Investigation of Fast-Charging and Degradation Processes in 3D Silicon–Graphite Anodes

Abstract

The 3D battery concept applied on silicon–graphite electrodes (Si/C) has revealed a significant improvement of battery performances, including high-rate capability, cycle stability, and cell lifetime. 3D architectures provide free spaces for volume expansion as well as additional lithium diffusion pathways into the electrodes. Therefore, the cell degradation induced by the volume change of silicon as active material can be significantly reduced, and the high-rate capability can be achieved. In order to better understand the impact of 3D electrode architectures on rate capability and degradation process of the thick film silicon–graphite electrodes, we applied laser-induced breakdown spectroscopy (LIBS). A calibration curve was established that enables the quantitative determination of the elemental concentrations in the electrodes. The structured silicon–graphite electrode, which was lithiated by 1C, revealed a homogeneous lithium distribution within the entire electrode. In contrast, a lithium concentration gradient was observed on the unstructured electrode. The lithium concentration was reduced gradually from the top to the button of the electrode, which indicated an inhibited diffusion kinetic at high C-rates. In addition, the LIBS applied on a model electrode with micropillars revealed that the lithium-ions principally diffused along the contour of laser-generated structures into the electrodes at elevated C-rates. The rate capability and electrochemical degradation observed in lithium-ion cells can be correlated to lithium concentration profiles in the electrodes measured by LIBS.

Silicon Graphite Composite Anode Degradation: Effects of Silicon Ratio, Current Density, and Temperature

“…Also, Si has low electrical conductivity; electrodes with high Si density are disadvantageous in terms of ionic and electrical conductivity than the porous electrode with less Si density. [33,34] The 10th cycle, which is the period where the capacity rapidly decreases, the voids slightly decreased in GrSi6, possibly due to the expansion of silicon and its SEI formation. However, in GrSi30, voids were formed around graphite, possibly due to the repeated volume expansion and shrinkage of graphite (%10%) induced debonding of silicon particles and graphite.…”

“…For the samples with a high Si ratio (i.e., GrSi30), the capacity decrease with cycles, and this can be in part due to the SEI formation and the loss of the electrical connection between the particles and the appearance of the cracks and voids seems negative effects on the capacity. [ 33 ] However, in the samples with a low Si ratio, the appearance of voids and cracks is not affecting the capacity, possibly due to the more graphite in the electrode, which increases the chance of maintaining the electrical connectivity between the Gr flakes or Si nanoparticles and Gr flakes.…”

Fast‐Charging Strategies for Lithium‐Ion Batteries: Advances and Perspectives

“…Furthermore, the sigmoid growth curve of Li concentration indicates that there are two stages of continuous nucleation and autocatalytic growth. Pfleging's group [88] used laser‐induced breakdown spectroscopy (LIBS) to establish a calibration curve, which can quantitatively determine the element concentration in electrode. The rate capability observed in LIBs is correlated to the Li concentration distribution in the electrode measured by LIBs.…”

An electrode design study: laser structuring of anodes for fast-charging of batteries

“…Several ways of modifying the electrode architecture to increase fast-charging capability are contrary to current research. For instance, multilayer coating, blending of different active materials, and structuring of the electrode with laser ablation are being investigated and show an increase in fast-charging capabilities [5][6][7][8][9][10][11]. Several patterns for laser structuring, including hole, line, and grid patterns are investigated in the literature [8,10,12].…”