Selection of Conductive Additives in Li-Ion Battery Cathodes

Abstract

The lithium-ion cell has been successively improved with adoption of new cathode electrochemistries, from LiCoO2 to higher-capacity LiNi1-x Cox O2 to lower cost LiNi1-x Cox O2. The addition of conductive additives to cathode materials has been demonstrated to improve each type. Four systems have emerged as important cathodes in recent studies: (i) the spinel LiMn2 O4, (ii) LiFePO4, (iii) the "Gen 2" material, Li (Ni0.8 Co0.15 Al0.05) O2, and (iv) the Li (Ni13 Co13 Mn13) O2 system. The architectures of model composite cathodes were generated using our prior approach in simulating packing of polydisperse arrangements; conductivity was then simulated for several realizations of each case. A key finding was that the conductive coatings significantly improve overall conductivity. Percolation was achieved for the volume fraction of active material (30%) in studied cases, which was larger than the percolation threshold (29%) for a 3D spherical particulate system. Neither surface nor bulk modifications of active-material particle conductivities seem desirable targets for improvement of laminate conductivity at present. As part of future work, trade-offs between conductivity and capacity will be considered. © 2007 The Electrochemical Society.