On the Role of Electrolytes and Particle Size on the Durability of the Anodes for Lithium-Ion Batteries: Continuum Model and Measurements
In this presentation, we report our recent studies on the roles of FEC as a co-solvent for binary and ternary solvent electrolytes used for sub-micron sized germanium electrodes. The binary solvent electrolyte consisting of 1 M LiPF6 in DMC/EC (1:1 by volume) displayed rapid capacity fading with the charge capacity retention of ~33% at the end of 120th cycle (361 mAh/g) while the one containing 1 M LiPF6 in DMC/FEC (1:1) by volume, retained ~96% of the charge capacity (~1210 mA/g) at the charge and discharge current density of ~0.31 C (500 mA/g). The ternary solvent electrolyte displayed a similar behavior. When cycled at 0.5 C (800 mA/g), the ternary solvent electrolyte consisting of 1 M LiPF6 in EC/DMC/DEC (1:1:1 by volume), the capacity retention at the end of 50th cycle was observed to be ~58% (645 mAh/g) whereas, using 1 M LiPF6in DMC/DEC/FEC (1:1:1 by volume), about 94% of the charge capacity was retained.
These results demonstrated that FEC as co-solvent significantly improves the performance of the Ge electrodes in a binary or ternary solvent electrolytes. Post analysis is carried out by using scanning electron microscopy and x-ray photoelectron spectroscopy to relate the SEI structure – electrochemical property relationship in our battery system. A continuum mechanics model is developed by considering the reduction and of diffusion of solvent. The model will be used to extract solvent diffusivity and predict the thickness of SEI layer in both Ge- and Si-based electrodes in binary and ternary compounds by using experimental data of Ge electrodes from this work and Si-based electrode in literature.
In addition, we report our studies on the effects of particle size on the electrochemical performance of Ge-based electrode. Ge particles of different sizes (0.1-0.3, 0.3 -0.5, 0.8-1, >1 µm, ) are obtained by varying the time of ball milling and their capacity performances were measured by assembling a coin cell with the lithium metal as the counter electrode.