A high-rate germanium-particle slurry cast Li-ion anode with high Coulombic efficiency and long cycle life

We report stable, high capacity cycling performance over 2500 deep cycles at variable C-rates (1C, 5C and 10C) for slurry-cast Li-ion battery anodes made using commercially-available germanium nanopowder. The determining factor in cycling performance was the use of fluoroethylene carbonate (FEC) rather than ethylene carbonate (EC) as a co-solvent in the electrolyte. Cycling tests for the FEC-based electrode showed stable performance close to 700 mAh g−1 through 500 cycles at 10C with near 100% Coulombic efficiency. These results show that a Ge-based slurry-cast electrode using active material structured only as a simple particle can be used to create an electrode system which is a candidate for optimization and scale-up. These cycling improvements obtained using the FEC-based electrolyte complements recent progress in Ge-based electrode research which has focused on improving performance through tailored structural and chemical modifications to the active material structure. The effect of the electrolyte on Li-ion transport, electrode stability toward oxidation, and electrode and SEI structural stability was studied using electrochemical impedance spectroscopy, differential capacity profiles, SEM and cross-sectional TEM imaging where we characterize the evolution of the electrode structure cycled with the FEC-based electrolyte considering the type and extent of SEI growth, particle agglomeration and fracturing.

► Ge-based slurry cast Li-ion anode performs stably at high C-rates for 2500 cycles. ► Fluoroethylene carbonate (FEC) based electrolyte critical to anode performance. ► Stable performance and near 100% Coulombic efficiency at 10C for 500 cycles. ► dq/dV show thermodynamic reversibility of FEC- but not EC-based electrode. ► Cross-sectional TEM with SEM show structure of cycled anode and SEI.