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

Abstract

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.

Composite Anodes for Secondary Magnesium Ion Batteries Prepared via Electrodeposition of Nanostructured Bismuth on Carbon Nanotube Substrates

“…Due to the 3-dimensionality of the bulk CNT network within an electrode, the volume changes of bismuth associated with charge and discharge cycles may be accommodated without a net loss of Bi-CNT electrical contact, especially since this general phenomenon has been observed with other anode materials such as silicon and germanium in lithium based batteries. [17][18][19][20][21][22] In addition to current collection, the CNT substrate is lighter weight and much more corrosion resistant than metal foils and the 3-D nature of the CNT substrate allows for electrolyte and ion access. 23,24 The weight reduction by eliminating metal foils can be significant where up to 76% electrode weight savings at the cell level can be realized.…”

Properties of electrophoretically deposited single wall carbon nanotube films

“…Not only does this represent many orders of magnitude improvement compared to the MEMS literature, but it approaches the speed of heavily loaded transistors with the potential for far lower power dissipation. Other major applications of freestanding CNT films include sensors [8], energy storage [9], and photovoltaic devices [10].…”

High Energy Density Germanium Anodes for Next Generation Lithium Ion Batteries

“…Demonstrating this double protection approach, Xue et al and Li et al demonstrated, separately, the much improved specific capacity, cycling performance, and rate capability of Ge@C/RGO nanocomposites, arising from the combined buffer and structural stability of the electrode [84,85]. In addition to carbon coating, combining Ge nanostructures and porous carbon had been shown to improve the cycling retention of the Ge-based anodes [87,88]. For instance, Ge NW-porous carbon composite anode displayed better stability and higher specific capacity, indicating a synergistic effect between the two components [87].…”

“…In addition to carbon coating, combining Ge nanostructures and porous carbon had been shown to improve the cycling retention of the Ge-based anodes [87,88]. For instance, Ge NW-porous carbon composite anode displayed better stability and higher specific capacity, indicating a synergistic effect between the two components [87]. A nanocomposite consisting of hierarchically porous Ge and modified carbon, synthesized via a facile hydrothermal method followed by annealing, had shown superior electrochemical performance, mainly due to the increase in electrode conductivity and buffering to accommodate the volume changes during cycling [88], as displayed in Figure 5(d).…”