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 LiCoO 2 to higher-capacity LiNi 1 − x Co x O 2 to lower cost LiNi 1 − x Co x O 2 . 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 LiMn 2 O 4 , ( ii ) LiFePO 4 , ( iii ) the “Gen 2” material, Li ( Ni 0.8 Co 0.15 Al 0.05 ) O 2 , and ( iv ) the Li ( Ni 1 ∕ 3 Co 1 ∕ 3 Mn 1 ∕ 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.