Particle compression and conductivity in Li-ion anodes with graphite additives

• Published in: Journal of the Electrochemical Society Vol. 151; no. 9; pp. A1489 - A1498
• Main Authors: WANG, C.-W, YI, Y.-B, SASTRY, A. M, SHIM, J, STRIEBEL, K. A
• Format: Journal Article
• Language: English
• Published: Pennington, NJ Electrochemical Society 2004
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology; Lithium battery; Particle size; Graphite intercalation compounds; Electrical conductivity; Organic electrolyte storage battery; Contact resistance; Secondary cell; Electrode material; Metal particle
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1783909

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 permeableimpermeable 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 kg/cm2) were examined. Experimental results indicated that electrical resistivities for unpressed materials were reduced with addition of amorphous carbon coating (for unpressed materials: rhoSL-20 > rhoGDR-6 > rhoGDR-14). 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 kg/cm2). Conductivities of SL-20 and GDR-6 anodes exposed to the highest pressure (300 kg/cm2) 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.