Selection of conductive additives in Li-ion battery cathodes - A numerical study

The lithium-ion cell has been successively improved with adoption of new cathode electrochemistries, from LiCoO2 to higher-capacity LiNi1-xCoxO2 to lower cost LiNi1-xCoxO2. 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 LiMn2O4, (ii) LiFePO4, (iii) the "Gen 2" material, Li(Ni0.8Co0.15Al0.05)O-2, and (iv) the Li (Ni1/3Co1/3Mn1/3)O-2 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. (c) 2007 The Electrochemical Society.