Investigation of the Porosity and Tortuosity of Silicon-Graphite Electrodes in Lithium-Ion Batteries

Tuesday, 3 October 2017
Prince George's Exhibit Hall D/E (Gaylord National Resort and Convention Center)
M. Wetjen (Technical University of Munich, Chemistry department), D. Pritzl, S. Niesen (Technical University of Munich), and H. A. Gasteiger (Technical University of Munich, Chemistry department)
Silicon-based electrodes are promising candidates for the next generation of Lithium-ion batteries with cell-level volumetric energy densities above 700 Wh L-1cell.1,2 However, the practical energy density of these electrodes is strongly influenced by the electrode porosity and the volume expansion during repeated charge-discharge.3 In addition, the electrode’s rate capability is largely determined by its tortuosity, which continuously increases upon cycling as a consequence of ongoing electrolyte decomposition at the silicon-electrolyte interface.4

In the present study, we investigate the influence of the porosity and tortuosity on the cycling performance of silicon-graphite electrodes. Hence, we prepared electrodes with a practical areal capacity of 4.0 mAh cm‑2, comprising 35 wt% nanometer-sized silicon and 58 wt% micron-sized graphite particles. Lithium poly(acrylic acid) binder and C65 conductive carbon accounted for the remaining 7 wt%. By use of a hydraulic press, the electrode porosity was adjusted to values ranging from 30% to 50%. As electrolyte solution, 1 M LiPF6 dissolved in a 3:7 (w:w) mixture of ethylene carbonate:ethyl methyl carbonate (LP57) with 5 wt% fluoroethylene carbonate (FEC) as additive was used.

First, the tortuosity and MacMullin number of the pristine silicon-graphite electrodes were determined by use of impedance spectroscopy on symmetrical cells in blocking conditions.5 The electrode polarization and rate capability of these electrodes were then investigated in coin-cells with lithium metal foil as counter electrode. After 50 cycles, the silicon-graphite electrodes were harvested from the cells and examined in terms of their thickness and morphological changes by cross-sectional scanning electron microscopy. Finally, the FEC consumption upon cycling was quantified by post-mortem 19F-NMR analysis of the residual electrolyte to estimate the pore volume of the electrodes that was occupied by electrolyte decomposition products.6

This contribution concludes with a comparison of silicon-graphite electrodes with different porosities and the quantification of the resulting degradation phenomena. Our research helps to better understand the limiting processes in silicon-graphite electrodes upon cycling and provides useful parameters for the modelling and simulation of these electrodes.


(1) Gröger, O.; Gasteiger, H. A.; Suchsland, J.-P. J. Electrochem. Soc. 2015, 162 (14), A2605–A2622.

(2) Andre, D.; Kim, S.-J.; Lamp, P.; Lux, S. F.; Maglia, F.; Paschos, O.; Stiaszny, B. J. Mater. Chem. A 2015, 3 (13), 6709–6732.

(3) Dash, R.; Pannala, S. Sci. Rep. 2016, 6, 27449.

(4) Radvanyi, E.; Porcher, W.; De Vito, E.; Montani, A.; Franger, S.; Jouanneau Si Larbi, S. Phys. Chem. Chem. Phys. 2014, 16 (32), 17142–17153.

(5) Landesfeind, J.; Hattendorff, J.; Ehrl, A.; Wall, W. A.; Gasteiger, H. A. J. Electrochem. Soc. 2016, 163 (7), A1373–A1387.

(6) Wetjen, M.; Jung, R.; Pritzl, D.; Gasteiger, H. A. ECS Meet. 230 2016, Abstr. #280.


The German Federal Ministry for Economic Affairs and Energy is acknowledged for funding (“LiMo” project with funding number 03ET6045D).