Particle Compression and Conductivity in Li-Ion Anodes with Graphite Additives

We performed coupled theoretical/experimental studies on Li-ion cells to quantify reductions in anode resistivity and/or contact resistance between the matrix and the current collector with the addition of amorphous carbon coatings and anode compression. We also aimed to identify microstructural changes in constituent particles due to anode compression, using models of permeable-impermeable coatings of graphite particles. We studied three anode materials, SL-20, GDR-6 (6 wt % amorphous carbon coating), and GDR-14 (14 wt % amorphous carbon coating). Four compression conditions (0, 100, 200, and 300 were examined. Experimental results indicated that electrical resistivities for unpressed materials were reduced with addition of amorphous carbon coating (for unpressed materials: Contact resistances were reduced for SL-20 anodes by the application of pressure. Overall, the two-dimensional (2D) impermeable particle mathematical model provided reasonable agreement with the experiments for SL-20 and GDR-6 materials, indicating that coatings remain intact for these materials even at moderate pressures (100 and 200 Conductivities of SL-20 and GDR-6 anodes exposed to the highest pressure (300 fell short of model predictions, suggesting particle breakage. For the GDR-14 graphite, both 2D models underestimated conductivity for all processing conditions. We conclude that the 2D simulation approach is useful in determining the state of coating. © 2004 The Electrochemical Society. All rights reserved.