%, among the highest ever reported for Si nanowires, as compared to 95% for the baseline uncoated samples. The capacity retention after 100 cycles for the nanocomposite was twice as high as that of the baseline at 0.1 C (60% vs. 30%), and more than three times higher at 5 C (34% vs. 10%). We also demonstrated that the microstructure of the coatings was critically important towards achieving this effect. Titanium dioxide coatings with an as-deposited anatase structure are nowhere near as effective as amorphous ones, the latter proving much more resistant to delamination from the Si nanowires core. We used TEM to demonstrate that upon lithiation the amorphous coating developed a highly dispersed nanostructure comprised of crystalline LiTiO2 and a secondary amorphous phase. In our third attempt, we explored the use of ALD of TiO2, TiN and Al2O3 on the inner, the outer, or both surfaces of hollow Si nanotubes (SiNTs) for improving their cycling performance. We demonstrated that all three materials enhanced the cycling performance, with optimum performance being achieved for SiNTs conformally coated on both sides with 1.5 nm of Li active TiO2. Substantial improvements wer achieved in the cycling capacity retention (1700 mAh/g vs. 1287 mAh/g for the uncoated baseline, after 200 cycles at 0.2C), and steady-state coulombic efficiency (~100% vs. 97-98%). TEM and other analytical techniques were employed to provide new insight into the lithiation cycling-induced failure mechanisms that turned out to be intimately linked to the microstructure and the location of these layers. In our last attempt, we showed that Banana peel pseudographite (BPPG) offers superb dual functionality for NIBs and LIBs anodes. The materials possessed low surface areas (19 - 217 m2 g-1) and a relatively high electrode packing density (0.75 g cm-3 vs. ~ 1 g cm-3 for graphite). Tested against Na, BPPG delivered a gravimetric capacity of 355 mAh/g after 10 cycles at 50 mA/g. A nearly flat ~ 200 mAh/g plateau that is below 0.1 V, and a minimal charge/discharge voltage hysteresis, made BPPG a direct electrochemical analogue to graphite but with Na. A charge capacity of 221 mAh/g at 500 m/Ag was degraded by 7% after 600 cycles, while a capacity of 336 mAh/g at 100 mA/g was degraded by 11% after 300 cycles, in both cases with ~ 100% cycling coulombic efficiency. For LIB applications BPPG offered a gravimetric capacity of 1090 mAh/g at 50 mA/g. The reason that BPPG worked so well for both NIBs and LIBs was that it uniquely contained three essential features: a) dilated intergraphene spacing for Na intercalation at low voltages; b) highly accessible near-surface nanopores for Li metal filling at low voltages; and c) substantial defect content in the graphene planes for Li adsorption at higher voltages. The < 0.1 V charge storage mechanism was fundamentally different for Na versus for Li. A combination of XRD and XPS demonstrates highly reversible Na intercalation rather than metal underpotential deposition. By contrast, the same analysis proved the presence of metallic Li in the pores, with intercalation being much less pronounced.

• Subjects / Keywords

  • Carbon
  • Sodium Ion Batteries
  • Silicon
  • Lithium Ion Batteries

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32B8VH7D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.