Hybrid Germanium Nanoparticle–Single-Wall Carbon Nanotube Free-Standing Anodes for Lithium Ion Batteries

Germanium nanoparticles (Ge-NPs) were synthesized through a one-step chemical vapor deposition process and were included in a hybrid free-standing single-wall carbon nanotube (SWCNT) electrode. The Ge-NPs were characterized through scanning electron microscopy and Raman spectroscopy to confirm the presence of crystalline nanoparticles with average diameters of 60 nm. Electrochemical testing of the Ge-NPs shows high reversible lithium ion capacity up to 900 mAh g–1 and a Coulombic efficiency of 96% on the first cycle, with capacities realizing 1000 mAh g–1 and a Coulombic efficiency of 98% on the second cycle. The use of SWCNTs to provide a stable nanoscale electrical network to support Ge-NPs resulted in a hybrid three-dimensional free-standing electrode, which is an attractive alternative to the conventional composite-current collector approach. The Ge-NP:SWCNT hybrid electrode with thin film titanium contacts produced electrode capacities of 983 mAh g–1 versus Li/Li+ up to 3 V. The higher anode capacity for the hybrid is maintained at modest cycling rates up to 1C. The pairing of the hybrid electrode with a commerical LiFePO4 cathode showed excellent performance with anode capacities of 800 mAh g–1 over a 1 V discharge range. Even at higher discharge rates, up to 1C, the anode energy density changes by only 8.5%. Thus, this demonstrates the first full battery comprising a free-standing Ge-based anode with a high power cathode exhibiting improved energy and power density.